RESUMO
The association between the nutritional state of mongrel dogs naturally infected with Trypanosoma cruzi and their infectivity to Triatoma infestans bugs and immune response to Trypanosoma cruzi were studied in the rural village of Amamá, northwestern Argentina. All of the 97 evaluated dogs were classified into one of three categories of external clinical aspect (ECA) based on the degree of muscle development, external evidence of bone structures, state of the hair of the coat, existence of fatty deposits, and facial expression. ECA was significantly associated with two nutritional indicators, hematocrit and skin-fold thickness, but not with total serum proteins. For all dogs, hematocrit was significantly correlated with skin-fold thickness. The 2-year survival probability decreased significantly from 60.7% for dogs with good ECA to 45.9% and 31.2% for those with regular and bad ECA, respectively. The age-adjusted relative odds of infection for Triatoma infestans xeno-diagnosis nymphs that fed once on a dog seroreactive for Trypanosoma cruzi decreased significantly as ECA improved, when tested by multiple logistic regression analysis. A delayed hypersensitivity reaction was observed in all of the seroreactive dogs with good ECA but only in 45-50% of those with regular or bad ECA. Dogs with bad ECA had a 2.6 and 6.3 times greater probability of infecting triatomines after a single full blood meal than dogs with regular or good ECA, respectively. Our study shows that the reservoir competence of dogs for Trypanosoma cruzi was associated with ECA, which is a surrogate and valid index of nutritional state.
Assuntos
Doença de Chagas/veterinária , Doenças do Cão/parasitologia , Ectoparasitoses/veterinária , Distúrbios Nutricionais/veterinária , Animais , Anticorpos Antiprotozoários/sangue , Argentina/epidemiologia , Proteínas Sanguíneas/análise , Doença de Chagas/sangue , Doença de Chagas/complicações , Doença de Chagas/mortalidade , Doença de Chagas/transmissão , Estudos Transversais , Doenças do Cão/mortalidade , Cães , Ectoparasitoses/complicações , Ectoparasitoses/epidemiologia , Ectoparasitoses/transmissão , Feminino , Hematócrito/veterinária , Insetos Vetores/parasitologia , Masculino , Distúrbios Nutricionais/complicações , Distúrbios Nutricionais/mortalidade , Distúrbios Nutricionais/parasitologia , Estado Nutricional , Dobras Cutâneas , Taxa de Sobrevida , Triatoma/parasitologia , Trypanosoma cruzi/imunologia , Trypanosoma cruzi/patogenicidadeRESUMO
The risk of domestic reinfestation by Triatoma infestans after a single community-wide application of delta-methrin (2.5% suspension concentrate at 25 mg active ingredient/m2) was studied in Amamá, north-west Argentina, where no insecticide spraying had been done by official control services. The percentage of infested houses fell from 88% before spraying in 1985 to nil during the 6 months after spraying, and thereafter increased from 5% in 1986 to 96% before a second treatment in 1992, fitting closely to a logistic model (r2 = 0.997). Significant risk factors associated with domestic reinfestation determined from stepwise logistic regression and one-factor analysis were the density of T. infestans in bedrooms just before spraying and the surface structure of indoor walls. Peak densities of bugs in 1988-1989 significantly differed between levels of both risk factors. Our study suggests the existence of stable determinants of infestation linked to the household which, in the absence of effective control measures, would also determine the speed of house recolonization and the ensuing bug densities. Plastering of mud walls before application of insecticides to all domestic and peridomestic structures is supported by the study.
Assuntos
Doença de Chagas/transmissão , Controle de Insetos/métodos , Inseticidas , Piretrinas , Triatoma , Animais , Argentina , Insetos Vetores , Nitrilas , Fatores de RiscoRESUMO
The association between Trypanosoma cruzi parasitaemia in dogs and cats and Tryp. cruzi infection rates in domestic Triatoma infestans was studied in a cross-sectional survey of 31 houses (89%) in the rural villages of Trinidad and Mercedes, north-west Argentina, where no spraying of insecticides had ever been done. Similar prevalence rates of parasitaemia, determined by xenodiagnosis, were recorded among 68 dogs (41.2%) and 28 cats (39.3%). Bug infection rates were significantly associated with the presence of infected cats (those with positive xenodiagnosis) stratified by the number of infected dogs (relative risk = RR = 1.90; 95% confidence interval = CI = 1.51-2.38), and with the number of infected dogs stratified by the presence of infected cats (RR = 2.71; CI = 1.81-4.07). The percentage of infected bugs in houses with and without children stratified by the presence of infected dogs or cats was not significantly different (RR = 0.69; CI = 0.45-1.05). The combined effect of infected dogs and infected cats on bug infection rates fitted closely with an additive transmission model. Bug infection rates were significantly higher when infected dogs shared the sleeping areas of people than when they did not (RR = 1.79; CI = 1.1-2.91). Our study showed that infected dogs and infected cats increase the risk of domestic transmission of Tryp. cruzi to T. infestans.
