At the end of January The Zimbabwe Herald carried a report on an outbreak of tick-borne “January disease” (East Coast fever) in the north-eastern sector of the country. The report stated that 2 000 cattle had died of the disease. The actual number of deaths was probably higher.
The Herald quoted Zimbabwe’s Chief State Veterinarian Dr. Josphat Nyika as urging farmers to be more diligent about regular dipping, to which the farmers replied angrily that the state dip tanks were empty and had been for some time.
EFFECTS OF EAST COAST FEVER
East Coast fever (ECF) is a tick-borne disease that kills more cattle than any other disease in sub-Saharan Africa. As far back as 1992 Prof. Adrian Mukhebi, a Kenyan agricultural economist, calculated that ECF killed 1.1 million cattle every year in the sub-region. Some reports state that an animal dies of ECF every 30 seconds.
In 1999 financial losses caused by ECF in the region were given as US$300 million (R3.5 billion) (Mcleod and Kristjanson).
It is more than 20 years since these reports were published and the figures could be a great deal worse now. Although there is also the possibility that ECF has kept herds from growing and the numbers could have remained static.
However shocking they may be, these statistics do not reflect in a meaningful way what it means to a farmer to watch his cattle die and know that he is losing his livelihood.
WHERE EAST COAST FEVER OCCURS
This disease is endemic to parts of eastern and central Africa; Kenya, Tanzania, Zambia, Uganda, Mozambique, Zimbabwe, Burundi, Rwanda and the Central African Republic.
A disease is endemic to an area when that area has a permanent source of infection. In other words, these are places where cattle farmers must always expect an outbreak of ECF.
ECF occurs locally in Botswana, the Democratic Republic of the Congo and Swaziland, but outbreaks remain contained.
WHAT IS EAST COAST FEVER?
ECF is a disease caused by a protozoan (one cell) parasite, Theileria parva parva, which is transmitted through the saliva of the brown ear tick (Rhipicephalus appendiculatus) soon after the tick has attached to the animal.
The first part of the protozoan parasite’s life cycle happens in the gut of the tick and the second part in the lymphoblast cells of cattle. Lymphoblasts are immature white blood cells found in the lymph system.
White blood cells produce antibodies against disease, and attack invading foreign micro-organisms. ECF causes the spread of infected cells throughout the lymph system of cattle.
The brown ear tick, is an ectoparasite (on the outside) and the ECF vector (transmitter), and the protozoa, an endoparasite (on the inside).
The ECF parasite is the more dangerous of the 2, with mortalities from ECF often reaching 100% of an infected herd. The ECF parasite uses cunning and aggressive survival strategies.
Once it has invaded, through the tick saliva, it enters and infects the cells of its new host. There, it transforms infected cells so that they multiply in a rapid, uncontrolled manner, not unlike aggressive forms of cancer.
ECF has an incubation period of between 10 and 15 days, and death occurs between 18 and 30 days.
THE SIGNS AND SYMPTOMS OF ECF
- Adult animals that have survived in areas where ECF is endemic must have acquired some form of immunity to the disease.
- The real danger is to the calf population.
- From about 4 months calves lose the antibody protection passed on by their mothers, and it is then that they are likely to become victims of ECF.
- Brown ear ticks are the only vectors of ECF and their presence on cattle is a red alert to farmers looking out for the disease.
The early symptoms of ECF are a high temperature and swollen lymph glands. Temperatures between 38.3°C (101°F) and 38.8°C (102°F) are normal in calves. Temperatures above normal are a problem. Every stockman should have a thermometer and know how to take a temperature.
Click here to learn how to take your calf’s temperature correctly.
When an animal faces a disease threat, the glands, which could be called the stations of the lymph system, swell. We’ve all experienced this at one or other time; for instance a sore throat usually comes with swollen glands under the ear.
In the case of ECF, the parotid glands below the ear swell first because they are closest to the infected tick bite or bites, since the brown ear tick likes to congregate in the ears of the animal.
Swelling follows in the prescapular lymph glands, in front of the shoulder, and the prefemoral glands in front of the upper part of the back legs.
Click here to watch a Youtube video about the clinical signs of ECF.
The sick animal loses interest in feeding and may suffer from diarrhea. Breathing becomes difficult and labored because of fluid build-up in the lungs. The eyes are weepy and cloud over, and there are mucous and frothy discharges from the nose.
Animals die of respiratory failure caused by pulmonary edema, an excess of fluid in the lungs.
If the parasite gets into the central nervous system, blocked capillaries in the brain inflict neurological damage and cause the animal to turn continually – a symptom called “turning sickness”.
The problem with ECF is that once these symptoms are obvious, it may be too late to save the animal. There are drugs on the market that can successfully treat ECF but they are expensive, and they must be given early on if they are to succeed.
Next: Control and treatment of ECF