Human infectiousness and parasite load in chronic patients seropositive for Trypanosoma cruzi in a rural area of the Argentine Chaco

MACCHIAVERNA, NATALIA P.; ENRIQUEZ, GUSTAVO F.; BUA, JACQUELINE; FERNÁNDEZ, MARÍA P.; SARTOR, PAULA A.; GÜRTLER, RICARDO E.; CARDINAL, MARTA V.

Infection, Genetics and Evolution

ELSEVIER SCIENCE BV

Año: 2019 vol. 78 p. 104062 - 104062

1567-1348

A key parameter in the transmission of vector-borne infections, including Chagas disease, is the ability of thedifferent host species to transmit the parasite to the vector (infectiousness). Here, we determined infectiousnessto the vector of Trypanosoma cruzi-seropositive humans examined by artificial xenodiagnosis (XD), established itsrelationship with T. cruzi DNA levels (a surrogate of intensity of parasitemia) quantified by real-time PCR(qPCR), and assessed whether infectiousness was associated with the body mass index (BMI), age, ethnicbackground and parasite genotype. XD was performed to 117 T. cruzi-seropositive residents from Pampa delIndio and parasite load was quantified in 81 of them. Using optical microscopy (OM) 33.6% of the seropositivepeople tested were infectious and this fraction nearly doubled (66.0%) when XD triatomines were examined bykDNA-PCR. The mean infectiousness (defined as the percentage of all infected triatomines detected by OM at anytime point among the total number of insects examined by OM 30 days post-feeding) was 5.2%, and the meanparasite load was 0.51 parasite equivalents per ml. Infectiousness to the vector was associated negatively withage and BMI, and positively with the detection of parasitemia by kDNA-PCR, and parasite load by qPCR inbivariate analysis. Patients with a positive XD by OM exhibited a significantly higher mean parasite load. Usingmultiple regression, infectiousness was associated with parasite load (positively) and with the household presenceof T. infestans and Qom ethnic group (negatively); no significant association was observed with age or itsinteraction with ethnicity. We did not find significant associations between identified DTUs and infectiousness orparasite load. Infectiousness was aggregated: 18% of the people examined by XD generated 80% of the infectedtriatomines. Detecting and treating the super-infectious fraction of the infected human would disproportionallyimpact on domestic transmission risks. Nonetheless, treatment of all eligible infected people who meet theinclusion criteria regardless of their parasitemia should be ensured to improve their prognosis.