Distribution and ecological aspects of Rhodnius pallescens in Costa Rica and Nicaragua and their epidemiological implications

In light of the Central American Initiative for the control of Chagas disease, efforts were made on the part of Costa Rican and Nicaraguan teams, working separately, to determine the present status of Rhodnius pallescens in areas close to the common border of the two countries, where the insect has appeared within the last few years. The opportunity was also used to establish whether R. prolixus, a vector present in some areas of Nicaragua, has been introduced in recent years into Costa Rica with Nicaraguan immigrants. It became evident that wild adults of R. pallescens are common visitors to houses in different towns of a wide area characterized as a humid, warm lowland, on both sides of the frontier. Up to the present, this bug has been able to colonize a small proportion of human dwellings only on the Nicaraguan side. There was strong evidence that the visitation of the adult bug to houses is related to the attraction of this species to electric lights. There were no indications of the presence of R. prolixus either in Nicaragua or in Costa Rica in this area of the Caribbean basin. Triatoma dimidiata, a widespread domestic species in both countries, was totally absent in the explored areas of Costa Rica but occasionally occurs on the Nicaraguan side. Serological surveys in children of both areas showed that transmission of Chagas disease takes place in a rather small degree in Costa Rica and more commonly in Nicaragua, indicating that R. pallescens could be a potential threat as a vector in this particular region.

A survey on Triatoma dimidiata in an urban area of the province of Heredia, Costa Rica

Triatoma dimidiata has been found in several cities and towns of those countries where the insect is a domestic or peridomestic pest. In Central America, urban infestations occur in the capitals of at least five countries. During 2001 and 2002 a survey was carried out in the county of San Rafael, Heredia province, located 15 km northwest of San José, capital of Costa Rica, in order to determine the degree of infestation by T. dimidiata in an entire city block. Six peridomestic colonies of the insect were detected in the backyards of eight households. The ecotopes occupied by the insects consisted of store rooms with old objects, wood piles or firewood, and chicken coops. A total of 1917 insects were found in the six foci, during two sampling periods, and a mean infection rate by Trypanosoma cruzi of 28.4 percent was found in 1718 insects examined. The largest colony found in one of the households yielded 872 insects that were thriving mainly at the expenses of two dogs. Opossums and adult insects were common visitors of the houses and it became evident that this marsupial is closely related to the peridomestic cycle of the Chagas disease agent. Lack of colonization of the insect inside the human dwellings is explained by the type of construction and good sanitary conditions of the houses, in contrast to the situation in most peridomiciliary areas. Stomach blood samples from the insects showed that the main hosts were, in order of decreasing frequency: rodents, dogs, fowl, humans, opossums, and cats. The fact that no indication of infection with Chagas disease could be detected in the human occupants of the infested houses, vis a vis the high infection rate in dogs, is discussed.

Uso de encuestas en escolares para la evaluación de la cobertura y oportunidad de la vacunación en Costa Rica / Using surveys of schoolchildren to evaluate coverage with and opportunity for vaccination in Costa Rica

OBJETIVO: Identificar diferencias en el nivel de cobertura y en la oportunidad de la vacunación de escolares residentes en tres tipos de zonas de Costa Rica: urbana, rural y fronteriza (rural de la frontera norte del país). MÉTODOS: Mediante encuesta, previa selección de escuelas por probabilidad proporcional, se reunió al azar a alumnos de primero y segundo grados de enseñanza primaria de tres zonas: urbana (n = 961), rural (n = 544) y fronteriza (n = 811). Los datos de las vacunas aplicadas se obtuvieron del carné (cartilla) de vacunación. Se evaluaron las diferencias en la cobertura con BCG, DPT3, VOP3, SRP1 y SRP2 y en la oportunidad de la administración de DPT1 + VOP1 antes de los 3 meses, de DPT3 + VOP3 antes de los 7 meses y de DPT4 + VOP4 + SRP1 antes de los 24 meses de edad, entre las tres zonas. RESULTADOS: Del total de alumnos seleccionados, 80 por ciento presentaron carné de vacunación en la zona urbana, 73 por ciento en la rural y 72 por ciento en la fronteriza (P <0.05). Las coberturas con BCG, DPT3, VOP3 fueron >95 por ciento en las zonas urbana y rural, y se encontraron cifras significativamente menores (P <0,05) en la zona fronteriza: BCG, 83 por ciento, VOP3, 88 por ciento y DPT3, 88 por ciento. La cobertura con SRP1 y SRP2 fue similar en las tres zonas. El porcentaje de escolares con dos o más dosis de sarampión fue: 98 por ciento en la zona urbana, 92 por ciento en la rural y 85 por ciento en la fronteriza (P <0,05). Una proporción de 90 por ciento recibió DPT1 y VOP1 antes de los tres meses de edad en la zona urbana, 89 por ciento en la rural y 80 por ciento en la fronteriza (P <0,05). El porcentaje de aplicación del esquema básico completo (DPT4 + VOP4 + SRP1) antes de los 24 meses fue: 93 por ciento en la zona urbana, 95 por ciento en la rural y 84 por ciento (P <0,05) en la fronteriza. CONCLUSIONES: La zona fronteriza mostró menor cobertura y oportunidad en la aplicación de vacunas del esquema básico, con excepción de SRP. La realización de campañas de seguimiento para la erradicación del sarampión ha elevado las coberturas con la SRP1 y el refuerzo de sarampión en todas las zonas, pero el incremento ha sido mayor en la urbana. Debe hacerse un mayor esfuerzo por identificar a niños con esquemas incompletos, principalmente en zonas de alta migración.