Comparison of blood feeding response and infection of Aedes aegypti to Wuchereria bancrofti using animal membranes and direct host contact

A standardised low-cost membrane blood-feeder for Aedes aegypti made using common laboratory materials

Blood feeding is a necessary part of laboratory studies involving mosquitoes and other hematophagous arthropods of interest in medical and ecological research. However, methods involving hosts may present serious risks, require ethics approvals and can be expensive. Here we describe an insect blood feeder made using common laboratory materials, which is low cost (<US$100) and can be constructed and operated with little technical expertise. We compared the blood feeder containing an artificial blood diet, Skitosnack, to direct human arm feeding for Aedes aegypti (Diptera: Culicidae), in terms of engorgement rate, fecundity and hatch rate. No significant difference in fecundity between the two approaches was found, (mean ± SD); direct human arm: 56 ± 26 eggs/female, artificial method: 47 ± 25 eggs/female, P = 0.569. Engorgement rates (direct human arm: 97.8 ± 4%, artificial: 64.1 ± 23%, P < 0.05) and hatch rates (direct human arm: 75 ± 12%, artificial: 59 ± 14%, P < 0.05) were lower in the artificially fed mosquitoes. Despite these differences, we maintained a healthy mosquito colony for 10 generations using the artificial feeding approach. Results from this comparison are within the range of other studies which compared direct host feeding with an artificial feeding method. We anticipate that the blood feeder presented here could substantially reduce costs usually required to establish a standardised and effective blood feeding method for maintaining mosquito colonies or conducting experiments, extending the capability of laboratories especially where research resources are limited, but vector-borne diseases common.

Assessment of Synthetic Membranes for Artificial Blood Feeding of Culicidae

Potential pathogen transmission through hematophagy in Culicidae is a major public-health problem, and several studies have been performed to better understand this phenomenon. Research on these insects often requires the maintenance of colonies in the laboratory. Due to the hematophagic habits of these organisms, blood must be provided in order to guarantee the reproduction of individuals that constitute the colonies. Some species of mammals and birds are used as a direct blood source in many laboratories. Due to current bioethical parameters, the direct use of animals has been replaced by artificial blood feeding by using synthetic membranes to simulate animal skin. In this study, the efficiency of collagen and latex in the artificial feeding of mosquitoes of the Aedes aegypti and Culex quinquefasciatus species was evaluated and compared with Parafilm^®, a standard membrane that is frequently used for this purpose. Important aspects of the feeding and reproduction of these insects were considered. For both species, latex showed the poorest performance. Collagen membrane performed well in most parameters, but was not as efficient as Parafilm^® for fecundity in Aedes aegypti, and for the percentage of engorged females in Culex quinquefasciatus. We concluded that, although collagen is more resistant and easier to handle, Parafilm^® was the most efficient among the three evaluated membranes for the artificial blood feeding of mosquitoes.

Susceptibility of various mosquitoes of Thailand to nocturnal subperiodic Wuchereria bancrofti

Ten different mosquito species representing five genera were allowed to feed on human blood containing microfilariae (5.5-6.5 mf/microl) of nocturnal subperiodic Wuchereria bancrofti from Kanchanaburi Province, Thailand. Aedes aegypti, Aedes albopictus, Aedes desmotes, Downsiomyia species (=Finlaya Niveus Group), Culex quinquefasciatus, Anopheles dirus A, An. maculatus, An. minimus, Armigeres subalbatus, and Mansonia uniformis were fed under laboratory conditions using an artificial membrane feeding procedure. All species had adequate feeding responses (68-87.3%) and survival (66.4-81.3%) 12-15 days post-feeding. Anopheles maculatus was the most susceptible (73.1%) for development of infective third-stage larvae (L3), followed by An. minimus (61.0%), Downsiomyia species (27.3%), Ae. desmotes (24.2%), An. dirus A (24.7%), Cx. quinquefasciatus (19.2%), Ma. uniformis (9.2%), and Ae. albopictus (0.01%). Aedes aegypti and Ar. subalbatus were found to be completely refractory. An. maculatus produced the greatest mean number of L3 per infective mosquito (5.6 L3) and Ae. albopictus the least (1 L3). The two Anopheles demonstrated significantly greater susceptibility (P<0.05%) to W. bancrofti than the two Aedes species regarded as natural vectors.

Excito-repellency properties of essential oils from Melaleuca leucadendron L., Litsea cubeba (Lour.) Persoon, and Litsea salicifolia (Nees) on Aedes aegypti (L.) mosquitoes

We compared the behavioral responses of Aedes aegypti females to essential oils extracted from native plants Melaleuca leucadendron (ML), Litsea cubeba (LC), and Litsea salicifolia (LS) by using an excito-repellency test chamber. Mortality of Ae. aegypti females following 24 h holding period post-contact and non-contact trials were observed. No mortality was seen in escaped mosquitoes after direct contact with essential oils ML and LS, and low mortality (2.3-20.4%) with LC. Likewise, in all non-contact trials, no mortality was observed in escaped females from all three treatments, whereas low mortality was seen in non-escaped mosquitoes exposed to LC (0-14.3%) and LS (0-17.1%). Ae. aegypti showed significantly higher escape rates from contact chambers treated with ML and LC compared to LS, regardless of test concentrations (P<0.05). Non-contact repellent responses were significantly pronounced with LS, except at the highest (6.0%) concentration. We conclude that essential oils from all three botanicals exhibit significant irritant and repellent properties against Ae. aegypti and deserve further investigation for possible use as active ingredients in topical (skin) and indoor dispersed repellent systems.

Expression of defensin, cecropin, and transferrin in Aedes aegypti (Diptera: Culicidae) infected with Wuchereria bancrofti (Spirurida: Onchocercidae), and the abnormal development of nematodes in the mosquito

The temporal expression of defensin, cecropin and transferrin was assessed in Aedes aegypti naturally refractory to Wuchereria bancrofti upon infection with this worm, in parallel to analysis of filarial development in the insect. Compared to controls, transcription of defensin and cecropin was higher in infected mosquitoes as soon as 2h post infection and peaked before 48h. Transferrin transcription was higher in infected mosquitoes at 24h, and at 48h was almost leveled to controls. At 72h and 7 days post infection, levels of all transcripts in infected insects decreased gradually and were similar to controls in most cases. Worm development in A. aegypti was visually abnormal from the beginning of infection. Here, we report, for the first time, the up-regulation of endogenous immune molecules in A. aegypti infected with W. bancrofti and provide a description of the worm development inside the insect. The specificities of A. aegypti-W. bancrofti model compared to other mosquito-filaria systems are discussed.