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PubMed1979

Development of Onchocerca volvulus in Simulium ochraceum and Simulium metallicum.

The development of Onchocerca volvulus was compared in Simulium ochraceum and S. metallicum by maintaining infected flies under uniform conditions. Larval development in S. ochraceum was synchronous and orderly so that nearly all larvae reaching the thoracic muscles from a single blood meal matured to third-stage infective larvae within 192 hours. In contrast, development in S. metallicum was asynchronous, slower, and retarded. In this species many first-larvae were malformed and stunted after the 5th day of development; and microfilariae and first- and second-stage larvae were still present 8--10 days after a single infecting blood meal when third-stage larvae had developed. The development of O. volvulus in S. ochraceum is more compatible with the intense transmission associated with human disease.

Animals↗

PubMed1979

The cryopreservation and in vitro cultivation of larval Onchocerca volvulus.

A system developed in our laboratory for the in vitro cultivation of larval Onchocerca volvulus is being employed in a series of morphogenetic, physiologic, chemotherapeutic and immunologic investigations of this parasite. Because of the need for a large and readily available supply of living worms for this work, cryogenic techniques are being used for the long-term preservation of larval parasites collected in various endemic areas of Guatemala, C.A. To date, microfilariae have survived frozen storage in human cutaneous tissues (excised nodules and skin snips) for as long as 504 days, and viable larvae, in all stages of development have been recovered from the black fly vectors (Simulium ochraceum and S. metallicum) kept frozen for 396 days. That cryopreservation does not appear to affect these parasites adversely is indicated by the fact that microfilariae derived from frozen tissues do not differ from those obtained from fresh tissues on the basis of: 1) numbers and vigor of emergent microfilariae; 2) survival and morphogenesis of microfilariae during cultivation in vitro for 24 days; 3) glucose utilization during 72 hours of incubation; and 4) their incorporation of 3H-amino acids as determined after 18 hours of incubation. Details of methodology for cryopreservation and in vitro cultivation, together with resultant data, are presented herein.

Animals↗

PubMed1980

Serologic studies on onchocerciasis in Guatemala using fixed-tissue sections of adult Onchocerca volvulus.

Sera from 458 residents of a coffee plantation in an area of Guatemala endemic for onchocerciasis were examined for the presence of antibodies to Onchocerca volvulus using a fluorescent antibody (IFA) test with sections of adult worms as the antigen. Antibody response increased with age of the residents and microfilarial density. A total of 70.0% of the residents were serologically positive and 65.1% were positive for microfilariae. Males had higher microfilarial densities and higher IFA responses. Sixty-three individuals were positive for microfilariae and IFA-negative indicating a lack of sensitivity on the part of the test antigen. Seventy-four individuals were negative for microfilariae and IFA-positive, suggesting the possible usefulness of the test in the determination of present or past infection in the absence of microfilariae.

Adolescent↗

PubMed1980

Simulium exiguum, the vector of Onchocerca volvulus on the Rio Micay, Colombia.

Simulium exiguum were collected in the San Antonio area on the Rio Micay as they blood-fed on a volunteer naturally infected with Onchocerca volvulus. The daily dissection of specimens revealed that delayed larval development was common and 23% of the larvae were abnormally formed. However, third-stage larvae were recovered by late day 5 (140 hours) following engorgement. It is concluded that S. exiguum is the vector of O. volvulus at this Colombian endemic focus even though its host efficiency is somewhat limited. S. metallicum collected near Cali from a naturally infected San Antonio volunteer was shown to be a relatively poor experimental host for O. volvulus.

Aged↗

PubMed1981

Seasonal occurrence of Simulium ochraceum, the principal vector of Onchocerca volvulus in the southeastern endemic area of Guatemala.

Investigation of the seasonal occurrence of Simulium ochraceum, the principal vector of the Guatemalan strain of Onchocerca volvulus, were made from August 1978 until January 1980 in the upper reaches of the two main rivers of endemic onchocerciasis in Escuintla, Guatemala. The results showed that in the late dry season S. ochraceum larvae were restricted to permanent streams at intermediate altitudes. During the rainy season, though, the preimaginal sites of this black fly extended to the upper reaches of the numerous small intermittent streams due to partial subterranean flows. Seasonal occurrence of S. ochraceum in these temporary streams was observed throughout the wet season. However, this was most pronounced during the early months of the dry season (October-December) as long as these streamlets continued to flow. The adult population along the headwaters of these two rivers showed a high peak from October-December. This represented a pattern distinct from that of other places where the preimaginal sites of S. ochraceum occurred mostly in larger perennially running streams. The implications which the present findings have for any future larvicidal control program on the onchocerciasis-endemic region of Guatemala are discussed.

