Last update: April 2, 2012 02:10:00 PM E-mail Print

 

COXY BECOMES A SEVERE PROBLEM IN INTENSIVE FARMING CONDITIONS

 

G.F. Bath

Regional Veterinary Laboratory

Middelburg

 

 

Coxy is the popular term for the disease Coccidiosis, which is caused by a group of parasitic, single-celled, microscopic organisms most of which belong to the Eimeria group. These organisms are parasites of mainly the intestines, and many different species are found which all have a certain preferred host range. Some parasites have a fairly wide range, while others may be only found in a single species of host animal. Coxy is found locally particularly in Angora goats, but has also often caused problems in sheep and even cattle. In order to understand how and why they cause disease, and also to understand how control of the parasites must be approached, it is necessary to know something of their life cycle.

 

Life Cycle

Coccidiosis begins when an animal eats the matured "egg" of the parasite. This egg contains 8 smaller bodies, which are each capable of infecting the host. After being swallowed, the "egg" bursts open in the intestinal tract of the host animal, and the smaller bodies are released to invade individual cells lining the gut. These structures grow and multiply in a vegetative (non-sexual) manner until large bag-like structures (called schizonts) are formed. These mature to form little bodies just like the ones which invaded the host initially. When the process is complete, the host cell ruptures and the small bodies emerge to infest other cells. This process may be repeated for 1-4 generations, each time the number of small bodies coming from the original "egg" becoming progressively greater. They therefore destroy millions of gut cells.

This process of reinfection is however not indefinite and after a fixed number of vegetative cycles (depending on the species of parasite) the small bodies on their final invasion, undergo transformation to either large female cells, or cells which produce small male cells. These male cells invade the host cells once more. Those entering cells, containing the female counterpart, will merge to form a proto-egg, and this after development is released to pass out in the dung.

Outside the body the eggs can mature to form the small bodies inside the egg once again, provided moisture and temperature conditions are favourable. This maturation can take from one day to two weeks, and must be complete for the successful reinfection of another host animal. The time between eating the egg to passing of the first eggs in the faeces by the host is about two to three weeks, but this varies with the particular parasite and host. The life cycle is illustrated in the accompanying sketch.

 

 

It must be remembered that normally the animal will be consuming eggs daily over some time and the "waves" of infection at different stages will follow the life cycle pattern successively. Another important point in the life cycle is that one mature egg can, by the process of vegetative division inside the host, give rise to tens or hundreds of thousands of parasites which are each capable of eventually transforming into eggs. In some species of coxy over a million eggs can be passed in the dung, all of which originate from a single mature egg. This is not the rule, but it serves to illustrate how and why infections can build up so quickly and devastatingly. This situation can be contrasted with that of the roundworm parasites - here a single egg develops to a single adult, although the female worm may lay hundreds of eggs.

After a week or two following infection, the host will develop a resistance or immunity to that particular parasite but not to others (unless they were present as well). This is the usual course of events and most animals become immune without showing any signs of the disease. This immunity is usually permanent, but it can be broken down due to the presence of other disease, starvation, and stress.

Usually it is only under conditions of stress that coxy becomes a real problem, but in some cases no obvious cause of lowered resistance can be discovered.

 

 

Contributory factors

Coxy parasites are commonly found in small numbers in many healthy animals and their mere presence is not necessarily harmful. It is only when they invade the host's digestive tract in overwhelming numbers that the host is affected adversely. Since the parasite can be considered a normal and harmless parasite of the digestive tract under most circumstances, it is those animals harbouring parasites without systems that usually constitute the source of infection to susceptible animals. Sometimes, though, it is bedding, food or water which has previously been contaminated by carriers. Under the right circumstances the eggs can last under such conditions for many months outside the host.

By crowding animals together, as happens in feedlots, kraals and on irrigated pastures, the amount of contamination of fodder and water usually increases. This is particularly true when the feeding and drinking troughs are low enough

to permit contamination readily. Accordingly coxy is usually encountered under such crowded circumstances. Instead of taking in small numbers of eggs over a considerable period, the animals consume large numbers which then multiply so explosively that obvious disease results before natural resistance can develop.

One of the chief requirements for maturation of the egg outside the body is sufficient moisture. Therefore any factor which favours moist conditions and prevents drying of contaminated material also favours survival and maturation of the eggs. Leaking drinking troughs, moist conditions in feeding troughs, and irrigated pastures are some examples. Obviously open contaminated water can serve as the worst source of infection.

Another requirement for egg maturation is heat. At very low temperatures the maturation is slower, but survival is longer. This can be important in the survival of parasites and at low temperatures infection can lie latent for months. At very high temperatures the parasites are killed, but under moderately warm conditions the eggs mature very quickly and can result in a rapid, catastrophic build-up of infection.

The third requirement for maturation is oxygen. Water which is poorly oxygenated serves as a poor medium for the process. Under most conditions there is sufficient oxygen present and it is the other factors which determine how many eggs survive to maturity and how many eggs each animal may consume in a short period.

Lack of hygiene favours the build-up of infection. Drinking and feeding troughs which are never cleaned and disinfected, can become progressively more contaminated until they become highly dangerous. Water or feed spillage around troughs which is not cleaned up, results in another potential problem. In confined spaces like feedlots where dung accumulates and where edible weeds or grass still grow, this lack of hygiene can also cause problems. Similarly, bedding may become contaminated and subsequently eaten.

Young animals acquire infection from older ones and therefore mixing of age groups also favours the development of disease in the susceptible group.

