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PubMed1999

Pool screen polymerase chain reaction for estimating the prevalence of Onchocerca volvulus infection in Simulium damnosum sensu lato: results of a field trial in an area subject to successful vector control.

Detection of infective parasites in the vector population can be an early indicator of recrudescence in areas freed of new cases of onchocerciasis. However, dissection of vector black flies is inefficient in areas subject to effective control. Recently, a polymerase chain reaction (PCR)-based assay has been used to detect a single Onchocerca volvulus-infected black fly in pools containing large numbers of uninfected flies. This method had not been validated on wild-caught black flies in an area subject to effective vector control. Here, we report a method of restricting the pool screen PCR assay to infectious parasites and the results of a field test in an area subject to long-term vector control. The prevalence of infection determined by dissection did not differ from that determined by pool screen PCR. The results suggest that the PCR assay may be a useful tool for epidemiologic surveillance for 0. volvulus infection.

Animals↗
PubMed2002

Validity of nodule palpation in a Simulium neavei-transmitted onchocerciasis area in Uganda.

The objective of this study was to evaluate the prevalence of palpable nodules as a rapid indicator for onchocerciasis endemicity in at-risk communities where Simulium neavei s.s. is the transmitting vector. We used data collected from 13 villages in Uganda to determine the validity of this rapid assessment method. The prevalence of palpable nodules was closely associated with the microfilarial prevalence (R2 = 0.603, P = 0.002), with the community filarial load (R2 = 0.620, P = 0.001) and with the prevalence of onchodermatitis. Nodule palpation in males more than 20 years old, using a cut-off point of 40% and higher for the nodule prevalence, had a sensitivity of 92% and a specificity of 100% in correctly identifying communities in need of urgent intervention with ivermectin mass treatment. Cut-off points were based on World Health Organization recommendations. Thus, nodule palpation can replace skin snipping to identify communities at serious risk of S. neavei-transmitted onchocerciasis.

Animals↗
PubMed2002

Transmission intensity and the patterns of Onchocerca volvulus infection in human communities.

We focus on possible constraints upon Onchocerca volvulus establishment in humans in relation to exposure rates to infective larvae (L3) as measured by the annual transmission potential (ATP). We use mathematical and statistical modeling of pre-control west African (savanna), Mexican, and Guatemalan data to explore two hypotheses relating human infection to transmission intensity: microfilarial (mf) loads either saturate with increasing ATP or become (asymptotically) proportional to the ATP. The estimated proportion of L3 developing into adult worms ranged from 7% to 0.3% (low and high intensity areas, respectively). Relationships between mf prevalence and both mf and transmission intensity were nonlinear and statistically similar between west Africa (Simulium damnosum s.l.) and Meso America (S. ochraceum s.l.). This similarity extended to the relationship between mf intensity and ATP. The critical biting rates for onchocerciasis introduction and persistence (which depended on vector competence and host preference), were approximately 10-fold higher in settings where onchocerciasis is transmitted by S. ochraceum than in those where the vector is S. damnosum. A role for focal vector control in Mexico and Guatemala, in addition to nodulectomy and ivermectin, is suggested.

Africa, Western↗
PubMed2000

Onchocerciasis in Gilgel Ghibe River Valley southwest Ethiopia.

OBJECTIVE: To determine the prevalence of onchocerciasis and the entomological transmission indices such as the parous rate and annual transmission potential (ATP). SETTING: Gilgel Ghibe village, Gilgel Ghibe River Valley Southwest Ethiopia between April 1994 and March 1995. SUBJECTS: Two hundred twenty eight subjects of the total 400 population in Gilgel Ghibe village were subjected to parasitological and clinical examinations. METHOD: Two skin snips per person were taken and examined for microfilariae of Onchocerca volvulus. Fly collections were done from dawn to dusk from human baits seated in pairs at four representative sites at the river bank and away from the river bank. Flies were dissected for parity and infections with O. volvulus larvae. RESULTS: Among the 228 people examined, the prevalence of the disease was low (17%), being higher in males (19%) than in females (14%). The geometric mean of microfilarial density was 11.1 (range, 1-132) mf per skin snip. Itching followed by pigmentary changes were the most common clinical signs and symptoms. The predominant anthropophilic blackfly species was Simulium (Edwardsellum) damnosum s.l. The annual parous rate and ATP were 74.7% and 1669.5, respectively, being higher at the river bank than at sites further away suggesting a greater risk of infection by the river side. CONCLUSION: The low prevalence of onchocerciasis in Gilgel Ghibe area vis-a-vis the high ATP level could be due to the possible presence of bovine onchocerciasis in the area. Further studies employing molecular techniques are thus required to identify O. volvulus from other filariae in flies.

