The role of Amblyomma variegatum in the transmission of heartwater with special reference to Guadeloupe.

Heartwater has been diagnosed in Guadeloupe, Marie-Galante, and Antigua; it induces important losses among goats and European or cross-bred cattle when local zebu creole are highly resistant to infection. Amblyomma variegatum is the vector of the disease in the Caribbean. The tick strain of Martinique, occurring in that island that has apparently been disease-free since 1948, has not lost its ability to experimentally transmit the disease. In Guadeloupe 97% of nymphs and nearly 100% of adults feed on cattle and goats. Some immature ticks (4.5%) feed on wildlife, including birds that may be involved in the spread of infected ticks. Only 1 to 4% of adult ticks are infected and only a proportion of infected ticks are really infective: 53%, 9%, and 50% of nymphs, males, and females, respectively. Nymphs play the major role in the transmission: they are more numerous than adults and engorge faster. Infected ticks have the same maximum longevity as noninfected ticks, that is, 18 months for nymphs and nearly 23 months for adults. Cowdria is not transmitted immediately after tick fixation but after a delay of 2-3 days for nymphs and 4 days for adults. The disease is more often fatal when transmitted by tick biting rather than by needle transmission. The daily infection rate that summarizes all the parameters is very low (0.14% and 0.20% for goats and cattle, respectively), resulting in an unstable epidemiological situation. The transmission of Cowdria by A. variegatum in Guadeloupe shows significant differences compared with the transmission by A. hebraeum in Africa.