B102 - BOVINE BABESIOSIS

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B102 - BOVINE BABESIOSIS

Nature of the disease
Bovine babesiosis is a major tick-borne disease of cattle caused by protozoan parasites (Babesia spp). In tropical areas the agents are Babesia bovis and Babesia bigemina.
Classification
OIE List B disease
Susceptible species
Cattle. Bos indicus type cattle are less susceptible because of their greater resistance to tick infection.
Distribution
Babesia spp. are widely distributed throughout the world, with the geographic distribution only limited by the distribution of suitable tick vectors. The cattle tick, Boophilus microplus, is the vector for babesiosis in Australia and the infection is widespread throughout the tick’s endemic area.
Clinical signs
Cattle with advanced babesiosis have a low exercise tolerance and sometimes collapse and die while being driven to a yard for treatment. Older animals are more acutely affected (clinical babesiosis is rare in cattle younger than six months). Abortions may occur when pregnant animals are severely affected. Similar clinical signs develop during infection with both organisms. However, the course of the disease differs markedly. Infections are characterised by :
  • Fever
  • Anorexia
  • Depression
  • Increased respiratory rate particularly following exertion
  • Muscle tremor
  • Reluctance to move
  • Haemoglobinuria
  • Occasionally signs of cerebral derangement such as circling, head pressing, mania and convulsions.

While these signs are seen very early in the course of B. bovis infections, they only develop in B. bigemina infections in the latter stages when parasitaemia is well advanced. Anaemia and jaundice develop steadily with B. bovis, but much more precipitously with B. bigemina. B. bigemina-affected animals may exhibit irritability and aggression but not the central nervous system signs.

Post-mortem findings
Gross pathology seen in cases of babesiosis can be highly variable:
  • Varying degrees of congestion, pallor or jaundice
  • Blood is usually watery, and urine is red
  • Sub-serosal haemorrhages are common, particularly on the heart and intestines
  • Spleen is enlarged with a soft red pulp
  • Liver is enlarged and brown or yellow, with the gall bladder filled with thick, granular bile
Differential diagnosis
Other causes of haemolytic anaemia may need to be considered. These include:
  • Anaplasmosis
  • Leptospirosis
  • Bacillary haemaglobinuria
  • Rapeseed poisoning
  • Eperythrozoonosis
  • Chronic copper poisoning
Specimens required for diagnosis 
Babesiosis can be confirmed by microscopic examination of stained blood smears. Serological testing for antibodies may also be useful, particularly in convalescent animals, or for assessing the disease status of an individual or herd, ELISA tests have been developped.
Transmission
B. bovis and B. bigemina are parasites of red blood cells and their transmission depends on suitable vectors. A range of tick species has been shown to transmit babesiosis . The cattle tick (Boophilus microplus) is the only vector for babesiosis in Australia.

Transfer of parasitaemic blood via veterinary equipment and biting flies is theoretically possible, but does not appear to be important in the epidemiology of the disease.

Risk of introduction
The major risk of introducing bovine babesiosis is through the importation of infected livestock. Whether the disease would establish depends on the presence of suitable vectors.
Control / vaccines
Effective control of tick fevers has been achieved by a combination of measures directed at both the disease and the tick vector. Tick control by acaracide dipping is widely used in endemic areas.

Dipping may be done as frequently as every 4-6 weeks in heavily infested areas. The occurrence of resistance of ticks, chemical residues in cattle and environmental concerns over the continued use of insecticides has led to use of integrated strategies for tick control.

Babesiosis vaccines are readily available and are highly effective. The most commonly used vaccine is a live attenuated B. bovis vaccine produced from the blood of artificially infected, splenectomised calves. An anti-tick vaccine is also commercially available in Australia. This vaccine is of limited use, but can be used as part of an integrated program for the control of ticks.

References
  • Babesiosis, In Exotic Animal Disease, the grey Book, Bayer, 1998
  • Babesiosis, In Merck Veterinary Manual, National Publishing Inc. Eight ed, 1998, Philadelphia, p 429; 23-25
  • Babesiosis, In Veterinary Medicine, Saunders, Eight ed, 1997, London p.1171-1179
  • Office International des Epizooties, 2002