Adolescent↗
PubMed1987

Epizootic vesicular stomatitis in Colorado, 1982: some observations on the possible role of wildlife populations in an enzootic maintenance cycle.

Sera obtained from wild ungulates, carnivores, and rodents in Colorado were tested for neutralizing (N) antibody against vesicular stomatitis, New Jersey serotype (VSNJ), virus to determine their involvement in the 1982 Colorado VSNJ epizootic in domestic animals. Viremic and N antibody responses of two local rodent species to a 1982 Colorado isolate of VSNJ were determined in the laboratory. The rodents produced only weak viremias, but all developed N antibody. N antibody prevalences for VSNJ in sera from wild ungulates was sufficiently high to indicate their involvement during the epizootic. In addition, the demonstration of N antibody in elk (Cervus elaphus) and mule deer (Odocoileus hemionus) prior to the epizootic in cattle and horses suggests that an enzootic cycle may exist in Colorado.

Animals↗
PubMed1992

Insects feeding on desert bighorn sheep, domestic rabbits, and Japanese quail in the Santa Rosa mountains of southern California.

Desert bighorn sheep (Ovis canadensis cremnobates), a domestic rabbit (Oryctolagus cuniculus), and Japanese quail (Coturnix japonica) were used as bait animals to collect blood-feeding flies in an area of active blue-tongue and epizootic hemorrhagic disease virus transmission. Precipitin tests were used to confirm the blood source where feasible. Eight species of Culicoides, members of the Leptoconops kerteszi group, Simulium spp., Anopheles franciscanus, and Stomoxys calcitrans were collected from the bighorn sheep. Feeding on the bighorn sheep by Culicoides brookmani (n = 25), C. variipennis (n = 6), C. cacticola (n = 1), and Simulium spp. (n = 3) was confirmed by precipitin testing. Primary species attacking the rabbit were C. brookmani, C. variipennis, and the L. kerteszi group. The quail were attacked primarily by members of the C. copiosus group and the L. kerteszi group.

Animals↗
PubMed1997

Mortality in fledgling great horned owls from black fly hematophaga and leucocytozoonosis.

Black fly feeding alone and in concert with Leucocytozoon spp. infection caused mortality in fledgling great horned owls (Bubo virginianus) in the Yukon, Canada 1990 to 1991. These mortalities occurred during a year of food shortage corresponding with a decline in the population of snowshoe hare (Lepus americanus), the main prey for great horned owls. We hypothesize an interaction between food availability and the consequences of host-parasite interactions.

Anemia↗
PubMed1999

Rapid epidemiological mapping of onchocerciasis in areas of Uganda where Simulium neavei sl is the vector.

