26 August 2011


Overview: Zoonoses, also known as zoonotic diseases, are infections that may be transmitted from living animals to humans. The word zoonoses is derived from Greek words zoon (animal) and nosos (disease).



Overview: Zoonoses, also known as zoonotic diseases, are infections that may be transmitted from living animals to humans. The word zoonoses is derived from Greek words zoon (animal) and nosos (disease).

Vertebrate animals serve as reservoirs for zoonotic infections, which means they are long-term hosts for the disease-causing agents. Inside the host, the infectious agent may grow, thrive, and replicate.

Sometimes humans may become accidental hosts. Zoonoses may be transmitted to animals and humans through sources such as soil, water, invertebrate animals, animal corpses, excrement, and decaying plants. Although infected animals are sources of zoonotic diseases, transmission between humans may also be possible.

There are more than 200 zoonotic diseases that may be caused by bacteria (e.g., Bacillus anthracis, Brucella spp, Salmonella typhi), viruses (e.g., rabies virus, avian influenza virus, Ebola virus), parasites (e.g., Taenia solium, Toxoplama gondii, Giardia lamblia), fungi (e.g., Aspergillus fumigatus, Histoplasma capsulatum), and other rare agents such as prions. Prions are infectious proteins that may infect the brain and nervous tissues, causing zoonotic diseases such as Creutzfeld-Jakob disease (in humans) and bovine spongiform encephalopathy (commonly known as mad cow's disease) in cattle.

History: Zoonotic diseases are referenced in early literature dating back to historical times. Biblical passages have described plague spread by rodents infected with fleas to humans. During the Plague of Athens (430-425 B.C.), Greek historian Thucydides suggested that the plague spread from the city's port and food supply.

The plague was responsible for three great world pandemics. A pandemic is a rapid spread of infection that occurs over a large geographical area and affects a large size of a population. The first great pandemic appeared in 542 A.D. and lasted for about 60 years along the Mediterranean Sea, a busy coastal trade route. The second pandemic, also known as Black Death, began in the mid-1300s and spread from central Asia and across Europe (Bubonic plague) for nearly 400 years. The third pandemic began in the mid-1800s in northern China, spreading to all continents and lasting for more than 100 years.

Emergence of zoonoses: Zoonoses have become a major concern because of infectious disease emergence, potential to cause public health risks, and overall economic impact. It has been suggested that 75% of emerging infectious diseases are zoonotic, mainly of viral origin without a possible known cure. For example, recent emergence of Nipah virus infection in Malaysia during 1998-1999 caused viral brain infections (viral encephalitis) in 265 persons, with nearly 100 deaths. In addition, the re-emergence of some zoonotic diseases, such as brucellosis and plague, are of serious concern.

Zoonotic agents have species-jumping ability and may cross the species barrier, which may make outbreaks more extensive. For example, the acquired immune deficiency syndrome (AIDS) is a disease that originates from the human immunodeficiency virus (HIV). HIV first spread to humans from primates in Africa, but the virus has subsequently adapted to human-to-human transmission. AIDS is a potentially fatal disease in which the body's immune system is weakened and unable to fight infections. Severe acute respiratory syndrome (SARS) has also adapted to human-to-human transmission.

Bioterrorism: Bioterrorists are a form of terrorists, who may intentionally release the biological agents such as viruses, bacteria, fungi, or toxins from living organisms, to cause illness or death in living things. The biological agents used for bioterrorism are called bioweapons. Zoonotic agents may be used as bioweapons through aerosols, food and water contamination, or other methods. Common zoonotic agents that may be used as bioweapons include Bacillus anthracis (anthrax), Yersinia pestis (plague), Francisella tularensis (tularemia), Ebolavirus (Ebola), Brucella species (brucellosis), and Salmonella species (salmonellosis).


General: Zoonoses are infectious disease that can be transmitted from living animals (both wild and domestic) to humans. These diseases normally exist in animals but may also infect humans. Zoonotic infections are caused by bacteria (e.g., Bacillus anthracis, Brucella spp, Salmonella typhi), viruses (e.g., rabies virus, avian influenza virus, Ebola virus), parasites (e.g., Taenia solium, Toxoplama gondii, Giardia lamblia), fungi (e.g., Aspergillus fumigatus, Histoplasma capsulatum), and other rare agents such as prions. Prions are infectious proteins that may infect the brain and nervous tissues, causing zoonotic diseases, such as Creutzfeld-Jakob disease (in humans) and bovine spongiform encephalopathy (commonly known as mad cow's disease in cattle).

Animal sources :

General: In nature, vertebrate animals function as a reservoir for zoonotic infections, and humans are accidental hosts. A host is an organism that harbors an infectious agent, providing nourishment and shelter.

