A talk by Dr. Ian Carmichael, B.V.Sc., D.V. Sc Melb, Chief Veterinary Parisitologist at the South Australian Research and Development Institute at the
Marsupial Society of Australia Inc. General Meeting, Thursday 21st May, 1998.

Coccidiosis has had a direct effect on everyone: - twenty or thirty years ago, chicken was an exceptional dish in Australia and was a similar price to lobster. This was because up until that time, it was not possible to intensively house and produce chickens due to persistent outbreaks of coccidiosis. The situation changed with the development of prophylactic drugs against coccidiosis, when it became possible to intensively breed chickens.

This development of drugs has not happened in relation to other animal industries nor in relation to Australian marsupials. 

The Life Cycle of Coccidia.    Genus Eimeria

 There are many protozoa in the Subclass Coccidia, but this talk will deal only with the Family Eimeriina, in particular, the Genus Eimeria. Within the genus Eimeria, there are hundreds of different species, which cause disease in mammals, birds and reptiles. Each species is identifiable by a particular size and shape, as well as by various other distinguishing characteristics.

 Coccidia are single-celled protozoan parasites and are more complex than either bacteria or viruses. Each individual egg cell, or oocyst, contains 4 internal bodies, each of which have 2 even smaller bodies within them, called sporozoites.

 Eimeria infect the body by ingestion y. Firstly, the egg or oocyst is ingested by an animal as it grazes. It then enters the intestine of the animal and its outer shell is digested by the normal gastric secretions of the animal. When this happens, the 8 sporozoites are released and directly invade cells of the villi, the actual lining of the gut wall.

 Here they produce a membrane around themselves and rapidly multiply asexually, by division, up to 800 or 900 times, to produce what are called schizonts. The infected cells in the gut wall rupture due to this massive production and this releases the enormous number of schizonts, which invade more cells within the gut wall and continue this process of rapid asexual reproduction. Each time a cell ruptures, it is destroyed and there is massive death of cells due to the extremely rapid and enormous production of the schizonts.

 After the second or third division, the schizonts invade further cells, where gametogeny, or sexual division, occurs. This simply means that each schizont becomes either male or female, with the males fertilising the females and the fertilised oocyts breaking out of the affected cells and passing out of the infected animal’s body in its droppings. Under suitable conditions, further division occurs in the soil and the oocyst becomes infective.

 The coccidia are now ready to be ingested and repeat the cycle.

 There is massive multiplication within and destruction of, body cells from a single organism and the period from initial infestation to death may be only three or four days. The infected animal suffers acute pain - as the coccidia invade the wall of the intestine, they cause the cells to slough off and the area becomes like a huge ulcer. As the disease progress, the outside of the intestine becomes red and swollen.

 There are no toxins produced by coccidia - the infected animals die of dehydration, due to the fluid loss caused by the disease and of shock, caused by the extreme pain.

 Coccidia are strongly host specific and while there is some sharing of parasites between kangaroos and wallabies, there are still species specific ones - that is, some will cause disease in one particular species of animal, but will not cause disease in another species.

 Many species of coccidia affect Eastern Grey Kangaroos, but not all of these coccidia cause serious disease in them. Some species may only cause a mild flu-like illness in the animals.

 The presence of coccidia oocysts in an animals’ dropping does not mean that the animals has been infected by the disease and conversely, animals may die without having either large numbers of coccidia, or many of the different stages of the them, in their droppings. The immature stages cause massive cell destruction which may kill an animal before the mature forms of coccidia even develop.

 Macropods are host to many coccidia species, which can be easily identified, but little information is available on which particular coccidia species cause actual disease, or at what particular stage in their life cycle this occurs. Other species of coccidia infest the liver, particularly of rabbits, but the importance of these parasites in macropods is not known.

 However, if there is a very high level of oocysts in an animal’s droppings, this is generally associated with disease. Oocyst counts can be 80 to 90 thousand per gram of faeces - this means 360 thousand would be present per teaspoon of dung.

 If you have macropods, you will have coccidia oocysts in the soil on your property.

