Onchocerciasis In Ecuador Research Articles

Elimination of onchocerciasis in Ecuador: findings of post-treatment surveillance

BackgroundThe Esmeraldas focus of onchocerciasis in Ecuador expanded geographically during the 1980s and was associated with severe ocular and skin disease. Mass drug administration (MDA) with ivermectin started in 1991, initially once but later twice a year, in the principle endemic focus followed by all satellite foci. Treatment was stopped in 2009 when entomological assessments determined that transmission of Onchocerca volvulus had been interrupted.MethodsThree years after the cessation of ivermectin treatment in 2012, as defined by the WHO guidelines for onchocerciasis elimination, blackfly collections were done in four sentinel sites in former hyperendemic areas. The presence of infective larvae in local vectors, Simulium exiguum and Simulum quadrivittatum, was assessed by detection of O. volvulus DNA by PCR. Additional flies captured in four extra-sentinel sites located in former hyper- and mesoendemic dispersed isolated areas were also assessed.ResultsThe results from 68,310 captured blackflies, 40,114 from four sentinel villages in the previously hyperendemic areas (Corriente Grande, El Tigre, San Miguel on Río Cayapas and Naranjal on Río Canandé) and 28,197 from extra-sentinel locations, were all negative for the presence of O. volvulus. These extra-sentinel sites (Hualpí on Río Hoja Blanca, Capulí on Río Onzole, La Ceiba on Río Tululví and Medianía on Río Verde) were included to provide additional evidence of the impact of MDA on the transmission of O. volvulus in isolated endemic areas.ConclusionsOur data indicate that transmission of O. volvulus has been stopped in all endemic areas in Ecuador, including all satellite foci outside the main focus. These findings indicate that a strategy of ivermectin distribution twice a year to over 85% of the treatment-eligible population was effective in eliminating the infection from Ecuador in a focus with a highly competent primary vector, S. exiguum, and where the infection rates were equal to or greater than observed in many onchocerciasis foci in Africa.

Interruption of infection transmission in the onchocerciasis focus of Ecuador leading to the cessation of ivermectin distribution.

Introduction: A clinically significant endemic focus of onchocerciasis existing in Esmeraldas Province, coastal Ecuador has been under an ivermectin mass drug administration program since 1991. The main transmitting vector in this area is the voracious blackfly, Simulium exiguum. This paper describes the assessments made that support the decision to cease mass treatment. Methodology and Principle Findings: Thirty-five rounds of ivermectin treatment occurred between 1991–2009 with 29 of these carrying >85% coverage. Following the guidelines set by WHO for ceasing ivermectin distribution the impact on parasite transmission was measured in the two vector species by an O-150 PCR technique standard for assessing for the presence of Onchocerca volvulus. Up to seven collection sites in three major river systems were tested on four occasions between 1995 and 2008. The infectivity rates of 65.0 (CI 39–101) and 72.7 (CI 42–116) in 1995 dropped to zero at all seven collection sites by 2008. Assessment for the presence of antibodies against O. volvulus was made in 2001, 2006, 2007 and 2008 using standard ELISA assays for detecting anti-Ov16 antibodies. None of total of 1810 children aged 1–15 years (between 82 and 98% of children present in the surveyed villages) tested in the above years were found to be carrying antibodies to this antigen. These findings were the basis for the cessation of mass drug treatment with ivermectin in 2009. Significance: This fulfillment of the criteria for cessation of mass distribution of ivermectin in the only known endemic zone of onchocerciasis in Ecuador moves the country into the surveillance phase of official verification for national elimination of transmission of infection. These findings indicate that ivermectin given twice a year with greater than 85% of the community can move a program to the final stages of verification of transmission interruption.

