Cattle Tick

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Nature of the disease

The cattle tick, Boophilus microplus, is a significant ectoparasite of cattle and a vector for important diseases such as babesiosis and anaplasmosis.

 

Classification
SPC List D disease
Susceptible species
B. microplus is primarily a parasite of cattle. However, heavy infestations can also occur on horses, sheep, deer and water buffalo. Rarely, ticks have been reported on marsupials, goats, dogs, cats and pigs.
Distribution
The cattle tick is widely distributed in Central and South America, parts of the southern USA, Africa, Asia, and northern Australia. The distribution of the cattle tick is largely determined by climatic factors. B. microplus requires high humidity and ambient temperatures of at least 15-20o C for egg laying and hatching.
Clinical signs
Cattle tick infestation causes:
  • Damage to hides
  • Loss of production
  • Anaemia and death
  • Weakness leading to greater mortalities during droughts
Post-mortem findings
Animals may be in poor condition and anaemic. Infestations will be obvious by the presence of engorged ticks attached to the animal’s skin.
Differential diagnosis
Several species of ticks may be found on cattle and it is important to differentiate these from B. microplus. Other ticks include:
  • Haemophysalis spp
  • Ixodes holocyclus
Specimens required for diagnosis
Ticks should be collected and forwarded to an entomologist for confirmation of the diagnosis. B. microplus has pale legs, short mouth parts with transversely ridged palps, small eyes and lacks an anal groove.
Transmission

The life cycle involves free-living stages. After feeding on cattle, engorged female ticks drop to the ground and lay eggs (up to 5000). After hatching, the larvae survive on pasture for several months. The larvae then become quite active and climb up grass and transfer to animals as they brush past. The larvae attach and feed from the host. They moult to the nymphal stage and then undergo a further moult to the adult stage.

Risk of introduction
Cattle ticks are most likely to be introduced with the importation of infested cattle. Cattle tick was introduced to New Caledonia with cattle imported from Australia in this way.

Transport of ticks on dogs is considered a potential risk for introducing the tick to new areas, although egg production is much reduced in this species and the risk is considered low.

Control / vaccines
There are four methods available for controlling ticks:
  • Treatment with acaricides
  • Pasture spelling
  • The use of resistant cattle
  • Vaccination

Tick control by acaracide dipping has been widely used in endemic areas. Acaracides used for this purpose include various synthetic pyrethroids, amitraz, and some organophosphates. Dipping may have to be done as frequently as every 4-6 weeks in heavily infested areas. Many producers in tick endemic area have changed to Bos indicus type cattle because of their greater resistance to tick infection.

An anti-tick vaccine is also commercially available in Australia. The vaccine antigen, based on a tick gut protein and produced by recombinant technology, stimulates production of specific antibodies in cattle which damage the gut of engorging ticks, resulting in a fertility reduction of up to 70% in adult ticks, reducing tick population build-up. This vaccine is of limited use, but can be used as part of an integrated program for the control of ticks.

References
  • Boophilus microplus, In Merck Veterinary Manual, National Publishing Inc. Eight ed, 1998, Philadelphia, p 674-675