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1. Learning Objectives
- Be familiar with the common parasites listed below
- Know the three important eimeria species seen in poultry and how to diagnose an infection
- Be able to recognize, diagnose and make treatment recommendations for trichomoniasis in wild birds and poultry
- Understand the clinical significance of hemoparasites in birds
2. Ectoparasites
Poultry, especially the backyard variety, are commonly affected with ectoparasites and often show signs of irritation and react by frequent scratching and preening. Laying hens with this condition can show a drop in egg production which initially seems unexplained until mites are detected. Pet birds are much less likely to harbor ectoparasites unless recently captured from the wild or housed out of doors. Wild birds are very frequently infested with ectoparasites and can act as a source of infection for domestic birds if they are exposed to each other.
2.1. Mites
2.1.1. Knemidokoptes mites
("Scaly leg, or scaly face mites")
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Knemidokoptes mites are the most commonly encountered ectoparasite in parrots species and are also seen in poultry. Infestations in budgerigar are quite common. Diagnosis is usually based on the characteristic appearance of the beak and cere. Scrapings may reveal the parasite. Treatment with Ivermectin is very effective. "Mite protectors" sold in pet stores can be toxic, are usually ineffective and are not recommended.
2.1.2. Northern fowl mite
(Ornythonyssus sylviarum).
This is the most common external parasite of domestic chickens and turkeys in the US. The parasite is sometimes confused with the chicken mite but the northern fowl mite is seen on infested birds during the day as well as at night. Additionally, the life cycle is shorter and infestations occur during all months of the year.
In heavy infestations of white chickens, the feathers are blackened and the skin is scabbed and cracked around the vent. When heavily infested birds are examined, mites commonly crawl onto the examiner's hand and arms.
2.1.3. Chicken mite
(Dermanyssus gallinae).
Chickens are the common host for these mites but turkeys, pigeons, canaries and several species of wild birds are susceptible to infestation. The English sparrow may transmit this mite because of the habit of lining their nests with chicken feathers.
The chicken mite is a blood sucking parasite and infestation often causes anemia which may be fatal in young birds. The adult female mite is 0.7 X 0.4 mm and is gray or deep red depending on the amount of blood in the gut. This parasite feeds only at night and it is sometimes difficult to find during the day. It is most common during the warmer months becoming less active during the winter.
2.2. Lice
Lice are seen uncommonly in pet birds. They are capable of causing damaged feathers, pruritus, and unthriftiness. Treatment with dusting powder (Pyrethrin, Rotenone, low dose carbaryl or malathion) is effective. They are relatively common in chickens, especially in the winter when birds are inside and close together and are very common in wild birds.
2.3. Fleas, ticks, flies, mosquitoes
Fleas, ticks, flies, mosquitoes, etc. may be problems in outdoor aviaries when captive birds come in contact with wild birds.
2.4. Black flies
(Simulidae sp.)
Exposure to black flies often produces anemia in ducklings raised in an outdoor environment. Black flies hatch in the spring, summer and early fall and often reach high numbers during this time. This arthropod can serve as a vector for leukocytozoon - a hemoprotozoan that is transmitted to geese and ducks kept outdoor in ponds and other wet areas where flies inhabit during the egg laying part of their life cycle (see below).
3. Intestinal parasites
3.1. Protozoa
| Major Protozoal Diseases of Poultry |
| Coccidiosis |
| Histomoniasis |
| Hexamitiasis |
| Trichomoniasis |
3.1.1. Coccidiosis
Coccidiosis is a common, protozoal disease of poultry and other avian species characterized by enteritis and diarrhea. Coccidiosis manifests an enteric disease in most instances but it should be noted that renal coccidiosis in water fowl is caused by Eimeria truncata. Chickens are by far the most common poultry species affected with coccidiosis. Domestic turkeys are also susceptible to infection but the disease is less severe in this species. Intestinal coccidiosis has been reported in geese, ducks, guinea fowl, pigeons, pheasants, quail, and chukar partridge.
