Cattle ticks and Theileria

theileriaGeneral

  • The cattle tick (Haemaphysalis longicornis) is well established in New Zealand. They are more active in the warmer areas but have spread to other parts of both islands with the movement of cattle.
  • Blood-sucking ticks in low numbers on their own are not a serious threat to big healthy cattle, but animals in poor condition and calves can be seriously affected through loss of blood.
  • But an increasing number of farms are now carrying a protozoan parasite called Theileria, which is adding to the health problems caused by ticks.
  • You may not know if the ticks on your property are carrying Theileria until you see sick stock which are anaemic, lethargic, seem short of breath and pant a lot, have no appetite. They need urgent veterinary attention as they risk imminent death.
  • Favourite spots for ticks on cattle are on the ears, the rear of the udder and up in the crutch, and they are readily picked up on the dewlap as a beast moves through long pasture which ticks love to hide in and crawl up.
  • Ticks are easily killed on the animal with a specific pouron chemical, and after treatment they should be all killed and drop off in about 5 days.

Tick life cycle

  • The cattle tick is classed as a 'hard tick' and to survive they need to feed off their host's blood before each stage of the life cycle.
  • They favour cattle but can also infest deer, sheep, goats, horses, rabbits, hares, domestic pets – and humans.
  • Cattle ticks spend most of their life cycle in the dark and moist areas of the pasture, and only attach themselves to a passing host when they need to feed and complete their life cycle.
  • They usually complete only one cycle/year, but in warm conditions may complete more.
  • Cattle ticks are a '3-host' species, where they have to feed off three hosts (not necessarily of the same species) before completing each stage of their life cycle.
  • This cycle starts with mature male and female ticks (with 8 legs), fully engorged with their hosts' blood, mating, and the female producing large numbers of eggs.
  • An adult female full of blood can grow to 9mm long and 7mm wide.
  • The male dies soon after mating and the female dies soon after laying her eggs.
  • The 0.5mm diameter eggs hatch in the pasture (where they can remain for a long time) and after hatching develop into larvae with 6 legs. They attach to the animal and feed for up to 7 days or longer from late summer into autumn.
  • These larvae then drop back into the pasture and moult to develop into nymphs, 1.5mm long, and now back with 8 legs so are not easy to find or see on a beast.
  • Nymphs are 3mm long and feed on blood for up to 5 days, then grow into adults, which feed on the host for up to 7 days before mating and continuing the cycle. Fully fed they are 6mm long.
  • To get best benefit from the pouron chemical, veterinary advice is to treat cattle to kill nymphs in August, adults in November, and larvae in February. The recommended product kills ticks at all stages of their life cycle, as well as inhibiting egg laying or making eggs infertile.

Theileria life cycle

  • Theileria is a protozoan, which acts as a parasite spread by the saliva of ticks as they suck the host's blood.
  • This protozoan Theileria orientalis (ikeda) is the one currently causing problems and spreading south in New Zealand cattle. In veterinary terms – the disease is called 'oriental theilerisosis'.
  • Protozoans are single celled organisms like lumps of jelly, that reproduce by budding off more lumps through a series of complex stages of 'multiple fission'.
  • They get into the beast's red blood cells via the white blood cells where they do damage while feeding causing severe anaemia, which leads to other signs such as lack of appetite, lethargy and even death.
  • This is especially dangerous for stock that have not been exposed before to ticks with Theileria.
  • It's a very clever bit of biology where the life cycle of Theileria goes on inside the tick life cycle, so even if the host dies, the protozoan still lives on in some stage or other in the tick.
  • The Theileria parasite can not go through the eggs in the tick cycle, so eggs in the pasture are a 'dead end' to the cycle, making female ticks and larvae the critical stages in the annual spread of Theileria.

Examples of problems

Case 1. The farm had ticks with no problems. Mature steers were sent to the works and the stock agent delivered some more to replace them. Two school calf club calves (in a matter of 2-3 weeks) got very sick, and vet tests showed it was Theileria.
The parasite must have come in with the new cattle. The stock agent and vendors knew nothing about Theileria. They were both surprised and shocked!

Case 2. A sharemilker had Theileria confirmed and knows that it came from a sharemilking neighbour who (unknowingly) brought a herd down from Northland with it to join other cows he had for a larger contract job. Theileria has now spread to the 5 neighbouring farms. The owner of one infected herd has spent a fortune on pouron and antibiotics trying to keep the cows alive, and the worst hit neighbour has lost 20 odd cows from it so far. Worse may come later. They were dying even after having had blood transfusions at $600/cow.

Legal worries/questions. If you receive 'diseased stock' confirmed by a veterinarian, could you sue for damages, or if you were proved to be the source of the disease spread to a neighbour or purchaser of stock, could you be sued for damages?
The outcome of all of this could be very expensive, so it could be a good idea to increase your personal liability insurance.

The best you can do at present

You do NOT want ticks coming on to your farm carrying the Theileria protozoan. Once the disease (theilerisosis) is established in your tick population – then you have it forever, and can only rely on the animals' natural immunity building up to protect them from losses in the long term. There could be severe losses in the short term.

  • Find out if your farm has ticks by close inspection of your cattle, other stock and pets on the farm.
  • If your farm has ticks, you won't know if they are carrying Theileria. Assume they do!
  • Find out if there have been any sick stock around your property or on other farms, and if owners know their stock have ticks. If Theileria is in the area, the chances are that they do have it, and the risks will be high that it will spread to your farm.
  • For all stock coming on to your property (purchased bulls, leased bulls and returning heifers) they should be treated for ticks at their source (if possible) a week before leaving, and held on your farm in a quarantine area with short grass for at least 2-3 days.
  • If you cannot arrange this, they will have to be treated on your farm and held in quarantine for longer (5-7 days).
  • Inspect them daily to make sure they were treated correctly, and all ticks are dead before releasing them to other paddocks.
  • If you are not sure if the ticks are dead, check with a veterinarian.
  • Discuss with your veterinarian what actions are needed to treat any other animals on the farm (e.g. goats, horses or deer) that will harbour ticks.
  • You will need to kill all pests and vermin, and keep a regular check on pets for ticks and seek veterinary advice on treatment.

Treatment of sick animals

Discuss possible options and necessary actions with your veterinarian. These will include:

  • Treating animals at appropriate times to kill the ticks currently infesting them.
  • Sick animals will lose their appetite; so will need extra nursing to encourage them to keep eating. Offer them plenty of palatable concentrates.
  • They will need clean water and shade and not be stressed in any way.
  • The real key is to their recovery is for their natural immune system to kick in and start to repair the damage done by the Theileria.
  • Mineral supplements are known to help immune development in young cattle up to 10 months of age, and will boost immune systems of mature stock.
  • Some farmers claim success with homeopathic treatments.
  • Whatever you do for infected stock, recovery will take time, depending on how fast their immunity reacts.
  •  It's a bit of a dilemma, as if a cure depends on the animal using it's own immunity to build it back to health, then giving it a chemical pouron to kill the ticks may not help, and could indeed act as an immunosuppressant and compromise the cure.

Legal worries/questions

If you receive 'diseased stock' confirmed by a veterinarian, could you sue for damages, or if you were proved to be the source of the disease spread to a neighbour or purchaser of stock, could you be sued for damages?

The outcome of all of this could be very expensive, so it could be a good idea to increase your personal liability insurance.

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