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PubMed1987

Epizootic vesicular stomatitis in Colorado, 1982: epidemiologic and entomologic studies.

An epizootic of vesicular stomatitis (VS) caused by the New Jersey serotype of VS virus affected livestock and humans in 14 western states in 1982-1983. Epidemiological observations were made on at least 10% of the cattle in 4 dairy herds that were located in the vicinity of Grand Junction, Colorado. High rates of neutralizing antibody to the New Jersey serotype were seen in all cattle regardless of whether livestock in the dairy had clinical VS or a decrease in mild production. Antibody titers remained high in these cattle for as long as 2 years after the epizootic. No virus isolations were made from 32 humans with clinical signs compatible with viral disease. Entomological information was obtained during the epizootic from 23 premises in northwestern Colorado. Insect collections yielded 4 isolates from Culicoides spp. midges, 2 from C. variipennis, and 1 each from C. stellifer and C. (Selfia) spp. This is the first report of VS virus isolations from field-collected Culicoides.

Aedes↗
PubMed1987

Quantitative studies of onchocerciasis transmission by Simulium yahense and Simulium sanctipauli in the Firestone Rubber Plantation at Harbel, Liberia.

Black fly vectors of onchocerciasis from three ecologically different Simuliid breeding habitats in the Firestone Rubber Plantation at Harbel, Liberia, were surveyed by human-biting collections conducted at weekly intervals over a 13-month period. Black flies were identified morphologically and the monthly and seasonal contribution of different vector species to the transmission of Onchocerca volvulus at each site was determined. Simulium yahense was identified as the predominant vector species at each site. Greatest populations of this species occurred during wet season (May-Oct), but its impact on transmission of onchocerciasis was most profound during dry season (Nov-Apr) when parity, infection, and infectivity were high. S. sanctipauli was the only other vector species captured, but biting populations of this species were small, and during wet season confined primarily to the vicinity of its breeding site in the Farmington River. Dry season populations of S. sanctipauli were also characterized by lower human-biting rates, and by higher rates of parity, infection, and infectivity. Monthly transmission potentials at each site were attributed primarily to S. yahense, with peak monthly transmission occurring during the dry season months of January-April. Against the WHO standard of 100 as a "tolerable" annual level of onchocerciasis transmission, annual transmission potentials for the three sampling sites were 94, 1,877, and 4,900, with highest values being calculated for S. yahense breeding sites.

Animals↗
PubMed1988

Biting activity of black flies in Guatemala: parity rates and differences between localities and habitats.

Host-seeking activity of anthropophilic black flies at 4 localities in Guatemala with different prevalence rates of onchocerciasis was assessed using human attractants and semimonthly catches over one year. Density of host-seeking Simulium ochraceum was greatest at the locality with the highest incidence of onchocerciasis and very reduced at the 2 localities with low levels of human infection. The overall percentage of parous host-seeking S. ochraceum at the 4 localities ranged from 41%-49%. Host-seeking activity appeared to be concentrated near streams containing immature stages, and few females dispersed as far as 3 km away. S. metallicum was the second most frequently captured species; however, at the locality with the highest prevalence of onchocerciasis, its host-seeking density was much less than that of S. ochraceum. For S. metallicum, the overall percentage of parous females ranged from 28%-34% at the 4 localities. S. metallicum were consistently taken in much greater numbers in coffee cultivation areas than in housing areas. Host-seeking S. callidum and S. gonzalezi also were captured.

Animals↗
PubMed1988

Seasonality of adult black flies and Onchocerca volvulus transmission in Guatemala.

Transmission of Onchocerca volvulus, principally by Simulium ochraceum, 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 S. ochraceum 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 O. volvulus larvae in parous host-seeking S. ochraceum 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 S. ochraceum was less than 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 O. volvulus by S. ochraceum also varied seasonally. At the same hyperendemic locality, infective biting density of S. ochraceum attained its greatest magnitude in February-March. The survival rate of female S. ochraceum 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.

