TRICHOMONIASIS 

To My Quyen,  Nguyen Khanh Thuan, Nguyen Phuc Khanh, Nguyen Thanh Lam^*

            1. Introduction 

Trichomoniasis was once recognized as an important disease of turkeys and chickens, especially of ranged turkeys, but is seldom reported now. It is caused by Trichomonas gallinae, a flagellated protozoan. Pathogenicity varies greatly by strain. The disease is characterized by raised caseous accumulations in the throat and usually by weight loss in domestic fowl, pigeons, doves, songbirds, and hawks. It has been termed “canker,” “roup,” and, in hawks, “frounce.”(Chaves Hernández, 2014).

2. Aetiology 

Both Trichomonas gallinae and Trichomonas stableri are causative organisms of trichomonosis. These flagellated protozoa live in the sinuses, mouth, throat, esophagus, liver, and other organs. Trichomonosis is more prevalent among domestic pigeons and wild doves than among domestic fowl, although severe outbreaks have been reported in chickens and turkeys. Some trichomonad strains cause high mortality in pigeons and doves. Hawks may become diseased after eating infected birds and commonly show liver lesions, with or without throat involvement. Pigeons and doves transmit the infection to their offspring in contaminated pigeon milk. Contaminated water is probably the most important source of infection for chickens, turkeys, and songbirds, and the parasite has been shown to survive at least 2 hours and potentially up to 24 hours in distilled water. Cleaning of outside bird baths and waterers frequently is important to minimize transmission (Boulianne, 2012).

2.1 Bacterial characteristics

Trichomonas gallinae are small, 5 to 20 µm size, oval to pea-shaped flagellates with four free, anteriorly placed flagella, axostyle protruding from the posterior end, and an undulating membrane. Trichomonads have a direct life cycle and reproduce by binary fission. Described parasite forms include motile trophozoite and nonmotile pseudocyst stages. Trichomonads observed under the light microscope in freshly processed clinical samples are rapidly moving (circling in in a jerky manner with no clear direction, not escaping the microscope field), translucent small flagellates that may appear single or in clusters. Under higher magnification one can often observe wave like movements of an undulating membrane. Different strains of T. gallinae differ in their virulence from apathogenic to very virulent (Samour, 2015).

2.2 Classification 

Trichomonas gallinae belongs to the family Trichomonadidae, order Trichomonadida, class Trichomonadea, phylum Parabasalia(Brugerolle and Lee, 2000; Cepicka et al., 2010): 

Empire Biota 

Domain Eukaryotes 

Phylum Parabasalia 

Class Trichomonadea 

Order Trichomonadida 

Family Trichomonadidae 

Subfamily Trichomonadinae 

Genus Trichomonas 

Species Trichomonas gallinae 

All trichomonads are unicellular flagellated protists classified in the super group Excavata, which includes not only parasitic organisms, but also free-living and commensal ones (Sleigh, 1991). The species grouped in the order Trichomonadida are anaerobic and present a complex cytoskeleton, three to five flagella at the apical pole, one recurrent flagellum, axostyle, costa and pelta.

T. gallinae is classified in the subfamily Trichomonadinae, one of the two that represent the family Trichomonadidae. Other parasites of human and veterinary importance, like Trichomonas vaginalis or Tetratrichomonas gallinarum are also included in this subfamily. As these protozoa lack mitochondria, they have an alternative route for ATP synthesis that is fulfilled by hydrogenosomes. cytosolic organelles that do not require an oxygen influx. 

The genus name, Trichomonas, derives from the Greek word "thrix-" meaning hair and "monas" that indicates a single unit, regarding their one cell structure (Gómez Muñoz et al., 2018).

3. Epidemiology

The organism is fragile in the environment and transmission occurs only through contact with infected oral secretions or through water contaminated by oral secretions of carriers. Pigeons are believed to be the natural hosts and primary carriers. The prevalence of the infection is near 100% for adult pigeons. Carrier birds show no signs or lesion.

Pigeons and doves transmit trichomonads to their young during feeding of regurgitated partially digested crop content (pigeon milk). Transmission in raptors (hawks, owls, eagles, etc.) and their young, is through ingestion of infected prey. Turkeys and chickens probably contract the disease after consuming stagnant surface water containing T. gallinae. Other disease may predispose turkeys to clinical trichomoniasis.

In established flocks or lofts, trichomoniasis may only be noted as a clinical disease after introduction of a more virulent strain of T. gallinae by new birds or exposure to wildlife carriers (Boulianne, 2012).

3.1 Susceptible hosts

Susceptible species include birds in orders: Columbiformes, Falconiformes, Psittaciformes, Passeriformes, Galliformes, Anseriformes, and Gruiformes. Color canaries, suffering from hypervitaminosis A, often caused by massive administration of coloration, are extremely sensitive (Samour, 2015).

