Desiccated vector mosquitoes used for the surveillance of Japanese encephalitis virus activity in endemic southern India.

To monitor Japanese encephalitis virus (JEV) activity in endemic areas of Tamil Nadu, southern India, desiccated vector mosquitoes were screened for JEV antigen using ELISA, from 1996. A total of 133 233 specimens from eight index villages comprising 2816 pools (mainly Culex vishnui subgroup) were tested. Of these, 59 pools (2.1%) were positive for JEV antigen. Control measures were undertaken in positive villages accordingly. The average annual minimum infection rate was 0.8 at the beginning of the study and remained lower for nearly 8 years. A declining trend in JE cases was recorded.

Host feeding pattern of Japanese encephalitis virus vector mosquitoes (Diptera: Culicidae) from Kuttanadu, Kerala, India.

Identification of blood meals of vector mosquitoes is an important tool in the epidemiological investigations of vector-borne diseases. The blood meals of three mosquito species involved in the transmission of Japanese encephalitis virus (JEV) from the Kuttanadu area, Kerala, were determined using the agarose gel diffusion technique. A total of 4959 blood smears belonging to Culex (Culex) tritaeniorhynchus Giles (3273), Cx. (Culex) gelidus Theobald (64), Mansonia (Mnd.) indiana Edwards (735) ,and Ma. (Mnd.) uniformis (Theobald) (887) were tested. Cx. tritaeniorhynchus had predominantly fed on bovids (46.4%), and a good proportion (29%) had fed on more than one host. Cx. tritaeniorhynchus was highly zoophagic, and human feeding accounted for only 1.5% of those individuals successfully tested. Cx. gelidus showed bovid feeding at 36% and pig feeding at 12.5%. The test results showed 42.3% Ma. indiana and 12.2% Ma. uniformis had fed on humans. Multiple feeding was observed in Ma. indiana and Ma. uniformis, and most of the double feedings were from bovids and ovids (7.9 and 20.1%, respectively). Pig feeding accounted for 4.8% of the feedings by Cx. tritaeniorhynchus, 5.3% of Ma. indiana, and 6.4% of Ma. uniformis. This study is significant because of the role played by these mosquitoes in the transmission of JEV in the Kuttanadu area of Kerala, India.

Diagnostic methods for detection & isolation of dengue viruses from vector mosquitoes.

Dengue is a deadly mosquito-borne infection warranting urgent attention for its containment particularly in the tropical and subtropical countries. In the absence of a vaccine or any specific drug for its treatment, an early diagnosis is considered indispensable to prevent any casualty. Detection of viruses in human sera particularly in endemic areas is cumbersome, difficult and also not desirable. Therefore, as an alternative approach, detection of the dengue virus antigen in mosquitoes has provided a reliable tool to (i) comprehend the types of viruses circulating in nature; and (ii) help in designing vector-specific control strategies. A mélange of diagnostic techniques are currently available with some advantages or disadvantages. Traditionally, cell cultures and suckling mice have been employed for virus isolations. While the virus isolation method in baby mice is time consuming, slow and expensive, the mosquito cell cultures offer a good degree of specificity. Mosquito inoculation techniques have been reported for detection and propagation of flaviviruses. Though this technique is sensitive for routine virological confirmation of dengue fever, it requires large number of infected mosquitoes, besides being time consuming. Insect bioassays (Toxo-IFA) are generally cumbersome requiring special facilities and are not suitable for large-scale epidemiological surveillance. ELISA has been shown to be a rapid and sensitive alternative to insect bioassays for monitoring arboviruses in wild populations. Reverse transcriptase polymerase chain reaction (RT-PCR) is a recent molecular diagnostic technology used for detecting virus infections in mosquitoes, which gives rapid results but is expensive and prone to contamination. This review describes the development of various techniques involved in detection and isolation of dengue viruses in mosquitoes. Definite diagnosis of the impending dengue epidemic can be made using ELISA for virological surveillance system on dengue virus antigen in the mosquito vectors. Therefore, ELISA offers a potential tool and a convenient system for quickly screening large number of samples up to the serotype level which can be employed effectively and efficiently for large scale dengue surveillance programmes on wild caught mosquito vectors. ELISA positive samples can be screened further by Toxo-IFA system for virus isolation. On the other hand, techniques like mosquitoes cell culture, mosquito inoculation (Toxo-IFA) and RT-PCR techniques can be employed for dengue virus amplification.

Bdelloid rotifer, Philodina species in the breeding containers of Aedes aegypti and Aedes albopictus.

The vector mosquitoes of dengue and chikungunya fever, Aedes aegypti and Aedes albopictus have adapted to feed on humans and undergo larval and pupal development in natural and artificial freshwater collections. Although several studies reported, still, much information is required to understand the successful survival of Aedes mosquitoes in small temporary containers. In an investigation conducted in the chikungunya affected areas of Kerala state, India, the presence of Bdelloid rotifer, Philodina in 95% of breeding habitats of Ae. aegypti and Ae. albopictus was recorded. The role of Philodina in the breeding containers was investigated. It was found that while in control the number of Philodina was found increasing in the water sample during the study period of seven days, the number found decreased in the containers with larvae of Aedes. The gut content analysis also confirmed the presence of the rotating wheel, corona of Philodina in some of the specimen suggests its role as major larval food.