OBJECTIVE: To test whether Rapid Epidemiological Mapping of Onchocerciasis (REMO) was suitable for mapping of onchocerciasis in foci where S. neavei sl is the primary vector. DESIGN: Topographical maps of scale 1:250,000 were used in demarcating regions into ecotopographic divisions and zones in order to identify potential onchocerciasis endemic areas. SETTING: The study was conducted in Kabarole and Nebbi districts. High-risk communities were selected 30 km from each other, and closest to rivers where vector breeding appeared likely. Secondary and additional communities were selected 10 km and 20 km away from high-risk communities, respectively. SUBJECTS OR PARTICIPANTS: Communities were mobilised for nodule palpation. A sample of thirty males aged at least 20 years, from each community that had lived in the area for at least ten years, were randomly selected and examined. INTERVENTIONS: Individuals positive for at least one nodule were expressed in terms of Nodule Prevalence Rates (NPR) which were used to map the distribution of onchocerciasis. MAIN OUTCOME MEASURES: Coefficient of variation (CV) of Nodule Prevalence Rates between high risk secondary communities. RESULTS: In Kabarole district, the results indicated a low coefficient of variation (CV) of 75 in NPR between high risk and secondary communities while in Nebbi district, higher CV of 187.4 was attained. The less varied NPR implies that communities in Kabarole were almost equally exposed to onchocerciasis while highly varied situation in Nebbi indicated decreasing NPR with increasing distance from high-risk communities. CONCLUSION: REMO is applicable in areas where S. neavei sl is the primary vector, for identification and mapping communities requiring mass treatment with ivermectin.

Adult↗
PubMedDate not supplied

Infectivity and transmission dynamics of simulium damnosum s. 1 around Owena dam (Ondo State).

A twelve month study on the infectivity and transmission dynamics of simulium damnosum s.1 around Owena dam was conducted as part of a longitudinal study of onchocerciasis in the community living in the vicinity of the dam. A total of 3,133 flies (49.6% nilliparous, 50.4% parous) were caught during the period of study and dissected. The annual biting rate per year was recorded as 33,663 flies while the parous biting rate was recorded as 16,780 for these flies. 0.4% of the flies were infected with Onchocerca volvulus larvae while 0.3% of these had the infective larvae. However 0.3% of the nulliparous flies were found to be infected with mermithid larvae and 0.5% with trematodes. The biting activity of the fly was observed to be bimodal with a small peak in the morning hours (10.00-11.00 hours) and a more pronounced peak in the evening (16.00-17.00 hours). An annual transmission potential of 109 larvae per man per year was recorded with 64% of the infection being recorded during the early dry season when the parous rate was very high. The implications of these findings to the study area are discussed.

Animals↗
PubMed2001

Molecular and morphological phylogenetic analysis of an insular radiation in Pacific black flies (Simulium).

Ecological adaptation within islands may have figured prominently in the insular radiation of black flies (subgenus Inseliellum) in the Society Islands, French Polynesia. To aid in understanding the sequence of ecological shifts in this group, we have constructed a phylogeny by using morphology, the cytochrome oxidase I (COI) gene, and the small ribosomal subunit (12S) gene. The strong influence of COI on the combined analysis tree was evident from its contribution to the partitioned Bremer support (62%). The net effect of including 12S was to reduce overall tree support. Different character sets resolved different portions of the combined analysis tree, with COI resolving recent lineages, 12S resolving basal relationships, and morphology supporting the monophyly of taxa having smaller larval feeding fans (oviceps group). The Partition Homogeneity and Kashino-Hasegawa tests indicated significant incongruence between morphological and mitochondrial data. The Templeton test revealed that morphology and the combined (COI + 12S) mitochondrial data were incongruent. This conflict stems primarily from disagreement over the monophyly of taxa having much smaller larval feeding fans. Either convergence in a subset of morphological characters, low phylogenetic signal among mitochondrial sequences, or lineage-sorting causing the mitochondrial data to track an incorrect evolutionary history may be responsible for these results.

Animals↗
PubMed2002

Validation of parasite transmission models: the example of onchocerciasis.

Most parasites have complex life cycles; and mathematical models can help in targeting interventions and predicting disease-control efforts. For actual applications, quantification and validation of models is a key issue. We illustrate the process of validation by presenting a (re)analysis of fly-feeding experiments carried out by the Onchocerciasis (river blindness) Control Programme (OCP/WHO) in West Africa, with the objective to validate ONCHOSIM, an onchocerciasis transmission model. In these experiments flies were fed on human patients and dissected to count the number of microfilariae they had ingested. To assess microfilarial skin densities, skin snips (biopsies) were taken and examined. Originally, the resulting curve was interpreted as showing saturation and considered the main regulating (density-dependent) mechanism of onchocerciasis transmission in the model. Taking into account measurement errors in the skin microfilarial density of human subjects (on whom the flies were fed) we now conclude that the relationship is essentially linear. This prompts us to requantify ONCHOSIM. Possible alternative density-dependent mechanisms are discussed.

