Background & objectives : Entomological investigations were carried out in Warangal and KarimNagar districts of Andhra Pradesh during viral encephalitis outbreak in July 2003.Methods : Adult mosquito collections in outdoor were done using sweep cage method and in indoorwith the help of aspirator tube and flash light. Larval collections were done by dipping method. JEvirus positivity was tested by IgM capture ELISA test.Results : Outdoor collections revealed presence of Culex tritaeniorhynchus, Cx. bitaeniorhynchusand Cx. gelidus and in indoor collections —Cx. quinquefasciatus, Cx. tritaeniorhynchus, An. vagusand An. subpictus. In the outdoor collections Cx. tritaeniorhynchus was predominant (96.3% of totalcollection). Three samples out of 55 serum samples from human cases and five from contacts showedthe presence of antibodies against JE virus.Interpretation & conclusion : Cx. tritaeniorhynchus, a known vector of JE is predominant in outdoorsand playing a main role in JE transmission in this area. Vector control aimed at the outdoor restingpopulation might limit virus circulation in the mosquito vertebrate host cycle and prevent humaninfection

Bina Pani Das, Shiv Lal & V.K. Saxena

Journal of Vector Borne Diseases

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J Vect Borne Dis 41, March & June 2004, pp 32–36Outdoor resting preference of Culex tritaeniorhynchus, thevector of Japanese encephalitis in Warangal and Karim Nagardistricts, Andhra PradeshBina Pani Das*, Shiv Lal & V.K. SaxenaNational Institute of Communicable Diseases, 22 Sham Nath Marg, Delhi, IndiaBackground & objectives : Entomological investigations were carried out in Warangal and KarimNagar districts of Andhra Pradesh during viral encephalitis outbreak in July 2003.Methods : Adult mosquito collections in outdoor were done using sweep cage method and in indoorwith the help of aspirator tube and flash light.  Larval collections were done by dipping method.  JEvirus positivity was tested by IgM capture ELISA test.Results : Outdoor collections revealed presence of Culex tritaeniorhynchus, Cx. bitaeniorhynchusand Cx. gelidus and  in indoor collections —Cx. quinquefasciatus, Cx. tritaeniorhynchus, An. vagusand An. subpictus. In the outdoor collections Cx. tritaeniorhynchus was predominant (96.3% of totalcollection).  Three samples out of 55 serum samples from human cases and five from contacts showedthe presence of antibodies against JE virus.Interpretation & conclusion : Cx. tritaeniorhynchus, a known vector of JE is predominant in out-doors and playing a main role in JE transmission in this area.  Vector control aimed at the outdoor rest-ing population might limit virus circulation in the mosquito vertebrate host cycle and prevent humaninfection.Key words  Andhra Pradesh – Cx. tritaeniorhynchus –  outdoor resting habit – sweep cage method – viral encephalitisThe Andhra Pradesh state has been reporting out-breaks of Japanese encephalitis (JE) regularly since19791. During July 2003 yet another outbreak of viralencephalitis was reported from nine districts of thestate— Warangal, Karim Nagar, Nizamabad, Adila-bad, Krishna, Nellore, Medak, Nalgonda and Meh-boobnagar. A visit was made to Warangal and KarimNagar districts from where the state health departmentreported a total of 140 cases and 79 deaths due to vi-ral encephalitis during June 1 to July 13, 2003. Assuch both the districts are among 10 high incidencedistricts in Andhra Pradesh as far as JE is concerned.This communication reports entomological findings ofthe investigations carried out in July 2003.Material & MethodsWarangal and Karim Nagar districts are in the northernpart of Andhra Pradesh state and lie between 17°–19' N and 80°–31' E. Agriculture is the main occupa-tion of the people in the area. The predominant crop ispaddy while other minor crops include pulses andmaize.