Coccidiosis, caused by various Eimeria species, is one of the most economically devastating infectious diseases of poultry, raisedunderdeep litter system.It occurs mainly in caecaland intestinal systems, and results in high morbidity and mortality.The coccidia consists of a wide variety of single-celledparasitic animals in the sub-kingdom Protozoa. As a group, thecoccidia of the genus Eimeria are predominatelyhost-specific, i.e., each species occurs in a single host. Worldwide, the poultry industry spends significant amount of money in prevention and treatment of coccidiosis, which causes substantial economic losses due to malabsorption, bad feed conversion rate, reduced weight gain and increased mortality.
Parasites causing coccidiosis are commonly found in places where chickens are raised. Coccidia can multiply rapidly inside the cell lining of intestine or caeca. Many species of Eimeria genus can infect poultry with no cross-immunity between them. Eimeria have a self-limiting life cycle and are characterized by high tissue and host specificity. They show a wide variation in their pathogenicityas shown in Table-1.
Table-1: Characteristics of important Eimeria spp. infecting chickens
|Duodenum, Jejunum, Ileum
|* – non-pathogenic; + low pathogenic; ++ moderately pathogenic; +++ highly pathogenic
Wild birds, insects or rodents spread sporulated oocysts mechanically via contaminated boots, clothing, equipment or dust.The natural route of infection is by direct oral transmission. Following the ingestion of sporulated oocysts, the microenvironment of host digestive tract stimulates excystation of oocyst in gizzard resulting in the release of sporozoites that invade and destroy cells in intestinal mucosa and begin the reproductive cell cycle as seen in Fig-1.
Fig-1: Reproductive cycle of the sporulated oocyst.
- CLINICAL SIGNS
Young birds are more susceptible to Eimeria species involved to cause coccidiosis than older, as the Eimeria lifecycle varies from 4-7 days. The severity of an infection depends on the age of birds, number of sporulated oocysts ingested, immune status of flock and environmental management. Infected birds frequently display a typical ‘sick bird’ attitude with depression, prostration, tend to huddle together, have ruffled feathers, consume less feed and water, soiled vents, and the droppings are watery to whitish or bloody.
- acervulina lesions have a unique appearance, consisting of white patches or transverse white lines inside the gut that may be observed from outside. The lesions of E. maximaresults in multiple petechial haemorrhages,noted segmental ballooning or enlargement of mid-gut area with the presence of orange-tainted mucous. Gross lesions of E. tenellaare confined to caeca with the presence of haemorrhagesaround the wall of caeca;freeblood or chocolate-coloured fluid content inside caeca, thickening of caecal wall, and large core of cellular debris and blood.E.praecox and E. mitis are considered nonpathogenic or low pathogenic and experimental infections with these species may produce pathogenesis resulting in enteritis, diarrhea and reduced feed efficiencies.
- acervulina lesionsE. maximalesions E. tenellalesions
Fig-2: Gross lesions of Eimeria species.
- LABORATORY TECHNIQUE
Coccidiosis is often diagnosed by counting coccidia per gram of faeces and by microscopic examination of oocyst. The rRNA and rDNA probes were used for identifying individual species through characteristic restriction fragment patterns, randomly amplifying polymorphic DNA assay to differentiate E. acervulina, E. tenella and their strains.
- POULTRY HOUSE MANAGEMENT
In USA, removal of caked litter and aeration of poultry houses at an interval of 2–3 weeks is practiced and top dressing with fresh litter before placing a new flock is a rule. On the other hand, a thorough cleanout between flocks is a common practice in most European countries and Canada. Strict biocontrol measures adopted by caretakers of poultry houses can play a great role in restricting the spread of infective oocysts.
- PROPHYLACTIC APPLICATION OF ANTICOCCIDIALS
Now a day’s prevention and control of coccidiosis is dependent upon the proper usage of anticoccidial drugs or vaccines with proper cleaning and disinfection of farms along with better farm management practices. Eradication of coccidiosis by litter cleaning and disinfections is not feasiblein poultry farms because of the resistant capacity of coccidial oocysts to environmental conditions and some disinfectants.Hence, usage of various anticoccidials like ionophores or chemicals is necessary to avoid the losses due to coccidiosis outbreaks. Addition of starter and grower feed is referred as a straight program. The concentration of ionophore may be increased in grower feed for maximum protection at time of peak coccidian oocyst shedding (3-4 weeks) during straight program, which is referred as step-up program.Whereas, the decreased anticoccidial concentration in grower or finisher feed is referred as step-down program. The addition of chemical and ionophore anticoccidial in starter and grower feed respectively is referred as shuttle program. These practices minimize the risk of anticoccidial molecule resistance because time of exposure to same drug is limited. These rotation of anticoccidials involves the changing of the product every 4-6 month by giving proper rest to each category of anticoccidial molecules.