Assuntos
Doenças do Gato/parasitologia , Doença de Chagas/veterinária , Doenças do Cão/parasitologia , Triatoma/parasitologia , Trypanosoma cruzi/isolamento & purificação , Animais , Argentina/epidemiologia , Gatos , Doença de Chagas/epidemiologia , Cães , Insetos Vetores , Prevalência , Fatores de Risco , Saúde da População Rural , Trinidad e Tobago/epidemiologia , ZoonosesRESUMO
The influence of reinfections on the infectivity to Triatoma infestans of dogs seropositive to Trypanosoma cruzi was investigated in Amamá, north-west Argentina, before (1984) and after (1986-1987) elimination of domestic bugs with residual insecticides in 1985. Infectivity was quantified by the percentage of infected bugs in each xenodiagnosis of a seropositive dog, i.e. the infective force (IF). Exposure to reinfection was represented by the domiciliary density of infected bugs and by an index of the potentially-infective contacts (IPIC) experienced by each dog (calculated as the product of the relative density of bugs per dog, the proportion of infected bugs, and the proportion of bugs taking blood meals from the dog). IF was unrelated to the dog's age or sex, or the level of specific antibodies to T. cruzi. Before vector elimination, the IF of seropositive dogs was significantly associated with both the density of infected bugs and the IPIC. After vector elimination, seropositive dogs resident at houses which had 10-70 infected bugs before spraying showed a higher median IF (67-75%) than those living in houses with zero to eight infected bugs before spraying (47-55%). The age-specific IF of seropositive dogs aged one year or older, recorded before (45-64%) and after (52-56%) the elimination of domestic bugs, did not differ significantly. Our data suggest that the infectivity of seropositive dogs to bugs is modified by previous or current exposure to bug-mediated reinfections, and that this relationship might be irreversible in the short term.
Assuntos
Doença de Chagas/transmissão , Doenças do Cão/transmissão , Insetos Vetores/parasitologia , Triatoma/parasitologia , Fatores Etários , Animais , Anticorpos Antiprotozoários/sangue , Argentina , Doença de Chagas/veterinária , Doenças do Cão/parasitologia , Cães , Imunofluorescência , Testes de Hemaglutinação , Análise de RegressãoRESUMO
The association between household seroreactivity to Trypanosoma cruzi in dogs and children and T. cruzi infection rates in domestic Triatoma infestans was investigated in 1988-1989 in the rural community of Amamá, north-west Argentina, where house spraying with residual pyrethroids was carried out in 1985. Three years after spraying, a greater reduction of the average T. cruzi prevalence rate in dogs (from 83% to 40%) than in children (from 48% to 30%) was accompanied by a substantial decrease in vector infection rates from 51%-63% to 21%. At a household level, in homes with or without seroreactive children, the percentage of infected T. infestans was 4.5-4.7 times higher when seroreactive dogs were present (27.1%-34.8%) than when they were not (5.8%-7.7%; stratified relative risk [RR] = 4.58). The contribution of seroreactive children to bug infection rates was not significant (RR = 1.29). The combined effect of both seroreactive dogs and seroreactive children fitted equally well with additive or multiplicative transmission models. Bug infection rates showed an increasing trend with the number of seroreactive dogs and an inverse association with the age of the youngest seroreactive dog. Our study supports the hypothesis of a causal association between the presence and number of infected dogs and increased levels of T. cruzi transmission to domestic T. infestans.
Assuntos
Doença de Chagas/transmissão , Doença de Chagas/veterinária , Reservatórios de Doenças/veterinária , Doenças do Cão/epidemiologia , Adolescente , Animais , Argentina/epidemiologia , Criança , Cães , Humanos , Insetos Vetores , Prevalência , Fatores de Risco , Triatoma/parasitologiaRESUMO
A three-year demographic and seroparasitological follow-up of the canine population of a rural area of Argentina endemic for Chagas' disease was carried out in order to (a) describe the population dynamics of domestic dogs, and (b) predict the decrease in the prevalence of Trypanosoma cruzi among these reservoirs after indoor spraying of houses with residual insecticides. For the latter project we designed an age-structured model with a discrete time scale. We assumed a time-dependent exponential decay in the frequency of infected hosts proportional to the host mortality rate, and also assumed and that no differential mortality existed between infected and non-infected dogs. Validation of the model was carried out, and yielded an extremely close fit between observed and theoretical values. The relevance of the model as an aid to designing strategies for the control of animal domestic reservoirs of T. cruzi, and the role of dogs as efficient sentinels of re-infestation of an area, are discussed.