The Persistence of Acaricide Resistance in Ticks in Uganda and the Fight to Address it
In the last decade, Uganda has been faced with an upsurge in tick resistance to multiple acaricides, an endemic issue that is decimating cattle population and productivity, especially in the cattle corridor. The three most fatal tick-borne diseases in cattle in Uganda are theileriosis/East Coast fever (ECF), babesiosis and Anaplasmosis. These three account for 89 per cent of cattle farmers’ disease control costs, with East Coast Fever cited by most Ugandan farmers as the number one challenge arising out of tick resistance to chemical acaricides.
The issue of acaricide resistance
Today, there are over 25 classes of acaricides on the market in Uganda including organochlorines, organophosphates, synthetic pyrethroids, formamidines (e.g., amitraz), macrocyclic lactones, fluazuron and fipronil, which have historically been used to control tick infestations in the country, continue to lose their effectiveness.
SP and Amitraz, considered the best acaricides for ticks in Uganda, remain the most widely used acaricides for tick control in Uganda, and account for over 88% of the acaricide classes marketed in the country.
In the absence of a clear policy and limited livestock extension services to guide farmers on the right choice, application and use of acaricides, farmers have been left to their own devices, leading to irrational application and general misuse of acaricides, factors that have contributed to their failure, and the emergence of ticks with a very high level of resistance to acaricides.
Acaricide resistance in ticks has now become a national emergency. For instance, in the Western regions of the country, at least 90% of the most economically significant tick species are multi-acaricide resistant including R. appendiculatus and R. decoloratus ticks, showing 0% mortality to popular acaricides including amidines, synthetic pyrethroids (SP), organophosphates (OP) and OP-SP co-formulations (COF).
More worrisome is their potential to contaminate cattle meat, milk as well as the environment, which has necessitated the need to find an immunological solution that does not generate residues that contaminate the environment, meat, milk or otherwise pose a risk to human and animal health.
The economic impact of acaricide resistance in ticks in Uganda
According to the Ministry of Agriculture and Animal Industry and Fisheries (MAAIF), Uganda imports approximately 370,000 litres of different acaricides annually, and 83,000 litres of anti-tickborne disease drugs. The country collectively spends UGX 300 billion to deal with ticks and tickborne diseases (TTBDs), most of which go to tick control in the form of acaricides.
This excludes the cost of fatalities arising out of tick-borne diseases due to acaricide failure. As ticks become resistant to multiple acaricides, it will only worsen efforts to control tick-borne diseases, leading to even more loss of cattle or production of milk or meat. At the moment, the country loses between 20 and 60 heads of cattle on a monthly basis in some districts, representing losses of between 48-60 million UGX per day, or 18billion Ugandan shillings per year per district.
The causes of acaricide resistance in ticks
Farmers, especially those in the Western and Central cattle corridors have continued to suffer major cattle losses due to the rise of acaricide-resistant blue and red ticks that continue to inflict serious productivity constraints, especially among farmers with exotic cattle and cross breeds. These specific ticks are behind two of the most common tick-borne diseases in Uganda - babesiosis, and Anaplasmosis.
The major causative factors behind acaricide failure against ticks could have arisen out of the farmers’ improper and irrational use of the commercial acaricides during application, arising out of desperation and, ignorance or limited knowledge. While some farmers use lower/ higher doses, others do not know how to prepare the chemicals and continue to apply them inaccurately.
This has resulted in several farmers increasing their acaricide concentration, over spraying, applying acaricides more frequently and acaricide admixing, including mixing of agrochemicals with acaricides or even use of crop pesticides to spray cattle against ticks as coping methods. The use of unregistered acaricides as well as fake agro-chemicals smuggled into the country has only worsened the challenge of acaricide failure.
In the absence of a clear policy and limited livestock extension services to guide farmers on the right choice, application and use of acaricides, the need to develop and/or adopt an alternative non-chemical method for control of ticks and tick-borne diseases, has become paramount.
An alternative immunological intervention such as vaccination, can advance the prevention and treatment of ticks and tick-borne diseases. Vaccination of cattle with anti-tick vaccines has been established to be a more efficient, environmentally safer, and economically sustainable alternative to the use of chemical acaricides for tick control. In many Latin American countries such as Mexico, Brazil and Cuba, anti-tick vaccines have reduced acaricide use by up to 80 per cent, halving tick populations by 50 per cent in the process.
Anti-tick vaccine breakthrough
The recent anti-tick vaccine breakthrough by scientists from the Anti-Tick Vaccine Development Presidential Initiative at the College of Veterinary Medicine, Animal Resources and Bio-security (COVAB) at Makerere University represents a much urgently needed intervention in Uganda and East Africa, directed towards the containment and eradication of acaricide resistant ticks.
With support from the Ugandan government, the veterinary scientists led by Dr. Margaret Saimo-Kahwa have developed a new anti-tick vaccine candidate – TicVac-U, which can induce an immune response in cattle against common tick-borne diseases in Uganda, via the activation of antibodies.
The vaccine has already successfully shown positive results by eliciting an immune reaction in cattle that makes it close to impossible for ticks to survive when feeding on cattle.
“As ticks feed and become engorged with the blood meal from vaccinated cattle, host antibodies damage tick gut walls, resulting in death or diminished reproductive capacity,” Dr. Saimo-Kahwa said.
In clinical trials, the recombinant anti-tick vaccine has demonstrated the capacity to significantly diminish the number of eggs laid by ticks, subsequently reducing the number of ticks.
It is anticipated that vaccination using the new anti-tick vaccine will safely control the major tick species in Uganda, especially R. appendiculatus and R. decoloratus ticks, two tick species responsible for almost 60% of the most notable tick-borne diseases affecting cattle production in Uganda, i.e. East Coast Fever (theileriosis), Babesiosis (red urine) and Anaplasmosis (gall sickness). The vaccine has already shown 86% efficacy against the R. appendiculatus tick, making it the first feasible vaccine for tickborne East Coast Fever in Uganda.
The anti-tick vaccine is currently awaiting upscaling of production at Alfasan Uganda, a vaccine production facility with cGMP compliance. After this, it will undergo final clinical trials in live field conditions for assessment in cattle before commercial vaccine production commences.
Once commercialized, TicVac-U will offer farmers in Uganda and other African countries where similar tick infestations have become endemic, an affordable yet safe anti-tick vaccine that will reduce the ever-growing costs of acaricides.
Critically, unlike acaricides, the vaccine represents an immunological solution that does not generate residues that contaminate the environment, meat, milk or otherwise pose a risk to human and animal health or other collateral effects on cattle. This is because it works by stimulating cattle's immune mechanism to fight against ticks and tick-borne diseases.
The new anti-vaccine is expected to boost livestock productivity in Uganda, increasing food security, and household income, by creating a multiplier effect on the general economy through boosting investment in the livestock sector.
Concluding remarks
The issue of acaricide resistance in ticks in Uganda poses major challenges to the country’s economy and the livelihood of most Ugandans. However, the rollout of the TicVac-U anti-tick vaccine will play a major role in providing a lasting solution that is not only effective but affordable and environmentally friendly. Vaccinating cattle with TicVac-U, the first Ugandan vaccine for treating Babesiosis and East Coast Fever signifies a major positive stride towards mitigating the growing problem of acaricide failure against the most economically significant tick species affecting cattle in Uganda.
