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PubMedDate not supplied

[Entomology of onchocerciasis in Soconusco, Chiapas, México. VII. Quantitative variations in the transmission of Onchocerca volvulus (Nematoda: Filaroiidea) according to human activity space].

In this research we tried to demonstrate differences in transmission intensities of onchocerciasis by Simulium ochraceum in the community of Golondrinas, Municipality of Acacoyagua in the Soconusco area of the state of Chiapas. Adult females of this species were captured in the center of the villages, the coffee plantation, and the corn bean planted plots, during 7 to 10 consecutive days of the months of June, August, November and December of 1983, and January, March, and May of 1984. Captures were made from 7:00 to 11:00 h, by two persons (a human bait and a collector) in each of the mentioned areas. Variations in densities of S. ochraceum were not statistically significant among the different areas, although there was a predominance in the center of the villages during all the time periods. There was not a statistical significance in the number of oviparous females, although again the center of 50 villages showed the highest percentages (43.5%), as compared to the coffee plantation (37.8%), and the corn-bean plots (33.8%). Regarding the ratio infection: infectivity, only the infective mosquitoes with L3 showed a statistical significance in the three types of areas, being highest in the center of the villages. Transmission potentials were: center of the village 28.5 L3/human/period; coffee plantation, 73 L3/human/period; corn-bean plot, 5.8 L3/human/period. We discuss the possibility that the differences in densities among the various areas might depend on the variations of the breeding sites, mobility or permanence of the individuals during the hours of greater activity of S. ochraceum, and the wind and light local conditions.(ABSTRACT TRUNCATED AT 250 WORDS)

Analysis of Variance↗
PubMed1991

Onchocerciasis, malaria and trypanosomiasis in three resettlement schemes in western Ethiopia.

Epidemiological studies were carried out among 180 randomly chosen settler and 180 non-settler households in the three resettlement schemes of Kishe, Gera and Didessa located in river valleys and highland areas of Illubabor Administrative Region in western Ethiopia. Up to 49% of the indigenous populations (in Kishe) and 0.9% of the settlers had onchocerciasis, with a mean density of 13.6 filariae per slide/skin snip for indigenous people and 9.4 for settlers. Onchocerciasis prevalence rates were higher in males than females and were highest in the 20-59 age group. In the Kishe scheme, rates were inversely related to distance between residences and probable forest/stream habitat of Simulium damnosum. No onchocerciasis transmission appears to occur in the Gera scheme at 1,950 meters altitude, apparently due to the absence of suitable vectors. Eight of 622 (1.2%) persons had malaria (P. vivax and P. falciparum). The most common man-biting anophelines were A. gambiae and A. funestus. No human trypanosomiasis cases were found but high livestock mortality was reported by local populations in the lowland schemes of Kishe and Didessa.

Adolescent↗
PubMed1991

[April flies].

Explore the source record for details and available documents.

Animals↗
PubMed1990

Ocular onchocerciasis and intensity of infection in the community. III. West African rainforest foci of the vector Simulium sanctipauli.

The community pattern of ocular onchocerciasis is described for 11 villages from the forest area in Côte d'Ivoire where S. sanctipauli is the princial vector. An analytical method is applied which relates indices of ocular onchocerciasis with the Community Microfilarial Load (CMFL) and compares the results with the ocular onchocerciasis pattern found in the West African savanna. In spite of high transmission levels as estimated by entomological indices, the CMFLs were relatively low which complicated the characterization of the ocular disease pattern. Nevertheless, it could be shown that ocular onchocerciasis is less severe in the Sanctipauli forest than in the savanna, even after correction for differences in CMFL. The prevalence of onchocercal eye lesions and blindness were low and advanced sclerosing keratitis was completely absent. The differences are explained by presuming strain differences of the parasite Onchocerca volvulus. For given CMFLs the mean microfilarial loads in the eye were significantly lower than in the savanna which suggests that the parasite strain in the Sanctipauli forest is less invasive to the eye. Ocular microfilarial loads were too low to determine if the parasite is also less pathogenic to the eye, as has been concluded previously for foci of S. yahense, but this possibility cannot be excluded.

