Author:
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Loza, Ariel; Talaga, Adrianna; Herbas, Gladys; Canaviri, Ruben J.; Cahuasiri, Thalia; Luck, Laura; Guibarra, Alvaro; Goncalves, Raquel; Pereira, Juan A.; Gomez, Sonia A.; Picado, Albert; Messenger, Louisa A.; Bern, Caryn; Courtenay, Orin
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Abstract:
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BACKGROUND: Despite large-scale reductions in Chagas disease
prevalence across Central and South America, Trypanosoma cruzi
infection remains a considerable public health problem in the
Gran Chaco region where vector-borne transmission persists. In
these communities, peridomestic animals are major blood-meal
sources for triatomines, and household presence of infected dogs
increases T. cruzi transmission risk for humans. To address the
pressing need for field-friendly, complementary methods to
reduce triatomine infestation and interrupt T. cruzi
transmission, this study evaluated the systemic activity of
three commercial, oral, single dose insecticides Fluralaner
(Bravecto(R)), Afoxolaner (NexGard(R)) and Spinosad
(Comfortis(R)) in canine feed-through assays against Triatoma
infestans, the principal domestic vector species in the Southern
Cone of South America. METHODS: Twelve healthy, outbred dogs
were recruited from the Zoonosis Surveillance and Control
Program in Santa Cruz, Bolivia, and randomized to three
treatment groups, each containing one control and three treated
dogs. Following oral drug administration, colony-reared second
and third stage T. infestans instars were offered to feed on
dogs for 30 min at 2, 7, 21, 34 and 51 days post-treatment.
RESULTS: Eighty-five per cent (768/907) of T. infestans
successfully blood-fed during bioassays, with significantly
higher proportions of bugs becoming fully-engorged when exposed
to Bravecto(R) treated dogs (P < 0.001) for reasons unknown.
Exposure to Bravecto(R) or NexGard(R) induced 100% triatomine
mortality in fully- or semi-engorged bugs within 5 days of
feeding for the entire follow-up period. The lethality effect
for Comfortis(R) was much lower (50-70%) and declined almost
entirely after 51 days. Instead Comfortis(R) treatment resulted
in substantial morbidity; of these, 30% fully recovered whereas
53% remained morbid after 120 h, the latter subsequently unable
to feed 30 days later. CONCLUSIONS: A single oral dose of
Fluralaner or Afoxolaner was safe and well tolerated, producing
complete triatomine mortality on treated dogs over 7.3 weeks.
While both drugs were highly efficacious, more bugs exposed to
Fluralaner took complete blood-meals, and experienced rapid
knock-down. Coupled with its longer residual activity,
Fluralaner represents an ideal insecticide for development into
a complementary, operationally-feasible, community-level method
of reducing triatomine infestation and potentially controlling
T. cruzi transmission, in the Gran Chaco region. |