The first systematic study of surveillance techniques for the insect vector of Chagas disease in Amazonia, conducted by researchers from the Fiocruz Instituto Leônidas e Maria Deane, the Smithsonian Tropical Research Institute, the London School of Hygiene and Tropical Medicine and colleagues, concludes that tall palm trees with large amounts of debris on their crowns and stems should be targets for disease surveillance and control.
Chagas disease, caused by a parasite transmitted by blood-sucking bugs, results in severe heart, digestive and neurological lesions. Chagas disease is endemic in Latin America where Trypanosoma cruzi infects about 7.5 million people. “The burden of Chagas disease in the Latin American-Caribbean region is still consistently larger than the combined burden of malaria, leprosy, the leishmaniases, lymphatic filariasis, onchocerciasis, schistosomiasis, viral hepatitides B and C, dengue, and the major intestinal nematode infections,” write the authors of the study, published Mar. 2, 2010 in the open-access journal, PLoS Neglected Tropical Diseases.
However, in Amazonia, where there are at least 100,000 infected people, insecticide-based control is not feasible because the insects seldom breed within houses. Most transmission occurs when triatomine bugs emerge from their natural habitats–usually palm trees–and fly into houses, attack rural workers or contaminate food or food-processing equipment.
Ascertaining whether a palm tree is infested is problematic. The small, cryptically-colored bugs easily go undetected. The authors asked whether all palms are equally likely to harbor triatomine bug colonies – while explicitly acknowledging that no detection technique works perfectly. Then, they determined whether palm infestation rates were associated with environmental differences at the regional, landscape, or individual palm tree level. Their study also asked whether palm tree management could lower palm infestation rates.
Building upon analytical methods recently developed by wildlife biologists, the study emphasizes that a disease vector is not necessarily absent from a site where it was not detected during a survey. Such ‘detection failures’ are pervasive – a feature that is inherent to all vector studies. The robust methodology described in this paper is generally suited for investigating vector occurrence and ecology when detection is imperfect.
Based upon this study, vector surveillance teams can now draw upon clearly defined detection criteria. Surveillance teams should consider the circumstances at the origin of a disease outbreak or an isolated acute case. A ‘high-risk’ palm tree will very likely be found near the residence of the patients or near an unprotected fruit press used to prepare contaminated juice. These recommendations are consistent across different Amazon sub-regions and landscapes. Finally, the study suggests that simple environmental management practices, such as removing organic debris from the crowns and stems of peri-domestic palms, may substantially reduce the risk of vector-human contact.
Chagas disease, Latin American killer, pushed aside by swine flu
Geneva, Switzerland (GenevaLunch) – Chagas disease is one of the largest debilitating and killer diseases in Latin America, but it is not winning the battle it needs for public attention in order to reduce the number of its victims. It is considered a neglected tropical disease by the WHO (World Health Organization), which put it on the agenda for the May 2009 World Health Assembly, in part because it appears to be traveling, thanks to eco-tourism. It was bumped when the agenda was reduced to allow the meeting to focus on the new pandemic, A/H1N1.
Chagas disease appears to be spreading from isolated rural areas to urban areas as people move to cities, but there is little prevention for the insect-borne disease, no standardized diagnostic test and huge knowledge gaps remain about effective treatment.
Some 50,000 people are diagnosed every year, but it has until now remained mainly a disease of very poor and isolated populations, “making it a commercially unviable candidate for drug development,” according to SciDevNet in Reuters AlertNet. “Chagas is the disease with the highest impact in Latin America. It is probably causing over two-and-a-half times more lost years of healthy life than malaria, leprosy, bilharzia and leishmaniasis combined.”
A new National Institutes of Health initiative in the US, the Therapeutics for Rare and Neglected Diseases programme, is putting $24 million into research, but doctors, scientists and public health authorities are concerned that the insect-borne disease is getting ahead of them, with new clinical presentations and the disease showing up in Europe, North America and Japan. “Growing human migration and mobility have increased the geographic distribution of Chagas in recent decades and the disease now has the potential to become an international threat,” reports SciDevNet. Chagas disease can take up to 15 years to show its more serious symptoms, including heart and eye problems, which makes it difficult to detect. In the early stages it causes mild swelling at the site of the insect bite, often on the face, and mild headaches, slight fever.
The WHO in 2007 set up its Global Network for Chagas Elimination to coordinate global efforts to eliminate the disease by 2010 but the scale of the programme remains relatively small.
Source, July 30, 2009 – GenevaLunch