*Corresponding authorDAS et al :  OUTDOOR  RESTING  HABIT  OF  CX. TRITAENIORHYNCHUS 33Entomological investigations were conducted in twoencephalitis affected villages—Medipathi (PHCHasanpathi, District Warangal), Uppal (PHC Uppal,District Karim Nagar) and one village (PagadapalliPHC in Warangal district) which was not affected bythis outbreak. Day time outdoor resting adult mosqui-toes were collected from low level land vegetation bythe recently devised sweep cage method2. Land vege-tation in the area include widely distributed dense foli-age of wild shrubs about 30 cm in height and also lowseasonal cash crops like brinjal, pumpkin, etc. Numer-ous sites of the dense foliages provide suitable restingplaces for mosquitoes despite the ambient day tem-perature around 40°C.Methodology adoptedOutdoors : The collection method involved sweepinga mosquito cage, measuring 12"x12"x12" with itssleeves completely folded (sweep cage), through thevegetation by a series of quick forward, backward, upand down movements for about 1–2 min to disturb theresting mosquitoes and in the process they weretrapped in the cage. The sleeve of the cage was imme-diately folded and the trapped mosquitoes were re-trieved from the cage by an aspirator tube. Such at-tempts were made at least 10 times on vegetation, andthe adult mosquito density was then measured as aver-age number of mosquitoes per 10 sweep cages.Indoors : Mosquitoes were also collected from in-doors (cattlesheds and human dwellings) followingconventional hand catch method with the help of anaspirator tube and a flash-light. The density of mosqui-toes was expressed as per man hour (pmh). Presenceof immature stages of mosquitoes from the potentialbreeding habitats in the study areas—paddy nurserybeds, irrigated fields, wells, ponds were examined usingstandard techniques3. The data on larval survey werecalculated in terms of larval density per dip.Results & DiscussionA total of 215 mosquitoes were collected from out-door situations, resting in extensive dense foliage oflow-level wild shrubs and seasonal cash crops in peri-domestic area, near paddy nursery bed, etc and 235mosquitoes from indoor situations in 10 man hour.Outdoor collections revealed three species of mosqui-toes—Cx. tritaeniorhynchus, Cx. bitaeniorhynchusand Cx. gelidus, while indoor collections revealedfour species—Cx. quinquefasciatus, Cx. tritaenio-rhynchus, An. vagus and An. subpictus. In the out-door collections Cx. tritaeniorhynchus was the pre-dominant species (96.3% of the total collection) and inindoor situation Cx. tritaeniorhynchus accounted foronly 2.9% of the total mosquito collection. Cx. bitae-niorhynchus and Cx. gelidus were not found restingindoors.The density of Cx. tritaeniorhynchus was found tobe high on land vegetation in all the three study villag-es—Medipathi 50, Pagadapalli 87.5 and Uppal 71.6per 10 sweep cages each. The indoor density of thespecies in cattlesheds was 2.3 pmh (village Uppal, Ta-ble 1). Both males and females of Cx. tritaeniorhyn-chus were found resting outdoors on the same vegeta-tion. Female specimens collected were in all stages ofgonotrophic cycle (Table 2), indicating thereby pre-dominantly outdoor resting habit of the species in thearea. Mosquitoes in Cx. vishnui subgroup are knownto be mainly exophilic4,5 but during outbreaks of JE theyhave also been collected from indoor situations6–10.Breeding of Cx. tritaeniorhynchus was found inabundance (larval density range 7 to 34 per dip) innursery paddy beds, paddy fields and other large wa-ter bodies in the area (Table 3).The evidence of JE viral activity in the area for the past10 years (1992–2001) revealed presence of seroposi-tivity to JE virus in humans, pigs and other animals(Source : unpublished report of Veterinary BiologicalResearch Institute, Hyderabad). At the laboratory ofNational Institute of Communicable Diseases, 55 se-rum samples from human cases and five from contactsbelonging to the present episode were tested by IgMCapture Elisa test for the presence of antibodiesagainst JE virus.  