Motile Protozoans are a real trouble maker when rearing. Alan Pearson examines this enemy of the gamekeeper.
Motile Protozoan parasites have long been a problem in the game bird industry, causing huge losses in some years. There are two organisms thought to be the main culprits: Hexamita meleagridis and Trichomonas gallinae. Some vet practices refer to this infestation as Spironucleus or Spironucleosis, while others refer to the condition simply as Motile Protozoans. Many keepers will refer to Hex and Trikes. Another organism, Blastocystis, is also sometimes mentioned in textbooks, but there appears to be no real evidence that this is a major player.
What are they?
Both Hexamita and Trichomonas are single-celled, independent living organisms. They are propelled around by whip-like strands of flagellae, which cause the organisms to be mobile, or motile. Hexamita lives in the small intestine and has a much more frenetic action, darting around like something possessed when observed under the microscope, while Trichomonas lives in the large intestine and caecum (the blind gut) and is much slower and laid back. In fact, some people have questioned whether it is perhaps a normal inhabitant of the bowel and only damaging when its numbers are vast.
Where do they come from?
Little is actually known about the life cycle of this organism, given that it is such a major player in the diseases of our industry. Very little research has been done, but work by the University of Cambridge with the Game & Wildlife Conservancy Trust has suggested that, contrary to the early idea that there was a cyst stage which allowed the organism to overwinter and survive, the life cycle appears to be simple. Organisms shed in droppings are directly transmitted, being re-ingested by following birds. The same work appeared to establish that the organisms don’t survive long outside the body and infestation rates dropped after pens had been rested for a few days, particularly in a hot, dry summer. The fact that this disease gets going in warm, wet months accounts for its regular occurrence in late July and early August, which according to meteorological data is one of the wettest periods. It has often been noticed that the disease is not a problem until the weather gets damp and the disease is worst in wet summers.
Depression, fluffing up, scouring and rapid weight loss with weight melting away from birds in a matter of days, producing that characteristic knife-edged keel bone: all are signs of Hex and Trikes.
If the bowel wall of the infected birds is examined, there is surprisingly little damage to the lining of the bowel. It remains somewhat of a mystery as to why these organisms affect birds so badly and so quickly. Again, work sponsored by the GWCT suggested that this is caused by the organisms blocking the bowel’s ability to absorb glucose and sodium.
In both pheasants and, to a larger extent, partridges, the disease is made worse if Coccidiosis is present at the same time, so it is vitally important to control this disease. We do have very effective drugs to control Coccidiosis, but unfortunately we are currently less efficient at treating the Motile Protozoans.
I unashamedly look to prevention before looking at treatment, because the prevention is often cheaper and certainly is often as effective as our limited drugs range and doesn’t put money into the vet’s wife’s dress fund.
We have already had some clues. We know that the disease is transmitted directly and therefore all forms of biosecurity should help.
Cleaning drinkers and feeders and moving them to clean, dry ground will help. One of our major clients has now used nipple bars in the rearing pens for some years now because the bell drinkers just get so filthy. The resting of pens – if only for a few days – has been proven to help. Moving to clean ground in each season will also help, though I am aware of the struggle for new sites that many keepers are under. We have found that the addition of feeders and supplementary drinkers helps, because the birds feel so poorly that they don’t want to walk to food or water; you sometimes have to literally put it in front of them. One of our clients has gone to rearing pens with three boards as the base before the netting, because it gives the birds more shelter and protection. The provision of protection and shade has also proved useful for birds that feel so awful that they don’t want to move all the way back to the main shelter. None of these provisions are going to break the bank in terms of cost, but may well reap benefits in terms of disease control. Finally, birds are like sheep in some respects. A bird’s worst enemy is its neighbour and the closer that neighbour is the greater the threat, so reducing stocking density is a great method for disease control.
Historically treated by Emtryl, when that drug was banned the industry had to face life without it. It actually coped well and work by Tom Pennycott at the Scottish Agricultural College proved that by using good biosecurity and reduced stocking densities the disease incidence did not rise and cause the major epidemic, welfare issues and general industry meltdown which had been predicted. In fact, the situation got better – which proved you could prevent this disease using the above measures.
In terms of the commonly used drugs, there are a variety being used. All are used under the veterinary cascade system, under which the vet can prescribe a drug which he considers safe and suitable according to a series of prescribed rules where there is no appropriately licensed drug.
Water based drugs
- Oxytetracyline (OTC): it has been long suggested that high doses of this drug would have an effect on the causal organisms. As with its actions on bacteria, it is a drug which slows down the organism rather than kills it
- Chlortetracycline (CTC): a very similar molecule with very similar effects
- Doxycycline: this is another cousin in the cycline family, which has been used over the last few seasons because it allegedly has a faster knock-down and is quicker to reach higher levels in the bird’s bloodstream
- Tiamulin: available from various manufacturers, its main drawback is that it is very bitter and unless great care is taken to sweeten the water to remove the taste, the birds may refuse to drink
- Electrolytes and glucose: research from the GWCT and Cambridge University suggested that the organisms affect the uptake of glucose from the bowel, so adding additional glucose and electrolytes is beneficial.
As with all water treatments the water should be clean and wholesome, drinkers should be clean and plenty of drinker space available close to the birds. The medicated water should be the only source of drinking water available. The uptake of water after rain will be reduced because the birds will drink off the grass rather than any peculiar-tasting medicated water. There are a lot of factors involved in successfully medicating via the water.
As with water medication, there are no licensed drugs for this condition, but a variety of drugs may be used in food under the cascade system.
- The ‘cyclines’ OTC and CTC: as per the water medication. They are available as food additives and are usually used at the highest dose that is considered safe
- Tiamulin: also available as a food additive and has been used with some success by a number of practices
- Aivlosin: the new product from Eco Animal Health. It was tried last season on a home mixed basis and the results were promising. We hope to conduct a more scientific trial this summer.
In-feed medication is the only method of treatment available once birds have been released. It must be borne in mind that sick birds may not eat and the medicated diet should not form the entire diet, and because of this treatment very often shows variable and often poor results. To try and avoid such problems, many keepers and poult suppliers will now medicate birds for both Coccidiosis and Motile Protozoans before delivery. I hope you all have a good rearing season! ν