Impact of DDT indoor residual spraying on Phlebotomus argentipes in a kala-azar endemic village in eastern Uttar Pradesh.

Impact of DDT indoor residual spraying on Phlebotomus argentipes in a kala-azar endemic village in eastern Uttar Pradesh S.M. Kaul,1 R.S. Sharma,2 K.P. Dey,3 R.N. Rai,4 & T. Verghese5 Data on the operational efficacy of DDT indoor residual spraying against Phlebotomus argentipes, the vector of kala-azar in India, are scarce. We therefore undertook a study of the impact on kala-azar and its vector of DDT indoor residual spraying in the Varanasi district of eastern Uttar Pradesh. Preliminary results indicate that after two rounds of DDT spraying in one village no P. argentipes were found during the peak vector season; in contrast, a large number of these sandfies were collected in the unsprayed comparison village. Introduction Indoor residual spraying with DDT (1,1 -bis(4-chlo- rophenyl)-2,2,2-trichloroethane) forms an important component of the kala-azar (visceral leishmaniasis) control strategy in India. Use of DDT indoor spraying for such purposes has been carried out since the resurgence of the disease in the mid-1970s in Bihar State. Belief in the efficacy of this strategy against kala-azar rests largely on the high susceptibi- lity to DDT of the vector, Phlebotomus argentipes, as evidenced by tests carried out using the WHO procedure (1, 2) and the transient disappearance of kala-azar from India in the wake of antimalarial house spraying in the 1950s and the early 1960s. Very little operational data are, however, available to endorse the efficacy of DDT spraying on controlling populations of P. argentipes. Generation of such data was important for a concurrent evaluation of the vec- tor control strategy against kala-azar, and has be- come all the more important since P. argentipes has been reported to be resistant to insecticides in one area of Samastipur district, north Bihar (3). In view of the importance of this issue, we initiated a long- ' Assistant Director, Division of Helminthology, National Institute of Communicable Diseases, 22 Shamnath Marg, Post Box No. 1492, Delhi - 110054, India. Requests for reprints should be sent to this author. 2 Deputy Director and Chief, Division of Epidemiology, National Institute of Communicable Diseases, Delhi, India. 3 Research Assistant, Regional Filaria Training and Research Centre, Varanasi, India. 4Officer-in-Charge, Regional Filaria Training and Research Centre, Varanasi, India. 5 Director, National Institute of Communicable Diseases, Delhi, India. Reprint No. 5454 term entomological and epidemiological assessment of the efficacy of insecticides in the control of kala- azar. In this article, we report preliminary observa- tions on the impact of two rounds of DDT residual spraying on P. argentipes populations in a kala-azar- affected village in Varanasi district, eastem Uttar Pradesh. Materials and methods Observations were recorded in two contiguous vil- lages, Shujabad (population, approx. 5000) and Bhoj- pura (population, approx. 3600), which are situated on the banks of the Ganges. Cases of kala-azar and of post-kala-azar dermal leishmaniasis (PKDL) were reported in Shujabad in 1990 (4) and 1991 (National Institute of Communicable Diseases, unpublished data). Five active cases of kala-azar and two cases of PKDL were found in Shujabad up to September 1991, with no fresh cases of kala-azar being observ- ed subsequently. No kala-azar cases were found in Bhojpura. Shujabad was sprayed with DDT (dose 1 g/m2) in June and August 1991 by the district health author- ities, with the spraying being limited to about 1.7 m from the inner walls of premises. All human dwel- lings and cattlesheds were sprayed. The spray quality appeared to have been satisfactory as evidenced by villagers' reports. Shujabad had not been sprayed with insecticides in the previous two decades. Sandfly collections were made on 18-21 Sep- tember 1991, about a month after the second round of spraying, during a period when peak population densities of the vector species are encountered (5)- thus enabling a valid comparison to be made between vector populations in sprayed and un- sprayed areas. Although castor-oil-baited sticky traps are considered to be the most objective method of Bulletin of the World Health Organization, 1994, 72 (1): 7981 © World Health Organization 1994 79 SM Kaul et al. Table 1: Number of sandflies, by sex, collected from a DDT-sprayed and an unsprayed village in Varanasi district, eastern Uttar Pradesh, September 1991 Sprayed village Unsprayed village (Shujabad) (Bhojpura) No. of femalesa No. of No. of femalesa No. of UF FF GR P Total males Total UF FF GR P Total males Total Phlebotomus argentipes 18 140 83 23 264 71 335 P. papatasi ..