3.2 Transmissions 

T. gallinae is generally found in the oral-nasal cavity or anterior end of the digestive and respiratory tracts. The trichomonads multiply rapidly by simple division (binary fission), but do not form a resistant cyst. They therefore die quickly when passed out of the host. Because of the nature of the life cycle, transmission of the parasite from one bird to another occurs in one of three ways. In pigeons, transmission occurs when infected older birds (carriers) feed “pigeon milk” to newly hatched squabs. Adult birds, which do not show signs of disease, may carry the infection for a year or more and are a constant source of infection for their young. 

Turkeys and chickens likely become infected through contaminated drinking water or food. Because the trichomonads do not survive for long outside the bird, transmission must occur rapidly. Wild pigeons and other birds may be an important source of introducing the infection to domestic birds. 

The third method of transmission is more common to birds of prey. An infection may be established in a raptor that has fed on an infected prey bird (Agdex, 2001).

4. Life cycle

T. gallinae has a direct life cycle, with trophozoites multiplying by longitudinal binary fission, one cell will divide to form two new ones (Stabler, 1941). Their preferred location is the mucosa of the upper digestive tract, from the oropharyngeal cavity and crop to the proximal esophagus. Nevertheless, affection of internal organs such as liver, lungs, pericardium, air sacs and pancreas, has also been reported in certain strains of the parasite. Indeed, some strains target particular tissues, namely, Jones' Barn and Eiberg strains are hepatotrophic, while Mirza strain is cephalotrophic (head sinuses, orbital regions, brain and neck). However, the Jones' Barn strain primary showed tropism the lungs instead of the liver of mourning doves (Zenaida macroura) and rock pigeons (Columba livia) in I Maria Teresa Gómez Muñoz et al. experimental infections. Non-pathogenic strains, like Lahore and Stabler-gallinae (SG), have also been described. The primary route of transmission is by direct contact with the saliva of an infected bird, although contaminated food and water also act as sources of infection (Bunbury et al., 2007). Indeed, experimental transmission of the parasite through the ingestion of contaminated food has been proved in columbiformes. Recent studies have showed that bird baths may act as potential vehicles with viable trophozoites for at least 16 hours.

Contaminated carcasses also remain infective for at least 48 hours after death, acting as a reservoir for omitophagous and scavenging birds. Moist grains are also able to maintain the parasite's viability for at least five hours. Regarding the number of trophozoites needed to initiate the infection, it seems that only one trophozoite of the Jones' Barn strain is enough to develop the disease and cause death in pigeons in less than 15 days post-infection (Gómez Muñoz et al., 2018).

5. Clinical signs and pathology

5.1 Clinical signs

Birds that were subsequently diagnosed with trichomoniasis were described by the submitters as lethargic, with ruffled feathers, labored breathing, and poor flight ability. The birds would sit on a bird feeder for several minutes at a time with eyes closed before resuming feeding. Pictures submitted by the public revealed birds with debris attached by saliva to the feathers of their head and neck and small amounts of what was interpreted as regurgitated material at the commissures of their beaks (Forzán et al., 2010).

All the necropsied birds presented dehydration and cachexia, in addition to clinical signs such as a swollen head or eyelides, and wet feathers around the beak. Lesions compatible with trichomonosis were observed during necropsy in the esophagus, or crop, or both, in twelve birds (one booted eagle, one wood pigeon and ten common kestrels). In all cases, granulomas were found that had extended from the oropharyngeal cavity and which could be palpated in the neck of each bird before necropsy. The liver of a common kestrel and a rock pigeon also presented caseonecrotic lesions consistent with trichomonosis, in addition to those observed in the oropharyngeal cavity. 

Capillarid nematodes in the upper digestive tract were also found in three cases of goshawks, with lesions of fibrinonecrotic material extending through the mucosa of the upper and lower regions of the oropharyngeal cavity. In one of them, eggs and a capillarid worm were identified under the microscope from the smear of the oropharyngeal lesion (Fig.4A and 4B).

A number of birds showed lesions in areas far from the oropharyngeal opening, such as the choanal slit or the tip of the tongue (mild cases). Lesions at the beak angle, palate, infundibular cleft, or eye were observed in birds (moderate cases). Severe cases are reported with lesions being found in the esophagus, crop, or the base of the tongue, compromising the ability to swallow and worsening the prognosis. In the case of a marsh harrier and a barn owl, these lesions also affected the skull, with caseonecrotic lesions extending into the brain (Martínez-Herrero et al., 2020).

