Ecological studies on the brown dog tick Rhipicephalus sanguineus (Acari: Ixodidae) in southern Israel and its relationship to spotted fever group rickettsiae.

An outbreak of spotted fever group rickettsiae (SFGR) was investigated by studying free-living and parasitic stages of ticks in two settlements of equal size and population located 20 km apart in the Negev Desert. Although high morbidity from SFGR was found in one of the settlements (Kibbutz Ze'elim), no clinical cases were observed in the second (Kibbutz Re'im). Using flagging and CO2-trapping, approximately 9 times more ticks were collected in Ze'elim than in Re'im. Rhipicephalus sanguineus (Latreille) was the dominant species in Ze'elim, whereas in Re'im R. turanicus Pomerantzev was the most abundant species. Several physical factors that may account for these differences were investigated. Significantly higher maximum soil temperature as well as ambient temperature above the soil were found in Ze'elim. Differences in soil composition in the two sites were also observed. Tick numbers were especially high during April through October in Ze'elim, whereas in Re'im, ticks were found mainly from April to July. A significant positive correlation was found between temperature and tick population size in Ze'elim. Dogs, sheep, goats, Mus musculus, and Meriones crassus, were more heavily infested with ticks in Ze'elim than in Re'im. The percentage of mice and dogs seropositive to SFGR was the same in both sites. In Ze'elim, 7.1% of dog owners acquired Mediterranean spotted fever during the period 1984-1989 compared with only 1.4% of people without dogs.