5 research outputs found
Evidence of suppression of onchocerciasis transmission in the Venezuelan Amazonian focus.
BACKGROUND: The World Health Organization (WHO) has set goals for onchocerciasis elimination in Latin America by 2015. Most of the six previously endemic countries are attaining this goal by implementing twice a year (and in some foci, quarterly) mass ivermectin (MectizanÂź) distribution. Elimination of transmission has been verified in Colombia, Ecuador and Mexico. Challenges remain in the Amazonian focus straddling Venezuela and Brazil, where the disease affects the hard-to-reach Yanomami indigenous population. We provide evidence of suppression of Onchocerca volvulus transmission by Simulium guianense s.l. in 16 previously hyperendemic Yanomami communities in southern Venezuela after 15Â years of 6-monthly and 5Â years of 3-monthly mass ivermectin treatment. METHODS: Baseline and monitoring and evaluation parasitological, ophthalmological, entomological and serological surveys were conducted in selected sentinel and extra-sentinel communities of the focus throughout the implementation of the programme. RESULTS: From 2010 to 2012â2015, clinico-parasitological surveys indicate a substantial decrease in skin microfilarial prevalence and intensity of infection; accompanied by no evidence (or very low prevalence and intensity) of ocular microfilariae in the examined population. Of a total of 51,341âS. guianense flies tested by PCR none had L3 infection (heads only). Prevalence of infective flies and seasonal transmission potentials in 2012â2013 were, respectively, under 1Â % and 20Â L3/person/transmission season. Serology in children aged 1â10 years demonstrated that although 26 out of 396 (7Â %) individuals still had Ov-16 antibodies, only 4/218 (2Â %) seropositives were aged 1â5 years. CONCLUSIONS: We report evidence of recent transmission and morbidity suppression in some communities of the focus representing 75Â % of the Yanomami population and 70Â % of all known communities. We conclude that onchocerciasis transmission could be feasibly interrupted in the Venezuelan Amazonian focus. ELECTRONIC SUPPLEMENTARY MATERIAL: The online version of this article (doi:10.1186/s13071-016-1313-z) contains supplementary material, which is available to authorized users
Onchocerca±Simulium complexes in Venezuela: can human onchocerciasis spread outside its present endemic areas?
The compatibility between sympatric and allopatric combinations of Onchocerca volvulus±anthropophilic species of
Simulium was studied in the north-eastern focus of human onchocerciasis as well as in a densely populated locality of the
Amazonas State in Venezuela. The objectives were to test the conjecture that local adaptation exists between the parasite
and its vectors (the Onchocerca±Simulium complex hypothesis), and assess the possibility of the infection spreading from
its present distributional range. For the homologous combination, O. volvulus±S. metallicum cytospecies E in Anzoa! tegui
State (north-eastern focus), parasite yield was 45%in contrast to 1%for the heterologous, southern parasite±S. metallicum
infection. This was signiŸcantly lower than the parasite yield (4±10%) expected after allowing for the effect of densitydependent
limitation of infective larval output described in this paper for S. metallicum. The population of S. exiguum s.l.
from southern Venezuela allowed no larval development beyond the L1 stage of either northern or southern parasites.
Mechanisms for such refractoriness probably operate at the level of the thoracic muscles, not affecting microÂźlarial uptake
or migration out of the bloodmeal. The parasite yield of southern O. volvulus in S. oyapockense s.l. ÂŻies biting man at
Puerto Ayacucho (Amazonas) was about 1%, in agreement with the Âźgures recorded for highly compatible sympatric
combinations such as O. volvulus±S. ochraceum s.l. in Guatemala. No infective larval development of the northern parasite
was observed in southern S. oyapockense. These results, together with considerations of typical worm burdens in the
human host, presence}absence of armed cibaria in the simuliids, parasite-induced vector mortality, and ÂŻy biting rates,
suggest a lower potential for onchocerciasis to spread between the northern and southern endemic areas of Venezuela than
that between Amazonian hyperendemic locations and settlements outside this focus with high densities of S. oyapockense
s.l