Coccidial infections in birds

Coccidial Infections in Birds C. Douglas Page, DVM, and Kim Haddad, BA

Coccidian parasites are protozoans in the subphylum

Apicomplexa, class Sporozoa, which have a characteristic apical complex of organeiles in the infective stages that enable the parasites to enter host cells. These intracellular organisms cause a myriad of diseases in avian species by destroying the cells they invade. For the clinician, some of these parasites can present an antemortem diagnostic challenge owing to the variety of bird species and organ systems affected; therefore, instituting an effective treatment regimen can be an additional hurdle. This article reviews the following coccidian parasites of nondomestic avian species:

Eirneria, Isospora, Caryospora, Cryptosporidium, Atoxoplasma, Sarcocystis, and Toxoplasma. Life cycles, clinical signs, diagnostic tests, prevention, and treatment are discussed.

Copyright 9 1995 by W.B. Saunders Company Key words: Avian parasites, protozoans, coccidia, Api-

complexa, antiprotozoal drugs.

occidian parasites are members of the subApicomplexa, Sporozoa.

class The C phylum subphylum n a m e reflects the appearance of the infective stages, which have a complex of organelles in their apical pole that enables the parasite to e n t e r the host cell. a-3 T h e y are small, single-celled, obligate intracellutar parasites that cause a variety of diseases in many avian species. Depending on the species of parasite, birds can serve as either intermediate or definitive hosts; clinical signs can range from inapparent infection to acute death. 2'4-7 T h e zoite, a b a n a n a - s h a p e d cell with a pointed or apical end, migrates in the host and is the beginning and end point of the coccidian life cycle. A prefix designates the stage of the life cycle (eg, sporozoites are an infective f o r m within sporulated oocysts). Many coccidians u n d e r g o both sexual and asexual reproduction. T h e d e v e l o p m e n t a l stages consist of schizogony or m e r o g o n y (asexual reproduction)- producing merozoites, gametogony (sexFrom the Jacksonville Zoological Gardens, Jacksonville, FL (C.D.P.), and the University of Florida, GainesviUe, FL (K.H.). Address reprint requests to C. Douglas Page, DVM, Jacksonville Zoological Gardens, 8605 Zoo Rd, Jacksonville, FL 32218. Copyright 9 1995 by W.B. Saunders Company 1055-937X/95/0403-000555.00/0

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ual reproduction)- producing oocysts that contain a zygote, and sporogony-producing sporocysts that contain one or more sporozoites within the oocyst.l'2 Coccidia are usually transmitted by the fecal-oral route. T h e life cycle of the coccidian parasite may be m o n o x e n o u s (direct), requiring only a definitive host, or heteroxenous (indirect), requiring a definitive and an intermediate host. In m o n o x e n o u s life cycles, the oocysts mature or Sporulate in the environment, and once ingested by the host, the infective sporozoites are released by digestion. In one type of heteroxenous life cycle, gametogony and schizogony occur in a vertebrate definitive host, and sporogony occurs in an interm e d i a t e i n v e r t e b r a t e host; sporozoites are transmitted when the invertebrate bites the definitive host. In a n o t h e r type of heteroxenous life cycle, sporozoites are produced by a definitive host and infect a vertebrate intermediate host. Zoites f o r m e d within the intermediate host infect the definitive host when it practices carnivorism. 1,2 T h e following g e n e r a of coccidia are of greatest concern in nondomestic avian species: Eimeria, Isospora, Caryospora, Cryptosporidium, Atoxoplasma, Sarcocystis, and Toxoplasma. T h e life cycles, clinical signs, and diagnostic tests are discussed u n d e r each genus. Prevention and treatment are discussed at the end of the article.

Eimeria This genus is a general representation of the coccidian life history. It has been estimated that if all animals were examined, there would be a total of 45,000 species of Eimeria identified. 1,2 Eimeria spp have a m o n o x e n o u s life cycle, and the majority inhabit the intestinal epithelium of their host. Oocysts are passed in the feces; sporulation typically occurs in the envir o n m e n t producing f o u r sporocysts with two sporozoites each. T h e host ingests food or water c o n t a m i n a t e d with the infective stage