5.2 Pathology 

At necropsy, birds with trichomoniasis were emaciated, and some of them had a slightly to markedly thickened crop; rarely, there were white to yellow masses in the lumen of the oropharynx (cankers). Microscopically, the mucosa of the oropharynx, ingluvies (crop) and/or esophagus was severely thickened due to epithelial hyperplasia and a necrotic pseudomembrane. This hyperplastic epithelium had multifocal areas of erosive to ulcerative necrosis and variable amounts of inflammation composed of heterophils, macrophages, and lymphocytes. Opportunistic coccoid and cocco-bacillary bacteria proliferated on the surface of the exudate. Amongst the keratinized epithelial cells were numerous ovoids to leaf-shaped protozoan parasites that stained pale pink with a Periodic Acid Schiff’s stain, measured 5 to 8 mm in length, had a pale eosinophilic cytoplasm and a round basophilic nucleus, morphology consistent with Trichomonas sp. (Fig.6). Necrotizing and proliferative oropharyngitis, ingluvitis, and/or esophagitis due to trichomoniasis was diagnosed in 7 purple finches and 1 A. goldfinch. Additionally, an A. goldfinch, was diagnosed with hepatic trichomoniasis. The A. goldfinch that died of hepatic trichomoniasis was emaciated but had no other gross lesions. Microscopically, the liver had randomly scattered foci of necrosis with rare macrophages, plasma cells and lymphocytes (Fig.7). In the necrotic foci and free in the sinusoids were many protozoans identified morphologically as Trichomonas sp (Forzán et al., 2010).

Figure 6: Esophagi/crops of purple finches, Carpodacus purpureus. 

a) Normal tissue. Bar = 100 μm. b) Severe erosive and proliferative esophagitis/ingluvitis due to trichomoniasis. Note the intense staining of the basal layers that correspond to active replication (hyperplasia). Bar = 100 μm. c) Higher magnification of the lesion described in b, showing numerous protozoans (Trichomonas gallinae) among the keratinized epithelial layers. Bar = 20 μm (Forzán et al., 2010)

6. Diagnosis

The pathogenicity of T. gallinae is not well-understood. Death has been reported to occur as early as 4 days or late as 3 weeks post-infection, if infected with a virulent strain. There are several different strains of the protozoan. Examples of notable virulent strains include the Jones’-Barn and Eiberg strains that infect the liver, and the Mirza strain that causes lesions of the oropharynx (OIE, 2021). 

Clinical diagnosis 

In avian species, diagnosis is made based on clinical signs, microscopic examination of the protozoan, and necropsy. The organism is approximately 7-11 µm in length, oval to pyriform in shape, with four anterior flagella, an axostyle, and an undulating membrane. 

There are several different lesions and clinical signs that can result from infection with this protozoan. If infected with mild strains of the parasite, excessive salivation and mucosal inflammation of mouth and throat may be observed. Infection with a virulent strain can result in weight loss, dysphagia, dyspnoea, a pendulous crop, vomiting, ruffled feathers, diarrhoea, and loss of appetite. Lesions that prevent birds from feeding can develop and are characterized by greenish fluid and caseous lesions on oropharyngeal membranes. In doves and pigeons, trichomoniasis is generally observed in young birds. Immunity is thought to be conferred in birds based on infection with nonvirulent strains or recovery from a mild infection (OIE, 2021). 

Lesions 

Birds:

• Diphtheritic membranes
• Early oral lesions

+ Small cream to yellow spots on oral mucosa to large, thick, caseous lesions

• Acute infections

+Discharge, nodules in mouth

• Chronic infections

+Caseous lesions in mouth and  oesophagus; may travel to beak and eyes

• Lesions of pharynx and crop

+ Cream-colored to yellow and caseous

+ May extend to the roof of the mouth and sinuses

• Necropsy

+Fibrin covering the heart, liver and air sacs may be observed (OIE, 2021)

Laboratory diagnosis 

Samples for isolation of agent 

Birds 

○ Crop wash 

○ Throat swab 

○ Mucus 

○ Lesion sample 

Procedures 

Identification of the agent 

Birds 

○ Faecal wet mounts (juveniles)

Motile parasite is not often identified in faeces 

○ Giemsa stain of oral and crop swab samples 

○ InPouch™ TF (oral and crop swab samples) 

■ Examine organisms in the pouch directly under a microscope or using a wet mount slide of the media 

○ Microscopic identification of parasite from lesion at 20x-40x magnification 

■ Identify flagellated protozoa with wet saline mount of lesion

■ Can still identify protozoa in warmed saline solution after carcass has been refrigerated for several days 

 ○Polymerase chain reaction (PCR) (OIE, 2021). 

7. Treatment

Because trichomonads in pigeons are so readily transmitted from parent to offspring in the normal feeding process, chronically infected birds should be separated from breeding birds. In pigeons, recovery from infection with a less virulent trichomonad strain appears to provide some protection against subsequent attack by a more virulent strain. Successful treatments include carnidazole (10 mg/kg body wt), metronidazole (60 mg/kg body wt), and dimetridazole (50 mg/kg body wt, PO; or in the drinking water at 0.05% for 5–6 days). None of these drugs is approved for use in birds in the USA, but they could be used in non-food-producing birds by veterinary prescription (Richard W. Gerhold, 2020). 