Coccidiosis is usually a problem in young chickens but clinical disease can occur in older birds, especially when virulent strains of coccidia are involved. Birds are infected through ingestion of sporulated oocysts in feed, water, litter and soil. Conditions of warmth and high humidity facilitate survival and transmission of the oocysts in litter. The various species of coccidia can be identified by microscopic features of oocysts in addition to the location of shizonts and gametocytes in the GI tract.
Infection with one species of coccidia stimulates immunity to that species only and the host will remain susceptible to other species of coccidia. Birds are often simultaneously infected with more than one species. Clinical disease occurs when susceptible chickens ingest massive numbers of oocysts. This occurs when conditions for sporulation of oocysts are ideal, e.g., the litter is wet and temperatures are warm . If the number of ingested oocysts are low, birds will develop immunity without clinical signs of disease. Chickens maintain immunity to coccidia with repeated exposure. Immune chickens are asymptomatic and shed oocysts for long periods (coccidiasis).
3.1.1.1. Clinical Signs of coccidiosis
- Signs in chickens vary depending on the species of coccidia; less pathogenic species produce few or no signs. Pathogenic species cause diarrhea which may be mucoid or bloody. Dehydration often accompanies severe diarrhea. Anemia, listlessness, weakness, retraction of the head and neck and somnolence follow.
- Laying hens will have a drop in egg production with blanching of the yellow skin pigment.
- Growing birds, especially broilers, cease to grow satisfactorily.
- Morbidity and mortality vary - both may be very high.
- Coccidiosis in turkeys resembles the disease in chickens but diarrhea is seldom bloody and poults over 8 weeks old are seldom affected.
3.1.1.2. Diagnosis
The diagnosis of coccidiosis is made on the basis of clinical signs and gross lesions. Knowing the location in the digestive where oocysts, sporozoites, merozoites and schizonts are found is useful in determining the species of coccidia involved in the outbreak. Coccidiosis must be differentiated from coccidiasis (subclinical infection in an immune bird). Additionally, oocysts in the mucosal scrapings may be from non-pathogenic or mildly pathogenic species of coccidia which are of no diagnostic significance. It is also important to remember that E. necatrix does not form oocysts at the site where the most severe lesions occur. The pathogenic stage of coccidiosis precedes oocyst formation and schizonts may be overlooked in the mucosal scrapings from birds with severe gross lesions.
The most important species of coccidia produce lesions in specific regions of the GI tract.
Proximal third of the small intestine - Eimeria acervulina
Gray/white striations are often visible on the mucosal surface but may go unrecognized if they coalesce. Oocysts in mucosal scrapings are moderate in size and ovoid shaped. This type of coccidiosis occurs rather frequently in older birds. E. acervulina is a moderately severe pathogen. In severe cases the lesions can extend into more distal portions of the GI tract. Enteritis can be mild to severe and may lead to a thickening of the intestinal mucosa. Frequently, other species of coccidia will be present, complicating the diagnosis.
This location is also favored by 4 non-pathogenic species.
Middle third of the small intestine - Eimeria necatrix
The middle one-third of the intestine is often markedly dilated, and thickened. Yellow/white foci and petechia are visible through the serosa of the unopened gut. Lesions are seen in the middle third of the intestine but extend throughout the intestinal tract in severe cases. Enteritis is characterized by congestion, hemorrhage, necrosis and bloody feces. Oocysts develop in the ceca, and these may be minimal. Mortality may precede the appearance of oocysts in the feces. E. necatrix is a severe pathogen and often causes high mortality.
Distal third of the small intestine - Eimeria tenella
Typhlitis with occasional involvement of the adjacent areas of the intestine is the principle lesion. In early cases blood is apparent in the feces and cecal lumena. Later, cheesy cecal cores are found. Large schizonts are found in cecal mucosal scrapings. E. tenella is a severe pathogen producing high mortality in young chickens.
