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Colonization techniques were developed in order to select mating strains from four geographic populations of Simulium decorum. Although mating strains were established from each locale, emphasis was shifted toward developing permanent colonies from Dryden Lake, New York, USA and Warm Springs, Georgia, USA. The net reproductive rate (Ro) was computed for the parental, F1, and F2 generations of each strain in order to assess the effects of colonization through successive generations. Ro increased rapidly for both strains from parental (range of 0.34-3.5) through F2 generations (range of 16.2-21.6). Analysis of Ro components indicated that the increases in Ro were the result of two parameters that reflect the propensity of flies to mate in confinement, suggesting that selection for mating is rapid. Multiple regression analysis indicated no significant differences between strains or generations when tested against fecundity (range of 391-519) and survival of immatures (range of 90.3-97.2%). A slight positive correlation (regression coefficient of 0.0016, P less than .01) was observed between larval density (range of 284-4,439 larvae per rearing) and survival of immatures, suggesting that the limits of the rearing system with regard to crowding were not approached. Both strains readily adapt to the laboratory and are currently in the fifth generation.

The viability of Dirofilaria immitis microfilariae recovered from canine blood by different methods was determined. Microfilaria recovery techniques included saponin lysis, saponin lysis with a trypsin treatment, dextran sedimentation and phytohemagglutinin treatment. Criteria for evaluating viability were microfilarial motility in vitro at 37 degrees C, microfilarial development in mosquitoes and the ability of microfilariae to circulate in mice. Although each method produced motile microfilariae, differences among groups of microfilariae recovered by different techniques were apparent by each of the criteria for viability. Saponin lysis gave superior yields of viable microfilariae.

La Avellana and Puerto Barrios, two enzootic foci of Venezuelan encephalitis (VE) virus on the Pacific and Caribbean lowlands (respectively) of Guatemala have been studied over a 13-year period. Data from sentinel hamsters and guinea pigs and wild and domestic vertebrates are reported. VE virus strains were isolated from hamsters each period they were exposed during the rainy seasons 1968-1980 and at the end of the dry season 1974. Rates of isolation of VE virus ranged from 0.2%-5.7% hamster/days/exposure. All strains tested were free of epizootic virions. Although virus was isolated from sentinel guinea pigs, their deaths were not attributable to infection with VE virus. Antibody titers in 26 of 28 terrestrial mammals bled at La Avellana in 1971 were higher to enzootic than to epizootic VE strains. Thirty-seven percent of 109 residents of Puerto Barrios had antibody to VE virus. In 13 of 20 tested, antibodies were engendered by the enzootic strain. Nepuyo and Patois viruses were isolated from sentinel hamsters at both La Avellana and Puerto Barrios.

Of three species of Nearctic black flies tested, Simulium pictipes Hagen proved the most efficient laboratory vector of the bovine parasite Onchocerca lienalis. Among flies inoculated intrathoracially with 40 microfilariae, numbers of 3rd-stage larvae per fly were 7.63 for S. pictipes, 7.54 for S. vittatum Zetterstedt, and 0.83 for S. decorum Walker. S. pictipes survived the longest under laboratory conditions, with 83.3% of the females remaining alive 10 days after inoculation with 40 microfilariae of O. lienalis. Using an artificial membrane feeding system, S. pictipes could be routinely infected with O. lienalis by mouth. This black fly was also susceptible to infection with the Guatemalan strain of O. volvulus. Among flies injected with 10 microfilariae the rate of infection with 3rd-stage larvae was 93%, with a mean of three 3rd-stage larvae per fly. Successful techniques for the large-scale recovery and cryopreservation of 3rd-stage larvae of O. lienalis were also developed. A motility rate of 92.7% was observed in larvae cryopreserved within vector black flies.

Two species of Nearctic black fly, Simulium decorum and S. pictipes, exhibit partial susceptibility to infection with the bovine parasite, Onchocerca lienalis, when inoculated intrathoracically with microfilariae. In addition, a proportion of S. decorum females will support the development of the human parasite, O. volvulus, to the third larvae stage. Infection rates with second- or third-stage larvae seven or more days after varied among geographic strains of S. decorum, ranging from 6.5% in a strain from northern New York State to 48.7% in a strain from Georgia. The average number of larvae per infected female ranged from 1.00 to 1.78 in the three strains examined. Partial susceptibility to O. lienalis was found to persist in colonized strains of s. decorum, and cryopreserved microfilariae of this parasite retained their infectivity. Seven or more days after inoculation with microfilariae of the Guatemalan strain of O. volvulus, 16.7% of the females of S. decorum harbored second- or third-stage larvae. Development of O. lienalis and O. volvulus proceeded normally in these black flies, and moderate increases in susceptibility rate and number of infective larvae were noted in response to increased microfilarial dosages.

