Zoonoses is a general name for diseases which spread from animals to people who have close contact with them, or with their faeces. There are in fact few diseases from which animals suffer which can be spread to humans. Rabies, on the other hand, is easily transferred and all cases of rabies, which is always fatal once symptoms appear, are taken very seriously by the authorities.
Diseases that dogs spread to humans fall into two main groups, namely parasitic infestations, and bacterial or viral infections.
Most often diseases are spread from pets to people by means of bites, scratches or direct contact with the animal or its faeces. If a dog has bitten a person, immediate cleaning of the injured area with disinfectant soap and water will minimise the risk of infection, but if swelling and inflammations occur, it is best to see a doctor.
The main types of diseases which people can pick up from dogs are rabies, salmonella, campylobacter, giardia, cryptosporidium, roundworm and ringworm.
This fatal viral infection affects the brain and spinal cord, causing both irritation and inflammation. Pets can infect humans with this virus. What usually happens is that they themselves have been infected by an animal, usually a wild one, carrying the virus in their saliva. This virus is mostly spread by means of bites. The disease, though found more often in dogs than cats, can also be spread when any rabid animals bite humans. Once symptoms appear, rabies is always fatal to both animals and humans.
Who is at risk?
If a rabid animal bites a person, rabies usually results. People are at risk if they come into contact with wild animals, in South Africa particularly suricates (meerkatte), the black-backed jackal or the bat-eared fox, who may be infected with rabies. People who have pets who may have been bitten by a rabid wild animal or by another pet, which may have contracted rabies, are at risk. It stands to reason therefore that people living in rural areas or on the outskirts of cities are at greater risk than people living in urban areas. As bites are the source of rabies infection, which can be fatal, all bites should be treated as medical emergencies, particularly if the animal involved is wild, or is a pet that is showing abnormal behaviour.
Signs and symptoms
Symptoms of rabies can take anything from 20 to 60 days to manifest. Symptoms vary from person to person, but one in every five people who have rabies, develops rising paralysis. Symptoms often appear flu-like – sore throat, a headache, fever and nausea and vomiting. Depression, restlessness and insomnia often also mark the onset of rabies symptoms. Overproduction of saliva and uncontrollable excitement and aggression often marks the next phase, followed by spasms of the throat and voice box, which can be extremely painful. This happens because rabies affects the area in the brain responsible for breathing and swallowing. Attempts to drink water can also bring on these spasms.
Diagnosing rabies in its early stages, especially if a doctor is not told about an animal bite, is not easy, as the symptoms are varied and can appear to be the symptoms of many other diseases. In order to make a confirmed diagnosis of rabies, brain tissue of the animal that bit the person, must be examined. In the case of a pet, which shows no symptoms, the animal may be observed by a veterinarian for ten days to determine whether the animal was infected with rabies at the time of the bite. Viral testing of a person is ineffective in the case of rabies, but both a skin biopsy and a blood test can reveal the virus. In the case of the blood test, it will only help in diagnosing the condition once serious symptoms have set in.
Treatment and prevention
It is possible to vaccinate people against rabies. This is usually done in the case of people who, through their work, may come into contact with animals that may be infected. Game rangers, veterinarians and laboratory workers all fall into this group. The vaccine should be administered every two years.
Immediate preventative steps must be taken when someone may have been bitten by a rabid animal. This can prevent someone from developing rabies. Cleaning the contaminated area with hot water and disinfectant immediately after a bite also reduces the infection risk. Vaccination against rabies and a tetanus injection must also be given immediately after a bite. Before vaccination was available, death usually occurred within three to 10 days, and was usually caused by paralysis, asphyxia, convulsions or exhaustion. People can still die from rabies, especially if treatment is delayed after the initial bite occurred.
Rabies is best prevented when all animal bites are considered medical emergencies, especially if the animal who bit the person concerned is not known, is wild, or was acting strangely at the time the bite occurred.
People who regularly come into contact with a range of animals, especially through their work or hobbies, should be vaccinated regularly.
Human rabies can be prevented, even after someone has been bitten by a rabid animal. The important thing is to get the appropriate treatment before the person starts showing signs of rabies.
This bacterium causes intestinal infections and can be transferred easily from dogs, especially puppies, to humans. This happens easily when people do not wash their hands properly after coming into contact with animal faeces, especially diarrhoea. These bacteria are also found in meat and undercooked poultry, untreated water and unpasteurised milk, so direct contact with animal faeces is not the only source of these infection-causing bacteria.
Abdominal cramping and pain, diarrhoea, which is sometimes bloody, nausea and vomiting, as well as fever are all symptoms of this kind of bacterial infection, which can cause severe dehydration.
Usually no special treatment is needed. In severe cases, a healthcare professional can prescribe an antibiotic. Very few people die from a campylobacter infection.
It is nevertheless important to steer clear of having direct contact with dog faeces. Regular removal of dog faeces from the garden is recommended, as this will reduce the possibility of contact with these bacteria. Sandpits should be kept covered when they are not being used.
