Overview and Clinical Importance
Enteritis refers to inflammation of the intestinal tract and represents one of the most economically devastating disease categories in avian species. In poultry, enteric diseases cause billions of dollars in annual losses worldwide through mortality, reduced growth rates, poor feed conversion, and decreased egg production. For pet birds, enteritis can be life-threatening and requires prompt veterinary intervention.
Avian enteritis encompasses a diverse group of infectious and non-infectious conditions affecting the gastrointestinal tract. The NAVLE frequently tests knowledge of major enteric pathogens including Clostridium perfringens (necrotic enteritis), Eimeria species (coccidiosis), turkey hemorrhagic enteritis virus, coronaviruses, and various bacterial pathogens. Understanding the pathogenesis, clinical presentation, diagnosis, and treatment of these conditions is essential for NAVLE success.
Section 1: Bacterial Enteritis
Necrotic Enteritis (Clostridium perfringens)
Etiology and Pathogenesis
Clostridium perfringens types A and C are the causative agents of necrotic enteritis (NE). This gram-positive, anaerobic, spore-forming bacterium is a normal inhabitant of the avian intestinal tract. Disease occurs when predisposing factors allow bacterial overgrowth and toxin production. The key toxins include alpha-toxin (phospholipase C) and NetB toxin (necrotic enteritis B-like toxin), which cause intestinal mucosal necrosis.
Predisposing factors are critical for disease development: concurrent coccidiosis (especially Eimeria maxima and E. acervulina), high dietary levels of animal protein and fat, wheat/barley/rye-based diets (viscous non-starch polysaccharides), immunosuppression, and mycotoxicosis. The coinfection with coccidia damages intestinal mucosa, providing substrate for clostridial proliferation.
Clinical Signs and Gross Lesions
Species and Age Susceptibility
Diagnosis
Presumptive diagnosis is based on characteristic gross lesions in birds of appropriate age and management conditions. Confirmatory diagnosis requires histopathology showing mucosal necrosis with gram-positive rods adherent to cellular debris, and anaerobic culture of C. perfringens from intestinal contents. Note: Culture alone is insufficient as the organism is a normal intestinal inhabitant. Quantitative counts greater than 10^7-8 CFU/g intestinal content support diagnosis.
Treatment and Prevention
Prevention strategies include: effective coccidiosis control (vaccination or anticoccidials), proper litter management, avoiding high-viscosity diets, biosecurity, and ionophore anticoccidials which also have activity against C. perfringens.
Board Tip - Memory Aid: "COCCI CLOST" Coccidiosis Opens Cells, Clostridium Invades = Coccidiosis + Clostridium = Necrotic Enteritis. Remember that NE is almost always secondary to coccidiosis or another mucosal-damaging condition!
Section 2: Viral Enteritis
Hemorrhagic Enteritis of Turkeys (HE)
Etiology and Epidemiology
Turkey hemorrhagic enteritis virus (THEV) is a Type II adenovirus (Siadenovirus, Turkey adenovirus 3). It is antigenically related to Marble Spleen Disease Virus (MSDV) of pheasants and Avian Adenovirus Splenomegaly (AAS) of chickens. The virus is ubiquitous in turkey-producing regions worldwide and is highly contagious.
Transmission occurs primarily via the fecal-oral route. The virus can survive in frozen feces for months and in litter for weeks. Target cells include macrophages and B lymphocytes, with the spleen being the principal site of viral replication. The virus is highly immunosuppressive, predisposing birds to secondary bacterial infections.
Clinical Signs, Lesions, and Age Susceptibility
Age susceptibility: Turkeys greater than 4 weeks of age are clinically susceptible. Peak susceptibility is 6-12 weeks (most common at 7-9 weeks when maternal antibodies wane). Turkeys less than 4 weeks old are resistant due to maternal antibodies. Morbidity approaches 100%; mortality ranges from 1-60% (average 10-15%).
Diagnosis and Management
Diagnostic methods: Clinical signs and gross lesions are often presumptive. Confirmatory testing includes agar gel immunodiffusion (AGID) of splenic extracts, PCR for viral DNA detection, ELISA for anti-HEV antibodies, and histopathology demonstrating intranuclear inclusions.
No specific treatment exists. Management includes: supportive care, antibiotics to prevent secondary bacterial infections (especially colibacillosis), raising brooder temperatures, and avoiding crowded conditions. Antiserum from recovered birds (0.5-1 mL SC) may be used in outbreaks. Live avirulent vaccines administered in drinking water at 4-6 weeks of age are the primary prevention strategy.
Board Tip - Memory Aid: "HE MARBLE" Hemorrhagic Enteritis = MARBLE spleen + Bloody droppings + 7-9 week turkeys + Immunosuppression leading to E. coli. The mottled "marble" spleen is the key gross lesion!