Seminars in Avian and Exotic Pet Medicine, Vol 4, No 3 (July), 1995: pp 138-144

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Coccidial Infections in Birds

oocysts, and the oocysts excyst in the small intestine. The sporozoites are then free to penetrate the epithelial cells and undergo schizogony to produce merozoites. The infected cells are destroyed releasing the merozoites, which penetrate more cells and multiply; schizogony occurs a total o f three times. T h e thirdgeneration merozoites become male and female gametes (gametogony), and fertilization occurs producing zygotes, and then oocysts. The oocysts rupture the cells and are passed in the feces to start the process over again. Eimer/a spp oocysts usually have a micropyle cap (operculum) and contain only one cell (zygote) surrounded by a two-layer wall when examined in a fresh fecal sample. 1-4 As compared with other coccidian parasites, Eimeria spp are very host specific. In psittacines, E dunsingi and E haematodi have been reported. However, this is not a common parasite in these birds. 7-9 Intestinal Eimeria infections are more common in galliformes and columbiformes. 8 Enteric disease caused by species of Eimeria occurs when the epithelial cells are destroyed during asexual reproduction, causing mild to severe diarrhea. Severely infected birds will have bloody, greenish or brownish, and watery feces. Intestinal villous atrophy and subsequent malabsorption can occur leading to dehydration, hypoproteinemia, and anemia. 2'4'8 A few species of Eimeria parasitize other organ systems in birds. E gruis and E reichenowi can become extraintestinal in cranes and cause disseminated visceral coccidiosis (DVC).6'1 o, 11 This is a common disease of Whooping Cranes (Grus americana) and Sandhill Cranes (G canadensis) in North America. Endogenous stages of the parasite enter the blood or lymphatics and spread throughout the body. Crane chicks generally die from granulomatous pneumonia and tracheitis, hepatitis, myocarditis, splenitis, and enteritis. Of the extraintestinal eimeriid coccidia, only the species-infecting cranes can complete their development either in the respiratory or intestinal tract. An Eimeria sp has been reported in the bile duct epithelial cells of a Wild Magpie-Lark (Grallina cyanoleuca). 12E fraterculae has been associated with renal lesions in Atlantic Puffins (Fratercula arctica). The parasites were found in the collecting duct epithelium of medullary

cones. 1~ E truncata also infects the kidneys of various waterfowl. 6 Diagnosis of intestinal Eimeria parasitism is made using fecal flotation and direct smear of the fresh fecal specimen, which shows the typical oocyst containing the single cell, or zygote. The sporulated oocyst contains four sporocysts with two sporozoites in each. Oocyst shedding is intermittent so one negative fecal examination is not diagnostic. Oocysts from extraintestinal Eimeria spp infections will also appear in the feces. Those from the kidneys are excreted with the urates, and those f r o m the r e s p i r a t o r y tract are coughed up and swallowed. Therefore the species of bird, clinical signs, and other diagnostic tests such as serum chemistries and radiographs must be considered to achieve an accurate diagnosis.

Isospora Species oflsospora have a life cycle similar to Eimeria and therefore usually have a direct life cycle, although an indirect life cycle can occur. A sporulated oocyst containing two sporocysts each with four sporozoites is ingested and excysts in the small intestine. The sporozoites penetrate the intestinal epithelial cells and undergo asexual division forming many merozoites. On release, the merozoites destroy the epithelial cells and after the third generation, penetrate the epithelium. Once in the cell, they undergo sexual reproduction and oocyst production. The oocysts break out of the epithelial cells and are released in the feces as a single cell with a double wall and no operculum. Once in the environment, the oocysts sporulate.l'2'4 A paratenic or transport host may be involved in the life cycle. Sporozoites penetrate the intestinal tract, enter muscle, and stay there in arrested development until ingested by the proper species of bird. 24 When this occurs, the sporozoites complete the life cycle in the bird as described earlier. Isospora spp are also very host specific and are most common in passeriformes, psittaciformes, and piciformes. They have been found in struthioformes, falconiformes, galliformes, coraciformes, charadriiformes, and strigiformes as well. 4'5'8

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Severe infections of Isospora spp are associated with the very young or immunocompromised bird. Inapparent infections are common. Clinical signs and diagnostic tests are the same as those for Eimeria; oocysts may be sporulated or unsporulated in the feces.