 

 

Symptoms and Post Mortem

It is usually mainly the vegetative phase which does the damage to the intestine, although with some species of coxy it is the sexual phase of multiplication mainly responsible. Therefore in most cases by the time eggs are being passed in the dung in large numbers, the worst of the damage has already occurred.

The most general sign of coxy is purging, which can be seen as anything from very slightly soft dung to watery and even bloody diarrhoea. Usually several animals become affected at once, or else the disease rapidly spreads after the onset. It is usually almost only the younger animals (or newly introduced ones) which become affected. Sometimes up to 80 percent or more of a flock or herd can be affected. In most outbreaks the great majority recover, but sometimes there may be a high death rate. As a result of purging, the animals become listless, lose their appetite and condition. After prolonged diarrhoea dehydration, coma and death supervene.

At post-mortem examination, indicative signs include reddening of the intestines and watery bowel contents. The surface of the intestine is roughened inside and there may be characteristic white spots visible, especially in the later stages of the disease. The lymph nodes are usually swollen and watery.

Although a strong suspicion of coxy can be entertained if many or all of these symptoms are observed, it is not advisable to assume automatically that the problem must in fact be coxy. This is because there are many other specific diseases resulting in diarrhoea with all its attendant consequences, and which are not always easy to distinguish by the layman. Alternately even normal animals can have the characteristic white spots in the intestine, and not be suffering from coxy although the parasite is present. It is therefore advisable to have the diagnosis confirmed by the local veterinarian who will be able to distinguish other similar conditions and decide if coxy is the central problem or merely peripheral. Smears of affected intestine and dung samples may be useful specimens in confirming the diagnosis.

 

Control Measures

It must be emphasized straight away that many infections, including those causing diarrhoea or other symptoms, pass over and the animals become immune without any treatment whatsoever. For this reason one must be very cautious about reports of remedies or cures which are purported to have cleaned up an infection. Often the animals would have survived anyway.

Treatment must include removal of affected animals from the infected source of eggs, if this is at all possible. This prevents the development of further waves of infection. Animals should be transferred to a large, unoccupied camp immediately. If this is impossible then, a careful search for possible sources of infection should be made. Feeding troughs, drinking troughs and damp patches deserve special attention. Troughs must be thoroughly cleaned and disinfected and this must be done at regular intervals of only a few days. Any leaks in reservoirs and pipelines must be fixed and damp patches dried out, covered or fenced off.

Affected animals can be dosed daily for at least four days with one 9f the remedies to be discussed under prevention. Furthermore, they should receive a non-specific antidiarrhoea mixture containing, for example, kaolin, limewater and tannic acid. Those which have purged badly and are dehydrated, need fluid replacement which must also contain those salts which have been lost. These fluids or salts can be obtained from chemists, Co-operative Store or local veterinarian. Valuable animals should always be treated by a Veterinarian who can give life-saving intravenous fluids and other treatment. Antibiotic cover (like Tetracycline) is probably a wise precaution.

To prevent outbreaks of coxy, concentration of stock into kraals and feeding pens must be avoided as far as possible. Long-term and almost continual grazing or irrigated pastures is also dangerous, as it leads to a build-up of infection. All such areas should not be grazed or contain animals for indefinite periods, especially with the same type of animals. For example, goats, cattle and pigs could be alternated if it is economically essential to have animals present more or less permanently.

Another important way in which the infective challenge to susceptible animals can be cut down considerably, is by not mixing age groups of the same type of animal. It is nearly always the older animal, which may have picked up small numbers of parasites earlier but is still a carrier, which serves as a source of infection for younger animals which have had little exposure to the parasite and have therefore low or no resistance. Because young animals are most at risk, it is particularly advisable with them not to graze damp, irrigated pastures or to concentrate them into feeding pens.

Careful control of hygiene in the kraal or camp can be vital in preventing severe outbreaks. Troughs for drinking and feeding should be so designed and placed as to have a small chance of contamination by dung. It is probably wise to clean and disinfect them regularly in any case. This could be done once a week or even two or three times a week if severe problems have been experienced. Water must not be sluiced onto the ground and uneaten food may have to be discarded if contaminated. Leaks in drinking troughs or pipelines must be repaired and damp spots from any cause must be either eliminated or fenced off. It may be necessary to remove dung regularly and remove contaminated growing plants in feedlots.

Apart from these management aspects, there are specific substances, which if given orally, help to control Coccidiosis. It is vital to appreciate that these drugs only suppress the life cycle and do not cure in the normal sense. Therefore those who are tempted to rely on this preventative measure alone, are bound to encounter failure at some time.

These drugs must all be taken orally, usually daily for several days, to allow animals to develop resistance. They can also be included in the feed ration so that they are consumed on a long-term basis. The intensive battery poultry industry would be impossible today without these so-called coccidiostats in the ration. The decision on which drug and which method of intake (feed, water or dosing) to use, can only be taken with knowledge of the particular situation and circumstances on each farm.

The oldest drug still in use is Flours of Sulphur, which is generally only used in mild outbreaks. Latterly the large group known as the Sulpha drugs (e.g. Sulphanilamide, Sulphamezathine) has become widely used and several proprietary formulations, especially made for coxy control, are available. There are also other important drugs like Amprolium, the Nitrofuran, Zoaquin, Imidazole, which are also available for control.

It is however in the farmer's interest to consult his Veterinarian who will not only be able to make the right diagnosis, but will also be able to give specifically tailored advice on the correct management measures to be used, as well as the best specific drug and method of supply which will suit circumstances on the farm.

 

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