Zoonoses may be transmitted to animals and humans through sources such as soil, water, invertebrate animals, animal corpses, excrement, and decaying plants. Although infected animals are sources of zoonotic diseases, transmission between humans may also be possible.

Animals contribute to the distribution and transmission of infections, but they may not always play an essential role in the life cycle of the causative agent. Some animals may be just carriers (vectors) of the disease without being infected. For example, rodents and deer are carriers of Lyme disease. Lyme disease is transmitted through ticks that carry the bacterium Borrelia burgdorferi. These ticks are often present on deer, bats, weasels and rodents (such as squirrels).

In other cases, animals may become infected with zoonotic diseases and show signs and symptoms of the illness. For instance, rabies is a viral infection transmitted through the bite of an infected animal, such as dogs, skunks, foxes, bats, and raccoons. Animals may also transmit the disease to humans.

Some domestic animals that may cause zoonotic diseases include dogs (e.g., rabies), cats (e.g., cat scratch disease), cattle (e.g., brucellosis, taeniasis), sheep (e.g., campylobacter, toxoplasmosis), goats (e.g., brucellosis, toxoplasmosis), pigs (e.g., trichinosis, taeniasis), geese (e.g., West Nile virus disease), and horses (e.g., salmonellosis). Examples of wild animals and the zoonotic disease they cause include chimpanzees, rodents (e.g., hantaviral disease, plague, Lyme disease), bats (e.g., rabies), rabbits (e.g., tularemia), birds (e.g., avian influenza, psittacosis), deer (e.g., Lyme disease), fishes (e.g., diphyllobothriasis), skunks (e.g., rabies), foxes (e.g., rabies), and raccoons (e.g., scabies, rabies).

Routes of transmission :

General: Zoonotic agents may transmit infection to humans through air, water, food, animal secretions and excretions, and vectors. Vectors refer to agents such as mosquitoes, fleas, or animals that carry and transmit a disease from one host to another.

Aerogenic (airborne): Aerogenic transmission of infectious agents such as bacteria or viruses occurs through respiratory droplets, or spores. Aerosols refer to fine droplets or particles of infectious agent that are dispersed in air. Respiratory droplets are aerosols from the lungs that are released when people sneeze, cough, laugh, exhale, etc. Spores may be dormant (inactive) in harsh environments and become active in favorable environmental conditions.

For example, the hantaviral disease is a rare but fatal disease that causes cough, fever, shortness of breath, decreased blood pressure, and kidney failure. It is transmitted through inhaling air contaminated with rodent urine and droppings infected with the hantavirus. Another example is histoplasmosis, a fungal infection transmitted by exposure to bird or bat droppings that contain spores infected with Histoplasma capsulatum. The infected spores contaminate the soil and become airborne when the soil is disturbed. Inhalation of these spores causes lung infection that may present as fever, cough, and chest pain while breathing, which may be fatal if left untreated.

Food-borne and/or water-borne: Certain bacteria such as Salmonella and Escherichia coli cause intestinal infections that are acquired through the consumption of contaminated or undercooked eggs or meat, unpasteurized milk, or water from infected poultry, pork, or cattle. Other examples are parasites such as Cryptosporidium and Giardia, which cause intestinal infections that are transmitted through the consumption of water contaminated with feces from infected animals such as dogs, cats, cattle, beavers, muskrats, and waterfowl.

Animal secretions and excretions: Some zoonotic infections may spread through animal secretions and excretions.

For example, leptospirosis is a bacterial disease caused by a spirochete (spiral-shaped) bacterium that causes an enlarged spleen, jaundice (yellowing of eyes), and kidney failure. It is usually transmitted to humans through contact with urine from infected animals such as rats, mice, skunks, raccoons, and possums.

Another example is Ebola hemorrhagic fever, a severe viral disease presenting as high fever, external bleeding, internal bleeding, low blood pressure, and shock. This disease is spread by contact with infected blood, tissues, secretions, or excretions of bats, primates (chimpanzees, gorillas), and forest antelopes. (The natural reservoir of Ebola virus is unknown.)

Another example is rabies, which may be transmitted through a bite of an infected animal or after an open wound or mucus membrane is exposed to infected fluids such as blood or saliva.

Ticks, fleas, mosquitoes, and lice: Lyme disease is a bacterial disease that affects the joints, heart, and nervous system. Transmission occurs after a tick that is carrying the bacterium bites a person. These ticks are often found on deer, weasels, bats, and rodents (like squirrels). Another example is plague, a potentially fatal bacterial disease, that is transmitted through the bite of an infected flea (Xenopsylla cheopis) often found on animals such as rodents, and rabbits. Plague infects the lungs, lymph nodes, and blood.

