TRANSACTIONS OF THE ROYAL SOCIETY OF TROPICAL MEDICINE AND HYGIENE (2002) 96, 117-l 18 Enhanced sandfly attraction to Leishmania-infected hosts B. O’Shea, E. Rebollar-Tellez, R. D. Ward, J. G. C. Hamilton, D. El Naiem and A. Polwart School of Life Sciences, Keele University, Keele, Stafford- shire ST5 5BG, UK Abstract We report that hamsters infected with Leishmania infanturn are more attractive to female sandflies in bioassays. Entrained odours from infected ani- mals were shown by gas chromatography to con- tain peaks absent from uninfected individuals. Implications of enhanced transmission, potential for developing novel diagnoses and the signiti- cance to epidemiological models are discussed. Keywords: sandflies, Lutzomyia longipalpis, Leishmania infanturn, experimental infections, hamsters, host odour attraction There is abundant evidence that parasites are able to manipulate their hosts in ways that lead to enhanced transmission (MOORE, 1995). In some cases, parasites alter the behaviour of blood-feeding arthropods to in- crease the number and duration of haematophagous probes (KOELLA et al., 1998). In addition, infection may modify host odours, a fact that has been recog- nized by physicians for hundreds of years (PENN & POTTS, 1998). The link between infection and host odour has also been associated with changes in volatiles exhaled in breath and/or with changes in epidermal microbial flora (SMITH et al., 1998; BRAKS et al., 1999). There are, however, few experimental studies that demonstrate increased feeding of vectors on such parasitized hosts. DAY & EDMAN (1983) were able to show that mosquitoes had greater feeding success when exposed to malaria-infected mice, which they con- cluded was due to impaired host defensive behaviour. COLEMAN & EDMAN (1988) further studied feeding of sandflies on cutaneous lesions caused by Leishmania in mice and concluded that probing. and feeding were positively correlated with lesion location, but that initial landing was a random event. KNOLS & MEIJERINK (1997) reported circumstantial evidence that Leishma- nia-infected dogs are more attractive to sandflies than uninfected dogs, and one of us (D.E.N.) has observed that Sudanese patients with visceral leishmaniasis have a distinct odour. With this background we have carried out some preliminary investigations to determine whether labor- atory hamsters (A and B) infected with Leishmania infanturn (MHOMiBRi74iPP75) were more attractive to Lutzomyia longipalpis females (originally colonized from material collected in Jacobina, Brazil). The bioas- says were conducted by placing an infected animal (5- 7 months post-infection) into a 2-litre jar alongside a similar jar containing an uninfected control animal of the same sex and age. A 14-mL/s purified airflow was conducted over the animals and released from 2 ports into a 2 m X 0.3 m X 0.3 m perspex wind tunnel. Re- lease of odours from the ports of ‘uninfected’ and ‘infected’ air flows were alternated between ports after Address for correspondence: Professor R. D. Ward, Centre for Applied Entomology and Parasitology, Huxley Building, School of Life Sciences, Keele University, Staffordshire ST5 5BG, UK; e-mail r.d.ward@biol.keele.ac.uk each replicate to control for any bias in the experimen- tal set-up. Fifteen or 20 female 6-day-old Lu. longipalpis were released from the other end of the tunnel and allowed to fly upwind towards infected and uninfected port target areas measuring 0.3 m X 0.15 m. An infra- red-sensitive video camera was used to record the num- ber of fly landings on each of the target areas over a period of 20 min. Bioassays were conducted after 17:00, under 67% relative humidity and at 24°C and with only infrared lighting. All glass and perspex sur- faces were thoroughly cleaned between replicates. The preliminary experiment was replicated 4 times for each of 2 infected hamsters. These data, although insufficient for statistical testing, showed that 67% of flies were attracted to the ‘infected air flow’ port. In addition we also carried out a study of the chemi- cal odour profile of the infected individuals A and B. Gas chromatography profiles of the odours entrained from infected and uninfected animals showed the pre- sence of 10 peaks that were unique to infected animals. Thus peaks at the following retention times were observed only in both infected animals and not in the controls: 10.8, 11.2, 11.3, 11.8, 12.2, 12.4 and 13.9 min. The repeat wind-tunnel assays used 2 more infected hamsters (C and D) with 12 replicates per hamster (Table). A Sign test (data not normal and not symme- trical) on the median paired difference in this case showed a highly significant difference from zero (P < 0.001) for both animals. In addition we used en- trained host odour from animals C and D in a Y-tube olfactometer as described by HAMILTON et al. (1999) to compare the attraction of individual flies to infected or uninfected odour sources. Forty flies were used individually in each assay for both animals and in both Table. Wind-tunnel landings of female Lutzo- myia longipalpis attracted to an area of 0.3 m X 0.15 m surrounding the exit odour ports from hamsters C and D infected with Leishmania infantum or uninfected Total sandfly landings at each port Infected Uninfected Total Hamster C 67 34 101 E 27 86 7 29 14 10 24 ;z 14 31 13 38 13 7 20 12 8 20 42 30 19 11 Ii 19 12 31 21 13 Total 330 186 5:: Hamster D 29 27 56 27 22 49 12 18 1; ;: 48 33 81 19 11 30 44 40 84 37 2 70 55 10 6 16 69 51 120 50 39 89 Total 395 309 704 Odours from infected and uninfected hamsters were alternated between ports to eliminate any bias in the experimental set-up.