Anti-Protozoal Drugs
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Antiprotozoal agents are a group of endoparasiticides against protozooses, including anticoccidial agents (coccidiostats) and trypanocidal agents.
In the UK the major group of protozoa of significant economic importance are the coccidia. As such the pharmaceutical industry have spent a lot of money developing anti-coccidial drugs to ensure that production isn't affected. This group of drugs will be the main topic on this page but other groups of drugs that have anti-protozoal action will also be discussed.
Anti-Coccidial Agents
It must be remembered that very few drugs are licensed to treat avian coccidiosis, toltrazuril is one of the exceptions. The following drugs are thus used to prevent infections occuring.
Ionophores - Monensin, salinomycin, narasin
- The most popular drug group to treat avian coccidiosis, they have been developed from the fermentation products of Streptomyces moulds.
- They work by allowing an influx of sodium ions into the sporozoite, this leads to a water influx. The sporozoite uses up all its energy trying to restore its ion and water balance, eventually structural damage occurs and the organism dies.
- They are particular useful for avian coccidiosis because:
- They suppress clinical and subclinical coccidia
- As the entire coccidia population is not destroyed it allows natural immunity to develop
- They reduce oocyst build up in the litter
- They exert little selection pressure on the coccidia and so resistance develops slowly
- Some of these drugs are highly toxic to horses, turkeys and gamebirds.
Other Agents
Numerous chemicals have anticoccidial activity; they include nicarbazin, decoquinate, robenidine, diclazuril, clopidol and halofuginone. All these drugs will either kill the coccidia or stop it from reproducing. These drugs must therfore be used with care as they have a high selection pressure on the parasites, which can result in resistance. For that reason a lot of these drugs are only liscensed in combination therapy.
Anticoccidial Programmes
The aim of these programmes is to ensure that the birds in question develop natural immunity, without their production being affected, whilst ensuring that resistance doesn't develop in the population. This means that continous use of the same drug can not be used.
A shuttle programme is the alternative. This means that in a bird's growing period it experiences a number of different drugs in sequence. These programmes try to balance risk, productivity and cost. They are obviously very complex and only skilled specialists develop them for use on poultry farms.
Other Anti-protozoal Drugs
- The antibiotic clindamycin and atovaquone (no license for animals) are used in man to treat Babesia infections.
- Complex chemotherapy protocols are used to treat Leishmania.
- Metronidazole is used to treat Treponema hyodysenteriae, Trichomonas foetus, Histomonas and Giardia.
- Fenbendazole is used to treat Encephalitozoon caniculi and Giardia.