- - 1 2 - - 3 1 4 Sergentomyia babu 2 2 - - 4 4 8 3 10 6 2 21 4 25 S. punjabensis 1 1 - - 2 2 4 1 - - - 1 - 1 S. bailyi 1 - - - 1 1 2 - - - - - - - Total 4 3 - - 7 7 14 23 152 89 25 289 76 365 a UF = unfed, FF = freshly fed; GR = gravid; P = parous. collecting sandflies (6), we avoided their use since sticky traps mostly catch insects in flight, i.e., males seeking mates, or unfed or occasional parous flies in search of a blood meal, and would therefore be unsuitable for collecting sandflies that have taken a residual insecticide and are resting for completion of a gonotrophic cycle. Clusters of dwellings (human, cattle, or mixed) in both north-south and east-west directions were chosen for sandfly collections. In Shujabad a total of 71 dwellings were searched over 55 man-hours and in Bhojpura, 55 dwellings over 41 man-hours, by three collectors of average efficiency. The sandflies were collected using suction tubes from dark comers, crevices, and ceilings, or sometimes driven out of the thatch using cigarette smoke. Female sandflies were classified according to their abdominal condition. Sandflies were considered parous if they had one or a few mature eggs, irrespective of their abdominal condi- tions, retained from a previous oviposition. The sandflies were mounted in Hoyer's medium for iden- tification. Results and discussion The results of the sandfly collections from the sprayed and the unsprayed village are shown in Table 1. A total of 365 sandflies were collected in the unsprayed village of Bhojpura (average collec- tion rate, about 9 sandflies per collector per hour). These included 335 P. argentipes (264 females and 71 males), i.e., about 91.7% of the total catch. A total of 53.1% of the females were freshly fed, 31.5% were gravid or half gravid, 6.8% were unfed, and 8.6% were parous. Small numbers of P. papatasi sandflies and Sergentomyia spp. were also collected. Apparently, the population of P. argentipes in the unsprayed village (Bhojpura) was in state of high reproductive activity, as evidenced by the large num- ber of freshly fed and gravid sandflies. In the sprayed village (Shujabad) no P. argentipes were found, despite a careful search, indicating that the population of P. argentipes in this village was highly susceptible to DDT. Apparently, in the absence of selection pressure, P. papatasi is also susceptible, despite its high resistance to DDT in the neighbour- ing plains of north Bihar (1, 2). These findings suggest that the timely spraying with DDT was operationally highly effective against P. argentipes and apparently prevented the build-up of a population of the vector during the kala-azar transmission season, which appears to be the mon- soon in eastem Uttar Pradesh (7). Timely spraying with DDT thus helped to interrupt transmission of kala-azar and ensured its effective control. Further studies are being carried out on the epidemiological impact of these measures. Acknowledgements We thank Mr A.K. Ganesh, for secretarial help, and Mr M. Franciscose and the staff of the Regional Filaria Training and Research Centre, Varanasi, for technical assistance. Resume Impact des pulverisations remanentes de DDT a l'interieur des habitations sur Phlebotomus argentipes dans un village de l'est de l'Uttar Pradesh ou le kala-azar est end6mique 11 n'existe que peu de donn6es sur 1'efficacit6 ope- rationnelle des pulverisations r6manentes de DDT a l'int6rieur des habitations contre Phlebotomus argentipes, vecteur du kala-azar en Inde. De WHO Bulletin OMS. Vol 72 199480 Impact of DDT on Phlebotomus argentipes in Uttar Pradesh telles donn6es permettraient aux directeurs de programmes d'6valuer les strat6gies de lutte anti- vectorielle et de les modifier le cas echeant. Nous avons donc realis6 une etude de l'impact sur le kala-azar et son vecteur, de pulverisations rema- nentes de DDT a l'interieur des habitations dans le district de Varanasi, dans l'est de l'Uttar Pradesh. Nous decrivons ici les observations pr6liminaires sur l'impact de deux series de pulverisations. Des captures organis6es pendant la saison ou la pre- valence du vecteur est maximale ont montre que ces pulverisations avaient eu un impact consid6- rable puisqu'aucun specimen de P. argentipes n'a 6t6 trouv6 dans le secteur traite alors qu'un grand nombre de phlebotomes ont ete captures dans le village temoin non traite. References 1. Kaul SM et al. Preliminary observations on the sus- ceptibility status of Phlebotomus argentipes and P. papatasi to DDT in two districts of North Bihar (India). Journal of communicable diseases, 1978, 10: 208. 2. Joshi GC et al. Susceptibility of sandflies to or- ganochlorine insecticides in Bihar (India) - further reports. Journal of communicable diseases, 1979, 11:209. 3. Mukhopadhyay AK et al. Susceptibility status of Phlebotomus argentipes to DDT in some kala-azar endemic areas of Bihar (India). Indian journal of medical research, 1990 (November), 91: 458-460. 4. Rai RN, Sehgal PN. Kala-azar in Varanasi (U.P.) preliminary observations. Joumal of communicable diseases, 1990, 22(2): 120-123. 5. Sanyal RK et al. Some observations on the epi- demiology of current outbreak of kala-azar in Bihar. Journal of communicable diseases, 1979, 11(4): 170-182. 6. Dergacheva TI. Field methods of studies of sand- flies in leishmaniasis foci. Moscow, USSR Ministry of Health, Gamaleya Institute of Epidemiology and Microbiology, 1980: 1-20. 7. Lewis DJ. Phlebotomid sandflies. Bulletin of the World Health Organization, 1971, 44: 535-551. WHO Bulletin OMS. Vol 72 1994 81