 Factors affecting Oocyte Production

 Oocyst production may only need some small change to make it flare into clinical disease.
     - some species of coccidia are better breeders than others.
    - there may be some degree of competition within the gut between various coccidia species.
    - the degree of host immunity has an effect on oocyte development - while generally young animals are more susceptible than adults, if older animals which have never previously been exposed to coccidia are exposed at the same time as young ones, they also will become badly affected. In other words, no previous exposure whatsoever leads to disease infestation, just as adults tend to be sicker with chicken pox and measles than children do.
    - when there is “crowding” in the gut with high numbers of parasites, egg production of the individual coccidia species falls.
    - poor nutrition of the host increases their susceptibility.
   - some strains of coccidia from different geographical locations may be stronger than others.
    - geographical location may have a bearing - in some areas of Australia, animals are more likely to get ill than others. Cold, wet areas appear worse than hot dry areas.
    - climatic extremes, in particular cold, wind and rain, may precipitate outbreaks.
    - stress factors, while mainly based on evidence from mammals, are a very important factor in both mammals and birds, and it would appear that this is similar in marsupials. It is strongly suspected in kangaroos, but it can differ within species. While Eastern Grey Kangaroos are well known as “spooky”, or nervous animals and stress very easily, all macropods stress fairly easily.    Stress factors can act as triggers to increase susceptibility.
    - movement and transporting (In cattle, the longer the distance they are moved, the more there is an increase in the likelihood of them developing Salmonella.)
   - handling or disturbance by strangers
    - extremes of weather - wind, rain, heat, cold. (A clearly defined factor in mammals.)
    - changes in diet - these must always be introduced gradually.
    - specific types of food - e.g. unsuitable food.
    - crowding or overcrowding.
    - harassment, even if only mild, by other animals or children- noise or movement.
    - faecal contamination of food.
    - the size of the infecting dose - the higher number of oocytes ingested, the more likely it is than active disease will occur. It is never too late to move animals off contaminated ground.

Some species of coccidia live on the surface of the inner lining of the intestine and cause no problem. They are sloughed off naturally with normal body wear and are of biological interest only. It is only those parasites which burrow deep into the cells of the intestinal wall and rupture the nucleus of these cells which are of significance.

 While no work has been done in relation to macropod coccidia, it has been established that the coccidia species which affect chickens can last up to 20 months in the external environment.

It is suspected that macropod coccidia species, having evolved in a hot, dry country, may be capable of lasting much longer. It is known that wet, shady conditions help them survive. Certainly they have developed to cope with various ranges of conditions.

 The traditional disinfectants, Sulphuric Acid and Sodium Hypochlorite, hardly affect coccidia; indeed, they are used to clean them up for presentation for research. Ammonia appears to be the best disinfectant to use.

 It is illogical for a parasite to kill its host, as this only leads to self-extermination. Co-evolution over millions of years has brought about a certain balance between this parasite and its host.

 In normal circumstances, the parasite enters its host, reproduces, and drops out. Only if something extra happens is this balance thrown out to cause a diseased state in the host animal.

 Clinical disease is suspected to often follow confinement of animals and as this has been proven in the case of poultry, there is no reason to suspect macropods to be any different. Such enclosure may only be as little as enclosing an area with a fence, as in a Game Park, which, while they always try to provide ideal conditions, do not always provide ideal environments.

 Clinical Signs and Symptoms

    - there may be none at all - the parasite may be benign.
   - a failure to thrive - decreased growth rate, or poor weight gain.
   - on-going diarrhoea, which may be only mild, but could be prolific.
   - blood in the faeces - not always present - may be caused by other diseases, e.g. typhoid.
   - may be eggs in the faeces, but these are not always present.
   - may be little fragments of muscle or intestinal lining in the faeces.
   - great pain and shock.

It is suspected that recovered animals, like most animals, are carriers of the disease, but this is not necessarily a bad thing, as it stimulates immunity in the next generation. Recovered animals can, however, develop a recurrence of the disease.

Anti-Coccidial Drugs

 All such drugs currently available, such as the sulfonamides, are purely prophylactic - that is, they only help in its prevention, but once an animal has developed coccidiosis, there is no drug that will cure it. If a particular drug makes an animal well again, it was probably not suffering from coccidiosis.

 The prophylactic drugs available act against the asexual division by repressing the number of coccidia produced.

 To be of any use, prophylactic drugs must be used before and during periods of change - it is of no use to start them after changes to the animals’ lives.

 To be sure of giving animals the best chance of protection, they must be kept on the drugs all the time.


 Coccidia species differ in their ability to stimulate an immune response in an animal.