Risk factors :

General: Certain individuals may be at greater risk for contracting zoonoses. The immune system is body's defense mechanism against foreign agents entering the body such as viruses and bacteria. Individuals with decreased or compromised immune system include those with acquired immunodeficiency syndrome (AIDS), cancer patients, the nutritionally deficient, and anticancer drugs users. Other individuals who are at increased risk of contracting zoonotic diseases include veterinarians, farmers, slaughterhouse workers, poultry workers, zoo employees, food-industry operatives, animal handlers, researchers working in animal labs, children, and elderly persons. Other groups at risk include pregnant women living with pets or from petting zoos and farms, individuals who participate in outdoor recreational activities, such as hunting, kayaking, or swimming, and persons traveling to or transiting through endemic areas. Endemic refers to an organism that is native to or confined to a particular locality, region, or people.


General: Zoonoses are infectious diseases that normally exist in animals, but may also infect humans. Infectious agents such as bacteria, viruses, fungi, and parasites may cause zoonotic diseases and be transmitted from animals (both wild and domestic) to humans.

Factors that may contribute to zoonoses :

Overview: There are several factors involved in the emergence of new zoonotic diseases as well as the reemergence of zoonotic diseases that were previously under control and presented low risk.

Increased population: Increasing human population and increasing encroachment of humans into the wilderness are major factors responsible for emerging new zoonotic diseases. Increased contact between humans and infected animals in the wild may mean more contact with resident microorganisms that cause infection. For example, the construction of Panama Canal took humans into previously unexplored regions of the Central American jungle and exposed humans to yellow fever virus. Yellow fever is a viral disease transmitted from the bite of infected mosquitoes.

Environmental changes: Changes in the environment affecting the size and distribution of the populations of certain animal species may affect disease prevalence. For example, global climate change may directly or indirectly affect vector-virus relationships. Thus, increased geographic distribution and abundance of vectors, and hosts may lead to increased human exposure to zoonotic diseases.

Large-scale farming: Changes in farming practices and the industrialization of foods of animal origin may affect zoonoses rates. There is an increasing demand worldwide for the meat and dairy products over plant-based food, resulting in industrialization of animal agricultural practices. The industrialization of animal farming leads to increased production of animal waste, and disposal and recycling of waste requires environmental regulations and safety practices. Excrement from these animals is likely the largest source of infectious agents, increasing the risk of emerging water-borne zoonotic diseases.

Food-handling industries may require stringent safety and quality practices to deliver safe products to consumers. If these practices, systems, or inspection procedures do not keep pace with industrialization and mechanization of animal agricultural practices, outbreaks of zoonotic diseases may be the result.

Travel and transportation: Increasing movements of people as well as an increased trade in animals and animal products may lead to exposure to different infectious agents. For example, long-distance livestock transportation facilitated the movement of viruses and vectors when African swine fever virus migrated from Africa to the Americas in the 1960s and 1970s.

Breakdown in public health measures: Lack of financial and human resources due to economic crisis, social uprising, wars, and natural disasters may cause breakdown in public health measures.

New strains: Surveillance of zoonotic agents relies on the identification of human cases. For example, vaccines assist to control specific strains of the avian influenza virus (H5N1) infection, also known as the bird flu. However, newer strains of avian influenza virus that may cause severe infection on a large scale may develop due to complex interactions between environment and these viruses. This in turn may lead to difficulty in detection and identification of newer cases due to different characteristics of the viruses and due to the challenges of developing specific, inexpensive, sensitive, and rapid diagnostic tests for field situations.

Exotic hobbies: There is also an increased risk of exposure due to exotic hobbies and travel. Some of these activities include wild tourism, hunting, fishing, and keeping exotic animals as pets. For example, salmonella infection occurs in pet owners of turtles, iguanas, and snakes.

Prevention and control :

General: Simple preventive measures such as washing hands after handling animals and taking animals to their veterinarians for regular checkups may protect against zoonotic diseases.

Consuming clean drinking water, pasteurized milk and dairy products, and properly cooked foods may also help protect against zoonotic diseases. The best way to indicate that food is properly cooked is by measuring the internal temperature of the meat or poultry with a food thermometer. Food handlers and food-industry workers may follow stringent quality control during production, storage, and transportation of animal products to limit exposure to zoonoses.

Travel precautions: Persons traveling to areas where disease is common may consider preventive measures such as being vaccinated for certain zoonotic infections (e.g., yellow fever, Japanese encephalitis) or taking preventive drugs (e.g., antimalarials).

Limiting exposure to areas with abundant arthropods such as ticks, lice, and mosquitoes may also reduce the risk of disease transmission. Using insect repellents and wearing appropriate clothing (gloves, facemasks, clothes covering the whole body) and protective glasses or goggles may help protect against zoonotic diseases.

Surveillance by world bodies: The Global Early Warning System for Major Animal Diseases (GLEWS) is a coordination of the World Organization of Animal Health (OIE), Food and Agricultural Organization (FAO), and World Health Organization (WHO). GLEWS provides early warning and prediction of disease outbreaks and aids in prevention and control of animal disease threats such as zoonoses. Another example is the International Food Safety Authorities Network (INFOSAN), coordinated by WHO and FAO. INFOSAN promotes the exchange of food safety information and improves collaboration between food safety authorities at national and international levels.