Caryospora Caryospora is a third genus of coccidia that primarily infects the intestinal tract of birds, especially birds of prey. Nine species have been described from birds. 14 The life cycle is generally heteroxenous, and oocysts are produced in enterocytes of birds and carnivorous reptiles. Rodents serve as intermediate hosts after ingesting the sporulated oocysts. Sporozoites develop in the connective tissue and dermis of the rodent host and form caryocysts.~'14 Dogs and pigs have been infected by ingesting secondary hosts bearing caryocysts; this has been associated with a pyogranulomatous dermatitis in these animals. This parasite is also considered a potential zoonotic disease. 15 Oocysts can be identified in fecal flotations and are usually spherical. The unsporulated oocysts contain a single cell and lack an operculum. The sporulated oocysts have a single sporocyst with eight sporozoites. 14

Cryptosporidium For several years, Cryptosporidium spp has been recognized as a problem in the poultry industry. It is now emerging as a serious disease threat in other avian species including anseriformes, psittaciformes, ostriches, canaries, and finches. It is primarily a parasite of the gastrointestinal and respiratory tracts; however, it also infects the urinary tract of some avian species. It produces a very small oocyst that can be confused with yeast cells; the oocysts sporulate in the host and are thus infective when shed. Host specificity does not appear to be as rigid as other coccidian parasites.2,4-6,8.16 The life cycle is monoxenous; however, unlike other intestinal coccidians, there is an auto-infectious cycle because the oocysts are passed fully sporulated. Birds ingest the sporu-

lated oocysts in contaminated food or water. The oocysts excyst in the small intestine releasing the sporozoites that invade the microvillous border of the intestine or epithelial cells of the respiratory tract and u n d e r g o schizogony. Merozoites are produced and repeat the cycle; eventually gametes are produced and gametogony occurs producing oocysts. The oocysts sporulate to produce four sporozoites and then rupture out of the cell. They are either passed in the feces where they are immediately infectious to another bird or remain in the host to release their sporozoites and complete the auto-infectious cycle. 1,4,6,16 As in human acquired immunodeficiency syndrome (AIDS) patients, avian Cryptosporidium spp have an affinity for immunocompromised hosts; however, it is considered a primary pathogen in some cases, s'16 The organ system affected by this parasite depends on the species of bird involved. Cryptosporidium has been found in the respiratory, intestinal, and urinary tracts of chickens, the respiratory tract of ducks, the intestinal tract of psittacines, and the urinary tract of finches. 4'8'16'17 Clinical signs of intestinal cryptosporidiosis are similar to other coccidian infections. Mortality can reach 100% in certain species such as quail. In contrast, a Cryptosporidium sp identified in adult ostriches was asymptomatic.4'8 Infections in the respiratory tract inhibit normal function of the mucociliary elevator. Clinical signs include depression, anorexia, upper respiratory tract disease, air sacculitis, coughing, and dyspnea. Signs of urinary tract disease occur in those species where the renal epithelial cells are infected. 4's'16 The very small oocysts (2 to 5~m) can be found in direct smears of feces, or in fecal flotations. They contain four elongate sporozoites within a single sporocyst when passed in the feces. The small size and potentially low numbers of oocysts can make diagnosis difficult. Modified acid-fast staining and the indirect fluorescent antibody test aid in the diagnosis of cryptosporidiosis.4'5'8'16

Atoxoplasma Species of Atoxoplasma are coccidian parasites that infect the lymphoid-macrophage sys-

Coccidial Infections in Birds

tem and intestinal epithelium of passeriformes, especially canaries, finches, and mynahs. 4'8'18-2~ This has been a devastating disease for the captive population of the endangered Bali Mynah (Leucospar rothchildi). 18 These parasites exhibit strict host specificity. 4,s A serini has been well described in canaries, and its life cycle will be discussed here. Transmission of the disease is direct via ingestion of feces containing oocysts. Once ingested, the oocyst excysts in the small intestine and the sporozoites penetrate epithelial cells, lymphocytes, and macrophages and spread via the blood to parenchymal organs where several generations of schizogony occur. Organs primarily involved are lungs, liver, spleen, pancreas, pericardium, and intestinal epithelium. Gametogony occurs in the intestinal cells and oocysts are formed. Oocysts of Atoxoplasma resemble Isospora, containing two sporocysts each with four sporozoites. Unsporulated oocysts are passed in the feces and undergo sporulation in the environment. 4'19'2~ Infection with Atoxoplasma spp can have varied clinical signs including depression, anorexia, diarrhea, diminished appetite, weight loss, and ruffled feathers. Distention of the liver, spleen, and bowel loops can occasionally be observed. Infection is more severe in young birds, and adults are typically asymptomatic carriers. Mortality is highest among juveniles especially at fledging. Atoxoplasmosis is a parasitism of long duration, and adults surviving infection will continue to shed oocysts sporadically.4,8,18-20 Antemortem diagnosis of atoxoplasmosis is made using fecal flotation, but oocysts are frequently mistaken for species of Isospora. Asexual phases may be seen in peripheral blood smears or buffy coat smears stained by the Romanowsky method. At necropsy, impression smears of liver, spleen, or lungs may also demonstrate asexual phases of Atoxoplasma. 4'18'19