La Universidad de Guayaquil y su participación en el estudio de la Oncocercosis en el Ecuador

Es importante señalar que la Universidad de Guayaquil ha participado en la historia de la Oncocercosis ecuatoriana desde su inicio en 1980. El Dr. Ramón Lazo docente de parasitología de la Facultad de Ciencias Médicas y 1º Vicepresidente de la Federación Latinoamericana de Parasitólogos (FLAP), Invitó al parasitólogo guatemalteco Dr. Francisco Aguilar para participar en el Congreso Latinoamericano de Patología Clínica, en el Simposio “Enfermedades Parasitarias de mayor trascendencia en el trópico”, con el tema de Oncocercosis. Se realizó invitación al directorio de la FLAP; Dr. Rubens Campos (Brasil), Presidente; Dr. Francisco Aguilar (Guatemala), 2º Vicepresidente y al Dr. Benjamín Cimerman (Brasil), 3º Vicepresidente. Desconocíamos que al Dr. Francisco Aguilar le habían designado el tema de “Oncocercosis en Latinoamérica” para ser presentado en el congreso de Oncocercosis de Guatemala-Japón, organizado en Enero de 1981. En el Resumen de su trabajo sólo se incorporó la existencia del primer caso de Oncocercosis de Ecuador, al recibir comunicación personal del Dr. Lazo, que el Dr. Luis Carvajal había señalado el primer caso ecuatoriano. Con el trabajo de campo realizado con la asistencia de profesores de la Facultad de Ciencias Médicas, fue ampliado los datos del trabajo de investigación, siendo incorporada en la conferencia conjunta Guatemala-Japón, que fue reportada en las Memorias de dicho evento en 1981. La participación de la Universidad de Guayaquil fue elocuente, informada en Gaceta de Actualidad y en el Boletín Informativo del Vicerrectorado Académico de 1986, cuyos relatos se encuentran a continuación

Isolation by distance and a chromosomal cline in the Cayapa cytospecies of Simulium exiguum, the vector of human onchocerciasis in Ecuador

The population genetic structure of the Cayapa cytospecies of Simulium exiguum, the vector of onchocerciasis, was analysed using allozyme frequency and chromosomal inversion polymorphism data from 6 and 15 populations respectively, collected in Ecuador. Eight allozyme loci were scored. No unique allozyme markers were found enabling us to identify biting adults of the vector from the non-vector Bucay cytotype. Mannose-phosphate isomerase (Mpi) contributed largely to the significant heterogeneity in gene frequency among populations of the Cayapa cytospecies and also to the overall population structuring (F(ST) = 0.015 +/- 0.014) which fitted the isolation by distance model. However, heterozygote deficits were recorded for Mpi in four of the six populations, which could indicate that selection is acting at this locus but this hypothesis will require further convincing evidence. Furthermore the significant population structuring of allozymes was not evident when Mpi was omitted from the analysis. All inversion polymorphisms (IIS-B, IIS-F, IIL-A and IIL-B) were in Hardy-Weinberg equilibrium, showed significant heterogeneity between populations and revealed the occurrence of an altitudinal cline in inversion IIS-B frequency. The inversion polymorphisms revealed a significant degree of population structuring (F(ST) = 0.083 +/- 0.027), which can be explained by the isolation by distance model. A UPGMA cluster analysis revealed the relatively remote, high altitude Rio Mira populations to be the most genetically distinct.

Onchocerciasis and reproductive health in Ecuador

A retrospective study was performed comparing the number of spontaneous abortions in a hyperendemic area for onchocerciasis in Ecuador before and after ivermectin treatment with that of a comparable non-endemic area. The frequency of spontaneous abortions was associated with a change in the community microfilarial load, suggesting that there may be a relationship between spontaneous abortions and infection with Onchocerca volvulus. In the endemic area, a significantly greater rate of spontaneous abortions was seen in the period before ivermectin distribution compared to that after the start of ivermectin treatments every 6 months. In the non-endemic area, no change in the rate of spontaneous abortions was seen over the same time period. In addition to the well-documented improvements in skin and ocular disease, ivermectin may also improve the reproductive health of endemic populations.

