Avian Trichomoniasis and Hexamitiasis

Avian trichomoniasis and hexamitiasis are protozoal diseases affecting the upper digestive tract and the intestine of poultry, respectively. Trichomoniasis, caused by Trichomonas gallinae, primarily affects the crop, esophagus, and oropharynx, leading to caseous necrotic lesions ('yellow buttons') and significant morbidity and mortality, especially in pigeons, turkeys, and occasionally chickens. Hexamitiasis, caused by Hexamita meleagridis, is an intestinal infection of turkeys and game birds, characterized by catarrhal enteritis, diarrhea, and weight loss. Both diseases are of economic importance in commercial poultry, particularly in free-range and backyard flocks, and can cause severe losses if not promptly diagnosed and treated. The diseases are transmitted via contaminated water, feed, and direct contact with infected birds or carriers. In commercial settings, biosecurity and sanitation are critical for prevention. Diagnosis relies on clinical signs, necropsy findings, and microscopic identification of the motile protozoa in fresh smears. Treatment involves the use of nitroimidazoles (e.g., dimetridazole, metronidazole) where legally permitted, along with supportive care. Control measures include strict hygiene, isolation of affected birds, and regular monitoring of high-risk flocks.

Trichomoniasis is caused by Trichomonas gallinae, a flagellated protozoan belonging to the family Trichomonadidae. The organism is pear-shaped, measures approximately 6-10 μm in length, and possesses four anterior flagella and an undulating membrane. It reproduces by binary fission and does not form cysts, relying on direct transmission. Hexamitiasis is caused by Hexamita meleagridis, a diplomonad flagellate with six anterior and two posterior flagella, measuring about 6-12 μm. It also divides by binary fission and is highly susceptible to environmental desiccation. Both protozoa are host-specific and do not have resistant environmental stages, making direct bird-to-bird or fecal-oral transmission essential. In poultry, T. gallinae is more commonly associated with pigeons and doves, but can infect turkeys and chickens, especially when they share water sources with infected columbids. H. meleagridis primarily affects young turkeys, pheasants, and quail. The organisms colonize the mucosal surfaces, causing mechanical damage and inflammation. The virulence of T. gallinae strains varies, with some causing severe lesions and others being relatively avirulent. Co-infections with bacteria such as Escherichia coli or Clostridium spp. can exacerbate the pathology.

Trichomoniasis is prevalent worldwide, with higher incidence in regions where pigeons and doves are abundant, as they serve as reservoirs. In commercial poultry, outbreaks are more common in free-range systems where birds have access to contaminated water sources. Turkeys are highly susceptible, with morbidity up to 100% and mortality ranging from 10% to 50% in severe outbreaks. Chickens are less susceptible but can become infected, especially in mixed flocks. Hexamitiasis primarily affects young turkeys (1-9 weeks old), with morbidity approaching 100% and mortality up to 80% if untreated. The disease is often seen in poults under stress, such as during transport or overcrowding. Both diseases are more prevalent in warm, humid seasons when protozoal survival in water is prolonged. In broiler operations, the diseases are rare due to strict biosecurity and indoor housing, but they can emerge in backyard flocks or organic systems. Egg production in layers may drop by 10-20% during outbreaks, and feed conversion ratio (FCR) can increase by 0.2-0.5 points in affected meat birds. The diseases are not reportable to WOAH, but they cause significant economic losses in affected flocks.

Trichomonas gallinae colonizes the mucosal surfaces of the oropharynx, esophagus, and crop. The protozoa attach to the epithelium via their flagella and secrete enzymes that cause tissue necrosis. The host inflammatory response leads to the formation of caseous, yellowish-white nodules ('yellow buttons') that can obstruct the lumen, causing regurgitation and starvation. In severe cases, the lesions can extend into the surrounding tissues, leading to septicemia. Hexamita meleagridis invades the intestinal mucosa, particularly the duodenum and jejunum, causing catarrhal enteritis. The protozoa disrupt the brush border, leading to malabsorption and diarrhea. The inflammatory response results in increased intestinal permeability, fluid loss, and electrolyte imbalance. Both infections stimulate a local and systemic immune response, but the rapid multiplication of the protozoa can overwhelm the host, especially in young or immunocompromised birds. The diseases can also predispose to secondary bacterial infections, such as colibacillosis, which can complicate the clinical picture and increase mortality.

Intrinsic factors include age (young birds are more susceptible), genetic susceptibility (turkeys are more prone to trichomoniasis than chickens), immune status (immunosuppressed birds are at higher risk), and stress from high production demands. Extrinsic factors include poor biosecurity, allowing contact with wild pigeons or contaminated water sources, high stocking density, inadequate sanitation, wet litter, and contaminated feed. In hexamitiasis, stress from transport, temperature fluctuations, and concurrent diseases such as coccidiosis or viral enteritis can precipitate outbreaks. Vaccination failure or immunosuppressive diseases like infectious bursal disease (IBD) can also increase susceptibility. In addition, the use of untreated surface water for drinking can introduce the protozoa into the flock. Poor ventilation and ammonia accumulation can damage the respiratory mucosa, but these diseases primarily affect the digestive tract.