Sarcocystis Species of Sarcocystis are coccidians that parasitize a variety of mammals, birds, and reptiles. They have an obligatory two-host life cycle, or a heteroxenous life cycle.l'2'8 At least six species have been identified in birds. Sfalcatula

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is apparently restricted to North America and has been associated with severe disease and death in a variety of psittacine species; however, it has also been known to infect columbiforme and passerine species, s'zx-24 An unidentified species of Sarcocystis has caused encephalitis in raptors. 25 The life cycle of S falcatula is representative of other species of Sarcocystis. A sexual phase and sporogony occur in the intestines of the definitive host, the Virginia Opossum (Didelphis virginiana). Sporulated oocysts are passed in the feces and ingested by the avian intermediate host. Cockroaches and flies can serize as transport vectors of the infective sporocysts. Once ingested, the sporocysts release the sporozoites, and merogony begins in the lamina propria of the intestines. Meronts, or schizonts, are found in the endothelia of intestines, liver, spleen, kidneys, adrenals, and lungs within several days. They undergo asexual reproduction and produce merozoites by a process called endopolygeny, which is unique to the genus Sarcocystis. Merogony occurs primarily in the lung; the first cycle occurs in the walls of arterioles, and the second cycle in the capillary and venule walls. Eventually merozoites enter striated muscle where mature cysts (sarcocysts) containing bradyzoites are formed. After ingestion of the intermediate host by the opossum, the sarcocysts excyst in the intestinal tract; ultimately, fully sporulated oocysts are passed in the feces of the opossum to start the cycle over again. 8'22'24 For most species of Sarcocystis, clinical signs are evident only in the intermediate host. Symptoms can range from inapparent infection to anorexia, diarrhea, weakness, tachypnea, hemoptysis, ataxia, posterior paresis, and head tilt before death. Old world psittacines are the most susceptible to life-threatening disease caused by S falcatula, although new world species may also be severely infected and die. 8'21-24 Acute pneumonia in psittacine and columbiforme species is related to merogony in the lungs resulting in pulmonary edema and hemorrhage. In old world psittacines, the disease is peracute to acute; clinical signs may be limited to severe dyspnea and hemoptysis. Death can occur in these birds 8 to 10 days postinfection. The greater severity of the disease in old world

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versus new world psittacine species is believed to be caused by a lack of naturally occurring Sarcocystis spp in the environment where the old world species evolved. Therefore these birds are n~iive h o s t s . 21-24 Columbiforme and old world psittacine species have also shown symptoms of muscular weakness. This is apparently dose related where the bird has survived the pulmonary form and developed the muscular disease. There have also been reports of cardiac muscle disease presumably leading to heart failure in various species of birds. 22"26 Encephalitis is an unusual form of sarcocystosis. It has been reported in two species of birds of prey and in a cockatiel (Nymphicus hollandicus). 22,25 Diagnosis of sarcocystosis can be difficult because birds may appear normal the day before death. Evaluation of serum chemistries may show elevations in lactic dehydrogenase (LDH), aspartate transaminase (AST) (SGOT), and creatinine phosphokinase (CPK) enzymes. Radiographs may show increased lung density, splenomegaly, hepatomegaly,and renomegaly. Muscle biopsies may show the sarcocysts and/ or be helpful in ruling out other causes of elevated muscle enzymes. A strong presumptive diagnosis can be made based on clinical signs, the species of bird involved, results of serum chemistries and muscle biopsies, and radiographic findings. 8'21-24

Toxoplasma Toxoplasma spp are coccidian parasites with a facultative heteroxenous life cycle and a broad host range for the intermediate host, which is essentially any warm-blooded animal. It is probable that all bird species could serve as intermediate hosts and have the parasite in their tissues.l'2'4 T gondii is an enteric coccidian of the domestic cat (Felis catus), and the cat and other felids are the only definitive hosts for this parasite. Cats can become infected by ingesting sporulated oocysts containing sporozoites, by ingesting tissues containing tachyzoites or bradyzoites, or via intrauterine infection. After ingestion, the released zoites can either invade the epithelial cells of the small intestine and go

