Abstract
Cowdria ruminantium, causal rickettsia of heartwater in
ruminants, was until recently only known to occur in Africa. It
is transmitted by Amblyomma ticks.
Amblyomma variegatum, one of its African vectors, was introduced
into the Caribbean area with cattle from Senegal about 1830. Before
1900 only Guadeloupe and Antigua were known to be infested.
Martinique was invaded
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as late as 1948. The spread of the tick
accelerated afterwards, especially during the last decade. It has
now been found on Guadeloupe (Grande Terre and Basse Terre),
Antigua, Martinique, St. Croix, Puerto Rico, St. Lucia, Nevis,
St. Kitts, St. Maarten/St. Martin, Vieques, Anguilla, Marie-
Galante and La Désirade. All of these islands are probably still
infested today, except possibly St. Croix and La Désirade.
The existence of heartwater on Guadeloupe has been suspected
since 1966, and was at last confirmed in 1980, having almost
certainly been present for a century and a half. A strain of
C.ruminantium was isolated in 1982. Retrospectively, a bovine
disease with symptoms like those of heartwater has been known on
the island since 1932. Two other African infections of which A.
variegatum is a vector, Theileria mutans and T.velifera, also occur
in cattle on Guadeloupe.
Heartwater has so far been diagnosed only in Guadeloupe and in
near-by Marie-Galante. An investigation for its presence has been
started on other islands where A.variegatum occurs. However, it
has been shown that the American tick Amblyornma maculatum is a
good experimental vector, and that A.cajennense can also transmit
C.ruminantium, but probably not very efficiently. If the agent
can adapt to these and other American Amblyomma species, it could
spread to large areas in the western hemisphere, well outside those where the strictly tropical A.variegatum would find a
suitable habitat.
An assessment of the extent of this serious threat to the livestock
industry of the Americas should be followed by urgent action
while there is still hope of removing the danger as long as the
disease remains limited to a few of the smaller islands.
Apart from a survey of the distribution of the disease and
Amblyomma ticks, information is needed on animal movements between
islands, on migration routes of birds (hosts of immature stages),
animal husbandry methods, and species and numbers of domestic
animals, as well as wild hosts which may interfere with tick
eradication.
Severe dermatophilosis (cutaneous streptothricosis) of cattle
appears to be closely linked with the presence of A.variegatum and
causes high losses on the infested islands. This will make it
easier to obtain the collaboration of livestock owners and authorities
for eradication campaigns, even on islands where heartwater
does not (yet) occur.
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