Animals↗
PubMed1990

[Clostridium bifermentans serovar malaysia, a new anaerobic bacterium pathogen to mosquito and blackfly larvae].

A strain of Clostridium bifermentans individualized as serovar malaysia (C.b.m.) according to its specific H antigen is toxic to mosquito and blackfly larvae when given orally. The toxicity occurs in sporulated cells which contain, in addition to spores, proteinic parasporal inclusion bodies and feather-like appendages; the amino acid content of the inclusion bodies is similar to that of Bacillus thuringiensis serovar israelensis (B.t.i.) and B. sphaericus crystals. The toxicity to Anopheles stephensi is as high as that of B.t.i. and the best strains of B. sphaericus. Culex pipiens is somewhat less susceptible, and Aedes aegypti much less. Pure parasporal inclusion bodies, isolated by ultracentrifugation on sucrose gradients, are highly toxic to mosquito larvae. The larvicidal power is destroyed by heating at 80 degrees C or by treatment with 50 mM NaOH. It is preserved by freeze-drying. The innocuity to mice of the sporulated cells is shown by different routes of administration: force-feeding, percutaneous, subcutaneous, intraperitoneal or intravenous injections. The potential for the biological control of mosquito and blackfly larvae is suggested.

Animals↗
PubMed1991

The effects of ivermectin on the viability of Onchocerca lienalis microfilariae in vitro and on their subsequent development in the blackfly vector, Simulium ornatum.

Experiments examined the sensitivity of Onchocerca lienalis microfilariae (mf) to ivermectin in vitro using a range of parameters to measure viability. Incubation in drug (1 x 10(-4) and 5.71 x 10(-8) M) caused an immediate decrease in motility levels in a concentration dependent fashion with a continuing decline over 24 h; the inclusion of a monkey kidney cell (LLCMK2) feeder layer in the culture system partially abrogated drug effects. The use of feeder cells allowed the longer-term culture of mf; incubation in drug at low concentrations (5.71 x 10(-8) and 1 x 10(-10) M) significantly reduced motility levels during a 17 day trial. Using MTT colorimetry it was found that 10,000 untreated mf per replicate sample were required to produce a sufficient quantity of formazan to make comparisons, and that formazan formation was most rapid during the first 30 min of incubation in MTT but continued up to 3-4 h. Following incubation of mf in ivermectin (1 x 10(-4) and 5.71 x 10(-8) M) for 24 h, only the higher concentration inhibited formazan formation (51%), while motility levels were reduced by 94% and 45% respectively. Using the same drug concentrations, mf viability was assessed by measuring the uptake of [3H]2-deoxy-D-glucose; uptake was only significantly reduced (40%) by the higher concentration, while motility levels were reduced by 77% and 63% respectively.(ABSTRACT TRUNCATED AT 250 WORDS)

Animals↗
PubMedDate not supplied

[The fertility of Simulium noelleri in the floodplain of the Northern Donets River].

Potential, actual and ecological fertility of S. noelleri females has been examined. Such information has been so far available only for the southeastern part of the Ukraine. It has been established that the first ovipositor was only from autogenically developed oocysts. The females of the second generation were born with follicules developed to phase I and their mean potential fertility was 293.00 +/- 5.97. Females of the third generation were born with follicules in phase IIB of development. Their fertility was above 337.14 +/- 4.08. During postmortem examination of female individuals with mature oocysts, disturbances in chorion development have been observed in some of them. They give birth to nonviable larvae, which decreases the number of the population. Ecological fertility declines as compared to the actual one both due to stuck (2%) and defective (10%) oocysts. Both indexes should be taken into consideration while calculating the quantity of the population (at the stage of first age larvae).

Animals↗
PubMed1990

An appraisal of the epidemiologic situation of onchocerciasis in Ethiopia.