through schizogony and gametogony and p r o duce oocysts to be shed in the feces (enteroepithelial stage) or invade the mucosa, lymph nodes, white blood cells, and other organs and form tissue cysts (extraintestinal stage). T h e intermediate host becomes infected by ingesting any of the infective stage zoites or by transplacental migration as in the cat. Only the extraintestinal stage of the life cycle occurs in the intermediate host. Tissue cysts containing bradyzoites or tachyzoites are formed in the brain, heart, skeletal muscle, and other organs. 1'2'4's Most avian infections result from the ingestion of oocysts shed by infective cats, although birds of prey can become infected by eating the tissue stages. 4'6'8 Toxoplasmosis has been reported in many different bird species. In an outbreak in a zoo, 13 of 20 columbiforme and galliforme specimens died in a 3-week period. 27 Toxoplasmosis has also been confirmed in many species of psittacines, passerines, ratites, and raptors, 4'6'8'20'28 and as mentioned previously, it is likely that all species of birds are susceptible to infection. Most infections in birds are subclinical and asymptomatic. However, active infections may cause pneumonia, vasculitis, hepatopathy, myocarditis, and encephalitis. Clinical disease may also occur after reactivation of a latent infection. The pathology results from the rapidly dividing tachyzoites that destroy the cells they occupy. Clinical signs reflect the organ(s) involved and include lethargy, anorexia, diarrhea, gastrointestinal distress, dyspnea, paralysis, and blindness. 4'6'8'2~ The antemortem diagnosis of toxoplasmosis in birds is difficult because no oocysts are shed in the feces. An increasing antibody titer while the bird is symptomatic followed by a decreasing titer during convalescence is strongly suggestive of active toxoplasmosis. The modified agglutination test with formalin-fixed tachyzoites as antigens has been validated for several species of birds. 4'28

Prevention and Treatment Sound husbandry practices are paramount in preventing coccidian infections in birds. This includes providing clean and dry housing

Coccidial Infections in Birds

a n d p r o p e r nutrition, avoiding high stock density, controlling t r a n s p o r t hosts such as cockroaches a n d flies, a n d in the case o f those parasites with h e t e r o x e n o u s life cycles, eliminating contact with the feces o f the definitive host. Additionally, all new birds e n t e r i n g a collection should be q u a r a n t i n e d a n d screened f o r intestinal parasites. T h e use o f anti-coccidial d r u g s m a y also be helpful; however, they should not be used as a substitute for s o u n d h u s b a n d r y . U n d e r d o s i n g t h e s e d r u g s e n c o u r a g e s the emergence of drug-resistant populations of coccidia. L i v e - a t t e n u a t e d vaccines are used by the poultry industry a n d m a y one day find a place in the m a n a g e m e n t o f coccidiosis in captive, n o n d o m e s t i c avian species. 3 T h e d r u g s used to t r e a t intestinal coccidiosis in birds vary in effectiveness between the species o f parasite a n d the species o f bird involved. T h e toxicity o f these d r u g s m a y vary as well so it is i m p o r t a n t for the clinician to exercise caution w h e n e x t r a p o l a t i n g d r u g s and dosages b e t w e e n bird species.
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0.5 to 1.0 m g / k g given in conjunction with trim e t h o p r i m - s u l f a at a dosage o f 30 to 100 m g / kg; b o t h d r u g s are a d m i n i s t e r e d orally twice a day.Z1, 29

