Abundance of house dust mites in relation to climate in contrasting agricultural settlements in Israel.

The correlation between climatic conditions and mite numbers in houses from rural areas was studied in 13 agricultural communities (kibbutzim and moshavim) in nine geo-climatic subregions of Israel. Mites were present in 97% of the dust samples. The average number of mites per gram of dust in the different localities ranged between 84 and 2053. The maximum number of mites (7440/g dust) was found in a carpet from a house in Geva Carmel in the northern coastal region. The most prevalent species of mites were Dermatophagoides pteronyssinus and Dermatophagoides farinae, which were found in 85.6% and 71.3% of the samples, respectively. The house dust mites D. pteronyssinus, D. farinae and Euroglyphus maynei constituted 94.8% of the mites. Most of the mites were isolated from the carpets and sofas (37.0% and 33.7%, respectively), and a smaller number from beds (29.3%). The smallest number of mites (< or = 250/g dust) were found at a minimum relative humidity (RH) of 30% and lower, with a maximum temperature of 32 degrees C and higher, i.e. in the Jordan valley and Negev mountains. A greater number of mites (250-500/g dust) were found at a minimum ambient RH of 35-40% and a maximum temperature of 32 degrees C and higher, i.e. the Hula valley. A large number of mites (500-1000/g dust) were found at a minimum RH of 35-40% with a maximum temperature of 30 degrees C and lower, i.e. in the Judean and Samarian range, as well as in upper Galilee. The largest number of mites (1000-2000/g dust) was found at a minimum RH of 45% and higher, with a maximum temperature ranging between 30 and 32 degrees C. These conditions occur in the coastal strip, the coastal plain and in the Judean and Samarian foothills. A monthly examination of two houses in Zova, a kibbutz in the Judean hills next to Jerusalem, and two houses from Palmachim, a kibbutz in the coastal region, revealed that the highest prevalence of mites was found in the months April-November and May-November, respectively. In Zova, the highest number of mites were found during the months of June and July while the highest concentrations of D. pteronyssinus-antigen (Der p I) were measured during the month of September. A positive correlation between mite numbers and the quantity of Der p I in house dust was found.

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.