West Coast Fever

West Coast fever, also known as theileriosis, is a tick-borne disease affecting cattle, particularly in eastern and central Africa. It is caused by the protozoan parasite Theileria parva, which is transmitted by the brown ear tick, Rhipicephalus appendiculatus. The disease is a major constraint to livestock production, leading to significant economic losses due to mortality, morbidity, treatment costs, and reduced productivity.

The life cycle of Theileria parva is complex, involving both the tick vector and the bovine host. Ticks acquire the parasite by feeding on infected cattle. Within the tick, the parasite undergoes a developmental stage called sporogony, resulting in the formation of sporozoites. When the infected tick feeds on a new bovine host, it injects these sporozoites into the animal’s bloodstream.

Once inside the cattle, the sporozoites invade lymphocytes (a type of white blood cell). Inside the lymphocyte, the parasite transforms into a schizont, which multiplies rapidly, causing the lymphocyte to enlarge and divide. This process leads to widespread proliferation of infected lymphocytes throughout the animal’s body, particularly in the lymph nodes, spleen, and lungs.

Clinical signs of West Coast fever typically appear within 10-25 days after infection. Affected animals exhibit a range of symptoms including fever (hence the name), swollen lymph nodes, loss of appetite, depression, labored breathing (dyspnea), and a characteristic swelling of the parotid gland (located near the ear). Anemia, caused by the destruction of red blood cells, is also common. In severe cases, the disease can lead to pulmonary edema (fluid accumulation in the lungs) and death. Mortality rates can be very high, especially in susceptible cattle breeds and in areas where the disease is endemic.

Diagnosis of West Coast fever is usually based on a combination of clinical signs, microscopic examination of Giemsa-stained blood smears or lymph node biopsies to detect Theileria parva parasites within lymphocytes, and serological tests to detect antibodies against the parasite. Molecular diagnostic techniques, such as PCR (polymerase chain reaction), are increasingly used for rapid and accurate diagnosis.

Control of West Coast fever relies primarily on tick control measures, chemotherapy, and vaccination. Acaricides are used to kill ticks on cattle and in the environment, thereby reducing the risk of transmission. Chemotherapy involves the use of drugs, such as buparvaquone, to kill the Theileria parva parasite within the infected animal. However, chemotherapy can be expensive and may not be effective in all cases.

Vaccination offers a more sustainable approach to controlling West Coast fever. The most widely used vaccine consists of live, attenuated Theileria parva parasites, which are injected into cattle along with an antibiotic to control any severe reactions. This method, known as the “infection and treatment” method, provides long-lasting immunity against the disease. However, the vaccine needs to be carefully managed and requires cold chain maintenance, which can be a challenge in remote areas. Continued research focuses on developing improved vaccines that are more effective, easier to administer, and less reliant on cold chain requirements, ultimately aiming to reduce the devastating impact of West Coast fever on livestock farmers and food security in affected regions.