3.1.2. Histomoniasis
(Blackhead, Enterohepatitis)
Histomoniasis is a protozoal disease of turkeys, pheasants, peafowl, grouse, quail and chickens caused by Histomonas meleagridis. Turkey poults three month of age and younger are the most susceptible. In young poults morbidity and mortality is high and often approaches100%; older birds are more resistant. Birds are infected through ingestion of protozoa contaminated feces. Infected ova of the cecal worm Heterakis gallinarum and earthworms containing larva of infected cecal worms containing the protozoal organisms can also serve as a less common source of infection.
Lesions of histomoniasis are prominent in the liver and cecum. Chickens have low susceptibility to histomoniasis.
3.1.2.1. Clinical Signs
- Signs appears 7-12 days after exposure. Initially there is listlessness, moderate anorexia, drooping wings and sulfur colored feces. Comb, wattles and snood may be cyanotic.
- Mortality in poults can approach 100%.
- Emaciation is common in chronic cases; this is more likely to occur in older birds.
- Chickens with histomoniasis may have hematochezia.
3.1.2.2. Diagnosis
Gross lesions consist of bilateral enlargement of the ceca with thickened cecal walls and ulceration of cecal mucosa. The cecal lumen contains yellow/gray/green, necrotic, laminated cores. Peritonitis may be present if the cecal wall perforates. In quail, the cecal lesions may not be present, even though mortality is high. The natural surfaces of the liver have 1-2 cm diameter, round, depressed, yellow/gray to red, target-like, multifocal and coalescing lesions. Protozoal organisms can sometimes be found in cecal mucosal scrapings or from liver tissue imprints made from the margin of hepatic lesions. Histologic sections of the liver lesion reveal numerous histomonads.
3.1.3. Hexamitiasis
(Infectious catarrhal enteritis)
Hexamitiasis is an enteric protozoal disease affecting many avian species which include turkeys (under 9 weeks of age), ducks, pigeons, and peafowl. Pheasants, quail and partridge are also susceptible. At least two species of hexamita are associated with poultry. H. meleagridis is the cause of disease in young turkeys while H. columbiae causes disease in pigeons. The organism generally inhabits the intestinal crypts of the upper small intestine.
Hexamitiasis is a disease of young birds, older animals rarely show clinical signs and probably shed the organism continuously, which is a constant source of infection to young birds.
3.1.3.1. Clinical Signs
- Watery diarrhea with yellow, foamy feces. Dehydration ensues rapidly.
- Other signs are the result of dehydration and consist of lethargy, ruffled feathers drooped wings.
3.1.3.2. Diagnosis
Gross lesions are minimal. The small intestine is filled with watery feces and catarrhal (mucinous) exudate may be evident. The proximal small intestine is usually the principle site of involvement. Hexamita can be microscopically seen in fresh mucosal scrapings. The organism is approximately 3 X 9 micron with 8 flagella and two nuclei that resemble eyes. The organism degenerates rapidly after death of the host and may not be visible in birds that have been dead for some time prior to gross examination.
Many hexamita in the upper intestine is suggestive of hexamitiasis.
3.1.3.4. Prevention
Sanitation is important in the control of hexamitiasis. A thorough cleaning and sterilization of feeders and waterers should be carried out when disease has occurred. Many different products have been recommended both for prevention and treatment. These include Nithiazide (Hepzide), Ipronidazole, Furazolidone and tetracycline.
3.1.4. Trichomoniasis
(Canker, frounce)
Trichomoniasis is an upper digestive tract disease of pigeons and doves (canker), raptors (frounce), turkeys and chickens caused by Trichomonas gallinae. The mouth, esophagus and crop are the principle sites of involvement. The disease occurs commonly in pigeons and doves and raptor species that prey on them. Outbreaks are most common in the warmer months. Trichomonas gallinae varies considerably in pathogenicity. The organism is often present in oral secretions of carrier birds that show no signs or lesions.
Pigeons are believed to be primary carriers. They contaminate surface water or water containers with oral secretions that contain T. gallinae. Various species of birds can be exposed by drinking contaminated water. Pigeons and doves transmit T. gallinae to their young during the feeding of crop milk.