 While they may reduce the total number of coccidia present, circulating antibodies play only a minor role in protecting an animal. Local immunoglobulin A systems play some role in the lumen of the gut, but the parasites can evade this. The main reaction is cell-mediated in the gut wall. 

Attenuating (changing their level of virulence by weakening) parasites by the use of heat, cold and radiation have not worked. Strains can be attenuated successfully in chickens by passage through chick embryos in eggs, but this is not feasible in mammals.

The best option to date appears to be to expose young animals in the first few weeks of life to very low levels of virulent oocysts - the egg stage of coccidia.

 Selection is being done to find a species of coccidia in chickens which is precocious, that is, has fewer generations, so that there is not as much damage done in the gut. This would act as a live vaccine.


Eastern Greys are more prone to coccidiosis than other kangaroos.

 Field outbreaks can be triggered by overcrowding, stresses caused by flooding, inclement weather, shortage of feed, feed supplementation, contamination of feed (on ground) with droppings.

Outbreaks in captivity can be precipitated by any of the above stresses, or by strangers, changes to feeding or routine, transporting or relocating, confinement, lack of cleanliness or even by the stress of loneliness or separation.

 Any changes, no matter how minor, should be made slowly and the strictest of hygiene standards must be observed at all times - feed should never be placed on the ground but in containers, to prevent faecal contamination.

 Animals must be observed vigilantly and constantly to detect signs of stress.

“It is not going to be easy to develop a vaccine against coccidiosis. It is not going to be cheap and it may not even be successful.”

Dr. F.E.G. Cox, Division of Life Sciences, Kings College, London.

International Journal of Parisitology. January 1998.

 For the Questions and Answers section, Dr. Carmichael was joined by Michael O’Callaghan, Taxonomist, also from the South Australian Research and Development Institute.

 Questions and Answers about Coccidiosis

 Q. How long do coccidia last in the ground?

A. They may last for years. Other organisms which evolved in Australia are very tough, so coccidia probably are too. Oocytes can be dust-borne once they sporulate and the faeces break down.     Unless conditions are just right in Nature, they just lie there and build up. If animals are housed in small enclosed areas over a long period, oocysts are continually being built up.

 Q. If there are such a large number of coccidia, is it reasonable to think that they mutate in animals?

A. No. Species appear to remain consistent all over the world.   They may change, but this is more due to selection, not actual mutation.    They do not mutate like the flu virus does in humans.    Coccidia fossils have been found on Pearson Island which are the same form although they are 10,000 years old. There is no evidence of their mutating.

 Q. Does coccidiosis affect arboreal animals, such as possums and should you always clean feed trays?

A. Yes, it affects both possums and platypus, but the species involved are different to those involved in macropods and we don’t have any evidence of clinical disease.    Exposure is on the ground, when the animals come down to the ground or out onto land. All feed and water containers should be cleaned regularly.

 Q. Can you explain how no Reds, Damas or Euros have been affected, but Eastern Greys have?    There was no change in their diet or routine.

A. They may all have been exposed to the same parasite, but the Eastern Greys could have been more susceptible.    It could also be that that particular species was more dangerous to the Eastern Greys.

Q. Much research was carried out on coccidiosis from 1912 to 1972. What of the future?

A. The Australian poultry industry breeds 350,000,000 birds a year and has a turnover of $700,000,000.   The American industry even more. Despite enormous financial investment, they still have not been able to come up with a cure. It is hoped to be able to select a precocious parasite and introduce this as a living vaccine.

 Q. Can people get coccidiosis from macropods?

A. No. 

Q. If coccidiosis is host specific, is there one that affects both poultry and macropods?

A. No.   No poultry coccidia affects macropods.

 Q. Would soil differences, such as clay or sand, have any correlation on coccidia survival?

A. Coccidia have very good survival mechanisms, so it is unlikely, although moisture and overall season moisture may have some influence.   Fossils found have proved they can survive over eons.   Disease usually occurs when a large number of coccidia sporulate. If they are swallowed before they sporulate, they are harmless.

 Q. Would living in a hot, sandy area with a low rainfall make a difference?

A. Not much.   Kangaroo coccidia evolved in hot, dry conditions, so it is likely they are very tough, although moisture and shade do help their survival.   There may be taxonomical differences between species found in different areas as they have found in other animal parasites.

 Q. If you move animals to a new area, could that cause an outbreak?

A. Yes.

 Q. Does fire destroy coccidia in the soil?

A. We don’t know.   I suspect that fire would go right over the top of the coccidia which would be insulated in the dung, so it may very well survive.

