September 2023

Last weekend when I was on duty, I got called out to see a sick cow. The cow was walking very slow and had a sudden drop in milk production. On clinical exam, her heart, lungs and temperature were normal. She had a yellow vulva and when I took a blood sample, the blood was much ‘thinner’ than it should be. Those are typical signs of Theileria and the lab confirmed my diagnoses a few days later.

Interestingly enough, three of my other colleagues have seen Theileria cases in the Tokoroa/Mangakino area too this week. About eight to ten years ago when we saw the first new strain of Theileria (Ikeda) cases in cows in the North Island, we had some farms where a high percentage of the herd was affected, and I have done many blood transfusions to try to save cows’ lives (fortunately that was successful in all but one case!). Since then Theileria has become more endemic: it is a constant presence and most cows have at least some immunity against it. Therefore, we don’t see many very severe affected cows anymore.

Theileria is a tiny (only 1 cell!) parasite that gets transferred to cattle by ticks. When ticks carrying Theileria feed on cattle, the parasite gets into their bloodstream and enters red blood cells. In some animals, sufficient red blood cells are destroyed to cause anaemia: there are not enough healthy red blood cells to carry oxygen around. This often presents as weak/slow cows with a drop in milk production. Often these cows have a very white or jaundiced (yellow) mucosae. In cows it is often easiest to check the mucosal colour in the vulva (should be pink) or the third eyelid (should be white).

This week we had quite a few queries about Theileria, ticks and treatment, so here is a short refresher:

  • Ticks are present everywhere in the Waikato and so is Theileria. Cows under stress (calving, peak lactation, dry off etc) are most susceptible and that explains why we are seeing quite a few cases currently!
  • Cows that are sick now, have been infected by a tick bite 4-6 weeks ago.
  • Treatment: reducing stress (once a day milking, minimal walking, adlib feeding, gentle handling) is the MOST important treatment for affected animals. Engemycin has been used in the past with minimal success.

Ticks only spend about three weeks out of the year on cattle (they mainly live on pastures and also on rabbits, hares etc). Because tickicides have a limited duration of effect (3 to 6 weeks), it is unlikely that even with frequent tick application, Theileria can be totally prevented. Tickicides maybe useful in some cases, please contact your vet if you need farm specific advice.