3.1.4.1. Clinical Signs
Pigeons, doves and raptors with trichomoniasis often have difficulty in closing the mouth or in manipulating their food because of lesions in the oral cavity. They may also show ptyalism and make repeated swallowing movements.
 Trichomoniasis in an owl
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3.1.4.2. Diagnosis
Diagnosis in the live bird involves microscopic demonstration of the motile organism in a direct saline (body-temperature) preparation. Plaque-like lesions may also be visible.
Multifocal and confluent, yellow, well circumscribed plaques may be present on the upper digestive tract mucosa. These area are often surrounded by a thin zone of hyperemia. The build up of caseous material can be so extensive as to result in making closure of the mouth difficult. Lesions often invade deeply into underlying soft tissue. Although lesions are usually extensive in the mouth, pharynx or esophagus other sites including the crop, proventriculus or the nasal sinuses.
In raptors post-mortem lesions can be seen in the liver and may be accompanied with peritonitis. Lesions are similar in turkeys and chickens but are usually found only in the crop and esophagus of these species. Demonstration of large numbers of trichomonads in oral fluids is usually confirmatory. The presence of only a few organisms may not be significant especially in the absence of lesions or clinical signs. Many normal birds harbor trichomonads.
Differential diagnosis of the gross lesions of trichomoniasis should include wet pox, candidiasis, vitamin A deficiency, and nematodiasis (Syngamous trachea).
3.1.4.3. Treatment
Treatment in all but severe cases is usually successful with metronidazole or carnidazole (marketed for treatment of pigeons with trichomonas). Surgical debridement of large advanced lesions may be difficult and hazardous. Several weeks of medical therapy will reduce and help consolidate these lesions prior to surgery.
3.1.5. Giardiasis
Giardia lamblia is the most common protozoal infection seen in pet psittacines, most frequently in budgies and cockatiels. Clinical signs may be absent or may include weight loss, diarrhea or feather picking. Diagnosis is made on demonstration of the organism in the feces and/or using a fecal ELISA test. Treatment of pet birds for protozoal infections most often involves the use of metronidazole.
3.1.6. Toxoplasma, atoxoplasma, sarcocystis, microspora, cryptosporidium and others
These diseases have also been reported in birds. Recent reports indicate that the microspora Encephalitozoon hellem carried by some psittacines may be a problem for immunocompromised pet owners.
Atoxoplasma is a protozoal parasite in canaries and other birds. It has been reported to be a significant threat to captive populations of Bali Mynah, Leucopsar rothschildi. . The most prominent clinical findings are hepatitis and enteritis. Treatment is challenging and often unsuccessful. Sulfa drugs (including trimethoprim-sulfa), primaquine or sulfachlor-pyrazine may reduce morbidity and mortality and shedding of the organism.
3.2. Nematodes
Nematodes are rarely seen in captive psittacines with the exception of outdoor aviary birds. Many different nematode parasites occur in wild birds and poultry, Capillaria being the most important one. Nematode infestations may contribute to chronic weight loss problems.
3.3. Cestodes
Cestodes can be a problem in chickens kept outside (free-ranging) or inside if they have access to intermediate hosts (beetles and houseflies). These parasites are rarely seen in psittacines. They have been noted to occur in Macaws (MacMillan, pc), but are often missed in a fecal examination and go undiagnosed. Cestode infestations are seen quite often in passerines, waterfowl, and wild birds. Treatment with praziquantel is effective.
4. Other Internal Parasites
4.1. Air sac/tracheal mites
(Sternastoma tracheacolum)
These mites are very common in finches and canaries. They involve only a direct life cycle and can be very persistent in a flock situation. Disease ranges from mild respiratory compromise to complete tracheal/bronchial obstruction, pneumonia and death. Treatment with Ivermectin is effective but may require repeated dosing.