Coronaviral Enteritis of Turkeys (Bluecomb Disease)
Turkey coronavirus (TCV) causes an acute, highly contagious enteric disease affecting turkeys of all ages, though clinical signs are most severe in young poults. The disease is also known as "mud fever" or "bluecomb disease" (historical term). TCV is transmitted via fecal-oral route and can be carried by insects, vehicles, and personnel.
Clinical Features and Lesions
Diagnosis: RT-PCR for TCV RNA detection in intestinal contents or feces; virus isolation from GI tract; serology (ELISA, IFA) for anti-TCV antibodies. Differential diagnoses: astrovirus, rotavirus, reovirus, salmonellosis, cryptosporidiosis.
No specific treatment. Supportive care includes antimicrobials for secondary bacterial infections, raising brooder temperatures, and fluid support. Depopulation followed by thorough cleaning/disinfection with 3-4 weeks rest period between flocks.
Section 3: Parasitic Enteritis - Coccidiosis
Avian Coccidiosis (Eimeria spp.)
Coccidiosis is one of the most economically important parasitic diseases in poultry worldwide, causing an estimated greater than $3 billion in annual losses. It is caused by obligate intracellular protozoan parasites of the genus Eimeria (phylum Apicomplexa). Seven species affect chickens, and four primary species affect turkeys. Coccidia are strictly host-specific and do not cross-infect between poultry species.
Eimeria Species in Chickens: Location and Pathogenicity
Life Cycle and Pathogenesis
The coccidial life cycle takes approximately 4-7 days (species-dependent). Unsporulated oocysts are shed in feces and require warmth (25°C), moisture, and oxygen to sporulate and become infectious (each sporulated oocyst contains 8 sporozoites). Upon ingestion, sporozoites invade intestinal epithelial cells and undergo multiple cycles of asexual (schizogony) and sexual (gametogony) reproduction, rupturing cells with each cycle. This causes mucosal destruction, hemorrhage, malabsorption, and protein leakage.
Diagnosis and Treatment
Diagnosis: Fecal flotation with oocyst per gram (OPG) counts; Johnson and Reid lesion scoring system (0-4 scale) at necropsy; qPCR for species identification; histopathology showing parasites in epithelial cells. Clinical signs and characteristic lesions at specific intestinal sites are highly suggestive.
Prevention: Live vaccines (virulent or attenuated) administered at 1 day of age; shuttle/rotation programs with anticoccidials; good litter management; "all-in, all-out" production; biosecurity.
Board Tip - Memory Aid: "TEN = BLOODY CECA" E. TENella = Bloody CECAL coccidiosis (TEN = CECA). Also remember: "ACER = LADDER" - E. ACERvulina causes ladder-like white streaks in the duodenum.
Section 4: Enteritis in Pet Birds (Psittacines)
Proventricular Dilatation Disease (PDD)
Avian bornavirus (ABV) causes proventricular dilatation disease, a progressive neurologic disease affecting the GI tract and CNS of psittacines. The disease has many names: macaw wasting disease, neuropathic gastric dilatation, and psittacine ganglioneuritis. It affects macaws, African grey parrots, conures, and cockatoos most commonly, though all parrots are susceptible.
Clinical signs: Passage of undigested seeds in feces (pathognomonic), progressive weight loss despite good appetite, regurgitation, crop stasis, diarrhea, ataxia, and tremors. The disease is progressive and fatal once clinical signs develop.
Diagnosis: Radiographic proventricular dilatation; contrast studies showing delayed GI transit; PCR for ABV in feces/blood; serology; crop biopsy showing lymphoplasmacytic ganglioneuritis (definitive). Treatment: No cure. Supportive care, NSAIDs (meloxicam, celecoxib) to reduce inflammation, easily digestible diet.
Avian Chlamydiosis (Psittacosis)
Chlamydia psittaci is an obligate intracellular bacterium causing psittacosis in birds and humans (zoonotic and reportable disease). It commonly affects cockatiels, budgerigars, and small parrots. Clinical signs include anorexia, dyspnea, lime-green diarrhea, conjunctivitis, and nasal discharge. Carriers may be asymptomatic.
Diagnosis: PCR of combined conjunctival, choanal, and cloacal swabs (most sensitive); serology. Treatment: Doxycycline for 45 days (oral or injectable). Medicated water formulations available for cockatiels (200-400 mg/L) and African grey parrots (800 mg/L).
Avian Gastric Yeast (Macrorhabdosis)
Macrorhabdus ornithogaster (formerly "megabacteria") is actually an anamorphic ascomycetous yeast causing proventriculitis in budgerigars, canaries, and other small psittacines and passerines. Clinical signs include chronic weight loss, regurgitation, passage of undigested seeds, and diarrhea. Diagnosis is by wet mount microscopy of feces showing large rod-shaped organisms or histopathology. Treatment is difficult; amphotericin B (100 mg/kg PO BID) may be attempted.