The potential for dispersal of onchocerciasis in Ecuador in relation to the distribution of the vector Simulium exiguum (Diptera:Simuliidae).

The future dispersal of onchocerciasis in Ecuador is dependent on the distribution of cytotypes of the vector species complex Simulium exiguum. Over the last 14 years, collections of larvae have been made from over 25 rivers, between 80-1600 m altitude, from various sites on both sides of the Andes. Analysis of larval polytene chromosomes was used to determine the distributions of each cytotype. On the western side of the Andes, the Cayapa cytotype (the only cytotype directly incriminated as a vector) has a distribution from Santo Domingo de los Colorados northwards. The Quevedo and Bucay cytotypes occur from Santo Domingo de los Colorados southwards. On the eastern side of the Andes, the Aguarico cytotype occurs in the Rio Aguarico and a new cytotype is present in the tributaries of the Rio Napo. Whether the disease will spread south of Santo Domingo and on the eastern side of the Andes depends on vector capacity of the cytotypes and the dispersal patterns of individuals infected with onchocerciasis. At present the Aguarico, Bucay and Quevedo cytotypes are known to be efficient hosts, but their biting preferences and biting densities have not yet been evaluated.

The value of the larval head pattern for differentiating Simulium exiguum s.l. and S. gonzalezi (Diptera: Simuliidae) in the onchocerciasis focus of Ecuador

AbstractIn the Esmeraldas focus of onchocerciasis in Ecuador, the larvae of the primary vector Simulium exiguum Roubaud are found in sympatry with the non-vector S. gonzalezi Vargas & Díaz Nájera. Distinguishing the pre-ultimate stage larvae of these two species usually relies on the pattern of markings on the cephalic apotome. These patterns appear either as dark spots against a pale cuticle (positive head pattern) or as pale spots within a darkened area of the cuticle (negative head pattern). Larvae of S. exiguum s.l. usually exhibit positive or no head patterns whilst those of S. gonzalezi usually have negative head patterns. The purpose of this paper was to investigate head pattern variation (scored in one of six categories) in (polytene) chromosomally identified larvae of the two species and cytotypes of S. exiguum from three collection sites in Ecuador (including one in the onchocerciasis focus). The head patterns of a total of 1183 larvae were studied. Chromosomal identification of penultimate instar larvae revealed only the presence of the Cayapa and Quevedo cytotypes of S. exiguum (n=208). Both cytotypes exhibited a wide range of head patterns from positive to negative. The results indicate that negative head patterns cannot be used to reliably distinguish between larvae of S. exiguum s.l. and S. gonzalezi. All except one larva with negative head patterns were females (n=53), suggesting that head pattern in this species complex might be a sex-linked character.

Onchocerciasis in Ecuador: dermal depigmentation, ‘leopard skin’ and comparison with treponemal infection

Onchocerciasis in Ecuador: dermal depigmentation, ‘leopard skin’ and comparison with treponemal infection

Onchocerciasis in Ecuador: infection in children in the Santiago Basin focus, Province of Esmeraldas

The prevalence of onchocerciasis infection in children aged 1–12 in the Santiago Basin focus, province of Esmeraldas, Ecuador, was determined to see if active transmission of the disease had occurred in the past 6 years. An infection rate of 45·0% was found. Compared to that found in 1980 (14·5%), the infection rate had increased by 210·1%. The increase was greater on the Rio Santiago (340·5%) than on the Rio Cayapas (195·5%). An increase of 286% was seen in the skin microfilarial density in the 1–4 year age group, with a 56·8% increase in the 5–12 year age group. The prevalence of infection in children aged 0–4 years (those born since the first enquiry in 1980) was 64·3%, with an average skin microfilarial density of 12·2 microfilariae (mf)/mg and with 20% presenting nodules, of which 92·1% occurred in the head region. Of the 34 children examined aged less than one year, 25 (73·5%) were positive for microfilariae with an average microfilarial skin density of 9·6 mf/mg. These data suggest that there is active transmission of the disease in the Santiago Basin onchocercal foci.

