Introduction

Coccidiosis is a common parasitic disease of broiler and broiler breeder chickens caused by single-celled protozoan parasites of the genus Eimeria which are commonly referred to as coccidia.

There are two types of coccidiosis, clinical coccidiosis in which the affected birds show typical symptoms of the disease, such as bloody droppings and increased mortality. The other type is known as subclinical coccidiosis because the affected birds do not show visible symptoms of the disease but when a random sample of birds is examined, the presence of the gross lesions and the parasite is found.

The objective for the prevention of coccidiosis in broilers is different from that of breeder replacements as in the former the objective is to prevent the infection from adversely impacting flock performance while on the latter the objective is to achieve solid, uniform and long-lasting protection against clinical disease for the entire life cycle of the breeders.

Coccidiosis in Broilers

In most cases, the feed (perhaps with the exception of the withdrawal feed) that broiler chickens raised in confinement consume is supplemented with anticoccidial drugs, so cases of clinical coccidiosis are not as common as those caused by subclinical coccidiosis. According to past field surveys coccidiosis remains the most frequently diagnosed subclinical disease of broiler chickens in the USA^1,2. This type of coccidiosis is more difficult to diagnose and treat because the affected flocks appear normal but their performance is usually substandard.

This is the main reason that broiler chicken companies hold "posting sessions" on a regular basis. A representative sample of birds (usually five per house or farm), from a variety of farms and ages are examined for the presence of subclinical diseases, since coccidiosis is the most common subclinical disease of broilers, these posting sessions are sometimes called “cocci checks”.

As long as broiler chickens continue to be raised in confinement under the current production systems, the presence of subclinical coccidiosis is not likely to change in the foreseeable future.

In addition, there are no new anticoccidial drugs being developed by animal health companies, therefore; prevention and control methods must be optimized in order to minimise the negative impact of subclinical coccidiosis on broiler flock performance. Vaccination of broilers is feasible and more common than it used to be although it has not been as widely adopted as in broiler breeders. Production of drug-free broilers, increased resistance to anticoccidials and re-establishment of drug sensitive coccidia have been cited as reasons for the increased usage of live coccidiosis vaccines in broilers³.

Coccidiosis in Broiler Breeders

The life cycle of broiler breeders is much longer than the one of broilers and therefore the approach to coccidiosis prevention is different. In broiler breeder chicks the objective is to ensure the development of long-lasting protective immunity against the main species of Eimeria that can infect broiler breeders. Therefore, the majority of breeder chicks in the USA are vaccinated at the hatchery for the prevention of coccidiosis⁴.

The goal should be solid and uniform protection against coccidiosis as early as possible. The ability to produce a good immune response varies by species, for the more immunogenic (able to produce protection quickly) species like E. maxima, two coccidial life cycles (see "The Coccidia Life Cycle" below) may be enough to induce adequate protection while for the less immunogenic species like E. necatrix, four coccidial life cycles may be needed to achieve the same level of protection.

Since not all the birds ingest a full dose of coccidiosis vaccine at one day of age, it is generally accepted that solid protection against coccidiosis must be complete by 10 or 12 weeks of age and therefore no treatments should be needed after the flock reaches this age.

Coccidia Life Cycle

The coccidia of chickens have a direct life cycle with one phase of the cycle happening outside the chicken (the egg-stage) and another couple of phases (the parasitic-stages) inside.

Chickens first become infected by ingesting sporulated occysts (infective eggs) of coccidia. In the case of breeder chicks, in most cases, the sporulated eggs are delivered by a spray cabinet at the hatchery in the form of a live vaccine spray. The chicks pick up the sporulated eggs while "preening" following spray-vaccination, preening refers to the instinctive behavior by which the chicks clean, dry and oil their own feathers.

Preening activity can be enhanced by adding a coloring agent to the vaccine spray, chicks respond well to colours like blue, green and red, these gave the best results for increasing preening activity. An additional benefit of adding a colouring agent is that the hatchery personnel can visually evaluate the effectiveness of the spray in terms of coverage.