The existence of onchocerciasis in Ethiopia has been known since 1939 as a result of investigation by Italians in south-western Ethiopia. In the last fifty years onchocerciasis has been spreading to previously non-endemic regions of Ethiopia. Although comprehensive epidemiological surveys are lacking, it is estimated that 7.3 million people or 17.4% of the population of Ethiopia is at risk from this disease. The principal vectors are S. damnosum complex and S. woodi ethiopiense. The clinical picture is mainly dermal and ocular manifestations are rare. In view of agricultural development projects and resettlement of millions of people from the highlands into endemic areas in southern and north-western parts of Ethiopia, further spread of onchocerciasis is expected. Experience gained in the control of the disease in west Africa by WHO and the introduction of effective mass chemotherapeutic agents as well as primary health care programmes and activities currently underway in Ethiopia indicate the feasibility of starting control programmes. A plea is therefore made to consider the control of onchocerciasis in Ethiopia urgently.

Agricultural Workers' Diseases↗
PubMed1990

Species complex of vectors and epidemiology.

This work collates previous and recent cytotaxonomically defined segregates of the Simulium damnosum complex from western and eastern Africa. Standard cytotaxonomic procedures were used on new samples from Nigeria, Cameroon and Malawi. The main onchocerciasis vectors comprising cytotypes, cytoforms and cytospecies are highlighted and indications of host preferences are given. Thyolo form, the vector implicated in the Thyolo Highlands of Malawi, is reported for the first time. Also reported are new foci of two genetically distinct savanna taxa: Volta form and S. damnosum s.s.. The associations between forest taxa and onchocerciasis in the Forest Zone of west Africa together with the interplay of vector distributions at the interface of this and the Savanna Zone in relation to the epidemiology of onchocerciasis are discussed. The role of individual members of the species complex in epidemiology is less understood in east Africa and the Yemen but is briefly discussed.

Africa↗
PubMed1990

Review of vector control prior to the OCP.

It is a little over 60 years since Blacklock, in an elegant study, demonstrated that in Sierra Leone human onchocerciasis was transmitted by a Simulium fly. Amazingly within 6 years of Blacklock's discovery an attempt was made, mainly using environmental management, to control Simulium in the Chiapas focus of Mexico, though this was not successful. Later Buckley was successful in eradicating Simulium neavei from the small Riana focus in Kenya by clearing riverine forest. However, it was not until DDT became widely available that Simulium control entered its heroic phase with campaigns in Kenya, Uganda and Zaire, some of which were highly successful. This led to an interest in controlling the vector in West Africa. The very different pattern of disease with very large foci virtually contiguous across tens of thousands of square kilometers suggested a difficult proposition and early attempts were not very successful. There is much of interest in the East and Central African schemes and in the West African forerunners of the OCP. In this talk an attempt will be made to capture something of the flavour of these pioneering efforts, to give credit to the men involved, and to highlight the successes against both the S. neavei and S. damnosum complex, and the advances which contributed to the successful planning of the OCP.

Africa↗
PubMed1990

Human onchocerciasis--an overview of the disease.

The general characteristics of Onchocerca volvulus infection and its transmission are outlined in this overview of human onchocerciasis. The pathogenic role of the microfilariae, producing lesions of the skin, lymphatic system, eye and deep organs, are described, along with the main clinical manifestations of the disease. The global prevalence and distribution of onchocerciasis are given. Best estimates in 1985 gave 86 million persons at risk, 17.8 million infected, 336,400 blind and a like number suffering from severe visual impairment. The vast majority was in Africa. The impact of onchocerciasis on communities in the Sudano-Guinean savanna zone of Africa is outlined, emphasizing the very high blindness rates and the increased mortality among the blind. Communities so affected cannot remain economically viable. They are forced to desert their villages and the fertile land near rivers. The background to the establishment of the Onchocerciasis Control Programme in West Africa (OCP) is given and the successful 10-year results of this campaign, which is based on prolonged, regular Simulium larviciding, are outlined. In the context of the future of the OCP and of the control of onchocerciasis elsewhere in the world, the need for improved chemotherapy is discussed. The prospects for large-scale suppressive therapy have greatly improved following the registration of ivermectin in 1988 for use in human onchocerciasis. The potential and possible uses of this drug, as a single-dose, non-toxic microfilaricide, which excites very little Mazzotti reaction and has a prolonged microfilarial suppressant action, are discussed. It is considered that an effective non-toxic macrofilaricide is still a prime need for onchocerciasis control.

Africa↗
PubMed1990

Field evaluation of Bacillus thuringiensis var. israelensis for control of black flies in the North Littoral Zone of Brazil's São Paulo State.