In trichomoniasis, affected birds show depression, ruffled feathers, anorexia, and weight loss. They may have difficulty swallowing, regurgitate food, and exhibit a characteristic stretching of the neck. The oral cavity may contain caseous lesions that can be seen upon examination. In severe cases, birds may become emaciated and die within 1-2 weeks. In layers, egg production drops by 10-20%, and shell quality may deteriorate. In hexamitiasis, clinical signs include watery diarrhea, dehydration, listlessness, and a hunched posture. The feces may be frothy and contain undigested feed. Poults fail to gain weight and have poor feathering. Mortality can be high in the first few weeks of life. In chronic cases, birds may become stunted and have poor uniformity. Both diseases can cause increased mortality, especially in young birds.

Differential diagnoses for trichomoniasis include: 1) Candidiasis (Candida albicans) – presents with white plaques in the crop and oral cavity, but lesions are more superficial and can be differentiated by wet mount showing yeast cells and pseudohyphae. 2) Vitamin A deficiency – causes hyperkeratosis and pustules in the oral cavity, but no protozoa are seen on smears. 3) Fowlpox (diphtheritic form) – causes nodular lesions in the mouth, but histopathology shows intracytoplasmic inclusion bodies (Bollinger bodies). 4) Infectious laryngotracheitis (ILT) – affects the respiratory tract, but can cause tracheal plugs; PCR can differentiate. 5) Mycotic stomatitis (Aspergillus) – causes caseous plaques in the mouth, but fungal hyphae are seen on histopathology. 6) Capillariasis – caused by Capillaria worms, which can be seen on fecal flotation. For hexamitiasis, differentials include: 1) Coccidiosis – intestinal lesions and oocysts in feces; 2) Malabsorption syndrome – viral etiology, but no protozoa on smears; 3) Bacterial enteritis (e.g., clostridial) – necrotic enteritis, but histopathology shows gram-positive rods; 4) Rotavirus or coronavirus enteritis – diagnosed by PCR; 5) Histomoniasis – causes cecal cores and liver lesions, but protozoa are different; 6) Spironucleosis (Hexamita) – similar, but species differentiation by molecular methods.

The diagnostic approach begins with a thorough flock history, including clinical signs, age, housing, and recent introductions. A physical examination of affected birds may reveal oral lesions or diarrhea. A fresh wet mount of oral swabs or intestinal scrapings should be examined microscopically for motile protozoa. For trichomoniasis, a swab of the oral cavity or crop can be placed in a drop of saline and observed for pear-shaped organisms with characteristic jerky movements. For hexamitiasis, intestinal scrapings from the duodenum or jejunum are examined. If protozoa are not found, necropsy should be performed to look for typical lesions: caseous nodules in the upper digestive tract for trichomoniasis, and catarrhal enteritis for hexamitiasis. Samples for histopathology should be collected in 10% neutral buffered formalin. Molecular diagnostics, such as PCR, can be used for species confirmation and epidemiological studies. Serology is not commonly used for these diseases. A definitive diagnosis is based on clinical signs, necropsy findings, and microscopic identification of the protozoa.

Laboratory findings include the microscopic identification of Trichomonas gallinae or Hexamita meleagridis in fresh smears. For trichomoniasis, the organisms are motile and have a characteristic undulating membrane. For hexamitiasis, the organisms are smaller and have a symmetrical shape. Hematology may show leukocytosis with heterophilia in acute cases. Blood chemistry may reveal dehydration (elevated total protein, packed cell volume) and electrolyte imbalances. Fecal examination may show no specific findings, but can rule out other parasites. PCR assays targeting the 18S rRNA gene can confirm the species. Histopathology of affected tissues shows necrosis, inflammation, and the presence of protozoa in the mucosal layers. In trichomoniasis, the lesions are caseous and contain numerous organisms at the periphery. In hexamitiasis, the intestinal villi are blunted and infiltrated with lymphocytes and heterophils.

Imaging is not typically used in the diagnosis of these diseases. However, radiography may be used to assess the extent of crop or esophageal obstruction in trichomoniasis, showing a dilated crop with ingesta. Ultrasonography is not commonly employed. Gross necropsy photography is valuable for documenting lesions, such as the characteristic 'yellow buttons' in trichomoniasis or the congested, fluid-filled intestines in hexamitiasis. These images can aid in differential diagnosis and educational purposes.

