Susceptibility of eight species members in the Anopheles hyrcanus group to nocturnally subperiodic Brugia malayi

Abstract

BackgroundFilariasis, caused by Brugia malayi, is a public health problem in Thailand. Currently, at least two locations in southern Thailand are reported to be active endemic areas. Two and four Mansonia species are primary and secondary vectors, respectively, of the nocturnally subperiodic race, whereas, Coquillettidia crassipes is a vector of the diurnally subperiodic race. Although several Anopheles species have been incriminated extensively as natural and/or suspected vectors of B. malayi, little is known about vector competence between indigenous Anopheles and this filaria in Thailand. Thus, the susceptibility levels of eight species members in the Thai An. hyrcanus group to nocturnally subperiodic B. malayi are presented herein, and the two main refractory factors that affect them in different degrees of susceptibility have been elucidated.MethodsAedes togoi (a control vector), An. argyropus, An. crawfordi, An. nigerrimus, An. nitidus, An. paraliae, An. peditaeniatus, An. pursati and An. sinensis were allowed to feed artificially on blood containing B. malayi microfilariae, and dissected 14 days after feeding. To determine factors that take effect at different susceptibility levels, stain-smeared blood meals were taken from the midguts of Ae. togoi, An. peditaeniatus, An. crawfordi, An. paraliae, An. sinensis and An. nitidus immediately after feeding, and their dissected-thoraxes 4 days post blood-feedings were examined consecutively for microfilariae and L1 larvae.ResultsThe susceptibility rates of Ae. togoi, An. peditaeniatus, An. crawfordi, An. nigerrimus, An. argyropus, An. pursati, An. sinensis, An. paraliae and An. nitidus to B. malayi were 70–95%, 70–100%, 80–85%, 50–65%, 60%, 60%, 10%, 5%, and 0%, respectively. These susceptibility rates related clearly to the degrees of normal larval development in thoracic muscles, i.e., Ae. togoi, An. peditaeniatus, An. crawfordi, An. paraliae, An. sinensis and An. nitidus yielded normal L1 larvae of 93.15%, 96.34%, 97.33%, 23.60%, 15.38% and 0%, respectively.ConclusionsAn. peditaeniatus, An. crawfordi, An. nigerrimus, An. argyropus and An. pursati were high potential vectors. An. paraliae and An. sinensis were low potential vectors, while An. nitidus was a refractory vector. Two refractory mechanisms; direct toxicity and/or melanotic encapsulation against filarial larval were involved in the refractoriness of development in the thoracic muscles of the mosquito.

The global distribution and transmission limits of lymphatic filariasis: past and present

“…Such an association probably reflects differences in the distribution of different vector species and their habitat preference and susceptibility to LF [108][109][110]. In rural areas of Africa, LF is transmitted by Anopheles species, whereas in urban settings in east Africa and the Nile Delta transmission is by Culex quinquefasciatus [111,112].…”

Cytogenetic, cross-mating and molecular evidence of four cytological races of Anopheles crawfordi (Diptera: Culicidae) in Thailand and Cambodia

“…Even though A. crawfordi could be found abundantly as a proven outdoor-biter of humans in certain localities of eastern and southern Thailand, its status as a vector of pathogens of human diseases remains obscure and needs to be investigated more intensively [2]. However, our recent experiments indicate that this anopheline species could be an important vector of the filarial nematode, nocturnally subperiodic Brugia malayi, as determined by 80-85% susceptibility rates and an average of six L 3 larvae per infected mosquito [4]. These results were in agreement with previous investigation indicating that A. crawfordi could provide satisfactory susceptibility to B. malayi in Malaysia [5,6].…”

Structural divergence of chromosomes between malaria vectors Anopheles lesteri and Anopheles sinensis

“…In addition, An. lesteri naturally transmits P. falciparum [8, 9] and also is a major vector of a filarial worm, Brugia malayi , in China [10, 11]. An.…”