VECTOR-BORNE DISEASES,SURVEILLANCE,PREVENTION Longitudinal Studies of Japanese Encephalitis Virus Infection in Vector Mosquitoes in Kurnool District, Andhra Pradesh, South India N. ARUNACHALAM, 1 U.S.N. MURTY, 2 D. NARAHARI, 3 A. BALASUBRAMANIAN, P. PHILIP SAMUEL, V. THENMOZHI, R. PARAMASIVAN, R. RAJENDRAN, AND B. K. TYAGI Centre for Research in Medical Entomology (Indian Council of Medical Research), 4, Sarojini Street, Chinna Chokkikulam, Madurai, Tamil Nadu, India J. Med. Entomol. 46(3): 633Ð639 (2009) ABSTRACT A 4-yr (2002Ð2006) entomological study was carried out in Kurnool district, Andhra Pradesh state, south India, to identify the mosquito vectors of Japanese encephalitis virus (family Flavi- viridae, genus Flavivirus, JEV). In total, 37,139 female mosquitoes belonging Þve genera and 18 species resting on vegetation were collected in villages and periurban areas at dusk. Mosquito species composition and pattern of JEV infection in mosquitoes varied in periurban and rural areas. In periurban area, Culex gelidus Theobald was abundant, msking up 49.7% of total catch followed by Culex tritaeniorhynchus Giles (44.5%). In rural area, Cx. tritaeniorhynchus was predominant, making up 78.9% of total catch followed by Culex quinquefasciatus Say (10.8%), Anopheles subpictus Grassi (7.1%), and Cx. gelidus (1.1%). In light trap collections, Cx. gelidus and Cx. tritaeniorhynchus predominated in periurban and rural areas, respectively. Of 50,145 mosquitoes screened JEV isolations were made only from Cx. gelidus and Cx. tritaeniorhynchus. Based on high abundance and frequent JEV isolation, Cx. tritaeniorhynchus was found to be the principal vector in both areas, whereas Cx. gelidus plays a secondary vector role in periurban areas only. KEY WORDS Japanese encephalitis, Culex tritaeniorhynchus, Culex gelidus, Kurnool, south India Japanese encephalitis virus (family Flaviviridae, genus Flavivirus, JEV) is currently one of the most important arboviral childhood viral encephalitis in Asia, causing at least 50,000 clinical cases and 10,000 deaths every year (WHO 2005). Japanese encephalitis (JE) is a zoonotic disease, with a complex life cycle involving pigs and ardeid birds and vector mosquitoes. Humans are only occasionally infected and are a “dead end” host, because viremia in human blood is too low and transient to infect mosquitoes. JE is predominantly a rural disease, and it occurs scattered over extensive areas and seldom in pe- ripheral localities of cities (Reuben and Gajanana 1997). In India, JE was Þrst reported in 1955 (Work and Shah 1956); subsequently, many epidemics have oc- curred in different parts of the country. JE outbreaks have been reported as many as 25 states/union terri- tories of India (Kabilan et al. 2004). In some states, such as Uttar Pradesh, Bihar, and Andhra Pradesh, JE has emerged as a perennial public health problem during the rainy season. In 2005, a major encephalitis outbreak was reported in Gorakhpur, Uttar Pradesh, which was the most severe JE epidemic so far re- ported, affecting 5,700 persons, mainly children, with 1,300 deaths (WHO 2006). JE virus has been recovered from several mosquito species (19 species) in different parts of India, and the most important vectors are Culex tritaeniorhynchus Giles and Culex vishnui Theobald from which the largest num- ber of isolations have been made (Geevarghese et al. 2004). In Asia, development of irrigation systems and the expansion of rice (Oryza sativa L.)-growing areas have facilitated the increase of JEV vectors (Lacey and Lacey 1990). Although epidemics invariably are preceded by increase in vector abundance, several other factors, in- cluding mosquito infection rate are involved (Gajanana et al. 1997). Our knowledge of the epidemiology of JE virus is still incomplete considering the diverse ecogeo- graphical regions in India. A detailed understanding of JE epidemiology will lead to the achievement of prediction of outbreaks and sound mosquito control methods. The present studies were undertaken to investigate the dy- namics JEV transmission between June 2002 and July 2006 in a JE-endemic district, Kurnool, Andhra Pradesh (AP) state, south India. The main objective was to de- termine the seasonal abundance and JE infection rates of mosquito vector population to understand their role in the transmission of JE. Materials and Methods Study Area. The study was carried out in Kurnool district, AP (Fig. 1), and its total population is 1,724,795. Most of the people are working in the ag- 1 Corresponding author, e-mail: crmeicmr@icmr.org.in. 2 Indian Institute of Chemical Technology, Hyderabad, Andhra Pradesh, India 500007. 3 Department of Health, Andhra Pradesh, India 500001. 0022-2585/09/0633Ð0639$04.00/0  2009 Entomological Society of America Downloaded from https://academic.oup.com/jme/article/46/3/633/861274 by guest on 13 February 2022