Occurrence and Economic Significance
Coccidiosis occurs world-wide and is a major cause of mortality
and suboptimal growth and feed conversion efficiency in immature flocks unless appropriate preventive measures are implemented.
The cost of anticoccidial feed additives and treatment is estimated
to exceed $300 million annually in all poultry producing areas of the world.
Transmission
The sporulated oocyst is the infective stage of the life-cycle.
Oocysts can be transmitted mechanically by personnel,
contaminated equipment, or in some cases, by wind spreading
poultry-house dust and litter over short distances.
Factors contributing to outbreaks of clinical coccidiosis include:-
-
litter moisture content exceeding 30% due to ingress of rain
or leaking waterers.
-
immunosuppression (Marek’s disease, IBD, mycotoxins)
-
suboptimal inclusion of anticoccidials or incomplete
distribution (poor mixing) in feed.
-
environmental and managemental stress such as
overstocking, inoperative feeding systems,
insufficient ventilation.
Clinical Signs
Coccidiosis is generally acute in onset and is characterized
by depression, ruffled plumage, and diarrhea. Birds infected
with E. tenella show pallor of the comb and wattles and
blood-stained cecal droppings.
Lesions
E. acervulina and E. mivati: 1-2mm areas of hemorrhage
interspersed with white foci visible through the serosa of the
distal duodenum and proximal jejunum.
E. necatrix: severe distention of the mid-jejunum with
hemorrhages in the mucosa and red-stained fluid in the lumen.
E. maxima: distention of the mid-jejunum with hemorrhages in
the mucosa.
E. tenella: hemorrhagic typhlitis
E. brunetti: hemorrhages of the mucosa of the distal jejunum
and colon.
Fibrinonecrotic enteritis may occur in chronic cases.
Diagnosis
Lesions of E. tenella and E. brunetti are diagnostic.
Microscopic examination of intestinal and cecal scrapings
reveals oocysts.
To confirm a diagnosis in a commercial operation the
following specimens should be submitted to a laboratory:
- Intestine from a sacrificed, affected bird preserved in
5% potassium dichromate for culture and identification of
Eimeria sp.
- Intestine showing gross lesions in 10% formalin for
histological examination.
- Representative feed samples for anticoccidial assay.
- Litter samples for oocyst counts.
Treatment
Administration of amprolium solution or sulfonamides
(sulfamethazine or sulfaquinoxaline) in drinking water. Administration of water dispersable vitamin A and K supplements
may enhance recovery.
Prevention
Management procedures which limit saturation of litter include:
- Appropriate installation and management of watering
systems. Nipple drinkers reduce spillage of water onto
litter compared to bell and trough drinkers.
- Acceptable ventilation rate.
- Maintaining recommended stocking density.
- Providing adequate feeding space.
- Inclusion of anticoccidials in diets at recommended levels
will prevent clinical infection.
- Chemical and ionophoric coccidiostats for broilers in
shuttle programs.
- Synthetic coccidiostats for breeders and floor-reared
commercial egg-production flocks.
Anticoccidial vaccines are appropriate for replacement breeding stock and roasters. This approach is cost-effective but requires experienced and diligent management and monitoring especially if the vaccine is applied over feed. Intraocular administration by spray or the insertion of a gelatine cylinder impregnated with oocysts in the chick delivery box contributes to an even distribution of vaccine through the flock.
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