Adult↗
PubMed2002

[Evaluation of cocoa oil for individual protection against Simulium damnosum s.i].

Thanks to larviciding and distribution of ivermectine, transmission of onchocerciasis was virtually halted in all countries covered by the WHO Onchocerciasis Control Program (OCP). However as a result of this success vector control has been stopped in most areas covered by the program and a recrudescence of files is an increasing problem. In some rural communities fly biting hinders normal agricultural activity. Since local farmers cannot afford ground larviciding, many rely on topical repellents. For this reason, development of an inexpensive method of individual protection is a major priority. The purpose of this study carried out in the savannah area of the Côte d'Ivoire was to assess the repellent properties of cocoa oil, which is frequently used in some rural areas of the Côte d'Ivoire to prevent fly biting. Results showed that cocoa oil provides excellent protection against Simulium damnosum s.l.

Administration, Topical↗
PubMed2003

Entomological evaluation by pool screen polymerase chain reaction of Onchocerca volvulus transmission in Ecuador following mass Mectizan distribution.

The prevalence of infected and infective black flies was estimated by pool screen polymerase chain reaction (PCR) amplification in the three river basins in Ecuador endemic for onchocerciasis. Mass distribution of ivermectin (Mectizan) resulted in dramatic declines in the prevalence of infected and infective flies. In the Rio Santiago river basin, no infections were detected, suggesting that transmission had ceased. The ratio of infected to infective flies in Simulium exiguum was 10-fold lower than the corresponding ratio for Simulium quadrivittatum, suggesting that S. exiguum is a more-competent vector for Onchocerca volvulus than S. quadrivittatum. However, the prevalence of infective flies in the two species was not different, suggesting that S. quadrivittatum may play an important vectorial role where it is the dominant human-biting species. The data demonstrate that pool screen PCR is an efficient way to monitor transmission in areas subject to control, and to certify an area as free of O. volvulus transmission.

Animals↗
PubMed2003

[Evaluation of the efficacity of coconut (Cocos nucifera), palm nut (Eleais guineensis) and gobi (Carapa procera) lotions and creams in indivirual protection against Simulium damnosum s.l. bites in Côte d'Ivoire].

With the interruption of larva treatments done by OCP as part of onchocerciasis control in West Africa, Simulium came back in abundance in forest regions and savannah fertile valleys. In addition to the severe discomfort, nuisance by Simulium is in certain cases incompatible with land use. Since ground treatment of larval breading sites using insecticides is not always possible or efficient, it is therefore a necessity to develop other methods among which individual protection against Simulium bites. The general objective of our study was to evaluate different vegetable oil compound repellent formulas against Simulium bites. Activities were carried out in savannah zone (Niakaramandougou) and in forest zone (Soubré) in Côte d'Ivoire. The methodology consisted in catching blackflies on volunteers whose legs were rubbed with a repellent. Gobi raw oil and coconut, palm nut and gobi formulas (lotions and creams) were tested. During each session, which lasted from 07:00 am to 12:00 and from 03:00 pm to 06:00 pm, one person did not apply any repellent and was used as the control person. The results of our experimentations show that for a given zone (savannah, forest), a repellent (coconut, palm nut, gobi) and a compound (shea butter, vaseline), there is no significant difference between protection rates obtained with lotions (maximum: 21 bites/person/day) and those obtained with creams (maximum: 30 bites/person/day). In other respects, the lotion of a given repellent seems to be efficient in savannah as in the forest, in protecting against Simulium bites. It is the same situation with creams. So, repellents can be an efficient solution against Simulium nuisance. However, experimentations should continue to confirm the high repellency of tested formulas, proceed to the identification of principles and evaluate the toxicity and irritant effect of repellents to be applied on the skin.

Administration, Cutaneous↗