Quarantine: Isolation through quarantine may help to prevent the spread of disease, allow for suitable treatment of infected animals, and facilitate proper disposal of dead infected animals.

Regulations: Sponsoring research and developing policies, guidelines, and strategies for the control of zoonotic and food-borne diseases may prove beneficial. For example, the European Union (EU) enacted a health policy in 2007 after a proposal by DG Sanco of the European Health Alliance for EU health. The policy addresses preparedness, surveillance, and response mechanisms aimed at combating zoonotic infections.


Bacterial zoonoses :

General: Bacteria are microscopic organisms that cause several zoonotic infections in humans, including anthrax, brucellosis, leptospirosis, Lyme disease, plague, salmonellosis, and tularemia.

Anthrax: The bacterium Bacillus anthracis causes anthrax. Anthrax is located globally but found most commonly in agricultural regions such as South and Central America, southern and eastern Europe, Asia, Africa, the Caribbean, and the Middle East. In the United States, the incidence of naturally occurring human anthrax declined from an estimated 130 cases annually in the early 1900s to fewer than two cases each in 2000, 2001, and 2002. In 2001, anthrax spores were distributed through the U.S. mail system in a bioterrorism attack.

Anthrax may be transmitted to humans through direct skin contact with bacterium spores. Spores are the dormant (inactive) stage of an organism that is capable of surviving in harsh environments. Spores become active when favorable environmental conditions such as heat and moisture are present. It may also be transmitted after exposure to an infected animal or animal product such as skin, wool, or meat (usually related to occupational exposure). Humans may also become infected after inhaling aerosolized spores or consuming undercooked meat or dairy products from infected animals.

Anthrax commonly involves the skin (cutaneous), causing itching and skin infection, later developing to a skin ulcer with blackened center. However, anthrax may also involve the lungs or gastrointestinal tract if the spores were inhaled or ingested.

Inhalation of anthrax spores may cause sore throat, mild fever, and muscle aches. If left untreated, the infection may spread through the whole body, causing difficulty breathing, shock and possibly death.

Gastrointestinal anthrax may cause loss of appetite, vomiting, and fever followed by abdominal pain, vomiting of blood, bloody diarrhea, shock, and possibly death.

Effective decontamination with antimicrobial soap and water and early antibiotic therapy may prevent and control the disease and its spread.

Anthrax infections may be prevented by avoiding direct contact with livestock and animal products and by avoiding meat that has not been properly slaughtered and cooked.

The anthrax vaccine (BioThraxTM) is available for livestock and humans.

Brucellosis: Brucellosis, also known as rock fever, Malta fever, or undulant fever, is caused by the bacteria Brucella spp.

Brucellosis is a highly contagious (capable of spreading from person to person) disease acquired from consumption of unpasteurized milk or cheese, or uncooked meat from infected animals, or close contact with their secretions (e.g., blood, urine). Brucella spp can infect cattle, goats, camels, dogs, and pigs. Brucellosis may present with flu-like symptoms, muscular pain, sweating, joint pain, and may persist for years.

Antibiotics are used to treat the condition and prevent recurrence. Using protective gear such as rubber gloves when handling infected animals may prevent zoonoses. There is no a vaccine for brucellosis available for humans.

Brucellosis has a worldwide distribution, but it is more common in countries that do not have standardized and effective public-health and domestic-animal health programs. Some of the areas where the brucellosis is more common include the Mediterranean Basin (Portugal, Spain, Southern France, Italy, Greece, Turkey, and North Africa), South and Central America, eastern Europe, Asia, Africa, the Caribbean, and the Middle East. The incidence of brucellosis in United States is less than 0.5 cases per 100,000 persons annually.

Leptospirosis: Leptospirosis, also known as Weil's disease, is caused by the bacterium Leptospira interrogans. The infection is transmitted to humans through contact with infected blood and body fluids such as urine from infected animals, including rats, mice, skunks, raccoons, cows, rabbits, and possums. Leptospira can enter the body through broken skin and mucous membranes. The bacterium may also enter the body when a person swallows contaminated food or water. The disease is not transmitted through inhalation.

Symptoms may include fever, headache, chills, nausea and vomiting, eye infections, enlarged spleen, jaundice (yellowing of skin and white of eyes), internal bleeding, and kidney failure. The infection is treated with antibiotics.

Prevention of infection is possible by wearing protective clothing such as waterproof boots or waders when participating in recreational or work activities that may result in contact with contamination.

