South Africa experienced a particularly hot summer this year, with many parts of the country also having received good rain by the time this article was written. Unfortunately, hot and humid weather often goes hand in hand with health problems that can cause havoc in a herd.
Single-host ticks reach peak activity in late summer and autumn, and once ticks become active, anaplasmosis, or tickborne gallsickness as it is commonly known, is one of the possible results.
Dr Jan Vorster, a veterinarian at Kathu Animal Clinic, says anaplasmosis is a common disease among cattle and can initially cause sudden mortalities. Fortunately, the use of modern, long-acting methods of tick control has made the incidence of anaplasmosis less prevalent.
The disease is caused by a tickborne blood parasite that attacks the animal’s red blood cells, eventually leading to anaemia and jaundice.
“Adult animals usually develop the clinical disease and it is often only contracted by a few individuals in the herd. A farmer who is quick to accurately diagnose the disease, can pull his herd through without much difficulty. However, if he fails to act in time, mortalities can be expected.”
Transmission of the disease
Under natural conditions anaplasmosis is transmitted via five different tick types. Ticks become infected when they feed on animals carrying the anaplasma parasites. Animals previously infected with anaplasmosis and which developed resistance, can remain lifelong carriers. In this way the ticks transmit the disease from one animal to the next.
As stated in a technical article by Drs Faffa Malan and Jan du Preez, the spread of this disease cannot be blamed solely on ticks. Anaplasmosis can be transmitted in other ways, especially in dairies and feedlots where there is close contact between animals.
Blood-sucking flies, such as stable and horse flies that feed on various animals at short intervals, can transmit the infection. It can also be transferred mechanically from one animal to the next through syringes and tattoo needles containing fresh infected blood. However, these methods of transfer can be controlled by practicing good farm management.
Signs of disease
There are various signs of disease that may indicate anaplasmosis infection. Fluctuating fever, anaemia, jaundice, a non-functioning rumen and constipation are all signs of this disease.
A drop in milk production is one of the first signs of anaplasmosis in dairy cattle. Calving stress or high demands placed on dairy cows in terms of milk production, can lead to repeated attacks of anaplasmosis in animals that had previously built up resistance.
According to Dr Vorster, there are two definite signs that demand attention. “Study the mucous membranes in the animal’s mouth. Pale membranes are indicative of anaemia, and jaundice may develop at a later stage. If the rumen slows down and/or stops, droppings become smaller, dry and hard. These signs require attention.”
However, these signs can be confusing and often the disease is confused with redwater. Dry manure can also be mistaken for dry gallsickness, and jaundice is frequently associated with plant poisoning. He believes that all the symptoms need to be assessed in order to make the right diagnosis.
Management and treatment
Dr Vorster says there are several schools of thought regarding the control of anaplasmosis. Completely eradicating the tick infestation or population is one method, while others believe animals must be regularly exposed to low tick infestations to build up resistance. Although much more difficult and time consuming, preventative vaccination with available vaccines is a third method of control.
The following steps are necessary in the treatment of sick animals:
- Kill the anaplasma organism in the animal’s body with effective medication.
- Help the rumen to function properly by using on-farm mixtures or commercial products.
- Flush the accumulated bile from the animal’s liver using an effective remedy.
- Provide the animal with the building blocks to aid the development of new red blood cells.
Natural resistance
Young calves don’t usually exhibit clinical disease signs. If they do become infected early in their lives, they will build up resistance. In areas with enough infected ticks, calves up to nine months of age should be infected, depending on tick control practices. These calves will develop resistance quickly and will be ‘naturally immunised’ at a young age.
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Although it is possible to immunise calves through natural infestation, the influence that nature exerts on the tick population and their infestation levels, such as through rainfall, cannot be controlled. As a result, a vaccine must be used to immunise those calves that did not built up resistance at a young age. This will protect them from the effects of natural infection when they are older. – Koos du Pisanie, Stockfarm
For more information, phone Dr Jan Vorster on 053 712 3037.