Animals↗
PubMed1988

Large scale production of the vertebrate infective stage (L3) of Onchocerca volvulus (Filarioidea: Onchocercidae).

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.

Animals↗
PubMed1988

Transmission of Onchocerca volvulus by secondary vectors in Guatemala.

A comprehensive study of the transmission of Onchocerca volvulus at 4 locations in Guatemala with different prevalence rates of onchocerciasis included observations on potential secondary vectors, the most prevalent of which were Simulium metallicum, S. callidum, and S. gonzalezi. Filariae encountered in S. metallicum were primarily of a Dipetalonema-like species, but third-stage larvae indistinguishable from O. volvulus were found in 4 flies of this species. Our findings suggest that O. volvulus may occasionally be transmitted by S. metallicum, but such transmission is likely limited to areas having both a high parasite prevalence maintained by S. ochraceum and a relatively high host-seeking density of S. metallicum. Two third-stage larvae that could not be differentiated from O. volvulus were found once in S. gonzalezi; however, transmission by this species appears to be inconsequential.

Animals↗
PubMed1988

Vector density, parasite prevalence, and transmission of Onchocerca volvulus in Guatemala.

Transmission of Onchocerca volvulus at 4 locations with different prevalences of human onchocerciasis in the Atitlán region of Guatemala is described in relation to vector density and infection rates. The percentages of residents with skin biopsies positive for microfilariae of O. volvulus at these locations were 13.8%, 33.3%, 65.4%, and 89.6%. The following variables associated with transmission were calculated from our observations (the values are presented in an order that corresponds with the above prevalence rates): frequency of third-stage larvae (calculated on an annual basis) in parous Simulium ochraceum, 0, 0.004, 0.005, and 0.004; estimated daily biting density of S. ochraceum, 23, 24, 254, and 1,509 flies per day; and estimated annual infective biting density (based on S. ochraceum), 0, 18, 185, and 1,101 potentially infective bites per year. The frequencies of third-stage larvae are very small compared with those observed in Africa, and suggest that transmission of O. volvulus in Guatemala depends on high vector density. Locations with low, and perhaps tolerable, levels of onchocerciasis (less than 15% of female residents with skin biopsies positive for microfilariae) have mean daily biting densities for S. ochraceum of less than or equal to 24 flies, and infected residents normally have mean microfilarial densities of less than or equal to 3 microfilariae per mg of skin. Stratification of prevalence rates by age group proved useful for assessing current transmission within a village.

Adolescent↗
PubMed1989

The effect of multiple ivermectin treatments on infection of Simulium ochraceum with Onchocerca volvulus.

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.

Adult↗
PubMed1990

Effect of mass treatment of a human population with ivermectin on transmission of Onchocerca volvulus by Simulium yahense in Liberia, West Africa.

The impact of mass treatment with ivermectin on the intensity of Onchocerca volvulus transmission by the black fly (Simulium yahense) was evaluated on the Liberian Agricultural Company rubber plantation in Liberia, West Africa. The adult pre-treatment prevalence of onchocerciasis was greater than 80%, and the average intensity of infection was 5.35 mf/mg of skin. The drug was administered at 2 annual intervals, reaching 58-60% of the approximately 14,000 people living in 73 camps. Landing/biting catches of black flies made in central and peripheral plantation zones indicated similar fly activity before and after ivermectin treatment (man hr index of 2.1 and 2.4 within the plantation, and 10 and 10.9 outside the plantation, respectively). The number of infected flies with developing larvae (L1, L2, L3 stages) of O. volvulus in treated areas was reduced by 93.4-95%; the number of infective flies with L3 larvae was reduced by 81.7-89.3%. Parasite loads of infected (L1, L2) and infective flies (L3 stages only) outside the plantation also decreased by 86.8% and 80%, respectively. Monthly transmission potential (MTP) showed a similar decrease: from 22.9 to 5.8 (74.6% reduction) in the treated area, and from 210 to 158.8 (24.4% reduction) in untreated areas. Mass treatment with ivermectin efficiently controlled, and at least temporarily interrupted, transmission of Onchocerca volvulus by black fly vectors.