Animals↗

PubMed1983

Further studies on the development of onchocerca spp. (Nematoda: Filarioidea) in Nearctic black flies (Diptera: Simuliidae).

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.

Animals↗

PubMed1983

Onchocerca volvulus: detection of circulating antigen by monoclonal antibodies in human onchocerciasis.

A monoclonal antibody of the IgM class recognizing Onchocerca volvulus circulating antigen (COA) was obtained. This monoclonal antibody was used in a radioimmunoprecipitation-PEG assay (RIPEGA) to detect circulating antigen in onchocerciasis patients' sera. COA could be detected in 63 (80%) of the 79 African patient sera tested, and in 126 (76%) of the 164 Indian (Venezuela) sera studied. There was no direct correlation between the presence of COA detected in the patient serum and the level of microfilarodermia. The RIPEGA using this monoclonal antibody detected COA in 91% of children under 10 years old, whereas the microfilarodermia in this group was positive in only 52% of the cases. The specificity of this test is improved compared to the results obtained with polyclonal antibodies. Immunofluorescence studies suggest that the COA might be located in the microfilaria cuticle.

Adolescent↗

PubMed1984

Descriptive statistics for the larval stages of Onchocerca volvulus in host-seeking Simulium ochraceum.

In four localities of Guatemala with dissimilar intensities of onchocerciasis, filarial larvae were recovered by dissection from host-seeking Simulium ochraceum. Measurements made on over 600 Onchocerca volvulus larvae were used to characterize the early first, late first, second, and third developmental stages. The numerical attributes used to characterize the third larval stage and the associated means were body length (657.3 microns); anterior body width (18.9 microns); posterior body width (20.2 microns); distance from anterior end to nerve ring (87.9 microns), to junction of muscular and glandular esophagus (137.6 microns), and to junction of esophagus and intestine (419.6 microns); and distance from anus to tip of tail (36.8 microns). Ratios to total body length were as follows: distance from anterior end to nerve ring, mean = 0.133, to junction of esophagus and intestine, mean = 0.634, and to anus, mean = 0.945. Differences between these phenotypic features and those reported for African O. volvulus appeared to be insufficient to distinguish the two forms. With very few exceptions, the filarial larvae found in host-seeking S. ochraceum were considered to be O. volvulus.

Anal Canal↗

PubMed1984

Morphogenesis of larval Onchocerca volvulus in the Panamanian black fly, Simulium quadrivittatum.

Simulium quadrivittatum Loew (Diptera: Simuliidae), a man-biting black fly, was shown, for the first time, to be capable of supporting development of Onchocerca volvulus Leuckart (Nematoda: Filarioidea) from microfilariae to third-stage (infective) larvae. The black flies were collected in Chiriqui Province, Panama and transported alive to Guatemala, where they were allowed to feed on a human subject infected with O. volvulus. Samples of these flies were dissected over an 11-day period to assess morphogenesis of the parasite. Vigorously motile microfilariae were recovered from the mid-gut during the first 24 hours postfeeding; second-stage larvae were found in the thoracic musculature on day 4; and fully developed third-stage larvae were obtained from the cephalic capsule by day 10. This rate of larval development is similar to that observed in Guatemalan S. ochraceum. Onchocerciasis is not known to occur in Panama. The results of the present study direct attention to a potential public health hazard there and possibly elsewhere in Central America.

Animals↗

PubMed1984

Development of Onchocerca volvulus larvae in Simulium pintoi in the Amazonas region of Venezuela.

The intake and development of Onchocerca volvulus in Simulium pintoi from the Parima mountain region of the Federal Territory of Amazonas in Venezuela, were studied experimentally. When wild females fed on the lower half of the legs and lower third of the back of an onchocerciasis patient harboring 23 and 264 microfilariae per skin snip, respectively, at each site, an average (median) of 14 (range, 1-77) and 245 (range, 58-495) microfilariae was ingested. However, within 24 hours of microfilarial ingestion a mortality of 47% (16/34 flies) was observed in the group of flies which fed on the back, as compared with 2% (2/101 flies) in the other group which fed on the legs. At a temperature varying between 16 degrees C and 24 degrees C, the development of O. volvulus larvae in S. pintoi was synchronous and orderly; no abnormal nor deformed larvae were observed. Third-stage larvae were first seen in the head of flies dying between 8 and 9 days after microfilarial ingestion, and 98 of 100 larvae recovered from days 10-16 were in the third stage. The proportions of females harboring third-stage larvae among flies which lived through day 8 in the two groups which fed on the legs and back, respectively, were 55% (21/38 flies) and 63% (5/8 flies). Although only two of five positive flies in the latter group contained third-stage larvae in the head (1 and 12, respectively), 71% (15/21 positive flies) of the former group had an average of 2.7 third-stage larvae in the head (range, 1-10).(ABSTRACT TRUNCATED AT 250 WORDS)

Animals↗

PubMed1985

The gonotrophic cycle of wild Simulium ochraceum and the associated development of Onchocerca volvulus.

