Onchocerciasis in San Vicente Pacaya, Guatemala *

Tada, Isao; Aoki, Yoshiki; Rimola, C. E.; Ikeda, Teruaki; Matsuo, Keitaro; Ochoa, A. J. Onofre; Recinos, C. Manuel M.; Sato, Susumu; Godoy, B.; Orellana, JJ; Takahashi, Hiroshi

doi:10.4269/ajtmh.1979.28.67

Cited by 14 publications

(9 citation statements)

References 1 publication

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“…Above 45 years, however, females surpass males as their mf loads rise at an increasing rate, reaching 140 mf per mg of skin at age 75. In central Guatemala and in agreement with other reports (11,19), mf burden is higher in men than in women for all ages, reaching a plateau for both sexes at Ϸ30 years. In southern Venezuela, there is less difference between mf loads in men and women, with both sexes exhibiting an increase with age similar in shape and magnitude to that of women in the Vina valley.…”

Section: Resultssupporting

confidence: 80%

“…of O. volvulus patterns from predictions generated by simple immigration-death models (7). No model, however, has also attempted to capture sex-related heterogeneities, despite infection and morbidity in some endemic areas differing markedly between males and females (11,(18)(19)(20)(21)(22)24). The relative contribution of ecological (behavior, environment, and body size) and physiological (hormonal and immunological) factors to sex-specific infection and disease has long been debated (35).…”

Section: Discussionmentioning

confidence: 99%

“…37). In Guatemala, onchocerciasis is transmitted mainly in coffee growing, mountainous areas, with men generally more exposed to vectors while working in such areas (11,19,24). Among the Yanomami, use of clothing is minimal, traditional houses lack enclosing walls, and men and women engage in activities around and outside villages (26,30).…”

Section: Figmentioning

confidence: 99%

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Human infection patterns and heterogeneous exposure in river blindness

Filipe

Boussinesq

Renz

et al. 2005

Proc. Natl. Acad. Sci. U.S.A.

100

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Here we analyze patterns of human infection with Onchocerca volvulus (the cause of river blindness) in different continents and ecologies. In contrast with some geohelminths and schistosome parasites whose worm burdens typically exhibit a humped pattern with host age, patterns of O. volvulus infection vary markedly with locality. To test the hypothesis that such differences are partly due to heterogeneity in exposure to vector bites, we develop an ageand sex-structured model for intensity of infection, with parasite regulation within humans and vectors. The model is fitted to microfilarial data from savannah villages of northern Cameroon, coffee fincas of central Guatemala, and forest-dwelling communities of southern Venezuela that were recorded before introducing ivermectin treatment. Estimates of transmission and infection loads are compared with entomological and epidemiological field data. Host age-and sex-heterogeneous exposure largely explains locale-specific infection patterns in onchocerciasis (whereas acquired protective immunity has been invoked for other helminth infections). The basic reproductive number,R 0, ranges from 5 to 8, which is slightly above estimates for other helminth parasites but well below previously presented values.age ͉ sex ͉ helminth ͉ mathematical model ͉ onchocerciasis

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Section: Resultssupporting

confidence: 80%

Section: Discussionmentioning

confidence: 99%

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Human infection patterns and heterogeneous exposure in river blindness

Filipe

Boussinesq

Renz

et al. 2005

Proc. Natl. Acad. Sci. U.S.A.

100

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“…For Tchollire¨, a village very close to the threshold biting rate and basic reproductive number, Mf prevalence is already su¤cient to classify this locality as mesoendemic according to Prost et al (1979). This fact con¢rms doubts expressed by other authors as to whether there is sustainable onchocerciasis transmission in hypoendemic localities (Tada et al 1979).…”

Section: Discussionmentioning

confidence: 48%

Population biology of human onchocerciasis

Basáñez

Boussinesq²

1999

Phil. Trans. R. Soc. Lond. B

110

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Human onchocerciasis (river blindness) is the filarial infection caused by Onchocerca volvulus and transmitted among people through the bites of the Simulium vector. Some 86 million people around the world are at risk of acquiring the nematode, with 18 million people infected and 600,000 visually impaired, half of them partially or totally blind. 99% of cases occur in tropical Africa; scattered foci exist in Latin America. Until recently control programmes, in operation since 1975, have consisted of antivectorial measures. With the introduction of ivermectin in 1988, safe and effective chemotherapy is now available. With the original Onchocerciasis Control Programme of West Africa coming to an end, both the new African Programme for Onchocerciasis Control and the Onchocerciasis Elimination Programme for the Americas, rely heavily on ivermectin self-sustained mass delivery. In consequence, the need for understanding the processes regulating parasite abundance in human and simuliid populations is of utmost importance. We present a simple mathematical framework built around recent analyses of exposure- and density-dependent processes operating, respectively, within the human and vector hosts. An expression for the basic reproductive ratio, R0, is derived and related to the minimum vector density required for parasite persistence in localities of West Africa in general and northern Cameroon in particular. Model outputs suggest that constraints acting against parasite establishment in both humans and vectors are necessary to reproduce field observations, but those in humans may not fully protect against reinfection. Analyses of host age-profiles of infection prevalence, intensity, and aggregation for increasing levels of endemicity and intensity of transmission in the Vina valley of northern Cameroon are in agreement with these results and discussed in light of novel work on onchocerciasis immunology.

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“…The present study area (SVP) being a highly endemic zone of bovine and equine onchocerciasis with O. gutturosa and O. cervicalis, respectively (Hashiguchi et al, 1981), it seems likely that these species including S. metallicum s. 1. and S. callidum are involved in the transmission of non-human onchocerciasis though the vector of the disease remains still to be determined in Guatemala. In addition, the area is also known as the endemic focus of human onchocerciasis with various intensities of the infections in the residents of villages and plantations within SVP (Tada et al, 1979). In such an area, the possible infection of S. metallicum s. 1. and S. callidum with the larvae of bovine or equine Onchocerca should be taken into consideration, especially in the evaluation of the vector control of the human disease.…”

Section: Discussionmentioning

confidence: 99%

Diurnal biting activity of four zoophilic species of Simulium in an area endemic for human onchocerciasis in Guatemala.

Hashiguchi

Tada

Floresc³

et al. 1982

Jap. J. Trop. Med. Hyg.

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Summary: The biting activity of four zoophilic species of Simulium was examined in an area endemic for human onchocerciasis in Guatemala, using bovine baits. The surveys were performed at three sites within San Vicente Pacaya county (SVP) from daylight until nightfall of two days in January 1979. A total of 8,203 blackflies were collected from the baits throughout the collections. Of these flies, 6,531 (79.6%) wereSimuliummetallicum s. 1.; 977 (11.9%), S. pulverulentum; 654 (8.0%), S. callidum; and 41(0.5%),S.rubicundulum. Biting activity of S. metallicum s. 1. peaked between 0800 to 0900 hours and a second peak was noted between 1500 to 1600 hours. S. callidum also exhibited two peaks, one in the morning and the other, more pronounced, in the late afternoon, immediately before the night-fall. The remaining two species, S. pulverulentum and S. rubicundulum were mainly mid-morning attackers of cattle. Thus, the rate of species composition was presumed to differ within a day.

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Onchocerciasis in San Vicente Pacaya, Guatemala *

Cited by 14 publications

References 1 publication

Human infection patterns and heterogeneous exposure in river blindness

Human infection patterns and heterogeneous exposure in river blindness

Population biology of human onchocerciasis

Diurnal biting activity of four zoophilic species of Simulium in an area endemic for human onchocerciasis in Guatemala.

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