An important variable in the epidemiology of arthropodborne diseases is the intensity of transmission, which is a function of host-vector contact and the prevalence of infection in the vector population. This latter value is often difficult to estimate. It is possible to envision the application of polymerase chain reaction (PCR) assays to this problem. To accomplish this, the assay must detect a single infected vector in a pool containing a large number of uninfected individuals. It must also be possible to calculate the prevalence of infection from the number of positive pools. A PCR assay for detecting Onchocerca volvulus in pools of vector black flies is described, and an algorithm is presented to calculate the prevalence of infection in the vector population, based upon the proportion of PCR-positive pools. This algorithm should be applicable to any disease for which a PCR assay is available.

We developed a DNA assay for bloodmeal identification in haematophagous insects. Specific host cytochrome B gene sequences were amplified by PCR and classified on the basis of their mobility in a heteroduplex assay. In the blackfly Simulium damnosum s.l. (Diptera: Simuliidae), human cytochrome B DNA sequences were identifiable up to 3 days following ingestion of the bloodmeal. In the tsetse Glossina palpalis (Diptera: Glossinidae) collected from tsetse traps in Ivory Coast, bloodmeals were identified as taken from domestic pigs on the basis of their heteroduplex pattern and DNA sequence. Evidently the cytochrome B sequence shows sufficient interspecific variation to distinguish between mammalian host samples, while exhibiting minimal intraspecific variation. The stability of DNA in bloodmeals, for several days post-ingestion by haematophagous insects, allows PCR-HDA assays to be used reliably for host identification.

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The standard assay for onchocerciasis diagnosis is microscopic detection of parasites in skin snips. Skin snipping is painful and may potentially transmit bloodborne infections. Thus, an alternative method for the diagnosis of onchocerciasis that does not require skin snipping is needed. A polymerase chain reaction (PCR) -based assay was shown to detect the presence of parasite DNA in superficial skin scrapings. Detection of parasite DNA in both skin snips and skin scratches was found to be more sensitive for detecting low-density infections than was microscopic examination of skin snips. The skin scratch PCR assay is minimally invasive and painless and does not present the risk of transmitting bloodborne infections. These properties make the skin scratch an attractive alternative to the skin snip for detecting O. volvulus infection. Onchocerciasis, or river blindness, is caused by infectionO. volvulus microfilariae reside in the uppermost layers of the dermis [6] and may be detected by skin scarification [7]. We with the filarial parasite Onchocerca volvulus. When measured in terms of the socioeconomic effects on afflicted communities, therefore hypothesized that it might be possible to detect O. volvulus DNA in the skin of infected persons, without resorting onchocerciasis is one of the most important infectious diseases worldwide [1]. As a result of the large socioeconomic impact to skin biopsy, by using the O-150 PCR. of the disease, several international programs underway in Africa and the Americas have the goal to eliminate onchocerciasis Materials and Methods as a socioeconomic and public health problem [1,2].In any disease control program, it is important to have safe After the Gnankoradji study, similar studies were carried out in four villages in southern Burkina Faso (Habré, Diourao, Zoulo, and Foungou). These villages are located in the savanna bioclime of West Africa and are included within the OCP control zone. The

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