Understanding East Coast Fever–Tickborne Diseases in Uganda
Ticks are among the most important vectors of pathogens that cause some of the most devastating tick-borne diseases (TBDs) in the livestock sector in East, Central and Southern Africa. In Uganda, three tick species are responsible for 90% of cattle's most economically debilitating diseases. The R. appendiculatus tick is the most widely spread of these three. It causes East Coast Fever (ECF), a cattle disease that causes up to 100% mortality in untreated exotic European breeds and their crosses. It is responsible for 30% of the losses in calves of local zebu cattle in Uganda. East Coast Fever remains the most prevalent and economically significant tick-borne disease facing Uganda’s livestock sector, contributing to almost 60 percent of losses in beef production and 48% of losses in milk production. These kinds of losses are not sustainable for either farmers or investment in the livestock sector and the economy. This article provides an in-depth overview of East Coast Fever, its causative agent, regional distribution, clinical signs, as well as new control and preventative measures anticipated to help farmers safeguard their livestock herd, including a look at TicVac-U, the new candidate vaccine for tick-borne East Coast Fever.
An overview of East Coast Fever
Bovine theileriosis, which is another name for East Coast fever (ECF), is a tick-borne cattle disease, the most widely spread and economically significant of the tick-borne livestock diseases in Uganda. It is enzootic and still endemic in 13 African countries across the East, Central and Southern Sub-Saharan region, including Kenya, Tanzania, Rwanda, Burundi, Malawi, Zimbabwe, South Sudan and the DRC.
East Coast Fever is caused by the protozoan haemo-parasite Theileria parva, whose principal vector is Rhipicephalus appendiculatus, the brown ear tick that remains the most widely distributed and economically significant tick species in Uganda.
The R. appendiculatus tick on its own contributes to almost 60% of losses in beef production and 48% of losses in milk production experienced by the livestock sector in Uganda. This is the attributable to value of controlling East Coast Fever, the disruption it causes to farming systems and loss in value to both animal and animal products due to the disease.
Mortality for East Coast Fever can be up to 100% especially for untreated non-native cattle and their crossbreeds, leading to very high morbidity and mortality rates among exotic European breeds, their crosses and increasingly on local breeds raised in a tick-free environment. It remains the leading killer of Uganda’s indigenous calves – contributing 30% losses in calves of local zebu cattle. Combating the deadly East Coast Fever disease has thus become a top priority for governments in endemic regions across Africa.
Distribution of East Coast Fever in Uganda
Since East Coast Fever is caused by R. appendiculatus ticks, its distribution overlaps the distribution of its principal vector. This particular tick species is prevalent in the western and central cattle corridor of Uganda, although it also occurs to a lesser extent in the Eastern region, which has traditionally been affiliated with A. variegatum ticks.
How does T. parva transmit East Coast Fever disease?
Hemoparasites such as Theileria parva are transmitted when an infected tick (that’s previously fed on an animal infected with these pathogens), inadvertently secretes them into a host’s blood along with the tick’s saliva during feeding (blood meal). The pathogens then infect the red blood cells of the animal and induce many of the clinical signs that are diagnosed as an ECF infection, such as swollen lymph nodes, hemolysis, fever, etc. The period between tick attachment to the cattle host and infection can be anywhere between 2-4days.
Immunohistochemical studies show that bovine mortality from East Coast Fever is brought about by respiratory failure arising from macrophage‐mediated vessel destruction. This leads to fluid leakage into surrounding tissues, including airways within the lungs (due to pulmonary oedema and restriction of lung expansion due to pleural effusion), a condition that results in respiratory failure.
The first symptom of this is that the animal begins to cough. In acute stages of East Coast Fever, the lungs become filled with fluid, froth filling the airways, which makes breathing very hard. Bovine death at this stage is precipitated by a mixture of choking and drowning, probably the most easily familiar sign of ECF at post mortem examination.
Clinical signs
What are the clinical signs of East Coast fever in cattle? Some of the clinical and diagnostic symptoms of East Coast fever infection in cattle include swollen lymph nodes, fever, listlessness, emaciation, discharge from eyes and nose, bloody diarrhoea, coughing and eventual respiratory failure as the disease progresses, followed by death in severe cases. Mortality usually occurs within a month of being bitten by an infectious tick.
It is worth noting that not all cattle that develop East Coast Fever succumb to death. Native cattle breeds such as the Zebu or Ankole are far less likely to die than exotic breeds (e.g. Holstein Friesian) and their crosses. Only between 20% and 50% of native cattle infected with East Coast Fever are likely to die, even when left untreated. On the other hand, up to 100% of exotic cattle may die, although cross-breeds show an intermediate degree of susceptibility.
Diagnosis and treatment
Diagnosis of East Coast Fever can be difficult because of the similarity of its symptoms to other tick-borne cattle diseases. A presumptive diagnosis can be made on the clinical signs, or microscopically on a bloodsmear. Lymph nodes of carrier cattle are usually greatly enlarged, making a lymph node smear also an effective option for diagnosis.
Animals diagnosed with East Coast fever can be treated with antiprotozoal parvaquones and buparvaquones drugs. However, treatment of East Coast fever of cattle with buparvaquone can be very expensive (one dose costs approximately US $10). Even with the high price tag, many ECF drugs are only effective if treatment is started early, making it critical that the disease is diagnosed promptly for effective treatment and management.
