Seasonal Dynamics of Ornithodoros (Pavlovskyella) Erraticus (Acari: Ixodoidea: Argasidae) and the Spirochete Borrelia Crocidurae in Egypt1

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Abstract
The seasonal dynamics of the burrow-inhabiting tick Ornithodoros (Pavlovskyella) erraticus and infection by the North African relapsing fever spirochete, Borrelia crocidurae, were investigated in a Nile Valley cultivated area near Cairo from April 1979 through March 1980. The tick host was the Nile Grass Rat, Arvicanthis n. niloticus. Nymphs constituted 19.6 to 45.3% of the tick population during different seasons. Only fully engorged larvae were collected by the sampling technique employed. Adults constituted 54.0 to 79.3% of the population from spring through fall (March–October), with peak numbers (61.0 to 79.3%) in summer (July). The male:female ratio (1.6: 1.0 to 2.1:1.0) was significantly higher for males in late winter and spring (February–April); during other seasons the ratio was 0.8:1.0 to 1.4:1.0. Females exceeded males in number only in December. Borrelia crocidurae infection rates were similar in male, female, and nymphal 0. (P.) erraticus. These rates were relatively low (5.8 to 14.3%) during winter and late springearly summer (December–May), afterward increased gradually to a peak (42.0%) in October, and declined (25.6%) in November. That the spirochetes may be transmitted transovarially, venereally, and during hyperparasitic feeding contributes to the high infection rate during summer and early fall, when 0. (P.) erraticus activity is greatest.