Found most commonly in temperate or tropical climates, leptospirosis may be the most widespread zoonotic disease in the world. Farmers (rice-field, sugar cane plantations), sewer workers, miners, veterinarians, fish workers, dairy farmers, animal caretakers, or military personnel are at increased risk of contracting leptospirosis. Swimming, wading, kayaking, and whitewater rafting in contaminated lakes and rivers are recreational activities that may place individuals at risk. Leptospirosis is no longer a reportable disease in the United States, but it still occurs other countries.

Lyme disease: Borreliosis, also known as Lyme disease, is caused by Borrelia burgdorferi. This disease is transmitted through the bite of an infected black-legged tick (also known as deer tick) often found on rodents, deer, weasels, and bats.

Lyme disease usually starts with a circular red skin rash (erythema migrans) along with fatigue, chills, fever, headache, swollen lymph nodes, and muscle and joint aches. If untreated, an infected person may present with loss of muscle tone on one or both sides of the face (facial or Bell's palsy), severe headaches and neck stiffness due to meningitis (infection of brain covering), sleep disturbances, dizziness due to changes in heartbeat, and recurring joint pain (arthritis or infection of joints).

Antibiotics are used to treat Lyme disease. Lyme disease may be curable with early diagnosis and treatment with antibiotics. However, the bacterium Borrelia burgdorferi may lie dormant in the body for years and reemerge.

Prevention involves protection against tick bites, control of ticks in animals around the home by using insecticides to repel or kill ticks, and avoiding areas where wild mice might live, such as the edges of yards, fields, and woods with low, dense groundcover. Tick bites may be prevented by wearing clothes with long sleeves and long pants tucked into socks, wearing a hat, neatly tying back hair, and using repellents containing the compound meta-N,N-diethyl toluamide (DEET) may be used on exposed skin except for the face.

Lyme disease is the most common tick-borne disease in North America and Europe. The incidence rate was nine cases per 100,000 persons in the United States in 2007.

Plague: Plague is caused by Yersinia pestis.

The disease occurs in three major forms in humans and cats: 1) bubonic, 2) septicemic, and 3) pneumonic plague. Bubonic plague is characterized by enlarged, tender lymph nodes; fever; chills; and severe weakness. Septicemic plague is characterized by fever, chills, weakness, abdominal pain, shock, and bleeding into skin and other organs. Pneumonic plague is characterized by fever, chills, cough, difficulty breathing, rapid shock, and possibly death (if not treated early).

The disease is transmissible through the bite of an infected flea that is often found on rodents (including rats, rabbits, and squirrels). Humans may also become infected if they come into direct contact with infected animals or their body fluids. Inhaling droplets from cats and humans with pneumonic (lung) plague may also lead to disease transmission.

When diagnosed with the plague, a patient should be isolated, state and local health departments notified, and drug therapy initiated with antibiotics.

Prevention and control of plague involves controlling rodents and flea populations. Additionally, antibiotics such as tetracycline or chloramphenicol may be prescribed post-exposure.

The worldwide incidence of plague is about 1,000-2,000 cases per year, particularly in localized geographic areas. Active plague foci exist in certain South American regions such as the Andean mountain region (including parts of Bolivia, Peru, and Ecuador) and in Brazil. Two regions in North America where the incidence of plague is high are northern New Mexico, northern Arizona, and southern Colorado regions, and another area in California, southern Oregon, and far western Nevada. Recent outbreaks have occurred in African countries such as Kenya, Tanzania, Zaire, Mozambique, Botswana, and Madagascar. Plague is widely distributed in an area of Asia ranging from the Caucasus Mountains in Russia, through much of the Middle East, eastward through China, and then southward to southwest and southeast Asia.

Salmonellosis: Caused by Salmonella enteritidis or Salmonella typhimurium, salmonellosis is the most common zoonotic disease occurring in humans. The disease is transmittable through the consumption of contaminated water or contaminated food such as raw or undercooked eggs and poultry, pork, or cattle meat.

Salmonellosis may cause fever, diarrhea (sometimes bloody), vomiting, dehydration, and severe stomach cramps. Milder infections usually resolve in 5-7 days with oral fluids as treatment. However, severe forms may be fatal if left untreated. In severe cases, antibiotics (such as ampicillin, trimethoprim-sulfamethoxazole, or ciprofloxacin) plus oral or intravenous fluids is generally prescribed. Salmonella strains are developing resistance to newer antibiotics (e.g., third generation cephalosporins and fluoroquinolones), and this may be attributed to increasing agricultural use of antibiotics.

Currently, there are no vaccines are available to prevent salmonellosis. Washing the hands after contact with animal feces; avoiding the consumption or raw or undercooked eggs, poultry and meat; and avoiding the consumption of unpasteurized milk or dairy products may help reduce the risk of infection.

Every year in the United States, about 40,000 new cases of salmonellosis are reported, with the occurrence of cases more common in the summer.