Although colouring agents are known to increase preening activity (and therefore intake of coccidiosis vaccine), the most effective method used to favour preening activity of chicks following spray vaccination has been increased light intensity for a few minutes following vaccination. A primary breeder was able to implement a programme to enhance preening activity and ingestion of coccidiosis vaccine at their hatchery by increasing light intensity to around 93 foot-candles (1,000 lux) for a period of six minutes post-spray-vaccination⁵.

Only sporulated eggs are infective, live coccidiosis vaccines for breeder chickens contain a pre-determined amount of sporulated oocysts of the various coccidia species, the amount contained from each species has been determined to be sufficient to produce a good immune response. This is important because in order to produce solid immunity the sporulated oocysts must be first ingested by the bird and then replicated in the intestines a number of times and then passed again as unsporulated oocysts in the droppings, then the oocysts under proper conditions of moisture, temperature and oxygen will sporulate in the litter to be ingested again and the cycle repeated a number of times to induce protection against infection.

Previous reports⁶ indicate that chicken house temperatures between 68 to 90°F (20 to 32°C) and litter moisture between 30 and 40 per cent are conducive to adequate sporulation of coccidial oocysts.

Once ingested by the chicken, the sporulated oocysts are crushed by the mechanical action of the gizzard each releasing up to four cysts (smaller eggs) known as sporocysts⁷. Each sporocyst contains two infective parasites known as sporozoites, the digestive action of the pancreatic secretions present in the upper small intestine breaks down the outer wall of the sporocyst releasing the infective parasites which are now free to swim in the contents of the intestine where they remain until they find a cell of the intestinal lining that they can infect.

Once inside one of the cells lining the internal side of the intestine, the parasites multiply very quickly by a mechanism known as fission, these multiplication results in a large number of “daughter parasites” contained in a large body known as a schizont, when the schizont fills up with parasites it will rupture out releasing them into the internal side of the intestine and causing destruction of the intestinal lining.

When the parasites at this stage are viewed with a microscope, they are shaped like a banana and are known as merozoites. This process of multiplication by fission will be repeated two or three times, the first generation of “daughter cells” or merozoites is known as merozoites I, the second generation as merozoites II and so on.

The entire stage of multiplication by fission is known as the “schizogony” or asexual phase of the life cycle. As the cells lining the internal side of the intestine are infected and then ruptured, damage is caused to the intestine impairing its normal ability to absorb nutrients. As the damage also changes the permeability of the gut wall, proteins and fluids may leak into the intestine resulting in wetter droppings and favouring the growth of pathogenic (disease-causing) bacteria like Clostridium perfringens, the agent responsible for outbreaks of necrotic enteritis⁷.

One final stage of multiplication with more destruction of the cells lining the intestine still occurs, this final stage is known as the “gametogony” or sexual phase of the life cycle. During this stage, the “daughter cells” sexually differentiate producing two types of cells, the smallest ones are mobile and are known as microgametes, and are the equivalent of the spermatozoa, the larger ones are known as the macrogametes and are the equivalent of the ova. The microgrametes fertilize the macrogametes resulting in multiplication and more destruction of the intestinal lining and the production of immature oocysts which will be passed through the droppings onto the litter to complete the cycle⁷.

The intensity of the infection is controlled by the dose of vaccine administered at the hatchery which is sufficient to induce replication of the parasites and subsequent protection but low enough to prevent mortality or severe symptoms of disease⁸.

Important Coccidia in Broiler Breeders

In broiler breeder chickens, there are nine species of coccidia⁹, however, generally speaking only four of them cause most of the problems related to coccidiosis; these are E. acervulina, E. maxima, E. necatrix and E. tenella^10,11.

