Dinâmica da transmissão do Trypanosoma cruzi numa área rural da Argentina: III. Persistência da parasitemia pelo T. cruzi em reservatórios caninos durante um seguimento de dois anos

A new cross-sectional survey of household- associated mongrel dogs as well as follow-up of previously parasitemic individuals was carried out in 1984 toy means of xenodiagnosis and serologic techniques to get a deeper insight into the relationship of T. cruzi parasitemia and age among canine hosts in a rural area of Argentina. Persistence of detectable parasitemia was age-independent, or at most, loosely related to age, confirming the pattern observed in 1982. Similarly no significant age-decreasing effect was recorded among seropositive dogs in: a) the probability of detecting parasites in a 2-year follow-up; b) their intensity of infectiousness (=infective force) for T. infestans 3rd-4th instar nymphs, as measured by the percentage of infected bugs observed in each dog xenodiagnosis. Moreover, not only was the infective force of seropositive dogs for bugs approximately constant through lifetime, but it was significantly higher than the one recorded for children in the present survey, and for human people by other researchers. Therefore, and since T. infestans field populations show high feeding frequencies on dogs, the latter are expected to make the greatest contribution to the pool of infected vectors in the rural household of Argentina. This characteristic should be sufficient to involve canine reservoirs definitely as a risk factor for human people residing in the same house. The increased severity of parasitemia observed among dogs in this survey may be related to the acute undernutrition characteristic of canine populations of poor rural areas in our country, which is expected to affect the ability of the host to manage the infection.Foi realizada em 1984 uma nova pesquisa epidemiológica dos cães domésticos e seguimento dos indivíduos que apresentaram parasitemia dois anos antes a fim de compreender a relação entre a parasitemia e a idade dos cães, empregando para isso técnicas sorológicas e xenodiagnóstico. A persistência da parasitemia foi independente ou pouco relacionada à idade, confirmando assim o padrão observado em 1982. Da mesma maneira, nos cães soropositivos não se registrou nenhuma diminuição significativa com respeito a idade em: a) a probabilidade de descobrir parasitas por meio de um seguimento durante 2 anos; b) sua capacidade de infecção para as ninfas de 3.ª 4.ª fase de T. infestans, medido pela porcentagem de barbeiros infectados que se observou em cada um dos xenodiagnósticos dos cães. A capacidade infectante dos cães soropositivos foi aproximadamente constante ao longo da vida, e significativamente maior que a registrada para as crian. ças no presente estudo, e para os agrupamentos humanos pesquisados por outros investigadores. Assim sendo e considerando as altas freqüências de alimentação no cão que são observados nas populações pelo T. infestans, espera-se que o cão contribua para o total de barbeiros infectados existentes nas áreas rurais da Argentina. Esta característica deveria ser suficiente para incriminar definitivamente os reservatórios caninos como um fator de risco para as pessoas residentes na mesma casa. A alta intensidade da parasitemia registrada entre os cães na presente pesquisa poderia estar relacionada com a acentuada desnutrição característica dos cães nas áreas rurais pobres da Argentina, o que poderia afetar a capacidade do hospedeiro para controlar a infecção

Dynamics of transmission of Trypanosoma cruzi in a rural area of Argentina: III. Persistence of T. cruzi parasitemia among canine reservoirs in a two-year follow-up

A new cross-sectional survey of household- associated mongrel dogs as well as follow-up of previously parasitemic individuals was carried out in 1984 toy means of xenodiagnosis and serologic techniques to get a deeper insight into the relationship of T. cruzi parasitemia and age among canine hosts in a rural area of Argentina. Persistence of detectable parasitemia was age-independent, or at most, loosely related to age, confirming the pattern observed in 1982. Similarly no significant age-decreasing effect was recorded among seropositive dogs in: a) the probability of detecting parasites in a 2-year follow-up; b) their intensity of infectiousness (=infective force) for T. infestans 3rd-4th instar nymphs, as measured by the percentage of infected bugs observed in each dog xenodiagnosis. Moreover, not only was the infective force of seropositive dogs for bugs approximately constant through lifetime, but it was significantly higher than the one recorded for children in the present survey, and for human people by other researchers. Therefore, and since T. infestans field populations show high feeding frequencies on dogs, the latter are expected to make the greatest contribution to the pool of infected vectors in the rural household of Argentina. This characteristic should be sufficient to involve canine reservoirs definitely as a risk factor for human people residing in the same house. The increased severity of parasitemia observed among dogs in this survey may be related to the acute undernutrition characteristic of canine populations of poor rural areas in our country, which is expected to affect the ability of the host to manage the infection