Parasites

       Eimeria are a genus of sporozoan protozoa. Sporozoa are the largest group of protozoa and are classified by be apicomplexan and having an extremely resistant cystic life stage. Eimeria are known for causing coccidiosis in poultry; the extremity of the disease depends on the species of Eimeria. They have a fecal-to-oral life cycle which means they have a direct life cycle and are therefore monoxenous. 

        Life cycle of Eimeria:

1) The oocyst is passed in the droppings where sporulation occurs.  This process, known as sporogony, requires warmth, oxygen, and moisture (the perfect conditions of a chicken house).  4 sporocysts develop within the oocyst and 2 sporozoites develop within each sporocyst through mitotic division.  This oocyst is now infectious.

2) The oocyst is then eaten by the chicken where mechanical abrasion breaks the oocyst apart in either the crop or gizzard freeing the sporocysts.

3) Once in the small intestine, the digestive enzymes free the sporozoites from the sporocysts where the sporozoites then attach to specific epithelial cells of the mucosa (different epithelial cells for different species). The apical complex is the part of the sporozoite that attaches to epithelial cells.

4) After entering the epithelial cell, the sporozoite develops into a trophozoite before undergoing the first cycle of schizogony (asexual multiple fission). Schizogony results in the production of first generation merozoites (many merozoites inside an intracellular cyst called a schizont).

5) This schizont then explodes destroying the cell it was connected to and surrounding tissue releasing about 18-30 merozoites depending on the species. The merozoite invades a close epithelial cell where it enters 2nd round of schizogony (producing 2nd generation merozoites). This continues for usually 2-3 schizogonous cycles, but this changes depending on species and other factors.  Merozoites are self-limiting so they eventually just don't recycle in the schizogony cycle.

6) After leaving schizogony, merozoites within epithelial cells develop into gametes which initiates the sexual reproductive stage of the life cycle (gametogony). The gamete looks like for a trophozoite for a couple hours but then will develop into either a macrogametocyte (female) or microgametocyte (male) by miotic division. 

7) Microgametocytes develops tiny microgametes by multiple fission which are biflagellated. These microgametes leave the ruptured host cell and penetrate specific neighboring epithelial cells that contain macrogametes.  The microgamete fertilizes the the mature macrogamete to form a zygote.

        Choanotaenia infundibulum is a cestode found in chickens and gallinaceous birds (fowls) but not very frequently, especially in domestic birds.  The adults are up to 25 cm long and usually don't have more than 30 proglottids (egg-containing body segments).  The eggs, like ascarids and other tapeworms, are ovoid shape.  Most tapeworms have eggs that look very similar to one another, as do most parasitic helminths, although there are always notable differences.

        This tapeworm has and indirect life cycle which comes with a large variety of intermediate hosts including flies, locusts, ants, and termites. The most common intermediate host, however, is Mucosa domestica (aka Common Housefly). 

        Life cycle of C. infundibulum

1) Proglottids are shed in a bird's feces where they move into surrounding vegetation quickly (they are very motile).

2) Intermediate host ingests these proglottids where they release the eggs into the gut after digestion.

3) In the body cavity of the intermediate host the eggs develop to cysticercoids.

4) The birds then ingest the intermediate host where the cysticercoids release the 2nd stage C. infundibulum into the gut of the bird.

        Raillietina cesticillus is a cestode. It is THE tapeworm of chickens and is found in broilers and replacement pullets. They have an indirect life cycle (heteroxenous)and the darkling beetle is its most common intermediate host. The life cycle of R. cesticillus is too long for short lived birds. There are no concerning pathogens but the largest detriment R. cesticillus does is reducing feed efficiency.  There is no realistic treatment today of R. cesticillus, the only thing with any degree of efficacy would be using very high levels of benzimidazoles.

        Capillaria obsignata (aka Capillaria columbae) is a nematode that lives in chickens and is the only common species for capillariasis in commercial chickens.  The adult male is about 9.5-11.5 mm in length and the female is about 10.5-14.5 mm.  The ova are operculated and the the larvae stay in the egg until it is ingested.  They have a direct life cycle (monoxenous).  The larvae reside against mucosa of the duodenum and maintain a prepatency of 3 weeks.  They are found only in older chickens (not broilers).  Pathogenesis and pathology of C. obsignata includes the following:

Enteritis with some hemorrhaging

Diarrhea

Loss of weight, droopiness, weakness, and mortality (lowered feed efficiency)

Villus atrophy and rejection is probable (thigmokinetic effect)

             H. gallinarum is a nematode (roundworm) that is known as the cecal worm found mostly in older chickens (replacement pullets and breeding hens and roosters).  The parasite is only prepatent in turkeys due to a high immune response to it but can cause histomoniasis usually killing the turkey.  

        The male is about 7-13 mm and the female is about 10-15 mm in length.  The ova are of similar type and size as that of Ascarids but have a thinner shell.  

        A major importance of H. gallinarum is a protozoa that is carried by the worm called Histomonas meleagridis.  This protozoa causes histomoniasis aka blackhead disease.  Histomoniasis causes a "bulls-eye" on the liver that cauterizes the liver, this entails typhlitis, hepatic, and peripheral necrosis.  The protozoa develops in the eggs of H. gallinarum. The protozoa is very weak and so it needs the protection of the egg but it thrives in the ceca of turkeys.

Life Cycle of H. gallinarum:

1) Eggs shed in droppings.  The eggs are very resistant to the environment.

2) 2nd stage larva is infective in the egg in about 3 weeks.  

3) Bird ingests eggs.

4) The larva hatch form the eggs in the intestinal tract.

5) All of the parasitic stages after the egg hatches are restricted to the ceca.

6) Prepatency is about 24-30 days.

         A. galli is a nematode (roundworm) that is the common roundworm of chickens.  The turkey counterpart to this parasite is Ascaridia dissimilis.                

         The more parasites that infect a chicken at one time, the lower the percent of the worms "take" to the host and the longer the prepatency period (time between infection and reproduction of an individual).  The rate of development of the parasite varies depending on the host's age, nutrition, individual and species genetics, gender, and degree of resistance.  The larvae located in the mucosa causes the greatest damage and can include all of the following:

Mucosal edema, protein loss, and hemorrhage

Anemia and leukocytosis

Diarrhea, lowered bird weight, dehydration

Anorexia and lowered feed efficiency

Decreased blood sugar

Increased gut weight

        The adult A. galli feeds only on mucosal filtrates and debris.  Ascaridiasis magnifies and aids debilitations induced by pathogens present.  An A. galli worm is found most commonly in young chickens due to immune response to the parasite increasing with the age of the chicken.

Life Cycle of A. galli:

1) Eggs are found in droppings.  The eggs are very resistant to their environment and are sticky allowing them to attach to most surfaces.

2) Eggs contain the infective 2nd stage larvae in 30 days depending on conditions.  Needs to be about 32 degrees Celsius with plenty of moisture and oxygen.

3) The egg containing the infective larvae is ingested by a chicken where it hatches in either the proventriculus, gizzard, or small intestine.  The hatching is stimulated by unique chemical and conditional signals of the intestines.

4) The larva gets close to the mucosa which is within the mucus where it molts to the 3rd stage after about 7-17 days after infection.  Some of this larvae enters the mucosal epithelium of the small intestine while the rest will stay in the mucus.  Eventually, all of the histotropic 3rd stage larvae emerge from the mucosa or else die in it, here in the mucus the 3rd stage molts to the 4th stage.  After about 10 days the 4th stage molts to the adult stage.

5) The prepatency is about 30 days at the earliest and the patency period for a female is about a few months.