Ivermectin, a broad spectrum antiparasitic agent, interrupted the uptake of Onchocerca volvulus microfilariae by Simulium ochraceum from a group of human volunteers given multiple oral treatments of 200 micrograms/kg body weight. Two treatments, given at 7 month intervals, resulted in almost complete suppression of developing or infective larvae in the vector population for a 6 month period. The overall decline following 2 treatments was an order of magnitude lower than the pretreatment level. Ivermectin administration, in addition to the beneficial clinical effects, also could be useful for the control of human onchocerciasis as an independent measure or in conjunction with vector control.

Oogenesis in Simulium ochraceum is characterized in terms of distinct stages of follicular development following emergence, sugar feeding, and completion of a blood meal. Changes in the ovary following the first oviposition are also described. This black fly species was found to be anautogenous and exhibited gonotrophic concordance. The formation of follicular dilatations after oviposition followed a distinct pattern with traces of cellular debris evident up to 144 hours. The presence of fructose, as detected by the cold Anthrone test, indicated that both parous and nulliparous flies routinely imbibe nectars as part of their foraging behavior. The availability and frequent use of nectar may contribute significantly to longevity of parous flies, hence increasing their vector potential.

Barriers to dissemination of Middle American epizootic hemagglutination inhibition subtype I-AB, and enzootic, subtype IE, Venezuelan encephalitis (VE) viruses were examined in a colony of the enzootic vector mosquito, Culex (Melanoconion) taeniopus. This species is highly susceptible to oral infection with enzootic, but not epizootic, virus strains. Adult female mosquitoes were intrathoracically inoculated with epizootic virus suspensions to ascertain whether a mesenteron infection barrier exists to these subtype I-AB strains. All inoculated mosquitoes became infected, including those receiving only 10 chick embryo cell culture plaque-forming units (CEC pfu). This confirmed that a mesenteron infection barrier exists to epizootic, but not enzootic Middle American VE strains. Mosquitoes were also given high titer hamster bloodmeals of epizootic viruses and dissected at 2-day intervals to determine the location of virus in the few infected individuals. With mean bloodmeal titers of up to 10(5.3) CEC pfu, only 20% or less of the mosquitoes became infected, and virus replication was confined to the mesenteron. This indicated that a mesenteron escape barrier to epizootic VE viruses exists in this mosquito. Mosquitoes were also given large and small oral doses of enzootic virus strains to compare viral replication patterns. With high titer bloodmeals, virus disseminated from the mesenteron within 4 days of infection, and titers in mosquitoes peaked 7-9 days after infection. All mosquitoes that ingested large doses became infected. Mosquitoes receiving small oral doses of enzootic viruses showed a different pattern of virus replication.(ABSTRACT TRUNCATED AT 250 WORDS)

Through preliminary experiments, an effective method for radiolabeling Brugia malayi-infected mosquitoes in order to produce labeled infective Brugia larvae was developed. Starting on the 6th day after the infective blood meal, mosquitoes were fed a 7% sucrose solution containing 100 microCi/ml 75Se-L-methionine for 5 days. Infective larvae, retrieved 2 days after this labeling period, averaged 381 +/- 136 counts/min. Jirds were infected with these infective, labeled larvae either by allowing infected mosquitoes to feed on uninfected jirds for 30 min or by inoculating jirds subcutaneously in the groin with washed larvae recovered from mosquitoes. Jirds were killed at various times after infection and were sliced into approximately 0.5 mm thick sagittal sections, which were dried and placed on X-ray film. Autoradiograms were developed after 30-60 days at 5 degrees C. In a sample of 26 inoculated jirds, approximately 30% of the infecting larvae could subsequently be accounted for as Ag degrees foci on autoradiograms. The Ag degrees foci representing larvae were apparent up to 2.5 weeks after infection. In jirds infected by mosquito feeding, the Ag degrees associated with the feeding site persisted for more than 6 weeks after infection.

