The role of other mosquito species and their risk behaviors which support their vector capacity transmit arbovirus diseases : Lesson learn from the African Chikungunya outbreak in Thailand, 2008-2009

Abstract

Chikungunya is the vector-borne diseases which cause by RNA virus in the family: Togaviridae and genus: Alphavirus. In Thailand was found sparsely each year. The virus strain which found in Thailand is the Asian genotype. There was the big outbreak of Chikungunya in the world during 2008 - 2009. Many countries in the world were affected by this disease, including island nations in the Indian Ocean, India, Sri Lanka, Singapore, Indonesia, Malaysia, Singapore and Thailand etc. The chikungunya virus that caused the pandemic outbreak was the Africa genotype. This species had never been found in Thailand. therefore, it was considered to be an emerging infectious disease of Thailand. The World Health Organization reported that the vectors of these events were Aedes aegypti and Aedes albopictus. Especially, Aedes albopictus was incriminated to be the main vector in the most outbreaking countries. However, it is necessary to study in detail what species of mosquitoes that can carry the disease. This is an entomology study which performed during the outbreak with the aims to identify the primary mosquito vectors involved in transmission, to confirm that Aedes aegypti and Aedes albopictus were infected by this strain of virus and to find the possible vectors of chikungunya virus in Thailand. Moreover, we studied about the vectors' behaviors which relate to the transmissions. These will be useful for the surveillance and control of mosquito-borne arboviruses in the future, according to each type of mosquitoes. The study focused on the adult mosquitoes and larvae of all species of male and female which found inside and outside of the patients houses, the houses which had the history of chikungunya patient and nearby houses that stayed within the range of 100 m from patients houses. We detected the virus by RT-PCR in laboratory. The mosquitoes were collected by sweeping nets for the safety of the collectors. The study sites were in Chumphon, Trang, Prachuap Khiri Khan, Phuket, Songkhla and Satun. All mosquitoes and larvae species were found 14 species. Adult mosquito larvae were found 12 species; Aedes aegypti, Aedes albopictus, Anopheles sinensis, Anopheles tessellatus, Armigeres (Leiseterior). sp., Armigeres subalbatus, Coquilettidia crassipes, Culex huchinsoni, Culex quinquefasciatus, Culex vishnui, Lutzia fuscana and Mansonia uniformis. The larvae were found 5 species: Aedes aegypti. Aedes albopictus, Culex brevipalpis, Culex quinquefasciatus and Tripteroides sp. There were 6 positive species of adult female mosquitoes which arranged by their infection rate (minimum infection rate (MIR)) or relative infection rates (%) from highest to lowest; Mansonia uniformis (NA, 100%). = Culex vishnui (NA, 100%) > Coquilettidia crassipes (333.33, 33.33%) > Aedes aegypti (112.32, 16.67%) > Aedes albopictus (23.02, 14.29%) > Culex quinquefasciatus (15.91, 5.88%)(table 14). All 5 species of female laevae were positive; Tripteroides sp. (NA, 100%) = Culex brevipalpis (NA, 100%) > Aedes aegypti (26.41. 12.50%) >  Aedes albopictus (19.76, 7.69%) > Culex quinquefasciatus (15.88, 9.09%), respectively (table15). Moreover, we also found 3 species of male larvae infected with the virus; Coquilidia crassipes (304.81, 40%) > Culer quinquefasciatus (26.91, 10.34%) > Armigeres subalbatus (15.97, 7.69%)(table14). It indicated that the Chikungunya virus could be transmitted from infected females through their offspring by eggs (transovarial transmission). The study concluded that the mosquito infection rates are higher in Aedes aegypti than Aedes albopictus. However, due to the topography and environment of the Southern Thailand were suitable for Aedes albopictus to grow and breed than Aedes aegypti or other mosquitoes. Furthermore, the most occupations of the people in the endemic areas who had to work on outside were farmers and rubber tappers that allowed Aedes albopictus bite them more than other mosquitoes. So, Aedes albopictus had more chances to bite people, and then the number of infected Aedes albopictus was high also. When compared the potential of Aedes aegypti and Aedes albopictus and concluded that both of them were the primary vectors of the African chikungunya. The nature of the transmission was consistent with the behaviors of the vectors which Aedes aegypti liked to feed the human blood and stayed in the house than outdoor, but Aedes albopictus like to feed and stayed outdoor. For indoor transmission, Aedes aegypti was the primary vector, and we found all positive female mosquito and larvae were in the houses only, Likewise for outdoor transmission, Aedes albopictus was the primary vector, and we found all positive female mosquito and larvae were of the houses only. Even though, some of the other positives mosquitoes had high infection rates, but the numbers of them were too small in the areas, we concluded that they might not play role as the important vectors. Moreover, they liked to feed on animal blood than human. In the area that found the high numbers of them might cause the disease more violent. Moreover they might cause some animal reservoirs, and then caused the long transmission too. So it shall be studied in the future.