Of these, three samples (two casesJ  VECT  BORNE  DIS  41, MARCH & JUNE  200434Table 1. Adult mosquito densities in Warangal and Karim Nagar districts, Andhra Pradesh during July 2003Mosquito species Warangal Karim NagarMedipathi (PHC Hasanpathi) Pagadapalli* (PHC Hasanpathi) Uppal (PHC Uppal)Outdoor** Indoor Outdoor** Indoor Outdoor** IndoorTotal PTSC+ Total PMH++ Total PTSC+ Total PMH++ Total PTSC+ Total PMH++Cx. tritaeniorhynchus 38 50 – – 76 87.5 – – 93 71.66 7 2.33(100) (95) (95.88) (16.67)Cx. bitaeniorhynchus – – – – 1 2.5 – – – – – –(1.25)Cx. gelidus – – – – 3 5 – – 4 3.33 – –(3.75) (4.12)Cx. quinquefasciatus – – 30 7.5 – – 18 6 – – – –(24.19) (26.08)An. vagus – – 92 20 – – 51 15 – – 34 7.66(74.19) (73.91) (80.95)An. subpictus – – 2 0.5 – – – – – – 1 0.33(1.61) (2.38)Total 38 50 124 28 80 95 69 21 97 74.99 42 10.32*Not affected by the epidemic; **Low level land vegetation; +Average no. of female mosquitoes collected per ten sweepcages; ++Per man hour for female mosquitoes; Figures in parentheses indicate prevalence of a mosquito species in this col-lection.Table 2. Analysis of mosquito species collected from viral encephalitis affected districts, Andhra Pradesh during July 2003Mosquito species Outdoor IndoorMale Female  M : F Male Female M : F           ratio  ratioNo. %* No. %*UF FF SG G UF FF SG GDistrict WarangalCx. tritaeniorhynchus 59 55 9.1 5.5 50.9 14.5 1.07 : 1 – – – – – – –Cx. bitaeniorhynchus – 1 – – 100 – 0 : 1 – – – – – – –Cx. gelidus 1 2 – 50 – 50 1 : 2 – – – – – – –Cx. quinquefasciatus – – – – – – – – 48 2.2 20.8 41.6 35.4 0 : 48An. subpictus – – – – – – – – 2 – – 100 – 0 : 2An. vagus – – – – – – – 18 125 28 16 20 36 1: 6.9District Karim NagarCx. tritaeniorhynchus 50 43 11.6 18.6 46.5 23.3 1.16 : 1 – 7 – – 42.9 57.1 0 : 7Cx. gelidus 2 2 – – 100 – 1 : 1 – – – – – – –An. subpictus – – – – – – – – 1 – – – 100 0 : 1An. vagus – – – – – – – 11 23 17.4 – 52.2 30.4 1 : 2.1*Physiological stage/Abdominal condition; UF — Unfed; FF — Full-fed; SG — Semigravid; G — Gravid; M : F — Male : Female.DAS et al :  OUTDOOR  RESTING  HABIT  OF  CX. TRITAENIORHYNCHUS 35and one contact) were positive (unpublished report ofNational Institute of Communicable Diseases). This in-dicates the recent infection with JE virus in these casesin the affected area.Cx. tritaeniorhynchus is considered to be the impor-tant vector of JE in India and virus isolation from thisspecies has been reported from adjoining states ofKarnataka11 and Tamil Nadu12. During 2003, ento-mological investigation was carried out when the viralencephalitis cases and deaths were at their peak in thearea. Presence of physiologically active Cx. tritaenio-rhynchus population in such a high density indicatesthe possibility of this species being involved in thetransmission of current outbreak of viral encephalitisthat conforms to the pattern of JE in the area. Thus, inorder to control the disease, vector control measurestargeted against the physiologically active populationof Cx. tritaeniorhynchus resting on outdoor vegeta-tion are required. Though the species is known to bemainly exophilic, however during outbreaks when itsdensity