A total of 1,700 host-seeking Simulium ochraceum were allowed to feed to repletion on human volunteers heavily infected with Onchocerca volvulus and then were marked and released. Seventy-three (4.3%) of the flies were recaptured. The gonotrophic cycle of S. ochraceum, including the host seeking and oviposition phases, was approximately 74-97 hr in duration; however, for a few flies the cycle was up to an additional 24 hr in length. The frequency distribution of recaptured flies indicated that 2 gonotrophic cycles may be completed in 7-8 days. The large proportion of flies recaptured with sac-stage follicular dilatations indicates that S. ochraceum may begin to search for and can rapidly locate a new host almost immediately after oviposition. Larvae of O. volvulus were found in 15 (20.6%) of the recaptured flies. Early first stage larvae were present in host-seeking flies that had completed 1 gonotrophic cycle: 12 of 13 infected flies recaptured between 74 and 97 hr had early first stage larvae. Development of O. volvulus larvae to the infective stage was estimated to require approximately 11 days at the study site. During this time, S. ochraceum would normally have completed 3 gonotrophic cycles and be in the host seeking phase of a fourth at approximately 11 days after ingesting microfilariae.

Animals↗

PubMed1987

Specific serodiagnosis with adult Onchocerca volvulus antigen in an enzyme-linked immunosorbent assay.

The cross-reactivity of the blood from onchocerciasis, loiasis, and dipetalonemiasis was tested by a micro-ELISA technique, utilizing adult Onchocerca volvulus antigen and blood samples taken on filter paper. The average ELISA values (OD at 500 nm) were as follows: 0.58 in persons with O. volvulus microfilariae (n = 81), 0.49 in microfilariae-negatives from the same endemic area (n = 39), 0.15 in dipetalonemiasis (n = 27), and 0.25 in loiasis (n = 12), while those of 65 Dipetalonema perstans-negative people were markedly low (average 0.14) and that of 22 Loa loa-negatives, 0.22, respectively. This ELISA could successfully differentiate onchocerciasis from dipetalonemiasis and loiasis.

Adolescent↗

PubMed1987

The paralyzing effect of midazolam on Onchocerca volvulus microfilariae in vitro.

Midazolam, a water soluble benzodiazepine derivative, inhibited the motility of Onchocerca volvulus microfilariae in vitro at concentrations of 25, 50, and 100 micrograms/ml. The effect was proportional to the concentrations used. Microfilariae regained motility after elimination of midazolam by washing. Diethylcarbamazine did not alter the midazolam effect. It is suggested that the Mazzotti reaction as the sequelae of diethylcarbamazine is caused by transient increased microfilarial migration. Combining midazolam with the diethylcarbamazine medication may prevent the Mazzotti reaction.

Animals↗

PubMed1988

Parasite antigens are present in breast milk of women infected with Onchocerca volvulus.

We used a noncompetitive two-site ELISA with 5 monoclonal antibodies to determine whether parasite antigens are present in breast milk from women infected with Onchocerca volvulus. Seven out of 13 available milk samples contained significant amounts of filarial antigens. Antigen indices in milk correlated with levels of microfilarodermia (Rs = 0.74, P less than 0.005). Antigen-containing milk samples markedly inhibited mitogen-induced proliferation of human mononuclear cells and activated cells within this population that suppressed the proliferative response of autologous lymphocytes to mitogens and antigens. These findings indicate that parasite products are present in breast milk of O. volvulus-infected women and suggest that these may induce immune tolerance and/or suppression in infants born of infected mothers.

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↗

PubMed1988

Ivermectin prophylaxis against experimental Onchocerca volvulus infection in chimpanzees.

Ivermectin was tested for possible prophylactic action against the third and fourth larval stages (L3 and L4) of Onchocerca volvulus inoculated into chimpanzees. The infective larvae (L3) were obtained from laboratory-raised black flies. Eighteen chimpanzees were inoculated, each with approximately 250 L3. Six were treated with ivermectin (200 micrograms/kg) on the day of inoculation, 6 were treated with ivermectin on day 28, and 6 were not treated. Monthly skin snips were taken for the next 30 months to detect patent infection. One of the chimpanzees treated with ivermectin on the day of infection developed a patent infection as did 4 of the 6 treated at day 28 and 4 of the 6 control animals. The results suggest that ivermectin may have a partial in vivo effect against the L3 of O. volvulus but has no effect against later larval stages of the parasite.

Animals↗