4.2. Gapeworms
The most common tracheal parasite is Syngamus trachea. These worms are occasionally seen in wild birds but also in chickens, turkeys, pheasants and peacocks raised on range where they have access to soil. Adult worms are found in the tracheal lumen, sometimes being present in such large numbers as to obstruct the lumen and result in severe clinical signs of dyspnea or "gapes". Young birds are most seriously affected as the rapidly growing worms can obstruct the small diameter tracheal lumen. The life cycle is direct with eggs coughed up and swallowed then defecated into the soil. Infection takes place through ingestion of infective larvae or the slugs and earthworms that passively take in the infective larvae through their soil feeding habits.
4.3. Hemoparasites
Hemoparasites are fairly common in many birds, especially wild birds. In pet birds they are seen most often in Cockatoos. Their clinical significance is often questionable, but a heavy infestation may contribute to anemia. The most commonly seen parasites in psittacine blood include microfilaria, haemoproteus, leukocytozoon and rarely plasmodium. Attempts at treatment are usually unsuccessful. Control efforts should be aimed at eliminating the vector (insects) in captive environments.
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4.3.1. Leukocytozoon
Leucocytozoonosis is a hemoprotozoal disease common to many birds. Black flies and culicoid midges are important in the transmission of this disease and leucocytozoonosis is prevalent where susceptible birds and these insects are present in high concentration. Various stages in the life cycle of this organism are found in RBCs and peripheral blood leukocytes (gametogeny) in addition to endothelial cells (schizogony). The disease occurs in many avian species including domesticated ducks, geese, turkeys, and guinea fowl. The chicken is rarely affected. Most acute outbreaks occur in young birds.
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The etiologic agent is currently classified as a leukocytozoon. Some species of leukocytozoon infect more than one species of poultry while others strains infect only one species. Common names of some of the more frequently encountered species include: L. smithi (turkeys), L. anatis (ducks), L. anseris (geese), L. neavei (guinea fowl) and L. andrewsi (chickens).
4.3.1.1. Clinical Signs
- Onset is sudden with many birds affected.
- There is depression, anorexia, thirst, loss of equilibrium, weakness, and anemia.
- Dyspnea is a common and may be the result of anemia associated with protozoal replication in RBCs.
4.3.2. Avian malaria
Malaria is the most common cause of mortality in penguins housed in outdoor exhibits in North American and European zoos. The causative agents are usually Plasmodium reticulum (P. praecox) or P. elongatum. Malaria in penguins is characterized by acute onset and death, often without any premonitory signs of illness.
4.3.2.1. Diagnosis
Gross lesions include hepatomegaly and splenomegaly with subcutaneous, pulmonary and epicardial edema. Exoerythrocytic schizogony is the most striking microscopic lesion. This lesion is most evident in the lungs, spleen and liver. Acute interstitial pneumonia is also present in addition to diffuse reticuloendothelial hyperplasia in the spleen and other organs.
Early diagnosis is extremely important. Evaluation of blood smears and monitoring the WBC count for a lymphocytic leukocytosis are considered to be a reliable method of ante mortem diagnosis. The normal WBC in penguins is @19,000 cells/mm3 with a differential of 50% or more lymphocytes.
5. Ancillary Material
5.1. Readings
5.1.1. Texts and Articles
Altman, Robert B., et al. Avian Medicine and Surgery. Philadelphia. W.B. Saunders Co., 1997. Chapter 21.
Cranfield, Mihael R, Graczyk, Thaddeus K., and Thomas F. McCucthan. Elisa antibody test, PCR and a DNA vaccine for use with avian malaria in African penguins. Proceedings of the AAZV and IAAAM Joint Conference, 2000: 39-41.
Field Manual of Wildlife Diseases : general field procedures and diseases of birds. M. Friend and J C. Franson, (eds.) U.S. Department of the Interior, U.S. Geological Survey, 1999.
Ritchie, Branson W., et al. Avian Medicine: Principles and Application. Lake Worth, Fla., c1994: Chapter 36
Snowden, K., Phalen, D., and C. Barton. Microsporidia: a common inapparent infection in pet birds. Proceedings of the Annual Conference of the Association of Avian Veterinarians, New Orleans, LA, 1999.
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