Experimental infection and transmission of <i>Leishmania</i> by <i>Lutzomyia cruzi</i> (Diptera: Psychodidae): Aspects of the ecology of parasite-vector interactions

<div><p>Several parameters should be addressed before incriminating a vector for <i>Leishmania</i> transmission. Those may include its ability to become infected by the same <i>Leishmania</i> species found in humans, the degree of attractiveness for reservoirs and humans and capacity to sustain parasite infection under laboratory conditions. This study evaluated the vectorial capacity of <i>Lutzomyia cruzi</i> for <i>Leishmania infantum</i> and gathered information on its ability to harbor <i>L</i>. <i>amazonensis</i>. Laboratory-reared <i>Lu</i>. <i>cruzi</i> were infected experimentally by feeding them on dogs infected naturally with <i>L</i>. <i>infantum</i> and hamsters infected with <i>L</i>. <i>amazonensis</i>. Sand fly attractiveness to dogs and humans was determined using wild caught insects. The expected daily survival of infected <i>Lu</i>. <i>cruzi</i>, the duration of the gonotrophic cycle, and the extrinsic incubation period were also investigated for both parasites. Vector competence was investigated for both <i>Leishmania</i> species. The mean proportion of female sand flies that fed on hosts was 0.40. For <i>L</i>. <i>infantum</i> and <i>L</i>. <i>amazonensis</i>, <i>Lu</i>. <i>cruzi</i> had experimental infection rates of 10.55% and 41.56%, respectively. The extrinsic incubation period was 3 days for both <i>Leishmania</i> species, regardless of the host. Survival expectancy of females infected with <i>L</i>. <i>infantum</i> and <i>L</i>. <i>amazonensis</i> after completing the gonotrophic cycle was 1.32 and 0.43, respectively. There was no association between <i>L</i>. <i>infantum</i> infection and sand fly longevity, but <i>L</i>. <i>amazonensis</i>–infected flies had significantly greater survival probabilities. Furthermore, egg-laying was significantly detrimental to survival. <i>Lu</i>. <i>cruzi</i> was found to be highly attracted to both dogs and humans. After a bloodmeal on experimentally infected hosts, both parasites were able to survive and develop late-stage infections in <i>Lu</i>. <i>cruzi</i>. However, transmission was demonstrated only for <i>L</i>. <i>amazonensis</i>–infected sand flies. In conclusion, <i>Lu</i>. <i>cruzi</i> fulfilled several of the requirements of vectorial capacity for <i>L</i>. <i>infantum</i> transmission. Moreover, it was also permissive to <i>L</i>. <i>amazonensis</i>.</p></div

Number of engorged, dissected, infected, and potentially infective <i>Lutzomyia cruzi</i> females in relation to host, number of days after the xenodiagnosis, and species of <i>Leishmania</i>.

<p>Number of engorged, dissected, infected, and potentially infective <i>Lutzomyia cruzi</i> females in relation to host, number of days after the xenodiagnosis, and species of <i>Leishmania</i>.</p

<i>Lutzomyia cruzi</i> females that fed during xenodiagnoses, according to host and species of <i>Leishmania</i>.

<p><i>Lutzomyia cruzi</i> females that fed during xenodiagnoses, according to host and species of <i>Leishmania</i>.</p

Estimates obtained for the Cox regression model adjusted by considering the covariates <i>L</i>. <i>infantum</i> infection, egg-laying, and egg-laying time.

<p>Estimates obtained for the Cox regression model adjusted by considering the covariates <i>L</i>. <i>infantum</i> infection, egg-laying, and egg-laying time.</p

Estimates obtained for the Cox regression model adjusted by considering the covariates egg-laying and egg-laying time.

<p>Estimates obtained for the Cox regression model adjusted by considering the covariates egg-laying and egg-laying time.</p

Digestion of amplified products of the ITS1 region of <i>Leishmania</i> with the <i>Hae</i>III restriction enzyme.

<p>1: 100-bp ladder marker; 2: negative control; 3–10: sand flies fed on hamsters infected with <i>L</i>. <i>amazonensis</i>; 11–14: sand flies fed on dogs infected with <i>L</i>. <i>infantum</i>; 15: positive control <i>L</i>. <i>amazonensis</i> (IFLA/BR/1967/PH8); 16: positive control <i>L</i>. <i>infantum</i> (MHOM/BR/1972/BH46); 17: sample not digested by <i>Hae</i>III; 18: 100-bp ladder marker.</p

Number of females exposed (1) in xenodiagnoses, and (2) to susceptible hosts, by species of <i>Leishmania</i> and infected host.

<p>Number of females exposed (1) in xenodiagnoses, and (2) to susceptible hosts, by species of <i>Leishmania</i> and infected host.</p

Attractiveness of hosts to sand flies, according to the different methods employed.

<p>Attractiveness of hosts to sand flies, according to the different methods employed.</p

Descriptive measures (in days) obtained using the Kaplan-Meier estimator, by host and species of <i>Leishmania</i>.

<p>Descriptive measures (in days) obtained using the Kaplan-Meier estimator, by host and species of <i>Leishmania</i>.</p

Estimates obtained from the Cox regression models for the female sand fly group that was engorged after xenodiagnosis with hamsters.

<p>Estimates obtained from the Cox regression models for the female sand fly group that was engorged after xenodiagnosis with hamsters.</p