The impact of three flowable concentrate formulations of Bacillus thuringiensis var. israelensis (H-14) upon Simulium pertinax larvae was evaluated in 24 coastal streams of Brazil's São Paulo State. While no significant differences were found regarding the three formulations' effectiveness, significant correlations were found between the discharge rates of individual streams and the distances over which at least two of the formulations were carried effectively downstream to produce 80% mortality. The relatively short carry distances found for small streams could pose difficulties for control programs that need to treat large numbers of such streams, and suggests a need for research directed at increasing the distances B. thuringiensis (H-14) formulations can be carried.

Animals↗
PubMed1990

Onchocerciasis prevalence in Tanzania.

Prevalence of human onchocerciasis in Tanzania is described. The prevalence is high in Bwakira (63.6 per cent), Mahenge (58.6 per cent) and Ruvuma (31.9 per cent); and low in Amani (22.4 per cent) foci when compared to that reported in 1970. The increase and decrease on the prevalence indicate that the disease transmission has been increasing and decreasing in the respective foci. It is speculated that bush clearing and deforestation in general, has positive effects on the transmission of onchocerciasis where Simulium damnosum complex is a vector and negative effects where Simulium neavei complex exists.

Animals↗
PubMed1990

[Epidemiological status of onchocerciasis in the Congo].

Analysis of 25 surveys carried out in the Congo between 1978 and 1987 (covering nine of the ten administrative regions), during which 6,215 subjects were examined, showed that onchocerciasis is endemic in the southern part of the country. Two main foci meeting at the southern exit of Brazzaville (Pool region) were identified. One focus in the Djoué basin. The other is the zone along the Congo river stretching from below Brazzaville south west to the Zaire border. Two secondary foci were noted, one in the region of the Bouenza and the other west of the Mayombe mountains. Surveys carried out in the north of the country and in the west did not reveal any onchocerciasis. However, certain areas of primary forest in these regions were found to be endemic for Mansonella streptocerca. Simulium damnosum s.l. in the sole vector of onchocerciasis. In both the Pool foci, and in the Mayombe focus, prevalences assessed from microfilarial and cyst counts were high but the mean microfilarial densities were relatively low. In certain villages over 90% of the population aged over 14 years may present with microfilariae and nearly 70% may present cysts.

Adolescent↗
PubMed1990

[Study of the transmission of onchocerciasis in the surroundings of a refugee camp located in the savanna zone of Cameroon].

Chadian refugees, most of whom are free from onchocerciasis, settled recently in a camp in a savanna area of the northern Cameroon where the prevalence is about 80% and the blindness rate is 4% of the adult population. In view of the risks of onchocerciasis facing the immigrants, the authors carried out an entomological survey in this region aimed at determining the modes of transmission and assessing the possibilities for the control of this disease. After a three-month survey in the study area, it appears clearly that 1) transmission takes place only during the rainy season, 2) the main vectors are the two savanna species, Simulium damnosum s.s. and Simulium sirbanum, 3) the larval breeding sites are not located on the principal river, the Faro, but on its small seasonal tributaries, 4) the local populations still free from onchocerciasis and the Chadian refugees who farm close to these tributaries run the risk of getting serious ocular lesions in the long run which could lead to blindness. The conclusions of this survey prompted the authors to envisage an onchocerciasis control campaign in this area against the larval stages of the vectors.

Animals↗
PubMed1990

Seasonal variation in onchocerciasis transmission in the Santiago focus of Ecuador.

Man-biting rates and natural infection rates with filariae were determined for anthropophilic black flies in a preliminary survey during the wet and dry seasons at three localities, either hypoendemic or hyperendemic for onchocerciasis, in the Santiago onchocerciasis focus of Ecuador. Simulium exiguum was an efficient vector associated with hyperendemicity whereas S. quadrivittatum was thought only to sporadically transmit the parasite. Parasite transmission by these two species varied seasonally. Two other man-biting species, S. bipunctatum and S. escomeli, were discounted as vectors because of their largely zoophilic habit and rarity, respectively. The need is emphasised to investigate species distributions thoroughly before entomological surveys to obtain baseline data for vector control are investigated.

Animals↗