Simuliid vectors of onchocerciasis in Guatemala.

Simulium ochraceum, S. metallicum and S. callidum are the three species of Simuliidae which are known to transmit onchocerciasis in Guatemala. Of these, S. ochraceum is often the most prevalent and displays the highest degree of anthropophily. Other potential vectors exist, but have never been found to harbour developing forms of Onchocerca.The average flight range of these insects was found to be about 7.5 miles, although they may be transported greater distances while feeding on horses.The Simuliidae are most prevalent in December, after which their density decreases, reaching its lowest level in June-August.Large-scale dissection of Simuliidae specimens has revealed the presence of metacyclic forms either in a free state in the abdomen or, as in the majority of cases, lodged in the Malpighian tubes. There was no indication of metacyclic forms in the cephalic region of the insect.