Animals↗
PubMed1992

Microepidemiology of onchocerciasis in Guatemala: dispersal and survival of Simulium ochraceum.

Wild Simulium ochraceum females, both blood engorged and non-blood engorged, were collected from human volunteers infected with Onchocerca volvulus, marked with fluorescent dyes, and released from the same locality as they were collected during February and March 1989. A small hyperendemic village located within 0.5 km of streams supporting large populations of S. ochraceum larvae served as the site for both collection and release of adult females. Fifteen sites for the recapture of flies were located within this same village, within two other villages located 1.0 and 3.7 km from it, and at other places spaced approximately 0.25-3.5 km within a coffee agroecosystem. Flies from both groups were recaptured at distances ranging to 3.5 km from the point of release. Non-blood-engorged flies, however, exhibited a greater tendency to disperse away from the release site. Of the total number of blood-engorged flies recaptured, 51.9% were collected at the release point, 25.7% at 1.0 km, and 1.6% at 3.3-3.5 km. The corresponding percentages for non-blood-engorged flies were 26.9%, 40.4%, and 4.4%, respectively. No flies from either group were recaptured at the most distant site, a large village that was 3.7 km away. Marked flies from both groups were recaptured 12-14 days after release, which was sufficient time for the development of infective O. volvulus larvae. A survival rate (4.7%) of marked, blood-engorged flies over the second and third gonotrophic cycles was estimated from the slope of the regression line of the log number of flies recaptured.(ABSTRACT TRUNCATED AT 250 WORDS)

Animals↗
PubMed1992

The effects of repetitive community-wide ivermectin treatment on transmission of Onchocerca volvulus in Guatemala.

The effects of biannual ivermectin treatment at the community level on transmission of Onchocerca volvulus during the dry season were measured over a 30-month period in Guatemala. In the Los Tarrales Transmission Zone, an area encompassing three villages, significant changes occurred in both the prevalence and quantity of infection in the Simulium ochraceum vector population. These included a 76% reduction in females with infective stage larvae (L3S) and an 80% reduction in number of L3S per 1,000 parous flies. Significant reductions in both the mean infective biting density (IBD) and mean transmission potential (TP) also occurred. In Santa Emilia, the prevalence of infection with L3S in S. ochraceum was significantly reduced by 77% from the baseline value. The number of O. volvulus L3S per 1,000 parous flies was also reduced by 92%. Changes in both the IBD and TP were substantial but not significant due to the high degree of variance in the occurrence of O. volvulus L3S in the vector population. This was due, in part, to the movement of infected migrant workers into the finca (coffee farm). In Los Andes, four recurrent treatments successfully blocked transmission of infective stage larvae. Prevalence (flies with all stages of developing larvae) in the vector population was reduced by 89% over the two-year period; yearly reductions in both the IBD and TP were also highly significant, ultimately ending in zero values. This finding is particularly striking since prior to treatment, Los Andes exhibited the highest IBD of the three study locations and the second highest TP.

Animals↗
PubMed1993

A study of onchocerciasis with severe skin and eye lesions in a hyperendemic zone in the forest of southwestern Cameroon: clinical, parasitologic, and entomologic findings.

