Risk of transmission of canine leishmaniosis in eastern Spain.

IN the Mediterranean area, human and canine visceral leishmaniosis is caused by the parasitic protozoan Leishmania infantum (Peters and Killick-Kendrick 1987). In Spain, 15 per cent or more of all dogs are seropositive in endemic areas (Molina and others 1994), and this is fairly typical of the situation in other countries of the Mediterranean basin (Bettini and Gradoni 1986). Since this region is a favourite holiday destination for tourists accompanied by their pets, the disease is also regularly diagnosed in northern Europe. Infection is transmitted to vertebrate hosts via the bite of a sandfly (Peters and Killick-Kendrick 1987). The most important vector of canine leishmaniosis in the Iberian Peninsula is Phlebotomus perniciosus (Molina and others 1994), followed by Phlebotomus ariasi (Killick-Kendrick 1990). Transmission depends on the presence and especially the abundance of the vector, which, in turn, varies with regional ecological factors. The period of activity of P perniciosus in eastern Spain is quite variable. It can range from the end of March to the middle of December (Morillas-Marquez and others 1983). The seasonal dynamics of P perniciosus in the Mediterranean area are bimodal, with peaks in June to July and September to October (Parrot and others 1933, Lucientes-Curdi and others 1991). Apart from the seasonal dynamics, little is known about the diurnal rhythm of the phlebotomine sandflies, which would help to establish the risk of transmission throughout the day. This short communication describes the analysis of the diurnal rhythm of sandflies in areas of eastern Spain where canine leishmaniosis is endemic. The experiments were carried out during the period of greatest risk of transmission, estimated to be in September and October (Lucientes-Curdi and others 1991). A dog was used as bait and placed in a 2·3 m long box covered with a mosquito net. The box was raised 20 cm off the ground to allow sandflies to enter. Any insects in the trap were collected every hour, from 19.00 to 08.00, and the temperature and relative humidity were recorded hourly. The experiment was repeated for five nights at intervals of 10 days. Fig 1 shows the percentage of sandflies captured and the temperature and relative humidity for each hour over the five nights. A total of 136 sandflies were captured, of which 131 were P perniciosus (96·32 per cent) and five were P papatasi (3·68 per cent). Most specimens were females (88·54 per cent). The average temperature varied between a minimum of 14·4°C between 05.00 and 06.00 and a maximum of 24·5°C at 19.00, when the experiment began. The relative humidity varied between 66·7 per cent at 19.00 and 92·9 per cent between 05.00 and 06.00. The activity period of the sandflies lasted between four to six hours and varied according to the environmental conditions. The greatest activity period was during the first part of the night, from sunset to midnight. Most of the sandflies (84·7 per cent) were captured between 20.00 and 23.00. These results agree with those reported by Rioux and Golvan (1969) and Killick-Kendrick (1983). Most of the insects were captured when the temperature was between 18·7 and 21·6°C and the humidity was between 77·4 and 86·3 per cent. Since the behaviour of the sandflies was directly influenced by the environmental conditions, lower temperatures should reduce their activity and extreme values would completely inhibit their movement. Rioux and Golvan (1969) and KillickKendrick (1983) reported that the minimum temperature at which sandflies remain active is 17°C, which is similar to the findings in the present study. More females than males were captured, since the females went to the animal bait to feed. They could also have been attracted by pheromones produced by other females during feeding, as occurs with P papatasi (Schlein and others 1984). The results of the present study suggest that dogs in eastern Spain are more likely to contract leishmaniosis during the first hours of the night, between one and three hours after sunset, given adequate environmental conditions. This information should be taken into account in order to prevent parasitosis in the Mediterranean region.