Factors affecting onchocerciasis transmission: lessons for infection control.

INTRODUCTION: Onchocerca volvulus infects in excess of 15 million people. The vectors are Simulium blackflies, varieties of which differ in their ecologies, behavior and vectorial abilities. Control of the vectors and mass administrations of ivermectin have succeeded in reducing prevalences with elimination achieved in some foci, particularly in Central and southern America. In Africa, progress towards elimination has been less successful. Areas covered: Even with community directed treatment with ivermectin (CDTI), control has been difficult in African areas with initial prevalences in excess of 55%, especially if only annual treatments are dispensed. This is partly attributable to insufficient coverage, but the appearance of incipiently resistant non-responding parasites and lack of attention to vector biology in modeling and planning outcomes of intervention programmes have also played their parts, with recrudescence now appearing in some treated areas. Expert commentary: The biology of onchocerciasis is complex involving different vectors with differing abilities to transmit parasites, diverse pathologies related to geographical and parasite variations and endosymbionts in both parasite and vector. Modeling to predict epidemiological and control outcomes is addressing this complexity but more attention needs to be given to the vectors' roles to further understanding of where and when control measures will succeed.

Oncocercosis de la mandíbula: a propósito de un caso / Onchocercosis of the jaw: about a case

Fundamento: la oncocercosis, enfermedad de Robles, es una enfermedad parasitaria crónica causada por un gusano nematodo; la filaria Onchocerca volvulus transmitida por moscas negras de la familia Simuliidae, cuyo único hospedero definitivo es el hombre. Es la segunda causa infecciosa de ceguera en el mundo. Objetivo: describir un caso de una paciente portadora de la enfermedad con un nódulo en la rama ascendente del maxilar derecho. Caso clínico: paciente africana, femenina, que acude a consulta por presentar aumento de volumen de la mandíbula derecha de varios meses de evolución y tumoración de seis centímetros de diámetro, a nivel del ángulo y rama horizontal derecha del maxilar inferior. En la citología se diagnosticó microfilariasis. Conclusiones: el parásito se trasmitió en esta enferma, como ocurre en todos los casos, por la picadura de una mosca del género Simulium, que al succionar la sangre de la paciente depositó sus larvas desencadenando la enfermedad.

Background: onchocercosis, also known as Robles’ disease, is a chronic parasitic disease caused by a nematode worm of the genus filaria onchocerca volvulus that is transmitted by black flies of the simuliidae family and the only host of which is man. It is the second infectious cause of blindness in the world. Objective: to describe the case of a patient carrier of the disease who present a nodule in the right ascending ramus of the lower jaw. Clinical case: an African female patient who came to consultation for presenting an increase in volume of the right area of the lower jaw of some months of evolution and a tumor of six centimeters in diameter at the level of the right horizontal angle and ramus of the lower jaw. Microfilariasis was diagnosed in the cytology. Conclusions: the parasite was transmitted to the patient like it happens in all the cases, by the sting of a fly of the genus simulium that sucks the blood of the person and lays the larvae causing the disease.

A preliminary analysis of the population genetics and molecular phylogenetics of Onchocerca volvulus (Nematoda: Filarioidea) using nuclear ribosomal second internal transcribed spacer sequences

Nuclear internal transcribed spacer 2 (ITS2) rDNA sequences were used for a molecular phylogenetics analysis of five Onchocerca species. The sister species of the human parasite O. volvulus was found to be the cattle parasite O. ochengi and not O. gibsoni, contrary to chromosomal evidence. The genetic differentiation of two African populations (representing the two African strains) and a Brazilian population of O. volvulus was also studied. Phylogenetic and network reconstruction did not show any clustering of ITS2 alleles on geographic or strain grounds. Furthermore, population genetics tests showed no indication of population differentiation but suggested gene flow among the three populations.

Algunos problemas en la investigación para el control de la transmisión de Ochocerca volvulus en México / Research for the control of the transmission of Onchocerca volvulus in Mexico

El tratamiento y control de la oncocercosis en México ha sustentado desde su inicio en la eliminación de las microfilarias con el uso de la dietilcarbamazina y la extirpación quirúrgica de los oncocercomas que arrojan los gusanos adultos. Estas medidas al parecer han disminuido la prevalencia e incidencia de la ceguera en aquellos individuos afectados por esa parasitosis. Sin embargo, no se ha logrado un impacto importante sobre la transmisión de la oncocercosis en México el control químico del vector ha tenido buenos resultados en otras regiones del mundo; en México, sin embargo no ha sido plenamente aceptado como parte integral del control de la oncocercosis por diversas causas. Más aún, pocas investigaciones se han realizado en relación a la búsqueda de nuevas alternativas para el control del vector. Recientemente, el resultado de investigaciones sobre la invermectina (agente microfilaricida) mostraron que esta droga es eficaz y segura para el tratamiento de la oncocercosis. En otros reportes se ha señalado tambien que la ivermectina tiene un efecto sobre la transmisión de esta filaria. No obstante, existen algunas interrogantes acerca de su capacidad para suspender la transmisión de la oncocercosis, discutiendo los problemas para su diagnóstico, tratamiento y control. Además se propone el empleo de parámetros para la evaluación correcta de las medidas de control, con énfasis en las determinaciones entomológicas

The treatment and control of onchocerciasis in Mexico has been supported only on the administration of diethy carbamazine and the removal of adult worms, which are in the onchocercomata. These actions seems to have diminished the prevalence and incidence of blindness in those individuals who are affected by this parasitosis. However, there has not been an important impact on onchocerciasis transmission. The objective of this paper is to critically analyze and discuss subjects related to diagnosis, treatment and control of onchocerciasis transmission in Mexico. Chemical vector control has been successfully archieved in other world regions; however, in Mexico, it has not been fully acepted as part of the integral onchocerciasis control due to several causes. Moreover, there has been few scientific research activties toward the search of new options for vector control. Recently, results of research on ivermectin (a microfilaricide agent) have indicated that this drug is effective and safe for the treatment of onchocerciasis. Additionally, it has been reported that ivermectin has an effect on the onchocerciasis transmission. However, there are several unanswered questions about the efficacy of ivermectin in toping onchocerciasis transmission. In this report, the ain efforts carried out in Mexico against onchocerciasis are analysed and problems related with diagnosis, treatment and control are also discussed Some parameters for the correct evaluation of onchocerciasis control, with entomological emphasis, are proposed.