Prior to the initiation of an onchocerciasis control program based on the mass administration of ivermectin in the rain forest of southwestern Cameroon, a preliminary baseline study of the area was conducted. The results of this study showed that onchocerciasis was hyperendemic in the area. Skin symptoms and signs were observed including pruritus (67.4% of the population examined), onchocerca nodules (51.6%), skin depigmentation (18.5%), and hanging groins (5.7%). Except for pruritus, the prevalence of these symptoms increased with age. Of the eyes examined, 44.9% had microfilariae in the anterior chamber, 33.5% had choroidoretinitis, 28.0% had punctate keratitis, 8.3% had papillary abnormalities, and 3.6% had sclerosing keratitis. Vision in 10.5% of the eyes examined was classified as blind or very poor (visual acuity = 0-0.10), in 15.7% as poor (visual acuity = 0.11-0.39), and in 73.8% as good (visual acuity = 0.4-1.00). Unlike previous reports that have linked serious ocular damage mainly to savanna onchocerciasis, the present study showed that forest onchocerciasis also caused significant ocular pathology, including blindness. Parasitologically, positive skin snips were recorded for 92.7% of the persons examined, with both sexes being equally infected. The parasite load, expressed as the geometric mean number of microfilariae per skin snip, was 53.6, and was much higher in males than in females. The flv vector, Simulium squamosum, had a high infection rate of 7.5% infective females in Bakumba and 6.8% infective females in Ngbandi, the two fly-catching points. The transmission potential was 266 infective larvae per person per month in Bakumba and 189 in Ngbandi.

Adolescent↗
PubMed1993

The blackfly Simulium buissoni and infection by hepatitis B virus on a holoendemic island of the Marquesas archipelago in French Polynesia.

The hematophagous blackfly Simulium buissoni causes skin lesions on an island in the Marquesas archipelago that is holoendemic for hepatitis B virus (HBV). To test the hypothesis of the possible role of this fly in the transmission of hepatitis B, 506 children (age range 2-11 years) were examined for the presence of skin lesions, and attempts were made to detect HBV DNA in and on blackflies using two polymerase chain reaction methods. The mean number of skin lesions showed a positive correlation with the age of these children (r = 0.12, P < 0.05). Furthermore, it was significantly higher in the rural zone than in the urban zone (mean +/- SD 41.02 +/- 31.71 versus 17.73 +/- 13.43; P < 0.05), and showed a correlation with a higher infection rate (73.9% versus 41.3%). Of the 45 pools of 10 insects tested, HBV DNA was not detectable on the inside of the insect, but was detectable on the flies (1-10 particles/insect in three positive pools). Infection by HBV conveyed by the flies is theoretically possible, but their indirect role via the numerous skin lesions caused on children is likely to explain such a high level of transmission.

Adolescent↗
PubMed1994

Vasodilative activity in black fly salivary glands.

Salivary gland extracts of several Simulium spp. were shown to contain vasodilative activity as measured by the rapid and persistent induction of erythema in response to intradermal injection into rabbit skin. Total salivary gland activities were approximately equal for S. vittatum, S. metallicum, S. bivittatum, and S. argus (titers of 0.03-0.02 pairs of gland). Total gland activity in the highly anthropophilic species S. ochraceum, however, was an order of magnitude greater, with erythema produced by as little as 0.002 pairs of glands. Tests for physical stability of the activities from two species (S. vittatum and S. ochraceum) indicated that the vasodilators were proteinaceous and heat stable. A two-step, reversed-phase high-performance liquid chromatography (HPLC) procedure was developed that isolated both activities with similar elution patterns. Homogeneity of the purified protein from S. vittatum was confirmed by capillary gel electrophoresis. Electrospray ionization mass spectroscopy of the S. vittatum protein detected a mass of 15,351 daltons. Similarity in elution times of the proteins from a TSK HPLC column predict some structural similarities between the S. vittatum and S. ochraceum vasodilator proteins.

Animals↗
PubMed1995

Vector competence of Simulium exiguum for Onchocerca volvulus: implications for the epidemiology of onchocerciasis.

In the transmission of human onchocerciasis, competence of the black fly vector influences intensity of transmission by regulating how many infective-stage larvae are produced. The disease is intensifying in Ecuador where Simulium exiguum is a highly efficient limitation-type vector comparable with African forest species in terms of the percentage of flies developing infective-stage larvae and the numbers of larvae per infected fly. In contrast, the endemic foci in Guatemala and southern Mexico have remained stable and closely circumscribed around larval development sites for S. ochraceum, a vector that exhibits a facilitation type of competence and must feed on people with comparatively high microfiladeremia to develop significant numbers of infective-stage larvae. This comparison indicates that assessments of vector competence should be included when planning regional control programs for onchocerciasis.