Studies on the biology of Simuliidae (Diptera) at the Santiago onchocerciasis focus in Ecuador, with special reference to the vectors and disease transmission

A survey showed the presence of seven simuliid species in the onchocerciasis focus in Ecuador Simulium exiguum and S. quadrivittatum were the two most common anthropophilic species and were shown to be both experimental and natural vectors of Onchocerca volvulus. S. antillarum only occasionally bit man. Observations were made on the biology of the two vector species and it was evident that S. exiguum was the primary vector of onchocerciasis in the rainy season. The relevance of these findings to the epidemiology and control of onchocerciasis in Ecuador are discussed.

Onchocerciasis in Ecuador, IV. Comparative studies of the disease relating to the Chachi and Black populations in the province of Esmeraldas

The frequency, intensity and clinical features of onchocerciasis in the two ethnic groups (Blacks and Chachilla—an indigenous tribe) in the endemic foci of the disease in Esmeraldas province (Ecuador) were evaluated. The incidence of infection and intensity of the disease seen in both groups were directly related to the frequency of man-vector contact and not to racial factors. Both groups showed the same rate of positivity in both the hyperendemic and hypoendemic areas. Males of both groups had a consistently higher positivity rate than did females. The Chachilla were found to have a higher mean microfilarial density than Blacks in both types of endemic areas. Certain clinical features of the disease analogous to those seen in the African form were present only in Blacks. No lymphatic involvement or hypertrophic scarring was seen in the Chachilla, suggesting that in the Blacks there may be a generaically related predisposition to lymphatic complications of microfilarial infections.

Onchocerciasis in Ecuador. III. Clinical manifestations of the disease in the province of Esmeraldas

Considerable variation in the frequency of the clinical manifestations of onchocerciasis was seen in the individual endemic foci of the disease in province of Esmeraldas, Ecuador. In hypoendemic areas, 84·6% of all microfilaria-positive inhabitants were found to be free of any clinical manifestations of the disease, whereas in the hyperendemic area clinical manifestations were present in 57·9% of those infected. Ocular keratitis, macular papular rash of the skin and subcutaneous onchocercal nodules of varying frequency were the major clinical variants. Long-standing onchodermatitis and hypertrophy of the skin were rarely seen. Clinical evidence of prolonged ocular and skin invasion by microfilariae was seen only in the hyperendemic area. Of the 26·1% of the microfilaria-positive inhabitants who had onchocercal nodules, 91·7% lived in the hyperendemic area. 41·1% of all nodules occurred in the region of the iliac crest. Clinical conditions associated with high microfilarial density, i.e., elephantiasis of the legs and scrotum, lymphadenopathy, hanging groin, hydrocele and inguinal hernia were seen only in the hyperendemic area. The clinical features were similar to those seen in Africa, but the low incidence of the clinical presentation and severity of the disease suggested a recent infestation of the province.

Report on a focus of onchocerciasis in Esmeraldas province of Ecuador.

A case suggesting the occurrence of onchocerciasis in Ecuador was first reported in 1952. The appearance of another case in 1977 provided the stimulus to do an epidemiologic survey on an isolated 20-km section of the Cayapa River in Esmeraldas Province. The Mazzotti test, skin biopsy, and nodulectomy were performed on 300 inhabitants of the area. Of the 300 who were tested, 210 (70%) reacted positively to the Mazzotti test, only 20 of whom had a negative skin biopsy. An additional 10 patients with a negative Mazzotti test had a positive skin biopsy. Combining the results of the Mazzotti test and skin biopsy show a 73% prevalence of onchocerciasis. Sixty-four patients (21%) had nodules, and evidence suggests that ocular pathology may be present.