Tularemia: Tularemia, also known as deerfly fever or rabbit fever, is caused by Francisella tularensis. Tularemia is commonly transmittable through rabbits and rodents, but it may also be spread by direct contact with infected animals through cuts and wounds, by consumption of poorly cooked meat from infected animals, inhalation of organisms, or bites from infected insects (ticks).

Tularemia often causes fever, tiredness, and skin infection, and it may lead to acute sepsis (infection of blood), pneumonia, and respiratory failure if left untreated.

Antibiotics are prescribed to treat tularemia. Wearing rubber gloves when handling animals, especially rabbits, may help reduce the risk of disease transmission. The vaccine for tularemia is currently under review by the U.S. Food and Drug Administration (FDA) and its use is restricted to persons with high risk of contracting tularemia such as laboratory workers and hunters.

Fungal zoonoses (zoonotic mycoses) :

General: Fungi cause a number of zoonotic diseases, such as aspergillosis, histoplasmosis, blastomycosis, coccidiomycosis. With soil as its natural habitat, fungal zoonoses occur throughout the world. Zoonotic mycoses are more common in persons with weakened immune systems.

Aspergillosis: The fungus Aspergillus fumigatus, which is commonly found growing on compost piles, decaying vegetation, dead leaves, and stored grain, causes Aspergillosis. Aspergillosis may be acquired after a person inhales fungal spores from host animals such as captive birds (mainly waterfowl and raptors like hawks, eagles, and owls).

Generally, healthy people are resistant to this infection. However, people with weakened immune systems, such as organ transplant recipients or those who have cancer, human immunodeficiency virus (HIV), or acquired immunodeficiency syndrome (AIDS), may be more prone to infection.

Aspergillosis commonly causes lung infection with symptoms such as dry cough, coughing up of blood, difficulty in breathing, fever, and weakness. If untreated, it may spread to heart, brain, bones, and joints.

The infection is treated with antifungal drugs such as voriconizole, amphotericin B, or itraconazole for several weeks.

Individuals can reduce their risk of infection by practicing good hygiene and being in areas with proper ventilation. People with weakened immune systems can take extra steps to reduce their risk. For instance, avoiding dusty environments and activities where dust exposure is likely (such as construction zones) may help minimize their risk.

Histoplasmosis: Histoplasmosis, also known as Ohio River Valley fever, is a fungal infection caused by Histoplasma capsulatum. It is widely distributed throughout the world and transmitted by inhalation of fungal spores from bird and bat droppings.

Infected persons usually develop flu-like symptoms with lung involvement. The disease may spread to skin, bones, joints, or the lining of the heart (pericardium) if untreated.

Infections are generally treated with antifungal drugs such as itraconazole or ketoconazole. People with weakened immune systems may also receive amphotericin B.

Prevention involves disposing of bird droppings that collect in roost areas and wearing a mask or self-contained breathing apparatus near such areas. In the United States, it is most prevalent in the southeastern, mid-Atlantic, and central states.

Parasitic zoonoses :

General: A parasite is an organism that grows, feeds, and shelters on a different organism without contributing to the survival of its host. In fact, many parasites harm or even kill the host. Some of the common parasites that cause zoonoses include Giardia lamblia, Taenia saginata, Taenia solium, Toxoplasma gondii, and Leishmania donovani

Giardiasis: Giardiasis is caused by the microscopic parasite, Giardia lamblia. This parasite inhabits a wide variety of wild and domestic animals such as beavers, muskrats, waterfowls, dogs, and cats.

Infection occurs after a person consumes contaminated water or food. It infects the intestines and may present with diarrhea, abdominal cramps, bloating, weight loss, and frequent loose, pale stools. The infection is treated with antiparasitic drugs and oral rehydration.

Prevention involves good personal hygiene and hand washing, and avoiding hand-to-mouth contact while handling any wildlife species.

Taeniasis/cysticercosis: Taeniasis, also known as tapeworm infection, is caused by the parasites Taenia saginata (beef tapeworm) or T. solium (pork tapeworm). T. solium also causes cysticercosis. These infections occur in humans who eat raw or undercooked meat from cattle or pigs infected by larvae in cysticerci (cyst forms).

After being ingested the larva develops into an adult tapeworm in the intestines (only in humans). Adult tapeworms live in human intestines and shed eggs in their feces. When cattle and pigs are exposed to egg-bearing human feces (by consuming contaminated vegetation, for instance), they may and ingest the tapeworm eggs. The eggs release the larvae in the cattle or pig's intestine. The larvae subsequently migrate to the muscles attached to the bones (skeletal), and heart (cardiac) muscle, where they form the cysticerci (cyst forms). In such a way, ingestion of the infected meat with cysticerci by humans results in taeniasis.

Tapeworm infections in humans are usually mild with slight stomach discomfort. The infection is recognizable when the infected person passes a segment of the worm in the stool.