Salmonella bacteria are found in the gut and faeces of humans and animals, as well as in many different foodstuffs, especially raw meat. Salmonella bacteria can cause food poisoning, which in turn leads to diarrhoea and vomiting.
People can be infected with salmonella through direct contact with their pets, or with their faeces. Proper washing of hands is essential after touching pets, or cleaning animal cages or after coming into contact with pet faeces.
The symptoms of salmonella poisoning are headaches, a fever, diarrhoea and abdominal cramps.
Cases of salmonella poisoning mostly clear up by themselves and do not require special treatment. In the case of the very young, the very old and those who have compromised immunity, medical attention must be sought. It is nevertheless wise to consult a doctor if the diarrhoea becomes severe in anyone, as dehydration may result.
To prevent salmonella infection from dogs, it is wise to be very careful when handling dog faeces. It is best to wear gloves when cleaning up dog faeces and to wash hands properly afterwards. Children's sandpits should be covered when not in use.
Giardia and cryptosporidium
These are parasites called protozoa that can cause intestinal disease. Dogs can be infected with these parasites, without having any symptoms themselves. Direct contact with pets can cause people to be infected with these parasites.
Diarrhoea and severe stomach cramps are the most common symptoms of this intestinal infection.
Once again, in most people, the symptoms disappear by themselves after two to three days, but in people who have immune system problems, this infection could be fatal.
Children should be taught to always wash their hands after playing with pets, as direct contact is the most common way in which these parasites can infect people.
DOG Roundworm (Toxocariasis or Visceral Larva Migrans)
The type of roundworm found in dogs, is called Toxocara Canis, and can infect humans. Children who eat sand can easily ingest roundworm eggs. Infestation of humans by roundworm is common, especially in developing countries, where sanitation is often poor and access to clean drinking water limited. Roundworms are cylindrical in shape and can be short or long.
The causes of roundworm infection follow the pattern of most worm infestations. Eggs of the worm are discharged in the stool of an animal or human. Eggs can be ingested directly if contaminated hands touch the mouth. The eggs hatch in the intestine, releasing larvae which can penetrate the gut wall, enter the bloodstream and spread throughout the body.
Signs and symptoms
Symptoms vary depending on a person's age, the intensity of the exposure and sensitivity to the larvae. Symptoms are varied and include pneumonia, coughing, fever, skin rash and liver enlargement.
The above-mentioned symptoms may alert a doctor to the presence of roundworms. High levels of certain white blood cells is another warning sign. If doubt exists, a biopsy of liver tissue may reveal the presence of roundworm larvae.
Treatment and prevention
Dogs should be dewormed regularly. People who have been infected with roundworm usually rid themselves of the parasite without treatment in six to 18 months. Mebendazole (Vermox) is often prescribed for people infected with roundworm.
Ringworm is a skin disease caused by a fungus. It is also known as dermatophytosis. It causes circular lesions under the skin. It is not caused by a worm, but was once thought to be the case, hence the name. Ringworm is an infection in the dead layer of the skin, hair and nails. It can be transmitted between pets and people easily through touch. Children are very susceptible to ringworm infections.
Dogs can transmit ringworm to people through direct contact with the fungus spores that causes this infection.
Several different types of fungi can cause ringworm and it is usually named after its location on the body, eg. jock itch or athlete's foot, to name two examples. Tricophyton and Epidermophyton are both fungi that can grow in moist warm areas of the body, such as the groin or between the toes.
Signs and symptoms
The most common sign of ringworm is an itchy and raw, painful rash. Sometimes the rash can become scaly and blisters can form. Ringworm can typically affect the feet, the groin, the scalp and the nails. There is also a form of ringworm called body ringworm that can develop anywhere on the skin.
Most often these skin infections can be cured by antifungal creams. It is important that instructions be followed carefully, as fungal infections can recur easily if treatment is stopped too soon. Persistent cases of ringworm can be treated with griseofulvin, but sometimes this can cause unpleasant side effects.
Keeping the infected areas clean and dry is important. It is also important to treat cats and dogs if they show any signs of ringworm, as it is so easily transmitted through direct contact with humans.
Prevention of diseases dogs can spread to humans
The prevention of these diseases is fairly simple. People must avoid coming into contact with dog faeces in gardens. Gloves must be worn when removing dog faeces. Hands must be washed properly after direct contact with dogs. Sandpits must be kept covered when not in use, to avoid children coming into contact with dog faeces. Dogs should be dewormed regularly and children must be taught not to play roughly with dogs or to avoid being licked by the dogs, especially in the face.
When to see a doctor
All animal bites should be taken very seriously and should be given medical attention. Fever and diarrhoea are often symptoms of diseases, which dogs can transmit to people. If unusual symptoms occur, it is always best to seek medical advice.
Written by Susan Erasmus, Health24, 2003