Each species of coccidia has a unique predilection for an area of the intestinal tract, for example, E. acervulina lesions will be found in the upper small intestine, while E. maxima and E. necatrix lesions will be located in mid-gut and E. tenella lesions will be found in the caeca.

It is important to know what type of coccidia is affecting the flock as the response to treatment may vary. The intestinal species (E. acervulina and E. maxima) are more susceptible to sulpha drugs, while the hemorrhage producers (E. necatrix and E. tenella) are more susceptible to amprolium^10,11.

Diagnosis of Coccidiosis

Since most broiler breeder replacement flocks are vaccinated against coccidiosis at the hatchery or those not vaccinated are started and maintained for a number of weeks on an anticoccidial medication until immunity is complete, clinical outbreaks of coccidiosis are not common. When an outbreak occurs it signals that something went wrong that interfered with proper development of immunity.

Nevertheless, following vaccination at the hatchery with a live coccidiosis vaccine, gross lesions for the various species will be observed at various times as the development of immunity progresses. Depending on the species lesions may be seen up to 35 days or even later for E. necatrix.

Remember that in order for the vaccine to produce protection against the disease, it must first cause the infection and replicate in the intestines a number of times. Along with the infection and replication, lesions will be found. Therefore, finding gross lesions in vaccinated birds should be expected and not a good reason to treat a flock. Treatment with an anticoccidial medication (even at low levels) may interfere with the development of active immunity, especially if the flock is treated early (during the first 14 days). The manufacturers of live non-attenuated vaccines for broiler breeders no longer recommend administering anticoccidial medications as a routine practice but only as a specific treatment option when needed.

Birds with clinical cases of coccidiosis frequently display depression, prostration, huddling under the heat source as if chilled, soiled vents and watery or bloody droppings. A more sensitive indicator of coccidiosis is pigmentation, when flocks of broilers or broiler breeders are affected by clinical and even subclinical coccidiosis, paleness may be the first sign that something is wrong and that coccidiosis may be the cause. Naturally, this sensitive indicator of coccidiosis may only be used in birds consuming feed containing natural pigments such as yellow corn or corn gluten meal.

In order to determine the type of coccidiosis affecting a broiler breeder flock, if obvious symptoms or mortality are present, then it would be desirable to examine a sample of birds showing symptoms or fresh dead birds.

The intestinal tract and the caeca should be examined from the outside as well as the inside for the presence of gross lesions typical of coccidiosis. Gross lesions caused by E. acervulina are usually the most prevalent and are usually confined to the upper small intestine (duodenum), although some times they may extend to the mid-gut (jejunum), these lesions can be identified by their unique appearance, consisting of white patches or transverse lines sometimes already observed from the outside of the gut but easily detected when the internal side of the gut is exposed and examined.

Gross lesions of E. maxima are found in the mid-gut and consist of multiple petechial (pin-point size) haemorrhages often seen from the outside, in addition, segmental ballooning or enlargement of the mid-gut with presence of orange-tainted mucous or blood in more severe cases may be noted. However, unless the lesions are typical or severe, they are harder to identify than those caused by E. acervulina, E. necatrix and E. tenella and therefore it is highly desirable to confirm its presence by identifying the presence of coccidial oocysts (eggs) in a scraping from the mid gut (ideally from an affected or suspected area) examined with the aid of a microscope. The presence of significant numbers of oocysts or other life stages of the parasite with the typical size and shape of E. maxima should confirm the gross diagnosis.

Gross lesions of E. necatrix are also found in the mid-gut and can also produce bloody contents but are relatively easy to differentiate from those caused by E. maxima because in addition to the ballooning of the mid-gut area and the pin-point size hemorrhages (dark dots) present on the external side there are also white dots intermingled with the dark dots ("salt and pepper effect"), these white dots are schizonts of E. necatrix that are large enough to be observed with the naked eye.