Live vaccines are commonly used in summer season because live vaccines containlive non-attenuated coccidian which induce some lesions, stimulate active immunity and predispose birds to necrotic enteritis. Broiler breeders are vaccinated twice intramuscularly during brooding growing phase which will help to pass maternal antibodies to their offspring and immunity to infection that has been demonstrated with E. acervulina, E. maxima, E. mitis and E. tenella.Developed countries like United States and Canada use vaccines like recombinant vaccines or live vaccines likelivacox (consisting of precocious and egg-passaged lines), coccivacandimmucox which contains several virulent coccidia species.
- NATURAL ALTERNATIVES TO PREVENT COCCIDIOSIS
Recently use of natural products like fungal extracts, plant extracts and probiotics to reduce problems caused by coccidiosis has improved.Varying effects of some diet supplements include immune stimulation, anti-inflammatory effect, antioxidant activity and cytoplasmic damage.
Sources of fat containing docosahexaenoic acid, eicosapentaenoic acid and linolenic acid (known as n-3 fatty acids) in high concentrations from fish oils or flax seeds was observed to reduce the severity of Eimeria tenella infection in young broiler chicks. Diets supplemented with 2.5 to 10% fish oil, 10% flax seed oil, or 10% linseed oil significantly decreased cecal lesions, reduced parasitic invasion rate and development.
Antioxidant molecules plays an important role to control and reduce oxidative stress caused by increased levels of reactive oxygen species and free radicals. This can initiate chain reactions in the cell, resulting in the death or serious damage to cell. Usage of antioxidants from natural sources can restore balance of oxidants/antioxidants which helps to recover the coccidiosis affected birds. Curcumin extracted from Curcuma longa, may be useful to reduce the lesions caused by E. acervulina and E. maxima in upper and middle part of small intestine.An extract from Artemisia annua, Artemisinin,is useful in reducing oocyst shedding of E. acervulina and E. tenellathan E. maxima infections.
- ESSENTIAL OILS
Addition of essential oils in the formulations or diets of poultry to control coccidiosis has been practiced recently. It was reported that in vitro destruction of Eimeria oocysts after a three-hour contact period was observed with addition of essential oils from artemisia, thyme and tea tree.Eimeria oocystsare destroyed by essential oils extracted from artemisia, thyme, tea tree and clove.
- HERBAL EXTRACTS AND MEDICINAL PLANTS
Some plant extract has anticoccidial effects.The effect of 15 different herbs were assessed and found thatUlmusmacrocarpa, Pulsatillakoreana, Torilis japonica, Artemisia asiatica and Sophoraflavescens have shown higher survival rates in day old infected broilers with E. tenella,than those of the infected control.
- IMMUNE RESPONSE MODULATORS
Diet with lyophilized powder of plums extract in chickens reported an increased body weight gain, reduced fecal oocyst shedding rate and an increased mRNA’s for IFN-γ and IL-15, greater spleen cell proliferation and enhanced immune responses.Recently, trend of probiotics and prebiotics usage as an alternative for antibiotics has increased. Use of these products had shown to control the establishment of pathogens in intestinal tract of chicken, which not only helped to improve the body weight gain and reduced feed conversion ratio but also livability and immunomodulation of chicken. A study showed that the commercial probiotics contacting Pediococcusacidilactici and Saccharomyces boulardii acts as prophylactic drug alternative for controlling coccidiosis. Diet containing Lactobacillishowed immunomodulatory effect by stimulating gut associated bacteria in neonatal chicks, which protect chickens from disease without any effect on growth performance, and can also be used as a possible replacement for antibiotics.
- Drugs which are effective to control the coccidiosis outbreaks are preferred.
- Sulfa trimethoprim,tolrazuril or sodium sulfachloropyrazinemonohydrate,amproliun with vitamin K,sulfadimethoxine or sulfamethazine (sulfadimidine) are generally used to control the coccidiosis outbreaks.
- Proper water lines flushing to be done to ensure that it does not contains residues of drugs and supplements given through water (vitamins, electrolytes, etc.,).
- Sulphonamides are more stable and effective at neutral to alkaline water pH.
- The required withdrawal periods vary between sulphonamides, which must be taken care during treatment.
- Be awareof label directions and withdrawal periods to ensure efficacy and avoid tissue residues.
- Choosing proper anticoccidial molecules through feed by following golden rules of anticoccidial rotation must be implemented by giving sufficient rest to each molecule, which will minimize coccidiosis outbreaks throughout year.
by Venkat M Shelke, Kemin Industries South Asia Pvt Ltd