Impact of repeated NeemAzal®-treated blood meals on the fitness of Anopheles stephensi mosquitoes

Abstract

BackgroundHerbal 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.MethodsBatches 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.ResultsA 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.ConclusionsThe 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.

Azadirachtin effects on mating success, gametic abnormalities and progeny survival in Drosophila melanogaster (Diptera)

“…This molecule interferes with the endocrine system by impairing juvenile hormone (JH) and 20‐hydroxyecdysone (20E) pathways, which are involved in the regulation of many physiological functions . Thus azadirachtin induces growth and moulting abnormalities and can cause significant alterations in the reproductive system of both male and female insects, including ovarian and testes development, fecundity, fertility, oviposition and egg viability . Azadirachtin also shows moderate to strong cytotoxicity, neurotoxicity and antimitotic effects .…”

“…9 Thus azadirachtin induces growth and moulting abnormalities and can cause significant alterations in the reproductive system of both male and female insects, including ovarian and testes development, fecundity, fertility, oviposition and egg viability. 9,12,[30][31][32] Azadirachtin also shows moderate to strong cytotoxicity, neurotoxicity and antimitotic effects. 9,33,34 It acts on the expression of genes related to development in Drosophila melanogaster.…”

O uso de plantas medicinais para doenças parasitárias

“…Estudos apontam atividade favorável em bloquear a ação de vetores como Anopheles coluzzii na transmissão do Plasmodium falciparum (Yerbanga et al,2014). Bem como ação anti-vetorial sobre o Anopheles stephensi, que é considerado um dos principais transmissores da malária (Dembo et al, 2015).…”

Neemazal ® as a possible alternative control tool for malaria and African trypanosomiasis?

“…In fact, a substantial number of studies conducted with neem extracts, limonoid enriched preparations or purified azadirachtin report ovicidal, larvicidal, adulticidal, anti-feedant, and repellent properties against different mosquito vectors [ 17 – 23 ]. For example, a recent study by a coauthor of the present work showed an impact of NeemAzal ® (a commercial methanol extract from seed kernels of A. indica rich in azadirachtin A, the major bioactive compound) on the blood volume intake of Anopheles stephensi after repeated feeding on mice treated with the product at an azadirachtin concentration of 60–150 mg/kg [ 24 ]. After the 5th blood meal at the highest dosage, mosquitoes’ oviposition was reduced by 50–65 % and egg hatchability by 70 %.…”

“…After the 5th blood meal at the highest dosage, mosquitoes’ oviposition was reduced by 50–65 % and egg hatchability by 70 %. [ 24 ]. The possible activity of neem extracts on tsetse fly biology has, to our knowledge, never been explored.…”