Laboratory-derived Simulium yahense and S. sanctipauli females were used to produce large numbers of Onchocerca volvulus infective stage larvae (L3) for use in assessing the possible chemoprophylactic potential of ivermectin in the chimpanzee model. Engorgement rates and subsequent post-prandial survival were correlated with the time at which adult flies were offered a carbohydrate source following emergence and the age of flies that fed on microfiladermic volunteers.

The ocular changes that occur with diethylcarbamazine treatment of onchocerciasis seriously restrict its usefulness. Ivermectin, a newly developed antifilarial drug, was compared with diethylcarbamazine for treatment of onchocerciasis in a double-masked, placebo-controlled trial. Thirty men with moderate to severe infection and ocular involvement were randomly assigned to receive ivermectin as a single oral dose (200 micrograms/kg), diethylcarbamazine (administered for eight days), or placebo. Detailed ocular examinations were performed serially over a 12-month period. Diethylcarbamazine treatment caused a marked increase in living and dead microfilariae in the cornea, punctate opacities, and limbitis during the first week of therapy. Ivermectin had no such effect. However, ivermectin therapy resulted in a long-term reduction in intraocular microfilariae comparable to that seen with diethylcarbamazine. Ivermectin appears to have few ocular complications and be a better-tolerated and more effective microfilaricidal agent than diethylcarbamazine for the treatment of onchocerciasis.

The lectin-binding properties of microfilariae of Onchocerca volvulus, O. lienalis, Brugia pahangi, Wuchereria bancrofti, Dirofilaria immitis, and Monanema (= Ackertia) marmotae share a number of characteristics. Carbohydrates specific for lectins are associated with the egg shell or sheath. N-acetyl-D-glucosamine is the predominant carbohydrate associated with the ensheathed forms with lesser quantities of D-galactose and/or alpha-lactose and D-galactosamine. The density of these carbohydrates on the sheath surface diminishes as the larvae undergo normal growth and development. Similar carbohydrates are not found on the cuticle as exsheathed microfilariae show virtually no ability to bind lectins.

Ivermectin, given to onchocerciasis patients as a single oral dose of 200 micrograms per kilogram of body weight, substantially reduced the uptake of Onchocerca volvulus microfilariae by Simulium yahense, an efficient black fly vector of the parasite in the tropical rain forests of West Africa. Three months after treatment, patients given ivermectin infected flies at a significantly lower rate than those who had received diethylcarbamazine or placebo, thereby reducing the number of developing larvae in the vector population. This diminished rate of infectiousness was also evident 6 months after treatment. These results strongly suggest that ivermectin could be effective in interrupting transmission of Onchocerca volvulus for epidemiologically important periods of time.

Laboratory vector competence of Culex (Melanoconion) cedecei was examined for Venezuelan equine encephalomyelitis (VEE) viruses. Colonized adult female mosquitoes originating from a southern Florida population were given bloodmeals from viremic hamsters circulating various titers of 3 hemagglutination inhibition (HI) subtypes of VEE viruses. Following extrinsic incubation of about 3 weeks, mosquitoes were allowed to refeed on uninfected hamsters for transmission trials. Cx. cedecei was highly efficient in becoming infected with and transmitting its sympatric, HI subtype II "Everglades" virus. With bloodmeal titers of 10(0.9) chick embryo cell culture (CEC) plaque forming units (PFU), the infection rate was 9% and transmission occurred following extrinsic incubation. Infection rates were greater than or equal to 80% with oral doses of greater than or equal to 10(1.8), and all infected mosquitoes were capable of transmission following incubation. Cx. cedecei was also highly sensitive to infection with allopatric HI subtype IE Middle American VEE virus isolates. Infection rates were greater than or equal to 50% with bloodmeal titers undetectable by CEC assay. Rates were 100% with oral doses of greater than or equal to 10(0.8) CECPFU. Transmission rates were 100% in all experiments. Similar results were obtained with HI subtype IAB "epizootic" VEE virus isolates from the 1969 Middle American outbreak. Infection rates were 100% with oral doses of greater than or equal to 10(1.2), and transmission rates were 100% after extrinsic incubation. Comparisons with laboratory vector competence of the Middle American enzootic VEE virus vector, Culex (Melanoconion) taeniopus, are discussed.