Anopheles darlingi (Diptera: Culicidae) displays increased attractiveness to infected individuals with Plasmodium vivax gametocytes

Abstract

Background: Most hematophagous insects use host odours as chemical cues. The odour components, some physiological parameters and host attractiveness are affected by several conditions, including infection by parasites, e.g., plasmodia and, therefore, change the epidemiological scenario. This study evaluated the attractiveness of individuals with vivax malaria before, during (7 days) and after treatment (14 days) with specific antimalarial drugs.

Findings: Mosquito attractiveness to vivax-infected patients was assessed using a vertical olfactometer using the foot as a source of body odour. The ratio of Anopheles darlingi mosquitoes in the lower chamber of the olfactometer was used to calculate the attractiveness, and patient temperature was measured using a digital thermometer. An increased attractiveness was found only in patients bearing vivax gametocytes during the first experiment (early infection) (P<0.001). Patients in the first experiment tended to have a higher body temperature, but grouping patients into fever and non-fever resulted in a higher attractiveness only in the fever group of gametocyte carriers, suggesting a synergistic effect of temperature and gametocytes in the host attractiveness to A. darlingi.

Conclusions: Gametocyte presence and fever in vivax malaria patients increased short distance host attractiveness to An. darlingi.

Figure 1

Anopheles darlingi attractiveness to vivax malaria patients during different periods throughout treatment. Two-Way Anova Repeated Measures and Tukey’s test (comparisons). Different letters indicate significant (P < 0.05) differences in mosquito attractiveness to patients bearing gametocytes during the treatment period. NS indicate non-significant (P > 0.05) differences in mosquito attractiveness to patients with no detectable gametocytes during the treatment period. * indicates a significant (P < 0.01) difference in the mosquito attractiveness between patients with detectable gametocytes (gametocytes) (N = 3) and non-detectable gametocytes (no gametocytes) (N = 3) during the infection phase.

Figure 2

Body temperature of vivax malaria patients during different periods throughout the treatment. One Way RM Anova. N = 6.

Figure 3

Anopheles darlingi attractiveness to symptomatic vivax malaria patients related to body temperature and parasite stages. Gametocyte carriers were defined as patients with detectable sexual stages of the parasite in blood smears using microscopy. Fever = Individuals with body temperature >37.5°C; No Fever = individuals with body temperature <37.5°C. Two-way ANOVA (fever and gametocytes) and Sidak’s test (comparisons). * indicates significant differences (P < 0.05). NS indicates non-significant differences (P > 0.05). N = 2 for each variable combination (i.e., fever and gametocytes, fever and no gametocytes, no fever and gametocytes and no fever and no gametocytes).