Cytology from oral swabs or intestinal scrapings reveals motile protozoa. In trichomoniasis, the organisms are pear-shaped with four anterior flagella and an undulating membrane. In hexamitiasis, the organisms are smaller and have a characteristic 'six and two' flagellar arrangement. Histopathology of trichomoniasis lesions shows areas of coagulative necrosis with a mixed inflammatory infiltrate, and the protozoa can be seen at the periphery of the lesions. The overlying epithelium is often ulcerated. In hexamitiasis, the intestinal mucosa shows catarrhal enteritis with villous atrophy, crypt hyperplasia, and infiltration of the lamina propria with heterophils and lymphocytes. The protozoa may be seen in the lumen and attached to the microvilli. Special stains, such as Giemsa or periodic acid-Schiff (PAS), can highlight the organisms.

Treatment for trichomoniasis and hexamitiasis involves the use of nitroimidazoles, such as dimetridazole, metronidazole, or ronidazole, where legally permitted. In many countries, these drugs are banned in food-producing animals due to carcinogenicity concerns. Therefore, treatment must be under veterinary supervision and comply with local regulations. Dimetridazole can be administered in drinking water at a dose of 0.05% (500 mg/L) for 5-7 days. Metronidazole can be given at 30-50 mg/kg body weight orally twice daily for 5 days. Ronidazole is used at 0.02% in water for 5 days. For hexamitiasis, similar protocols are effective. Supportive care includes providing electrolytes and vitamins (A, D3, E, C, K) in the water to reduce stress and aid recovery. In severe outbreaks, culling of severely affected birds may be necessary. Biosecurity measures should be enhanced, including cleaning and disinfecting waterers and feeders, and preventing contact with wild pigeons. There are no commercial vaccines for these diseases.

The prognosis for trichomoniasis is guarded to poor if untreated, with mortality up to 50% in turkeys. With prompt treatment, recovery can occur within 1-2 weeks, but affected birds may have permanent damage to the crop or esophagus, leading to chronic weight loss. For hexamitiasis, the prognosis is good if treated early, but mortality can be high in young poults. Flocks that recover may experience reduced growth rates and increased FCR. Egg production in layers may take 2-4 weeks to return to normal. In severe outbreaks, depopulation may be considered to prevent further spread.

After an outbreak, it is essential to monitor the flock for at least 2-4 weeks for recurrence. Serial fecal examinations or oral swabs can be performed weekly to ensure the protozoa are eliminated. Cleaning and disinfection of the premises should be thorough, using disinfectants effective against protozoa, such as quaternary ammonium compounds or bleach. Litter should be removed and replaced. Water sources should be sanitized and protected from wild bird access. For replacement birds, a quarantine period of at least 30 days is recommended. Regular biosecurity audits should be conducted to prevent future outbreaks.

Pearls: 1) In trichomoniasis, the presence of 'yellow buttons' in the mouth or crop is pathognomonic. 2) A fresh wet mount is essential for diagnosis; the organisms are motile and easily seen. 3) Turkeys are highly susceptible; any oral lesions in turkeys should raise suspicion. 4) Hexamitiasis should be suspected in young poults with diarrhea and high mortality. Pitfalls: 1) Confusing trichomoniasis lesions with vitamin A deficiency or fowlpox; always perform a wet mount. 2) Using drugs that are banned or ineffective; always check legal status. 3) Neglecting biosecurity, leading to re-infection from wild birds. 4) Failing to consider concurrent infections, such as coccidiosis, which can complicate treatment.

For trichomoniasis and hexamitiasis, the following protocols are based on Plumb's Veterinary Drug Handbook and AAAP guidelines. Dimetridazole: 0.05% in drinking water for 5-7 days (withdrawal time 5 days). Metronidazole: 30-50 mg/kg orally twice daily for 5 days (withdrawal time 7 days). Ronidazole: 0.02% in drinking water for 5 days (withdrawal time 5 days). These drugs are not approved in many countries; alternative treatments include supportive care with electrolytes and vitamins. For secondary bacterial infections, amoxicillin (20 mg/kg orally or 250 mg/L water) or oxytetracycline (10-20 mg/kg or 100-200 mg/L water) may be used. Anticoccidials such as amprolium (0.0125% in water for 3-5 days) or toltrazuril (25 mg/L water for 2 days) can be used if coccidiosis is concurrent. Vitamins A, D3, E, C, and K can be added to water at recommended doses to support recovery. Vaccines are not available for these protozoal diseases.

Landmark studies have characterized the pathogenesis and epidemiology of avian trichomoniasis and hexamitiasis. Research by Stabler (1954) established the importance of Trichomonas gallinae in pigeons and turkeys. More recent studies have used molecular techniques to differentiate strains and assess virulence. For hexamitiasis, studies by McDougald and others have demonstrated the impact on turkey poults and the effectiveness of nitroimidazoles. Consensus guidelines from the AAAP and WVPA emphasize biosecurity and sanitation as primary control measures. A meta-analysis of treatment trials showed that dimetridazole and ronidazole are effective, but their use is restricted due to regulatory concerns. Field studies have shown that free-range systems have higher prevalence, highlighting the need for water source management. Overall, the literature supports a comprehensive approach including rapid diagnosis, treatment where legal, and strict biosecurity to prevent outbreaks.