Disease identification

In Australia, the tick-borne diseases of significance in cattle are tick fever (caused by Babesia bovis, Babesia bigemina and Anaplasma marginale) and theileriosis (bovine anaemia caused by variants of Theileria orientalis).

Preliminary suspicion of tick-borne disease may be obtained by noting clinical signs in the cattle. It is not possible to use clinical signs alone to identify the different tick-borne diseases. Similar clinical signs may also be present with other diseases. Pale and/or yellow mucous membranes (gums, eyes/conjunctiva, vulva), fever, weakness, urine colour changes and lack of appetite are possible clinical signs of all these diseases. There are some differences in clinical signs caused by these diseases: nervous signs are possible with Babesia bovis; red urine possible with Babesia bovis and Babesia bigemina; and brown urine more usual with Anaplasma marginale.

Diagnosis of tick fever and theileriosis is normally confirmed by finding the parasite in blood smears when using a microscope (Figure 1). Laboratory examination of blood smears prepared from the tip of the tail or ear is the most common method of diagnosis. In the case of dead animals, organ smears (including brain smears for Babesia bovis) and blood smears can be taken. Theileriosis can be difficult to diagnose as the organisms are readily seen in blood smears taken from healthy animals, so assigning significance to the finding can be challenging. Molecular techniques to detect the organisms, and serology to detect previous exposure, are also useful tests.

Ixodes ticks may cause paralysis, which is diagnosed by clinical signs and/or evidence of paralysis ticks. Normal evidence would be the presence of paralysis ticks or craters left in the skin where paralysis ticks have been (Figure 2). Occasionally, very heavy burdens of the cattle tick itself may cause weakness by sucking large amounts of blood.

Figure 1. Microscopic comparison of the different species that cause tick fever. Image courtesy of Lyn Knott (Common Parasites of Veterinary importance).
Figure 1. Microscopic comparison of the different species that cause tick fever. Image courtesy of Lyn Knott (Common Parasites of Veterinary importance).


 

Figure 2. Paralysis tick feeding. Image courtesy of Lex Turner.
Figure 2. Paralysis tick feeding. Image courtesy of Lex Turner.