Adult↗
PubMed1996

In vitro cultivation and development of Onchocerca volvulus and Onchocerca lienalis microfilariae.

Onchocerca volvulus and O. lienalis skin-derived microfilariae (mf) were cultured in vitro; parasite viability was assessed at intervals by measuring their ability to develop in Simulium ornatum. In the presence of monkey kidney feeder cells, both species retained full viability when cultured for up to 5 hr before intrathoracic injection into Simulium. In the absence of feeder cells and in contrast to O. lienalis, O. volvulus mf rapidly lost their viability. In further trials (including feeder cells), O. volvulus mf retained full viability for 14 days, while O. lienalis mf retained full viability for a least 19 days but with a proportion able to develop to third-stage larvae (L3) after 70 days in culture. In experiments using this system to culture O. volvulus mf (ex utero) derived from adult female worms but with the addition of reduced glutathione and/or 20-hydroxyecdysone, parasites were consistently more active over a 70-day period than those cultured without these additives. None of the mf cultured without additives were able to develop to L3 in Simulium when tested for up to 51 days in culture, while a proportion of mf incubated with reduced glutathione and/or 20-hydroxyecdysone produced small but significant numbers of L3 after 28, 43, and 51 days, representing the first time that uterine mf have been cultured to a form infective for the vector.

Animals↗
PubMed1997

Vector competence of select black fly species for vesicular stomatitis virus (New Jersey serotype).

Black flies collected from southern Arizona were evaluated for their vector competence to the Oaxaca and Camp Verde isolates of vesicular stomatitis virus (New Jersey serotype) (VSV-NJ). The Camp Verde isolate is the index isolate of the 1982-1983 VSV-NJ epizootic that infected humans and livestock in 14 western states. Previous experiments have shown that colonized Simulium vittatum females are competent laboratory vectors of both virus isolates. However, under controlled laboratory conditions, Simulium bivittatum and S. longithallum were found to be incompetent vectors of both virus isolates. After oral infections, the Oaxaca isolate replicated in 35% and 38% of S. bivittatum and S. longithallum, respectively, but did not disseminate to the salivary glands. Thus, virus was not detected in the saliva of either black fly species with either VSV-NJ isolate, indicating the presence of a midgut barrier. Simulium notatum was found to be a competent laboratory vector of both virus isolates. Infectious virions were detected in the saliva of 23% and 26% of S. notatum infected orally with the Oaxaca and Camp Verde VSV-NJ isolates, respectively. This study suggests that the black fly identified as S. bivittatum was probably not involved in virus dissemination during the 1982-1983 epizootic in the western United States. Because the geographic distribution of S. notatum is not known, its involvement in that epizootic remains obscure.

Animals↗
PubMed1998

Current status of onchocerciasis in Colombia.

To assess the current epidemiologic status of onchocerciasis in Colombia two surveys were undertaken in 1995 in a suspected new focus on the border between Colombia and Ecuador and in the known focus located on the Micay River. No new focus was found along the Colombia-Ecuador border. In the known focus, communities along the upper Micay River and its tributaries were surveyed; 655 adults underwent physical examinations and skin biopsies. Infected individuals were found almost exclusively in the community of Naiciona, where prevalence of infection was 40% (36 of 91). Polymerase chain reaction detection of onchocercal DNA in skin snips correlated with the skin-snip biopsy results. The prevalence of punctate keratitis, the only ocular manifestation found, was 33%. A rapid entomologic assessment demonstrated Simulium exiguum infected with Onchocerca volvulus. This is the first finding in Colombia of naturally infected black flies and confirms S. exiguum as a vector species. These data will be used for implementing a control program using periodic ivermectin distribution.

Adolescent↗