Sometimes an infected human may ingest the eggs found in its feces (autoinfection). In this case, cysticerci may develop throughout the tissues of the human body, particularly the brain. Cysticercosis in humans comes to medical attention if located around the central nervous system or the eye and its surrounding tissues.

Taeniasis may be treated with use of certain drugs (e.g., niclosamide, praziquantel and albendazole); Unresponsive cases of cysticercosis may require different drug treatments (e.g., praziquantel, corticosteroids, and albendazole) or warrant the surgical removal of cystecerci.

Prevention involves meat inspection, education about good hygiene, avoiding consumption of raw or undercooked pork and beef, hand washing after using the toilet, and installation of good sewerage systems.

Viral zoonoses :

General: The emergence and re-emergence of viral zoonoses are mainly due to their species-jumping ability, as they are able to adapt quickly to changing environmental conditions

Avian influenza (bird flu): Avian influenza is caused by the influenza A virus. The virus occurs naturally in birds, including domesticated birds, chickens, ducks, and turkeys. Infected birds may transmit the flu virus to humans by their saliva, nasal secretions, and feces (droppings). Avian influenza infection in humans results from contact with infected poultry or surfaces contaminated with secretions or excretions from infected birds.

Avian influenza may cause flu-like symptoms such as fever, cough, sore throat, muscle aches, eye infections (conjunctivitis), severe lung infection (acute respiratory distress, viral pneumonia), and other severe, life-threatening complications.

The condition may be treated with antiviral medicines such as oseltamavir (Tamiflu©) and zanamavir (Relenza©) may be useful.

There is no vaccine available for humans against the avian flu. To help prevent avian bird flu, poultry should be prepared using hygienic practices, and it should be cooked thoroughly. Additionally, minimizing exposure to infected birds and their secretions or excretions may be beneficial.

Rabies: Rabies is a fatal disease caused by Rhabdovirus (rabies virus).

It may be transmitted through an animal bite, or by exposing an open wound or mucus member to infected saliva. It may also be transmitted through infected aerosols from bat droppings in caves.

Early symptoms include fever, headache, and general discomfort (malaise). Eventually, the infection causes partial or complete paralysis of the muscles, and difficulty swallowing. Symptoms may progress further to mental confusion, convulsions, and eventual death due to lung-muscle paralysis.

Treatment involves cleaning the wound thoroughly with soap followed by administration of immunoglobulins and vaccines. Immunoglobulins (e.g., RABIGAM© IM) are antibodies that offer immediate protection against the disease. Antibodies are specific proteins produced as an immune response to an antigen such as a virus, bacterium, toxin, or foreign protein.

Animals that are rabid may be foaming at the mouth or behaving strangely. They may be less afraid of humans than normal.

Safe and effective vaccines are available to prevent rabies in animals and humans before and after suspected exposures. Rabies may also be prevented by reducing the risk of animal bites. Generally, it is suggested to avoid contact with unknown animals, be cautious with animals that are new mothers, and not to provoke or tease animals. It is recommended that individuals keep their pets up-to-date with rabies shots.

Yellow fever: Yellow fever is a viral infection caused by yellow fever virus (flavivirus) that is transmitted through the bite of mosquitoes. This disease is common in South America and in sub-Saharan Africa.

At the onset, the infected person may experience fever, chills, headache, and backache, followed by nausea and vomiting. Symptoms may progress to high fever, jaundice (yellow coloring of skin and white of eyes), and often intestinal bleeding (seen as black-colored vomit), kidney failure, brain dysfunction, shock, and death.

Supportive treatment such as transfusion of blood products (fresh frozen plasma) for severe bleeding, dialysis for kidney failure, and fluids through veins (intravenous fluids) may be indicated. Dialysis is a procedure used in patients with kidney failure by which waste products are removed from the body through a machine.

Vaccines for yellow fever are available for persons who travel to places where yellow fever is endemic. A disease is said to be endemic in a region if it is constantly present in the population over a long period of time.

Zoonoses by prions :

General: Prions are infectious agents composed of protein that infects the brain and nervous tissue causing prion-related diseases (e.g., Creutzfeldt-Jakob disease). Proteins are complex organic (carbon-containing) compounds made of amino acids, which are composed of carbon, hydrogen, oxygen, nitrogen, and sulfur.

Creutzfeldt-Jakob disease (CJD): CJD, also known as transmissible spongiform encephalopathy in humans, is a rare, incurable, invariably fatal brain disease caused by prions.

CJD may cause rapidly progressive dementia (loss of mental ability). Initially, infected persons may have problems with muscle coordination and show personality changes along with impaired memory, judgment and vision. They eventually lose the ability to move and speak and enter into coma and death.