While treatment of East Coast Fever can be expensive, it is worth knowing that cattle that recover from the disease post-treatment are strongly immune to re-infection (at least with the strain of the T. parva pathogen with which they were infected).
However, the only challenge for farmers is that while cattle that have recovered are immune to re-infection, they are likely to remain carriers of the disease, capable of infecting ticks that feed on them. This raises the risk of East Coast Fever infection, especially among new calves and any other cattle that’s added to the herd.
Furthermore, ticks can survive for a long time on the ground without feeding, often up to two years. This means that even when cattle are dipped or sprayed regularly with acaricides and all ticks are eliminated, it can take up to 2 years to eliminate all traces of East Coast Fever infection from a farm. Farmers thus ought to remain vigilant of the risk of East Coast Fever, especially among new calves and any other cattle that are added to the herd, even when there has been no incidence of ECF cases for more than a year on a farm.
Control and Prevention of East Coast Fever
How do you control East Coast fever in cattle then? Control and prevention depend on two strategies: i) tick control using acaricide treatment and ii) vaccination.
i) Tick control of R. appendiculatus (brown ear tick) as well as other kinds of ticks in Uganda has been attempted mostly through chemical acaricide treatment. In the absence of a practical, low-cost vaccine against the lethal cattle disease East Coast fever, farmers in Uganda rely on using chemical acaricides to control tick populations, primarily through spraying and dipping their cattle.
The period between the time a tick attaches to a cattle host and ECF infection can be anywhere between 2-4days. So farmers have to dip or spray cattle at least twice a week so that ticks do not attach long enough to transmit ECF. But this is both labor-intensive and expensive due to the frequency with which acaricide application needs to be carried out.
It is this frequent dipping and spraying that has further led to the emergence of acaricide-resistant ticks, on top of challenges of acaricide contamination of meat, milk and the environment, and other risks to human and animal health or other collateral effects on cattle.
ii) Vaccination using an anti-tick vaccine offers veterinary scientists the ability to enhance or modulate the immune system of cattle, which carries unique promises for control and prevention of East Coast Fever.
The feasibility of using anti-tick vaccines to control and prevent tick-borne diseases has already been demonstrated with commercially available anti-vaccines such as TickGARD® (Australia), Gavac® (Cuba) and Go-Tick® (Colombia), which have successfully been used to control tick populations in their countries. But none of these works on localized ticks in Uganda.
In Africa, vaccination against East Coast Fever has primarily been carried out using live pathogens based on a 50-year-old infection and treatment technique known as the muguga cocktail treatment.
It is an outdated and very costly vaccine approach, with the cost of vaccination starting at US$ 7 per animal and rising to approximately US$ 40 per animal in cross‐bred dairy systems (making it cost 20 times more than other common livestock vaccines). It is also labor intensive, time-consuming to manufacture and requires a steady supply of liquid nitrogen for storage of the vaccine straws, making it impractical for adoption except in large-scale dairy systems, hence its limited applicability and adoptability by grassroots farmers in Uganda.
It is these limitations of current vaccination methods that highlight a need for a new vaccine solution to sustain long-term parasite control in localized environments.
“We’re struggling to control East Coast Fever in endemic areas across Africa. Acaricides are not working, and ticks are becoming resistant. The lack of a practical vaccine has forced us to develop a thermostable vaccine that is practical, user-friendly and low-priced,” Principal Investigator of the Anti-Tick Vaccine Development Initiative, Dr Margaret Saimo-Kahwa noted.
The Anti-Tick Vaccine Development Initiative, a collaboration by scientists from Makerere University College of Veterinary Medicine, Animal Resources and Bio-security (COVAB) led by Dr Margaret Saimo-Kahwa, has researched and developed a candidate vaccine to advance the prevention of East Coast Fever and other common tick-borne diseases in Uganda.
TicVac-U, as it’s called, works by stimulating an immune response in cattle via activation of antibodies. Once activated, the antibodies in immunized cattle incapacitate ticks' ability to feed, reproduce, and lay eggs, drastically reducing common ticks and their infestations in a herd.
“The candidate vaccine has already shown 86% efficacy against the R. appendiculatus tick, making it the first thermostable vaccine for tickborne East Coast Fever,” Dr. Saimo-Kahwa further commented.
Currently undergoing clinical trials before commercialization, successful targeting of ticks that cause East Coast Fever provides a strong rationale to continue further development and use of recombinant proteins as a sustainable, cost-effective and scalable alternative to chemical acaricides, drug treatment and the live attenuated pathogen infection and treatment technique.
Conclusion
East Coast Fever poses a serious threat not just to cattle health but also to the livestock economy it supports in Uganda. By understanding its cause, clinical signs, diagnosis, and management strategies, stakeholders, including farmers and the government, are better positioned to take proactive measures to protect cattle herds and the livestock industry.
The potential to immunize cattle with an efficacious candidate vaccine presents all stakeholders with an effective control and prevention measure that surpasses current control levels by chemical acaricides, drugs or other outdated vaccine approaches that are very expensive.
It is hoped that vaccination using TicVac-U can help maintain economic levels of tick control and endemic stability, while achieving consistent performance against R. appendiculatus populations in Uganda and around endemic regions in Africa, ultimately supporting the agricultural economy and food security in Uganda and other affected regions in Africa. That’s how success would be defined by the multiple actors working behind the scenes to make the vaccine available to farmers as soon as possible.