References 1. Bowman DD: Protozoans, in Georgis' Parasitology for veterinarians (ed 6). Philadelphia, PA, Saunders, 1995, pp 83-111 2. Schmidt GD, Roberts LS, in Brake DK (ed): Foundations of Parasitology (ed 4). St Louis, MO, Times Mirror/Mosby, 1989, pp 114-138 3. Shirley MW: Research on avian coccidia: an update. Br VetJ 148, 6:479-499,1992 4. Patton, S: An overview of avian coccidia. Scientific Proceedings of the Annual Conference of the Association of Avian Veterinarians, Nashville, TN, 1993, pp 47-51 5. Greve, JH: Parasitic diseases, in Fowler ME (ed): Zoo & Wild Animal Medicine (ed 2). Philadelphia, PA, Saunders, 1986, pp 242-243 6. Ruff, MD: Protozoan diseases of birds. Scientific Proceedings of Joint Conference of the American Association of Zoo Veterinarians and the American Association of Wildlife Veterinarians. Toronto, Ontario, 1988, pp 25-41 7. Keymer IF: Parasitic diseases, in Petrak, ML (ed): Diseases of Cage and Aviary Birds (ed 2). Philadelphia, PA, Lea & Febiger, 1982, pp 535-554 8. Greiner EC, Ritchie BW: Parasites, in Ritchie BW, Harrison Gl, Harrison LR (eds): Avian Medicine: Principles and Application. Lake Worth, FL, Wingers Publishing, 1994, pp 1014-1019 9. Hooimeijer J, Peek HW, Vertommen MH: Coccidiosis in lorikeets infectious for budgerigar. Scientific Proceedings of the Annual Conference of the Association of Avian Veterinarians, Nashville, TN, 1993, pp 59-61 10. Carpenter JW: Infections and parasitic disease of cranes, in Fowler ME (ed): Zoo & Wild Animal Medicine, Current Therapy 3. Philadelphia, PA, Saunders, 1993, pp 229-233 11. Carpenter JW, Novilla MN, Hatfield JS: The safety and physiologic effects of the anticoccidial drugs monensin and clazuril in sandhill cranes (Grus canadensis). J Zoo Wildl Med 23:214-221, 1992 12. Reece, RL: Hepatic coccidiosis (Eimeria sp) in a wild magpie-lark (Grallina cyanoleuca). Avian Path 18:357362, 1989 13. Leighton FA, Gajadhar AA: Eimeriafraterculae in the kidneys of Atlantic puffins (Fratercula arctica) from Newfoundland, Canada: Species description and lesions. J Wildl Dis 22:520-526, 1986 14. Lindsay DS, Blagburn BL: Cuospora uptoni n sp (Apicomplexa: Eimeriidae) from red-tailed hawks. J Parasit 72:762-765, 1986 15. Euzeby J: A potential zoonotic parasitosis: Coccidial dermatitis due to Caryospora. Bull Acad Natl Med 175: 1991 16. Ley DH: Avian cryptosporidiosis - - An emerging dis-

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17.

18.

19.

20.

21.

22.

Page and Haddad

ease. Scientific Proceedings of the First International Conference, Zoological and Avian Medicine, Oahu, HI, 1987, pp 299-303 Goodwin MA, Davis JF: Fatal bronchopneumonia associated with Cryptosporidium sp in a wood duck (Aix sponsa). J Assoc Av Vet 7:77-78, 1993 Partington CJ, Gardiner CH, Fritz D, et al: Atoxoplamosis in bali mynahs (Leucospar rothschildi). J Zoo Wildl Med 20:328-335, 1989 Flarnmer K: Clinical aspects of atoxoplasmosis in canaries. Scientific Proceedings of the First International Conference, Zoological and Avian Medicine, Oahu, HI, 1987, pp 33-35 Dorrestein GM, Hage MN, Zwart P: Diseases of passerines, especially canaries and finches. Scientific Proceedings of Annual Meeting of the Association of Avian Veterinarians, Boulder, CO, 1985, pp 53-70 Page CD, Schmidt RE, English JH, et al: Antemortem diagnosis and treatment of sarcocystosis in two species of psittacines. J Zoo Wildl Med 23:77-85, 1992 Bicknese EJ: Review of sarcocystosis. Scientific Proceedings of the Annual Conference of the Association of Avian Veterinarians, Nashville, TN, 1993, pp 52-58

23. Hillyer EV, Anderson MP, Greiner EC, et al: An outbreak of Sarcocystis in a collection of psittacines. J Zoo Wildl Med 22:434-445, 1991 24. Clnbb SL, Frenkel JK, Gardiner CH, et al: An acute fatal illness in Old World psittacine birds associated with Sarcocystis falcatula of opposums. Scientific Proceedings of Annual Meeting of the Association of Avian Veterinarians, Miami, FL, 1986, pp 139-149 25. Aguilar RF, Shaw DP, Dubey JP, et al: Sarcocystis -associated encephalitis in an immature n o r t h e r n goshawk (Accipiter gentilis atricapiUus). J Zoo Wildl Med 22:466-469, 1991 26. Page CD, Schmidt RE, Hubbard GB, et al: Sarcocystis myocarditis in a red lory (Eos bornea). J Zoo Wildl Med 20:461-464, 1989 27. Hubbard G, Witt W, Healy M, et al: An outbreak of toxoplasmosis in zoo birds. Vet Path 23:639-641, 1986 28. Orosz SE, Mullins JD, Patton S: Evidence of toxoplasmosis in two ratites. J Assoc Av Vet 6:219-222, 1992 29. Ritchie BW, Harrison GJ: Formulary, in Ritchie BW, Harrison GJ, Harrison LR (eds): Avian Medicine: Principles and Application. Lake Worth, FL, Wingers Publishing, t994, pp 458-467