Background: Herbal remedies are widely used in many malaria endemic countries to treat patients, in particular in the
absence of anti-malarial drugs and in some settings to prevent the disease. Herbal medicines may be specifically designed
for prophylaxis and/or for blocking malaria transmission to benefit both, the individual consumer and the community at
large. Neem represents a good candidate for this purpose due to its inhibitory effects on the parasite stages that cause
the clinical manifestations of malaria and on those responsible for infection in the vector. Furthermore, neem secondary
metabolites have been shown to interfere with various physiological processes in insect vectors. This study
was undertaken to assess the impact of the standardised neem extract NeemAzal® on the fitness of the malaria
vector Anopheles stephensi following repeated exposure to the product through consecutive blood meals on
treated mice.
Methods: Batches of An. stephensi mosquitoes were offered 5 consecutive blood meals on female BALB/c
mice treated with NeemAzal® at an azadirachtin A concentration of 60, 105 or 150 mg/kg. The blood feeding
capacity was estimated by measuring the haematin content of the rectal fluid excreted by the mosquitoes
during feeding. The number of eggs laid was estimated by image analysis and their hatchability assessed by
direct observations.
Results: A dose and frequency dependent impact of NeemAzal® treatment on the mosquito feeding capacity,
oviposition and egg hatchability was demonstrated. In the 150 mg/kg treatment group, the mosquito feeding
capacity was reduced by 50% already at the second blood meal and by 50 to 80% in all treatment groups at
the fifth blood meal. Consequently, a 50 – 65% reduction in the number of eggs laid per female mosquito
was observed after the fifth blood meal in all treatment groups. Similarly, after the fifth treated blood meal
exposure, hatchability was found to be reduced by 62% and 70% in the 105 and 150 mg/kg group respectively.
Conclusions: The findings of this study, taken together with the accumulated knowledge on neem open
the challenging prospects of designing neem-based formulations as multi-target phytomedicines exhibiting
preventive, parasite transmission-blocking as well as anti-vectorial properties.