 Q. If it is going to be a long time till anything is developed, can we only work to reduce stress and concentrate on hygiene?

A. Yes, this is all you can do. This is why we need the research.   We need to be able to recognise exactly which species of parasites are responsible for death and or disease.

Q. Could we develop a test kit for coccidiosis?

A. Aspects of immunity can be measured already. In the first week, there is a very high antibody level, which is gone by week four - but with coccidiosis in mammals and chickens, this doesn’t work.    Immunoglobulin A movement does not work with coccidiosis.    A test kit of any sort would need a great deal of work done on it.

 Q. Would colostrum substitute help prevent coccidiosis?

A. It would be of considerable benefit in decreasing other stresses and infections which may predispose young animals to coccidia.    Colostrum deficiency is a common cause of many diseases in young animals and a substitute is a good general immune booster. 

Christine Irving from Native Animal Network, who is a qualified laboratory technician with many years experience, stated that she and NAN’s President, Dot Berris, have been working on the subject for some five years now.    Over the last couple of years, she has been isolating, identifying and documenting coccidia in faecal specimens and has made the following findings over that time:

    - Red Kangaroos and Euros do not carry as many species of coccidia in their droppings as do Eastern Greys - Reds carry three species and Euros carry only one.
   - Reds and Euros carry the parasites without them being pathogenic (causing clinical disease) to them. Disease only occurs if the animals become overburdened with the parasites.
   - the isolation of many species from Dot Berris’s yard, two of which are pathogenic to Dot’s kangaroos.

Dot Berris stated that she has found that the immediate start of a high dose of Baycox as soon as clinical disease is suspected, gradually decreasing in dose, can help an animal survive. Baycox is no good once animals are symptomatic.  She also said she has found that Gamma globulin helps kangaroo joeys and Manfred Heide said he as found this helps wombat joeys, also. She said she has been investigating and experimenting with various treatments for coccidiosis for 8 years.

 Dot feels it is vital to follow the rules:- 

- know your animals well and watch them carefully. 
- if you even suspect one is sick - get Baycox into it in a high dose and fast. 
- watch all your other animals extra carefully if one of them becomes sick.
- do not ever feed them on the ground.
- be constantly vigilant and act quickly.

Q. I had a highly infected youngster, with many species of coccidia in its droppings, including cat coccidia, which I treated with Baycox.     Its droppings were clear from coccidia on the last faecal testing. Could you give a reason?

A. Baycox is “relatively” new and interferes with the sporozoite stage.   By giving it at such an early stage, it could well be helping animals survive.

 Q. Is coccidia self-limiting.

A. Yes. 

Q. Is coccidia part of the normal bowel flora?

A. Yes 

Q. How would we go about developing a register for all kangaroos who die from coccidiosis?

A. They would need to be clinically diagnosed, by autopsy.   Ideally, every vet, would have to submit a sample of their gut for analysis. 

Q. Coccidiosis seems to have been only more commonly diagnosed in the last ten years.    Would there be any tie up between this and climate changes?

A. I doubt it.    I think there is just much more awareness now.   There was much good pathology work done in 1927. 

Q. If animals are treated with Baycox, will they build up a resistance?

A. Coccidia have shown resistance to other drugs already, although this is more common in the poultry industry where there is high dose, on-going drug use. There is not a high concern that it will happen with coccidia in macropods. 

Q. Is it correct that most kangaroos seem to die of it at about 18 to 20 months?

A. I am not aware of this. 

Q. Is there likely to be the same level of immunity to coccidia in wild and hand-raised animals?

A. I don’t know.   To find out if orphaned and hand-reared animals have similar problems to wild ones, they would have to be compared at maturity.   You may be able to look into this, as you’ve said you already take surplus bucks and joeys from Cleland. 

I feel Dot’s actions are a perfect example of prompt and good action in animal care.    If you have a new animal coming in, you would be wise to isolate it, as you do not know what it carries. Kangaroos and Euros may be carriers, but may not be affected by the parasites themselves, maybe because they come from hotter, drier areas.    It is vital that you know your animals well and can detect small changes in them and act accordingly. 

I very much admire the work that Christine Irving is doing, as she is in the field and not in a laboratory and can do a lot of valuable work.    I would suggest that we all give her our full support in her research. 

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