Another easy way to differentiate these species is by scraping the mucosa of the mid-gut and the caeca to detect the presence of oocysts, while both species produce lesions in the mid-gut the oocysts of E. maxima are found in the mid-gut while those of E. necatrix are found in the caeca.

Gross lesions of E. tenella are confined to the caeca and consist of the presence of haemorrhages on the outside or inside of the wall of the caeca, free-blood or a chocolate-coloured fluid content inside the caeca with a thickening of its wall or the presence of a large chore of cellular debris and blood. E. maxima, E. necatrix and E. tenella can kill birds so dead birds in a breeder replacement flock with increased mortality should always be examined for the presence of lesions compatible with coccidial infection.

When conducting “cocci checks” or evaluating mortality for typical lesions of coccidiosis, diagnosticians frequently score the lesions based on a system developed originally for the scoring of lesions by coccidiosis researchers, based on their creators, this system is widely known as the method of Johnson and Reid¹².

In this method, the severity of lesions is scored on a scale ranging from 0 (no visible lesions) to +4 (very severe lesions). The intended purpose of the Johnson and Reid method for scoring coccidial lesions was to achieve uniformity of lesion scoring among coccidiosis researchers, however, the system has been widely adopted by veterinarians, parasitologists and poultry health professionals examining chickens.

Keep in mind that because most flocks of broiler breeder replacements are either vaccinated at the hatchery or receive preventive medication in the feed until immunity develops, scores of +4 are seldom observed in the field. Keep in mind as well that although each species of coccidia is often reviewed separately, mixed infections are frequently found in the field.

Coccidiosis Prevention

Coccidial oocysts are extremely resistant to environmental conditions and disinfectant agents, therefore, eradication of coccidiosis from chicken houses by litter removal, cleaning and disinfection is not feasible.

Since the early 1950s, there have been two main tools to prevent and control coccidiosis in broiler breeder replacement flocks. Anticoccidial agents added to the feed have been used since 1954 and they are still used today although the most common method to protect breeders today is by vaccination with a live coccidiosis vaccine at the hatchery⁴.

Table 1 shows anticoccidials that are approved in the US for use on either heavy breeder or light breeder replacements, for accuracy always check the most updated copy of the Code of Federal Regulations (CFR). Other anticoccidials have been used too although they are not specifically labelled for use in broiler breeder replacements.

The first vaccine developed for vaccination of broiler breeder replacements has been available since 1952.

For many years, the use of live coccidiosis vaccines in breeder replacements in the US was minimal but with the introduction of better and more practical vaccination techniques like the administration by coarse spray cabinet at the hatchery that has produced more uniform administration and better protective immunity, their use has increased and today more than 80 per cent of total breeder placements rely exclusively on vaccination at the hatchery for the prevention of coccidiosis⁴.

Although the number of companies producing coccidiosis vaccines for broilers has increased from one to five, the number of companies producing coccidiosis vaccines for breeders remains at only two, this is probably related to the market potential when comparing sales of vaccines to broilers vs. breeders.

Table 2 shows the two vaccines that contain strains that may infect broiler breeder replacements and broiler breeders.

Coccidiosis Treatment

In spite of our best efforts, cases of clinical coccidiosis may occur from time to time. This could be due to a variety of reasons, for example, the feed mill may have inadvertently added an anticoccidal drug to a feed intended for a flock of vaccinated pullets. It is also possible that resistance to an anticoccidial drug might have developed or that something interfered with proper development of immunity.

Outbreaks of coccidiosis in breeder pullets may occur due to indirect causes, for example, birds immuno-compromised or with a deficient immune system (regardless of the cause) are more likely to suffer from outbreaks of coccidiosis, particularly when diseases like infectious bursal disease, Marek's disease, infectious chicken anaemia or feed contaminated with mycotoxins have depressed the immune system¹¹.

Keep in mind as well that if the conditions in the chicken house are such that will allow for the litter to be either too dry or too wet this will create problems of excessive challenge or insufficient cycling of oocysts. In both cases, breeder hen performance will ultimately be adversely impacted.

