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A New Method for Forensic DNA Analysis of the Blood Meal in Chagas Disease Vectors Demonstrated Using Triatoma infestans from Chuquisaca, Bolivia

10 Nov 2008

Marcia Triunfol

Citation: Pizarro JC, Stevens L (2008). A New Method for Forensic DNA Analysis of the Blood Meal in Chagas Disease Vectors Demonstrated Using Triatoma infestans from Chuquisaca, Bolivia. PLoS ONE 3(10): e3585.

Despite many efforts to control the dispersal of Chagas’ disease in Bolivia, approximately 50% of Bolivian territory is endemic to Triatoma infestans, the main vector of the disease in the region.

While insecticidal spraying in many South American countries has been able to control the disease and reduce rates of T. cruzi house infestation, similar efforts in Bolivia have not achieved the same result.

The explanation may lie in the existence of sylvatic populations of T. infestans that may move from natural areas to domestic and peri-domestic areas that have been treated with insecticides, which may cause re-infestation of such areas. To better understand vector movement through the analysis of their feeding patterns, a new approach based on molecular biology techniques (PCR) has been developed to help identify potential sources of reinvasion in these areas.

In this study, the researchers analyzed the blood meal of T. infestans found in domestic vs. peri-domestic areas by searching for the DNA of 11 different species of vertebrate (cow, pig, chicken, dog, guinea pig, cat, mouse, donkey goat, sheep and humans) in the meal of T. infestans. The researchers analysed 81 T. infestans collected in Chuquisaca, Bolivia. The sample was stratified by habitat with insects from domestic and peri-domestic sites. A total of 29 insects came from human habitations, 11 from chicken coops and 41 from corrals, in which cows were kept

The researchers investigated three main issues in this study. The first was whether any similarity existed in the meals found in insects collected in different habits. If the meals were revealed to be similar then it could be assumed that insects were circulating among habitats (domestic vs. peri-domestic). If different, then insects in each habitat did not move and fed exclusively from the animals found in their respective habitats.

DNAs from seven vertebrates were detected in insects collected from domestic habitats. Pig DNA was the most common DNA found, followed by dog DNA. The DNA species found in houses were also found in insects collected in peri-domestic areas. Pig DNA was again the most common, followed by chicken, dog, goat, guinea pig and human. In nine peri-domestic insects no vertebrate DNA was found. It should be mentioned that all insects were tested for infection with T. cruzi.

As expected, human DNA was more frequently found in insects from houses than in those from peri-domestic areas. DNAs from all other species were equally distributed between habitats. The variation of meals in insects collected in both habitats indicated that insects were moving from one habitat to another. However, how frequent was this movement? To answer this question, the researchers investigated the frequency of multiple feeding and found that most insects (52%) had DNA from more than one species in their meal. Nevertheless, those insects that fed on humans or cows were less likely to have fed on other additional animals. This may be explained by host abundance and proximity as cows are very abundant in these areas, if compared to the limited numbers of other animals (goats, dogs, pigs, etc.), and are kept in open corrals close to human houses.

Next, the researchers asked whether the rate of T. cruzi infection varied between habitats and whether it was associated with a specific blood type. It is known that the likelihood of parasite transmission is host-dependent. For instance, bugs that feed on infected dogs have higher chances of becoming infected than those that feed on humans. Although infection with T. cruzi was higher in those insects collected from houses, the difference was not significant.

The technique presented in this study is useful for understanding vector movement, which may be essential for designing better strategies that rely on insecticidal spraying. The results show that insects are constantly moving between habitats and that the role of animals such as pigs and dogs should be taken into account in the dynamics of T. cruzi infection in the endemic areas of Bolivia.

2008 Pizarro et al. This is an open-access article distributed under the terms of the Creative Commons Attribution License, which permits unrestricted use, distribution, and reproduction in any medium, provided the original author and source are credited.

Source

Title:
A new method for forensic DNA analysis of the blood meal in chagas disease vectors demonstrated using Triatoma infestans from Chuquisaca, Bolivia.

Authors:
Pizarro JC, Stevens L

References:
PLoS ONE 2008: Vol. 3 no. 10, pp. e3585

Abstract:
BACKGROUND: Feeding patterns of the vector are important in the epidemiology of Chagas disease, the leading cause of heart disease in Latin America. Chagas disease is caused by the parasite, Trypanasoma cruzi, which is transmitted by blood feeding insects. Historically, feeding behaviours of haematophagous insects have been investigated using serological reactions, which have detection limits in terms of both taxonomic resolution, and quantity and quality of the blood meal. They are labor intensive, require technical expertise, need fresh or frozen samples and antibodies often are either not available commercially or the resources for synthesis and purification are not available. We describe an assay to identify vertebrate blood meal sources, and the parasite T. cruzi using species-specific PCR assays from insect vectors and use the method to provide information regarding three questions: (1) Do domestic and peri-domestic (chicken coop and animal corral) habitats vary in the blood meals detected in the vectors? (2) What is the pattern of multiple blood meals? (3) Does the rate of T. cruzi infection vary among habitats and is it associated with specific blood meal types? METHODOLOGY/PRINCIPAL FINDINGS: Assays based on the polymerase chain reaction were evaluated for identification of the blood meal source in the heamatophagous Chagas disease vector Triatoma infestans. We evaluate a technique to identify 11 potential vertebrate food sources from the complex mixture extracted from the vector's abdomen. We tested the assay on 81 T. infestans specimens collected from the Andean highlands in the department of Chuquisaca, located in central Bolivia, one of the regions in South America where sylvatic T. infestans have been reported. This area is suggested to be the geographic origin of T. infestans and has very high human infection rates that may be related to sylvatic vector populations. CONCLUSION/SIGNIFICANCE: The results of the assays revealed that a high percentage of insects collected in human dwellings had fed on peri-domestic animals. In contrast, one insect from a chicken coop but no bugs from corrals tested positive for human blood. Forty-eight percent of insects tested positive for more than one vertebrate species. T. cruzi infection was detected in 42% of the specimens. From the epidemiological point of view, the results reveal an overall pattern of movement from peri-domestic structures to human habitations for T. infestans in this region of Bolivia as well as the important role of pigs, dogs, chickens and guinea pigs in the dynamics of T. cruzi infection.

PMID: 18974787
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