Dr Elifas N. Junias

Parasites like ticks and worms can develop resistance against drugs when dosed incorrectly.
Resistance means that the drug does not work effectively against the parasite anymore and the parasites continue to burden the animal, despite treatment. Anti-parasitic drug resistance is becoming a major problem worldwide and Namibia is not an exception. Communal farming areas tend to be particularly affected, due to a lack of knowledge about the correct use of anti-parasitic drugs and people taking advantage of farmers.
Deworming, sometimes also referred to as drenching, is the process of ridding animals off worms living in the animal’s body, with a dewormer (which is an anti-parasitic drug). Controlling these worms is important in order to prevent economic losses due to heavy worm infestations that can lead to both decreased production and reproduction. Certain internal parasites can also be zoonotic (lead to diseases in humans).

It now happens that lay-people, without any training or sufficient knowledge on parasite control are buying anti-parasitic drugs and walking around villages treating livestock. These people often choose the incorrect drug, they dose the wrong amount and they do not know when the treatment needs to be repeated. These individuals price as they wish, wasting the farming community’s money. In many instances the farmer does not even have a guarantee that the paid for drug was really administered, it could have been merely water.
When an animal is given a dose of dewormer, not all the worms necessarily die and surviving worms, having now been exposed to the drug, can pass on their resistant genes to their offspring, rendering the previously used dewormer increasingly ineffective on the farm in the future. In order to prevent an increasing number of resistant worms on a farm, with subsequent uncontrolled worm infestations and economic losses in future, one needs to:

a) Have good management on your farm.
This includes treating the right animals. Only animals clearly suffering from worm infestations should be treated and not blanket treatment to all animals every time. Your veterinarian or animal technician can help you with scoring individual animals and using a FAMACHA and 5-point system.

b) Choose the appropriate dewormer and deworming strategy (as advised by a trained animal technician, pharmacist or your local veterinarian). An example of a strategy often used to prevent resistance forming, is to rotate dewormers (from different chemical classes), to ensure you also kill genetically modified parasites that were not killed by the previous drenching.

c) Drench the chosen drug at the correct dose and give it at the correct frequency.
Anti-parasitic resistance in the communal areas primarily arise as a result of under-dosing the drug or giving diluted drugs; this means the animals get less drug than needed and the drug cannot work.

If parasites become resistant, farmers will spend money on drugs, which are not effective and their animals will fail to grow and reproduce, and even die. Therefore, its good practice to deworm your following the directions clearly outlined on the drug’s package insert, following directions given by a pharmacist or a veterinarian where the drugs were purchased. In this way, you will achieve maximum effects and it will be worth your money spent.
Veterinarians are there to assist farmers in making good choices for their animals on a daily basis, not just for crisis management. Parasite epidemiology plays an important role on which dewormers to use, and your local veterinarians that know the area and diseases in the area well, are best to advise you on which dewormers to buy according to your environment.

Some internal parasites are environment bound, for example, liver-flukes need low-lying, marshy ground, covered with water and snails to complete their lifecycle, which means deworming against them may not be a priority in areas without stagnant water. That professional knowledge is needed to avoid spending money on drugs, which are not essential in your herds.
Communal farmers training for both external and internal parasite control can be done during the time when animal health technicians together with their extension officers do compulsory vaccinations. Such training can include a practical demonstration of administrating drugs and discuss the decision making process.

I would like to use this opportunity to advise livestock keepers to make sure they get the right person to do the right work and give the right advice for their animals. You as a farmer can buy your own dewormers (and other anti-parasitic drugs) based on the advice of a knowledgeable person, and treat your own animals. This will save your money, it will save your animals and it will help prevent anti-parasitic resistance in future.
-elifasjunias@gmail.com