Domestic dogs and cats as sources of Trypanosoma cruzi infection in rural northwestern Argentina

Abstract

The reservoir capacity of domestic cats and dogs for Trypanosoma cruzi infection and the host-feeding patterns of domestic Triatoma infestans were assessed longitudinally in 2 infested rural villages in north-western Argentina. A total of 86 dogs and 38 cats was repeatedly examined for T. cruzi infection by serology and/or xenodiagnosis. The composite prevalence of infection in dogs (60%), but not in cats, increased significantly with age and with the domiciliary density of infected T. infestans. Dogs and cats had similarly high forces of infection, prevalence of infectious hosts (41-42%), and infectiousness to bugs at a wide range of infected bug densities. The infectiousness to bugs of seropositive dogs declined significantly with increasing dog age and was highly aggregated. Individual dog infectiousness to bugs was significantly autocorrelated over time. Domestic T. infestans fed on dogs showed higher infection prevalence (49%) than those fed on cats (39%), humans (38%) or chickens (29%) among 1085 bugs examined. The basic reproduction number of T. cruzi in dogs was at least 8.2. Both cats and dogs are epidemiologically important sources of infection for bugs and householders, dogs nearly 3 times more than cats.

Fig. 1

Age-specific prevalence of Trypanosoma cruzi infection in dogs, as determined through the composite results of serodiagnosis and xenodiagnosis (A), and relationship with the density of domestic T. infestans infected with T. cruzi (B). Trinidad and Mercedes, September and December 1988, respectively. The line in (A) is the fit of the catalytic model with constant force of infection over time and age. Numbers close to data points represent the numbers of dogs examined for infection.

Fig. 2

Age-specific prevalence of dogs seropositive for Trypanosoma cruzi and infectious to bugs (A) and percentage of xenodiagnosis bugs infected with T. cruzi after taking a single bloodmeal on seropositive dogs (infectiousness to bugs) (B). Trinidad and Mercedes, September and December 1988, respectively. Numbers close to data points in (A) represent the numbers of seropositive dogs examined by xenodiagnosis, or numbers of xenodiagnosis bugs examined for infection. Each symbol in (B) represents the percentage of bugs fed on a single dog.

Fig. 3

Frequency distributions of individual infectiousness to bugs of all dogs seropositive for Trypanosoma cruzi at 3 survey dates, September—December 1988, March 1989 and September 1989 (A); and individual infectiousness to bugs of dogs that were ever seropositive for T. cruzi and tested on 2 or 3 occasions (B). Trinidad and Mercedes.

Fig. 4

Age-specific prevalence of infectious hosts in the dog and cat populations, assessed by xenodiagnosis, regardless of serological data. Trinidad and Mercedes, September and December 1988, respectively. Numbers close to data points represent the numbers of hosts examined by xenodiagnosis.

Fig. 5

Association between Trypanosoma cruzi infection and host bloodmeal source in 1085 domestic T. infestans collected in Trinidad, Mercedes and Amamá from 1988 to 1992, which were examined for T. cruzi infection. Numbers on top of bars represent bloodmeals identified on each host blood source.