rises it has been collected from indoor situa-tions, which might be aiding JE virus transmission inhumans. Transmission reduction might, therefore, beachieved in such areas, if the outdoor breeding andresting population of the vector is targeted for its ef-fective control using chemicals or bio-control agents inwell-identified outdoor habitats during inter-epidemicperiods.AcknowledgementThe authors are grateful to Dr Laxhmi Rajan, DirectorHealth Services, Andhra Pradesh, for providing facili-ties during the field work and Dr. S.K. Patnaik, Re-gional Director, Health and Family Welfare, Hydera-bad for his kind cooperation. Mr. K. Jagan MohanRao, Deputy Director (Malaria), Hyderabad and theEntomological team of Warangal Zone also assisted inthe field investigation.References1. JE in Andhra Pradesh.  Hyderabad : Department of Health& Family Welfare  1999.2. Das BP.  A new technique for sampling outdoor restingpopulation of Culex tritaeniorhynchus, vector of Japaneseencephalitis. New Delhi :  XIV National Congress of Para-sitology,  23–26 April 2000 (Abstr. No. PS-15); p 133–4(Unpublished).3. Methods and tehcniques.  Manual on practical entomol-ogy in malaria, pt II. Geneva : World Health Organization1975.4. Kulkarni SM, Rajput KB. Day-time resting habitats of culi-cine mosquitoes and their preponderance in Bastar district,Madhya Pradesh, India. J Com Dis 1998; 20 : 280–6.5. Rahman SJ, Wattal BL, Bhatnagar VN. Culex tritaenio-rhynchus Giles in village Arthala, Uttar Pradesh (India) andpossible methods of its control. J Ent Res 1978;  2 : 79–87.6. Rajagopalan PK, Menon PKB, Panicker KN. An ecologicalappraisal of the mosquitogenic conditions and probablecauses of the 1978 epidemic of  ‘Encephalitis’ in Tirunelvelidistrict, Tamil Nadu. J Com Dis 1978; 10 : 157–64.7. Saxena VK, Baig MH, Bhardwaj M, Rajagopal R. Entomo-logical investigations of Japanese encephalitis outbreak inGorakhpur and Deoria districts of  Uttar Pradesh. J ComDis 1986; 18 : 219–21.8. Angani K,  Chakravarty SK, Das MS, Mukherjee KK. Se-roepidemilogical study of Japanese encephalitis in Di-mapur, Nagaland. J Com Dis 1989;  21 : 87–95.Table 3. Mosquito breeding detected in Warangal and Karim Nagar districts, Andhra Pradesh during July 2003District/PHC Village Type of Density/Dip  Mosquito speciesbreedingplace                     Culicine      AnophelineWarangal/Hasanpathi Pagadapalli Pond 34 1.8 Cx.tritaeniorhynchus, An. nigerrimusPaddy field 7 – Cx. tritaeniorhynchusMedipathi Clay pot – – Culex* sp, Ae. albopictusKarim Nagar/Uppal Uppal Paddy nursery 24.6 3.6 Cx. tritaeniorhynchus, An. nigerrimus*Species could not be identified.J  VECT  BORNE  DIS  41, MARCH & JUNE  2004369. Sharma RC,  Saxena VK, Bhardwaj M,  Sharma RS,  Vergh-ese  T, Datta KK. An outbreak of Japanese encephalitis inHaryana 1990. J Com Dis 1991; 23 : 168–9.10. Saxena VK, Das KK. Bio-ecological factors play keyrole in determining transmission dynamics of arbo-viral infection in man. J Basic Appl Med 1995; 3 : 51–4.11. Kaliwal MB. Entomological investigation of Japanese en-cephalitis outbreak during 1991 in Goa. Bull Vect BorneDis 1991; 3 : 13–7.12. Carey DE, Reuben R,  Mayers RM. Japanese encephalitisstudies in Vellore, South India. Pt-I, Virus isolation frommosquitoes. Indian J Med Res 1968; 56 : 1309.

Outdoor resting preference of Culex tritaeniorhynchus, the vector of Japanese encephalitis in Warangal and Karim Nagar districts, Andhra Pradesh

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Outdoor resting preference of Culex tritaeniorhynchus, the vector of Japanese encephalitis in Warangal and Karim Nagar districts, Andhra Pradesh

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