%

Overview of Coccidiosis
in Poultry
By Richard W. Gerhold, Jr., , Assistant Professor of
Parasitology, Department of Biomedical and Diagnostic
Sciences, College of Veterinary Medicine, University of
Tennessee

Coccidiosis is caused by protozoa of the phylum

Apicomplexa, family Eimeriidae. In poultry, most species
belong to the genus Eimeria and infect various sites in the
intestine. The infectious process is rapid (4–7 days) and is
characterized by parasite replication in host cells with
extensive damage to the intestinal mucosa. Poultry coccidia
are generally host-specific, and the different species
parasitize specific parts of the intestine. However, in game
birds, including quail, the coccidia may parasitize the entire
intestinal tract. Coccidia are distributed worldwide in
poultry, game birds reared in captivity, and wild birds. (Also
see Cryptosporidiosis.)

Etiology: +

Clinical Findings: +

Diagnosis: +

Control: −
Practical methods of management cannot prevent coccidial
infection. Poultry that are maintained at all times on wire
floors to separate birds from droppings have fewer
infections; clinical coccidiosis is seen only rarely under such
circumstances. Other methods of control are vaccination or
prevention with anticoccidial drugs.

Vaccination:
A species-specific immunity develops after natural infection,
the degree of which largely depends on the extent of
infection and the number of reinfections. Protective
immunity is primarily a T-cell response.

Commercial vaccines consist of live, sporulated oocysts of

the various coccidial species administered at low doses.
Modern anticoccidial vaccines should be given to day-old
chicks, either at the hatchery or on the farm. Because the
vaccine serves only to introduce infection, chickens are
reinfected by progeny of the vaccine strain on the farm.
Most commercial vaccines contain live oocysts of coccidia
that are not attenuated. The self-limiting nature of
coccidiosis is used as a form of attenuation for some
vaccines, rather than biologic attenuation. Some vaccines
sold in Europe and South America include attenuated lines
of coccidia. Research has shown promise for vaccination in
game birds.

Layers and breeders maintained on floor litter must have

protective immunity. Historically, these birds were given a
suboptimal dosage of an anticoccidial drug during early
growth, with the expectation that immunity would continue
to develop from repeated exposure to wild types of coccidia.
This method has never been completely successful because
of the difficulty in controlling all the factors affecting
reproduction of coccidia under practical conditions.
Although anticoccidial drugs have been preferred for
protection of these birds, vaccination programs are gaining
popularity. Better administration techniques and choice of
coccidia strains in the product are improving the feasibility
of vaccination in broilers.

Anticoccidial Drugs:
Many products are available for prevention or treatment of
coccidiosis in chickens and turkeys (see Table: Drugs for
Prevention of Coccidiosis in Poultry and see Table: Drugs for
Treatment of Coccidiosis in Chickens). Detailed instructions
for use are provided by all manufacturers to help users with
management considerations and to ensure compliance with
regulatory approvals.

Drugs for Prevention of Coccidiosis in

Poultry

Withd
Druga Use Level (% in feed)
Time (

Chickens Turkeys

&
Amprolium 0.0125– 0.0125– 0

Drugs for Treatment of Coccidiosis in

Chickens

Feed Use Level,

Withdraw
Druga or Treatment
Time (da
Water Duration

Amprolium Water 0.012%– 0

0.024%, 3– &

Anticoccidials are given in the feed to prevent disease and

the economic loss often associated with subacute infection.
Prophylactic use is preferred, because most of the damage
occurs before signs become apparent and because drugs
cannot completely stop an outbreak. Therapeutic
treatments are usually given by water because of the
logistical restraints of feed administration. Antibiotics and
increased levels of vitamins A and K are sometimes used in
the ration to improve rate of recovery and prevent
secondary infections.
MERCK MANUAL
'
Continuous use of anticoccidial drugs promotes the
Veterinary Manual (
emergence of drug-resistant strains of coccidia. Various
programs are used in attempts to slow or stop selection of
resistance. For instance, producers may use one
anticoccidial continuously through succeeding flocks,
change to alternative anticoccidials every 4–6 mo, or change
anticoccidials during a single growout (ie, a shuttle
program). While there is little cross-resistance to
anticoccidials with different modes of action, there is
widespread resistance to most drugs. Coccidia can be tested
in the laboratory to determine which products are most
effective. “Shuttle programs,” in which one group of chickens
is treated sequentially with different drugs (usually a change
between the starter and grower rations), are common
practice and offer some benefit in slowing the emergence of
resistance. In the USA, the FDA considers shuttle programs
as extra-label usage, but producers may use such programs
on the recommendation of a veterinarian.

The effects of anticoccidial drugs may be coccidiostatic, in

which growth of intracellular coccidia is arrested but
development may continue after drug withdrawal, or
coccidiocidal, in which coccidia are killed during their
development. Some anticoccidial drugs may be
coccidiostatic when given short-term but coccidiocidal when
given longterm. Most anticoccidials currently used in poultry
production are coccidiocidal.

The natural development of immunity to coccidiosis may

proceed during the use of anticoccidials in the feed.
However, in the production of broilers during a short
growout of 37–44 days, this may be of little consequence.
Natural immunity is important in replacement layer pullets,
because they are likely to be exposed to coccidial infections
for extended periods after termination of anticoccidial
drugs. Anticoccidial programs for layer and breeder flocks
are intended to allow immunizing infection while guarding
against acute outbreaks.

Anticoccidials are commonly withdrawn from broilers 3–7

days before slaughter to meet regulatory requirements and
to reduce production costs. Because broilers have varying
susceptibility to infection at this point, the risk of coccidiosis
outbreaks is increased with longer withdrawal.

