Heartwater, also called cowdriosis, is a tick-borne septicemic, rickettsial
disease of ruminants caused by Cowdria ruminantium. It is mostly found
in Sub-Saharan Africa and Madagascar. It can also occur in some Indian
Ocean islands and a few Caribbean islands, occasionally in Europe. Heartwater
is one of the most important diseases in Africa. It is a major threat to
exotic breeds which are highly susceptible. The disease is transmitted
exclusively by three- host Amblyomma ticks under natural conditions.
These ticks can become infected during the larval or nymphal stages and
transmit the infection during one of the subsequent stages. In endemic
areas, cattle are usually infected and immuned early in life. There are
usually very little or no clinical cases in these areas. Cattle from non-endemic
areas, however, are very susceptible to the disease. Precautions are needed
when moving susceptible cattle to a heartwater endemic area to prevent
heavy loses. Vaccination with a live vaccine is the most effective method
against heartwater. Dipping or spraying animals at risk with acaricide
at weekly interval can also reduce the risk of infection.
Clinical signs:
Heartwater may be peracute, acute and chronic. The incubation period
after an infective bite is two to four weeks. In peracute cases, the infected
animals develop high fever which is rapidly followed by hyperesthesia,
lacrimation and convulsions. Death can usually happen within on or two
days. However, acute form is more common. The first sign is high fever
followed by diarrhoea and nervous signs which consist of depression, a
stiff gait, high stepping, eye and lip movements, and terminating in convulsions
and prostration. Infected animals may die within a few days of the appearance
of the first clinical signs. The clinical signs in chronic cases are not
so remarkable.
Treatment:
Early treatment is essential. Tetracyclines are usually effective early
in the disease before nervous signs develop.
Control measures:
Vaccination with a live vaccine is the most effective control method
against heartwater. Animals born in an endemic areas may be infected and
immuned early in life. However, all domestic ruminants which are not naturally
infected early in life are susceptible to heartwater. These include animals
born in the winter months when ticks are inactive, animals imported from
a non-endemic area. These animals should be vaccinated to avoid heavy loses.
Dipping or spraying animals at risk at weekly intervals can also reduce
the loses from heartwater.
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