There is no known cure for CJD, only supportive treatments to relieve the symptoms and provide comfort. For example, opiate drugs may help to relieve pain, and drugs such as clonazepam and sodium valproate may treat brief involuntary muscle twitching (myoclonus).

CJD can be transmitted from an infected person through grafts of dura mater (a tissue that covers the brain), transplanted corneas (the transparent outer covering of the front of the eye), implantation of inadequately sterilized instruments (electrodes) in the brain, and injections of contaminated pituitary growth hormone derived from human pituitary glands taken from cadavers (a dead body intended for medical dissection). Healthcare workers, caregivers, and undertakers are at high risk of contracting CJD. CJD infection can be prevented by avoiding blood transfusions, tissue transplants or organ transplants from CJD infected persons. It recommended that persons at high risk should follow precautions such as hand washing of exposed skin before eating or drinking, wearing gloves when handling a patient's tissues and fluids, and avoiding accidentally cutting or sticking themselves with instruments contaminated by the patient's blood or other tissues.


Factors associated with research: Zoonoses are caused by infectious agents that can be transmitted from living animals (both wild and domestic) to humans. The health and safety of future generations may depend on several factors, such as uniform surveillance systems, reliable specimen collection, safe shipping and handling of food, advance and rapid methods to identify the disease organisms, suitable treatments, newer vaccines, and means for rapid communication.

Advance diagnostic aids: Advanced detection systems have been developed to identify contaminated areas and high-risk populations.

For example, a handheld advanced nucleic acid analyzer (HANAA), a real-time polymerase chain reaction (RT-PCR) based system may be used to detect infective agents used in bioterrorism attacks. The device may make it possible to deliver treatment immediately, and avoid complications related to infection.

Polymerase chain reaction (PCR) is an enzymatic method used to copy the two DNA strands of a particular gene sequence many times for laboratory study.

Also, the Lab-on-chip (LOC) device is used for detecting bioweapons, thereby facilitating immediate treatment. The LOC device combines several laboratory functions on a single chip that is only a few millimeters to square centimeters in size. The chip contains one or more sample deposit areas, measuring devices, mixing chambers or fluid channels to move the mixtures around, and reaction chambers that are temperature-controlled. LOC devices are simple to handle, and provide fast and accurate results within a short period of time using minute amounts of samples. These devices are portable, are much faster than the traditional methods, and are used for preliminary information of the disease or disease-causing agent. However, these devices do not eliminate the need for larger laboratories. The HANAA detects infectious agents based on their characteristic genes (nucleic acids), while the LOC detects a disease based on the biochemical markers from a sample (e.g., blood, urine) collected from an infected person.

Newer vaccines: Research is underway to develop vaccines for several zoonotic diseases such as malaria, tuberculosis, tularemia, avian influenza, and acquired immunodeficiency syndrome (AIDS).

The U.S. Department of Defense has designed an experimental tularemia vaccine for high-risk people (e.g., laboratory workers).

Vaccines to protect humans against disease-causing types (strains) of influenza A virus (H5N1) are currently under development. However, newer strains of avian influenza virus that may cause severe infection on a large scale may develop due to complex interactions between environment and these viruses. This may lead to difficulty in developing vaccines due to different characteristics of the viruses.

In addition, research is underway on methods to make large quantities of vaccine more quickly.

Developing vaccines for HIV may be difficult because of different geographic varieties and the propensity to change its genetic characteristics (mutations) frequently.

Risk-factor identification: Researchers have developed predictive models that can identify the occurrence of a specific zoonotic disease outbreak in terms of location and time. With the help of predictive models, suitable preventive and protective measures (e.g., vaccination, antibiotics for treatment) may be used to control the development and spread of zoonotic diseases.

For example, with predictive models researchers were able to predict outbreaks of malaria in southern Mexico and in Asia, Rift Valley fever in Kenya, Lyme disease in Illinois, and, in the southeastern United States, African trypanosomiasis and schistosomiasis in humans and livestock.

The use of predictive models involves analysis of information from devices, systems, and research. For example, remote sensing (RS) devices, geographic information systems (GIS), longitudinal studies for infectious agent activity, and rodent population dynamics can provide input for a predictive model. RS devices gather digital images of the Earth's surface from airborne or satellite platforms and convert them into maps. GIS is computer software that organizes and displays digital map data from RS or other sources and facilitates the analysis of relationships between mapped features with zoonotic disease hosts and human population.

This long-term study involves examining the characteristics of an infectious agent such as its infectivity, host organisms, life cycle, and mechanism of transmission. Population dynamics is the study of the short and long-term changes in the size and age composition of a population (e.g., rodents), and the biological, and environmental factors influencing those changes. Information is analyzed by a surveillance team consisting of researchers, epidemiologists, and technical experts (software, digital imaging), to predict when and where zoonotic disease outbreaks may occur.


This information has been edited and peer-reviewed by contributors to the Natural Standard Research Collaboration (

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