Turkeys are given a preventive anticoccidial for confinement-

reared birds up to 8–10 wk of age. Older birds are
considered less susceptible to outbreaks.

The modes of action of anticoccidial drugs are poorly

understood. Some that are better known are described
below. Knowledge of mode of action is important in
understanding toxicity and adverse effects.

Amprolium is an antagonist of thiamine (vitamin B1).

Rapidly dividing coccidia have a high requirement for
thiamine. Amprolium has a safety margin of ~8:1 when used
at the highest recommended level in feed (125–250 ppm).
Because amprolium has poor activity against some Eimeria
spp, its spectrum has been extended by using it in mixtures
with the folic acid antagonists ethopabate and
sulfaquinoxaline. The primary use of amprolium today is for
water treatment during clinical outbreaks.

Clopidol and quinolines (eg, decoquinate,

methylbenzoquate) are coccidiostatic against early
development of Eimeria spp by inhibiting mitochondrial
energy production. Clopidol and quinolines have a broad
species spectrum and are sometimes mixed together for
synergism. However, resistance may develop rapidly during
extended use.

Folic acid antagonists include the sulfonamides, 2,4-

diaminopyrimidines, and ethopabate. These compounds are
structural antagonists of folic acid or of para-aminobenzoic
acid (PABA), which is a precursor of folic acid. (The host does
not synthesize folic acid and has no requirement for PABA.)
Coccidia rapidly synthesize nucleic acids, accounting for
activity of PABA antagonists. Although resistance to
antifolate compounds is widespread, they are commonly
used for water treatment when clinical signs are already
evident. Diaveridine, ormetoprim, and pyrimethamine are
active against the protozoan enzyme dihydrofolate
reductase. They have synergistic activity with sulfonamides
and often are used in mixtures with these compounds.

Halofuginone hydrobromide is related to the antimalarial

drug febrifuginone and is effective against asexual stages of
most species of Eimeria. It has both coccidiostatic and
coccidiocidal effects, but coccidia may become resistant
after extended exposure.

The ionophores (monensin, salinomycin, lasalocid,

narasin, maduramicin, and semduramicin) form
complexes with various ions, principally sodium, potassium,
and calcium, and transport these into and through biologic
membranes. The ionophores affect both extra- and
intracellular stages of the parasite, especially during the
early, asexual stages of parasite development. Drug
tolerance was slow to emerge in chicken coccidia, probably
because of the biochemically nonspecific way these
fermentation products act on the parasite. Recent surveys
suggest that drug tolerance is now widespread, but these
products remain the most important class of anticoccidials.

Some ionophores may depress feed consumption when the

dosage is above recommended levels. Primarily, this is the
result of reduced feed consumption, but the reduced
growth may be offset by improved feed conversion.

Nicarbazin was the first product to have truly broad-

spectrum activity and has been in common use since 1955.
Although not completely understood, the mode of action is
thought to be via inhibition of succinate-linked nicotinamide
adenine dinucleotide reduction and the energy-dependent
transhydrogenase, and the accumulation of calcium in the
presence of ATP. Nicarbazin is toxic for layers, causing
mottling of egg yolks, decreased egg production, and
blanching of brown egg shells. A 4-day withdrawal period is
required in broilers. Medicated birds are at increased risk of
heat stress in hot weather.

Nitrobenzamides (eg, dinitolmide) exert their greatest

coccidiostatic activity against the asexual stages. Efficacy is
limited to E tenella and E necatrix unless combined with
other products.

Robenidine, a guanidine compound, allows initial

intracellular development of coccidia but prevents
formation of mature schizonts. It is coccidiostatic when
given short term and coccidiocidal long term. Drug
resistance may develop during use. A 5-day withdrawal
period is needed to eliminate untoward flavor caused by
residues in poultry meat.

Roxarsone is an organic arsenical compound. It has

significant activity against E tenella and is used in
combination with ionophores to improve control of that
species. A withdrawal period is required.

Diclazuril and toltrazuril are highly effective against a

broad spectrum of coccidia. Diclazuril is used mostly for
prevention at 1 ppm in the feed, whereas toltrazuril is used
primarily for treatment in the water.

Resources In This Article +

Coccidiosis

Overview of Coccidiosis in Poultry

ALSO OF INTEREST

Tweets by ​@MerckVetManual
Merck Vet Manual Retweeted

National Geographic @NatGeo

Photo of the Day: Fox and Ice
on.natgeo.com/2irXpz0 #photography #pod

← →
Icelandic Fox Image | National Geographic Your Sh…
A blue morph arctic fox hunkers down in an Icelandic
blizzard in this National Geographic Your Shot Photo of
the Day.
nationalgeographic.com

Nov 17, 2017

Embed View on Twitter

Merck and the Merck Veterinary

Manual

Merck & Co., Inc., Kenilworth, NJ, USA is a global healthcare leader
working to help the world be well. From developing new therapies
that treat and prevent disease to helping people in need, we are
committed to improving health and well-being around the world.
The Merck Veterinary Manual was first published in 1955 as a service
to the community. The legacy of this great resource continues as the
Merck Veterinary Manual in the US and Canada and the MSD
Manual outside of North America.

DISCLAIMER

PERMISSIONS

PRIVACY

MERCK LICENSING
MANUALS
TERMS OF USE

CONTACT US

HUMAN HEALTH MANUALS

GLOSSARY

© 2016 Merck Sharp & Dohme Corp., a subsidiary of Merck & Co., Inc.,

Kenilworth, NJ, USA

# $