Canktrix (Vemedim) is a single dose treatment for canker in racing pigeons. To ensure the full benefit of Canktrix, all pigeons should be treated at the same time, whenever canker is seen. Young birds should be treated at weaning or before flying out, Pigeons should be treated before pairing or during the first half of each brood period to prevent canker being passed to the newly hatched young. 

Indications: Canktrix is indicated for oral treatment of trichomoniasis (canker) in omamental and homing (non-food) pigeons. 

Recommended dosages: For direct oral administration. One (12 mg) tablet per adult pigeon. Half tablet (6 mg) per newly weaned pigeon. Treatments for only one day. 

Routine treatment: Young pigeons at weaning begin routine treatment approximately December 1st. Adult pigeons before mating or approximately October 1^st, during the first part of the brooding period, and after returning from races when e been in the travel boxes for a long time.

8. Control and prevention 

Sanitary prophylaxis 

● In captivity or sites where feeding wild birds is common (e.g., backyard bird feeders), it is recommended to ensure feed is properly stored and contained to prevent moisture and inappropriate access by other birds. 

○ Change feed and water daily 

● Generally, large gatherings of doves and pigeons at feeding and watering sites should be discouraged to reduce the possibility for transmission 

● Infected birds should be removed from group housings 

● Check wild reptiles for Trichomonas spp. before housing with captive reptiles 

● Particularly for captive reptiles, maintain proper sanitation and diet to prevent an increase in parasite burden 

Medical prophylaxis 

● Bird treatment 

○ Strategic antiprotozoal administration 

○ Infection with lentogenic strains to confer immunity against virulent strains 

○ Check doves and pigeons being fed to raptors for T. gallinae infection 

● Birds held in captivity for rehabilitation with apparent clinical disease, particularly doves and pigeons, should be isolated until clinical signs resolve (OIE, 2021)..

9. References 

Agdex, 2001. Trichomoniasis in Birds, in: AGRI-FACTS (Ed.), Practival Information for Alberta's Agriculture Industry.

Boulianne, M., 2012. Avian disease manual.

Brugerolle, G., Lee, J., 2000. Phylum parabasalia. An illustrated guide to the protozoa 2, 2.

Bunbury, N., Jones, C., Greenwood, A., Bell, D., 2007. Trichomonas gallinae in Mauritian columbids: implications for an endangered endemic. Journal of Wildlife Diseases 43, 399-407.

Cepicka, I., Hampl, V., Kulda, J., 2010. Critical taxonomic revision of parabasalids with description of one new genus and three new species. Protist 161, 400-433.

Chaves Hernández, A.J., 2014. Poultry and Avian Diseases. Encyclopedia of Agriculture and Food Systems, 504-520.

Forzán, M.J., Vanderstichel, R., Melekhovets, Y.F., McBurney, S., 2010. Trichomoniasis in finches from the Canadian Maritime provinces--An emerging disease. Can Vet J 51, 391-396.

Gómez Muñoz, M.T., Herrero, M., del Carmen, M., Sansano Maestre, J., Garijo Toledo, M.M., 2018. Oropharyngeal trichomonads in wild birds. Jenkins, Owen P.(ed.)(2018). Advances in Animal Science and Zoology. Volume 11.

Martínez-Herrero, M.C., Sansano-Maestre, J., Ortega, J., González, F., López-Márquez, I., Gómez-Muñoz, M.T., Garijo-Toledo, M.M., 2020. Oral trichomonosis: Description and severity of lesions in birds in Spain. Veterinary Parasitology 283, 109196.

NCSU, Trichomonas gallinae NCSU Veterinary Parasitology, NC State University.

OIE, 2021. Trichomonas spp.

Richard W. Gerhold, J., 2020. Trichomonosis, MSD MANUAL. Veterinary Manual. Department of Biomedical and Diagnostic Sciences, College of Veterinary Medicine, University of Tennesseel.

Samour, J., 2015. Avian medicine. Elsevier Health Sciences.

Sleigh, M.A., 1991. Protozoa and other protists. Cambridge University Press.

Stabler, R.M., 1941. Further studies on trichomoniasis in birds. The Auk 58, 558-562.

Tomikawa, S., Nakagun, S., Watanabe, Y., Saito, K., Kobayashi, Y., 2021. Molecular characterization of Trichomonas gypaetinii isolated from the upper alimentary tract of Steller’s sea eagles (Haliaeetus pelagicus) and white-tailed sea eagles (Haliaeetus albicilla) in Hokkaido, Japan. Parasitology Research 120, 2189-2198.