Today’s plagues more complex
Last updated: Monday, November 24, 2008 Print"There appear to be common determinants of disease emergence that transcend time, place and human progress," says one of the study authors, Anthony Fauci, from the National Institute of Allergy and Infectious Diseases (NIAID). For example, international trade and troop movement during wartime played a role in both the emergence of the Plague of Athens in 430 BC as well as in the spread of influenza during the pandemic of 1918 to 1919. Other factors underlying many instances of emergent diseases are poverty, lack of political will, and changes in climate, ecosystems and land use, the authors contend.
"A better understanding of these determinants is essential for our preparedness for the next emerging or re-emerging disease that will inevitably confront us," says Fauci. "The art of predicting disease emergence is not well developed," says David Morens, another NIAID author. "We know, however, that the mixture of determinants is becoming ever more complex, and out of this increased complexity comes increased opportunity for diseases to reach epidemic proportions quickly."
More people travelling
More people travel more often over greater distances and in less time now than at any time in the past. One consequence of the increased mobility in the modern age can be seen in the 2003 outbreak of the novel illness SARS, which rapidly spread from Hong Kong to Toronto and elsewhere as infected passengers travelled by air.
To better understand and predict disease emergence, Morens and his co-authors stress the need for research aimed at broadly understanding infectious diseases as well as specifically understanding how disease-causing micro-organisms make the jump from animals to humans.
The Black Death, for instance, was borne westward along newly established land and sea trade routes from its probable origin, China, into multiple European countries. Similarly, patterns of human movement along trade routes, specifically truck routes throughout Africa, played a role in the spread of HIV throughout that continent. Greater consideration must be given, say the NIAID authors, to broader, interlinked factors such as climate, urbanisation, increased international travel and the rise of drug-resistant microbes, and the ways in which these factors combine to spark new epidemics.
Aside from commerce and travel, the NIAID authors point to several other factors that underlie many notable emerging diseases: poverty, the breakdown of public hygiene practices, and susceptibility of human populations to microbes against which they have no pre-existing immunity.
This last factor played a key role in the smallpox epidemic that afflicted the Aztecs of 16th century Mexico. Smallpox had ravaged European communities for centuries, but until the Spanish arrived on the Yucatan coast in 1519, the disease was unknown in the New World. Historians believe that some 3.5 million people in central Mexico died in the first year of the epidemic.
Rats could harm heart
In another study, researchers suggest that brown rats (the biggest and most common in Europe) may now be carrying bacteria that can cause serious heart disease in humans.
Scientists have found that rodents carry several pathogenic species of Bartonella, such as B. elizabethae, which can cause endocarditis and B. grahamii, which was found to cause neuroretinitis in humans. Although scientists are unsure about the main route of transmission, these infections are most likely to be spread by fleas. Ctenophthalmus nobilis, a flea that lives on bank voles, was shown to transmit different species of Bartonella bacteria. These pathogens have also been found in fleas that live on gerbils, cotton rats and brown rats.
The researchers took samples from 58 rodents, including 53 brown rats, two mice (Mus musculus) and three black rats (Rattus rattus). Six of the rodents were found to be carrying Bartonella bacteria; five of these were brown rats. Four of the rodents were carrying B. elizabethae, which can cause heart disease in humans, and one of the black rats was found to be harbouring B. tribocorum. However, the scientists noticed one strain that had not been identified in rodents previously. The strain was finally shown to be close to B. rochalimae.
"Because of the small sample size used in this study, we cannot say for sure that the common brown rat is spreading B. rochalimae," said Professor Chang. "However, several different Read more: November 2008
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