Table 5.

Expected kDNAemia (amastigote-equivalents) and proportion of infected Lutzomyia longipalpis calculated by Poisson distribution^* according to the presence of signs and symptoms of infection by Leishmania infantum and HIV infection

Study group	Observed mean kDNAemia (amastigote equivalents/mL)	Expected % of infected insects*	Observed % of infected insects by microscopy (CI)	Expected mean parasite load* (CI)
VL symptomatic without HIV	268	13	2.4 (1.1, 4.5)	48 (22, 92)
VL symptomatic with HIV	1876	62	9.2 (6.6, 12.5)	193 (136, 267)
VL asymptomatic without HIV	41	2	None	None
VL asymptomatic with HIV	933	38	4.3 (0, 21.9)	87 (0, 493)

CI = confidence interval; HIV = human immunodeficiency virus; VL = visceral leishmaniasis.

^*Calculation of the expected parasite load was performed by using the Poisson distribution $P=-\frac{\ln \left(1-x\right)}{\nu }$, where P is the expected parasite kDNAemia, ν is the assumed blood volume taken by the insect, considering that Lu. longipalpis takes 0.5 µL (Ready,²³ and x is the observed mean proportion of infected Lutzomyia tzomyialongipalpis in the group. The same equation was used to calculate the expected percent of infected insects. The underlying assumption are that at least one single amastigote would be able to determine infection to sand flies, that parasites are density independent, that sand flies are equally susceptible, and that once an infection is established it will progress (Miller and others).²²