Regardless of the cause, an outbreak of coccidiosis should be resolved promptly to prevent losses to the producer. Pick as the treatment the drug that is most likely to be effective for the type of coccidiosis that you want to control, ensure that the water lines have been flushed and do not contain residues of other drugs or water-administered supplements (vitamins, electrolytes, etc.) that may be detrimental to the drug to be used.

Sulphonamides are more stable and effective at neutral to alkaline water pH; the required withdrawal periods vary among the sulphonamides, from five days for Albon (sulfadimethoxine) to 14 days for Poultry Sulfa (triple sulfa).

Likewise be mindful of label directions and withdrawal periods to ensure efficacy and avoid tissue residues.

Table 3 lists the drugs available for the treatment of coccidiosis in broilers and broiler breeder replacements, the manufacturer’s recommended dosages, duration of therapy and type of coccidiosis most likely to respond favourably.

Acknowledgements: The author wishes to acknowledge the valuable contributions of the following people: Dr Jose Juan Bruzual, Aviagen; Dr Charlie Broussard, Merck and Dr Brett Rings, Cobb.

References

1. Cervantes, H. 2002. Incidence of pathological conditions in clinically normal broilers from different regions of the USA. 51st Western Poultry Disease Conference, May 1-4, Casa Magna Marriott Resort, Puerto Vallarta, Jalisco, Mexico, p220-223.
2. Cervantes, H. 2006. Incidence of subclinical diseases and pathological conditions in clinically normal broilers from 3 production complexes sorted by sex and age. 143rd Annual Convention of the American Veterinary Medical Association and 50th Annual Meeting of the American Association of Avian Pathologists, July 15-19, Hawaii Convention Center, Honolulu, Hawaii.
3. Mathis, G.F. and C. Broussard, 2006. Increased level of Eimeria sensitivity to diclazuril after using a live coccidial vaccine. Avian Dis. 50:321-324.
4. Mosizek, B., M. Burlenson, I. Alvarado, L. Newman, J. Radu and S. Fitz-Coy, 2014. Recommendations for effective coccidiosis vaccination: An update on pullet and cockerel management. Annual Meeting of the American Association of Avian Pathologists, July 26-29. Convention Center, Denver, Colorado.
5. Anonymous. Shedding light on spray cabinet vaccination. Cocci Forum, number 11. p4-6.
6. Frazier, M.N., 1987. Controlling coccidiosis in replacements. Poultry Digest, September. p380-383.
7. Cervantes, H.M. 2008. Coccidiosis Control. Proc. North Carolina Broiler Supervisor's Short Course. April 17, McSwain Extension Center, Sanford, North Carolina.
8. Chapman, H.D. Technically Speaking: Essential Elements. Cocci Forum #12. p14-15.
9. McDougald, L.R. and S.H. Fitz-Coy. 2008. Coccidiosis, in: Diseases of Poultry, 12th Ed. Iowa State University Press. p1068-1085.
10. Bafundo, K. 1995. The use of live coccidial vaccines in broiler breeder pullets. Ross Tech, October 1995.
11. Hofacre, C.L. Combating coccidiosis in broiler breeders. Cocci Forum #6. p15-17,26.
12. Johnson, J. and W.M. Reid. 1970. Anticoccidial drugs: Lesion scoring techniques in battery and floor-pen experiments with chickens. Exp. Parasitol. 28: 30-36.

The author of this paper, Hector Cervantes, DVM, MS, Dipl. ACPV, Hon. MAM (Senior Manager, Poultry Veterinary Services, North American Region, Phibro Animal Health Corp. of Watkinsville, Georgia, US) presented this paper at the 2014 North Carolina Broiler Breeder and Hatchery Conference.

Further Reading

Go to a recent article on coccidiosis by clicking here.
More information on coccidiosis is available by clicking here.

March 2015