By the Late Peter Jackson of Animal Health Products/Environmental Health at Cooper Zimbabwe.
Theileriosis is a disease caused by protozoa called Theileria parva bovis which destroy white blood cells in the lymphatic system and the lungs. The degree of the disease varies in severity from an acute form where the cattle die after 2 to 3 days of illness to a mild form where symptoms may not be noticed. Up to 80% of visibly infected animals die. Recovered animals, whether treated or not, remain carriers of the disease for life.
How do Brown Ear Ticks Become Infected? – By feeding on carrier animals when at the nymphal stage, around August and September.; nymphal ticks feed, engorge, and fall to the ground to change into adults. Adults are ready to start feeding from November onwards. In other words, the infection is on the ground in certain paddocks or on certain farms where nymphal ticks have dropped from carrier animals during August or September. Ticks cannot walk far on the ground and so do not move from farm to farm except when carried on an animal
How can Theileriosis Spread to my Farm?
1. When carrier animals are introduced onto a farm and there are nymphal Brown Ear ticks on them. The infected adult ticks then feed on your cattle from December to March.
2. If carrier animals from neighboring farms stray onto your land and nymphal Brown Ear ticks on your farm feed on them or if carrier cattle bring nymphal Brown Ear ticks with them which drop off on your farm.
3. If your animals stray during the summer months onto a farm where there are infected adult Brown Ear ticks on the ground.
What Signs do Sick Animals Show?
The disease usually occurs between December and March and it may exhibit the following symptoms;
1. Animals become very sick and show signs of difficult breathing, which progressively worsens until the animal dies.
2. All superficial lymph nodes are swollen.
3. The eyes may be cloudy.
4. There may be signs of struggling on the ground.
5. Salivation (drooling) and lacrymation (abnormal or excessive secretion of tear).
What Samples Should Be Taken to Confirm the Disease?
The protozoa are found in the lymph nodes, spleen, and lungs, pieces of these organs and or smears from them should be submitted for examination to the Veterinary Department or a private veterinarian.
How can Theileriosis be Controlled?
- Control of the Tick Vector
All ticks have basically the same life cycle and go through the following stages: –
Egg → Larva → Nymph → Adult.
Adult female ticks, after mating on the host, fall off and lay eggs on the ground. The eggs hatch into larvae which feed, engorge and change (moult) into nymphs. The nymphs feed, engorge, and change into male and female adults. Flat adult ticks climb onto cattle to feed. The females increase approximately 50-fold in size before falling off to lay eggs. Brown Ear ticks moult on the ground. Therefore, each succeeding stage feeds on a different animal. The life cycle of these ticks takes approximately one year. Each stage becomes particularly active and numerous at a certain time. This means that the different stages of the tick are mostly seen at the same time each year. The peak periods of activity are roughly as follows:
- Adults December to March
- Larvae April to August
- Nymphs August to October
These ticks also have short engorgement periods. Each stage spends less than a week feeding on a host. Therefore, it is relatively easy to control them by effective short-interval dipping at the periods of activity of each of the three stages. It is particularly effective at the nymphal stage because these ticks are not inside the ear but are on the external surface of the head. They are also much easier to kill than adults.
Animals should be examined to ascertain when periods of activity begin.
If nymphs are not effectively controlled, and adults are numerous in summer:
– It is possible to eliminate Theileriosis from an infected farm by short interval dipping throughout the year for a number of years.
- Control of Animal Movement
– Avoid acquiring animals from Theileriosis-infected farms, as the presence of carrier animals in a herd is probably the most important fact in maintaining the threat of subsequent outbreaks. (This is almost impossible if you speculate since many commercial herds contain carriers.
What Treatment Must be Given to Sick Animals?
– Good nursing by providing food, water, shelter, shade and protection as well as injecting the anti-protozoal drugs such as BUPARVEX at the rate of 1ml/ 20kg body weight.
Theileriosis is still a NOTIFIABLE disease and any outbreak must be reported to the Veterinary Department. At present, Buparvex can only be prescribed by a Veterinary Surgeon and supplied by a Veterinary Surgeon or Pharmacist.
- Treatment with oxytetracyclines such as Coopermycin LA at a rate of 1ml per 20kg is recommended in addition to Buparvex.
- Coopermycin LA can be used alone in treating Theileriosis in low-grade infections but is not effective once they have a fever (40 deg celsius and above).
Do Cattle Build up an Immunity?
Cattle may develop an immunity, but it cannot be relied on for control. On many farms, the disease occurs year after year. The only reliable prevention is sound dipping and management using dips such as Triatix, Supadip, Decatix, Amitik or Spoton. In the event of an outbreak, farmers should move to 5-5-4 dipping to break the life cycle of infected ticks.
a) At a dosage rate of 1ml Spoton per 10 kg body weight apply from ear base to ear base, on the tail head and as a strip down each side of the midline from shoulder to rump.
b) Decatix must be diluted with water before use. Premix the required quantity of concentrate with approx. 10 times its volume of water. Add the mixture to the bulk of water in the dip tank or spray race sump.
The Department of Veterinary Services has developed a vaccine using a milder strain that provides immunity. At one time it was administered with a covering injection of tetracycline. With an adjustment in the dose, this is no longer necessary.
‘Vaccinated animals remain carriers after vaccination’
If there was a more virulent Theileria infection on the farm at the time of vaccination, vaccinated animals will also become carriers of the virulent strain without showing symptoms and they will be able to transmit it to a new generation of ticks. If vaccination is discontinued, this virulent strain will still be present in those animals and in ticks that have fed on them. Non-vaccinated animals and your neighbours’ animals are again at risk.
The article was reproduced with the kind permission of Cooper Zimbabwe. For more information on the control of Theileriosis, contact on 086 77 000 329.