Volume 38, Issue 1
  • ISSN: 0002-9637
  • E-ISSN: 1476-1645



Transmission of , principally by , was studied over a 14-month period in the Atitlán region of Guatemala. Semimonthly catches of black flies were made on human volunteers at 4 localities with different prevalences of human onchocerciasis. Host-seeking activity of reached its greatest magnitude in the early dry season (October–January) but then declined rapidly and was lowest during the late dry season (February–May). The frequency of larvae in parous host-seeking also varied seasonally, and this variation was most pronounced for third stage larvae. At a hyperendemic locality, the highest frequency of this larval stage occurred during the February–March period (0.0142 in 1979 and 0.0095 in 1980). From June–January, the frequency of third stage larvae in was < 0.003. The frequency of early first stage larvae exhibited the least seasonal variation, ranging from 0.0354 in August–September to 0.0628 in April–May. The transmission rate of by also varied seasonally. At the same hyperendemic locality, infective biting density of attained its greatest magnitude in February–March. The survival rate of female from one gonotrophic cycle to the next was estimated from the ratio of flies with early first stage larvae to those with infective stage larvae. These rates varied seasonally and ranged from 0.2132 to 0.3974, with the highest rates occurring in the late dry season.


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