Use of real time PCR for Trypanosoma cruzi DNA quantification in naturally infected domestic dogs and cats and its association with infectivity to the vector.

ENRIQUEZ GF; BUA J; OROZCO MM; SCHIJMAN AG; GÜRTLER RE; CARDINAL MV

Porto de Galinhas

Congreso; 2nd International Congress on Pathogens at the Human-Animal Interface (ICOPHAI): One Health for Sustainable Development.; 2013

Domestic dogs and cats are major domestic reservoir hosts of Trypanosoma cruzi in the Americas. In the Gran Chaco region, they are also considered a risk factor for human infection and all the T. cruzi genotypes (i.e., Discrete Typing Units, DTUs) identified in humans have been found in dogs. Seropositive dogs also had a much higher infectivity to T. infestans bugs in xenodiagnosis than seropositive humans. The aim of this study was to estimate the intensity of parasitemia in peripheral blood by determining the parasite DNA concentration by means of a real time PCR in dogs and cats naturally infected with T. cruzi. We also evaluated factors associated with dogs´ infectivity. We conducted a cross-sectional xenodiagnostic survey of dog and cat populations residing in two infested rural villages in Pampa del Indio, in the humid Argentine Chaco, during 2008. To measure infectivity to bugs, 44 infected dogs and 14 infected cats were each exposed to 20 laboratory-reared fourth-instar nymphs of T. infestans for 20 min. The bugs were individually examined by optic microscopy (400x) for T. cruzi infection 30 and 60 days later. Infectivity to the vector was defined as the number of T. cruzi-positive bugs divided by the total number of bugs fed on a given host and examined for infection at least once, excluding those bugs that did not survive to the first examination. Parasite DTUs were identified by PCR strategies and parasite DNA concentration (expressed as equivalent amounts of parasites DNA per ml, eP/ml) by means of a real time PCR targeted to the nuclear satellite DNA. Dog and cat showed similar eP/ml (median = 8.0, min. = 0.7, max. = 214.0 for dogs; and 8.6 min. = 1.6, max. = 1102.0 for cats). The mean infectivity of seropositive dogs (52%; 95% confidence interval, CI, = 40-63%) did not differ from that of cats (32%, CI = 11-53%). Infectivity was positively and significantly associated with ln(eP) in a simple linear regression both in dogs (n = 32; P < 0.001; R2 = 0.37) and cats (n = 9; P < 0.01; R2 = 0.69). Multiple logistic regression analysis showed that dog infectivity clustered on subject was positively and significantly associated with the individual?s external clinical aspect (ECA) (OR = 3.00; CI = 1.24-7.24, P = 0.02) but not with age of dog, sex, infected-bug abundance at the dog house (as a surrogate of re-infection probability), and parasite DTU. The high infectivity of dogs and cats reinforces they are major sources of T. cruzi infection for domestic and peridomestic T. infestans. The ECA of dogs was strongly associated with infectivity to the vectors, as was found previously in the dry Argentinean Chaco. The ECA may be a useful tool to stratify dog population and accurately identify ?superspreaders?; allowing the implementation of novel strategies to reduce domestic transmission intensity. Xenodiagnosis usually played a unique role for assessment of infectiousness to the vector. However, given the high correlation between infectivity to the vector and eP, our quantitative PCR protocol could replace its use avoiding such a laborious and time-consuming technique. Moreover, based on our results we considered that quantitative PCR is a promising tool to monitor the effect of different treatments aiming to decrease peripheral blood parasitemia in domestic reservoirs.