In the present study, microscopic examination of 324 throat swab samples showed detection of
T. gallinae (Fig 1) in 87 cases with a prevalence of 26.85%. Similar findings were shown by workers as
Bahrami et al., (2012) from Iran (26.8%), Tasca and Carli (1999) from Brazil (26.5%), Al- Sadi and Hamodi (2011) from Iraq (16%) and
Qiu et al., (2012) from China (33.9%). The reason for such moderate infection might be due to transmission of the parasite by adults while feeding their young or in feeder and water as adult birds remain infected for a year or more acting as a constant source of infection for their young ones. However, higher infection rates (43-75%) have been reported by many workers:
Saleem et al., (2008) from Lahore, Pakistan;
McKeon et al., (1997) from Australia;
Begum et al., (2008) from Bangladesh. The differences in the rate of prevalence might be due to influencing factors of disease occurrence such as climatic conditions, geographical difference, seasonal variation, resistance of the host, different feeding habits, difference in husbandry practices as mentioned by
Saleem et al., (2008) and
Hafidth et al., (2011).
Examination of Giemsa stained swab smears showed single celled, oval to pyriform flagellated protozoan approximately 6.3-15.5 μm long and 4.0-8.3 μm wide with four anterior flagella (7-13 μm in length) arising from the basal granule lying at the anterior end of the body. The parasite showed an undulating membrane formed by a flagellum closely attached to the body surface and extended to two-thirds the length of its body. The ovoid nucleus (2.5- 3 μm diameter) was found close to the base of the anterior flagella. The axostyle originating at the pole opposite the nucleus was seen running from the base of the anterior flagella to the posterior end of the cell and protruding from it. Trophozoites of
T. gallinae were found to be morphologically identical to those reported by
Melhorn et al., (2009) and
Amin et al., (2010).
Prevalence of Trichomonas gallinae infection according to age group
Prevalence was found highest (56.25%) in squab followed by 22.38% in young and least in adult (10.90%) (Table1). Statistically, the percentage prevalence of
T. gallinae in different age group was significant (P<0.05) by Chi square analysis.
The prevalence of trichomoniosis was more in squabs as compared to the adult pigeons which is in accordance with the report of other workers (McDougald, 2003; Al-Sadi and Hamodi, 2011). The main route of transmission of the organism to the squabs is through feeding of “crop milk” which is a mixture of the secretion from the crop glands and regurgitated food containing this pathogen fed by the carrier adult parent pigeons. The present findings are in agreement with that of
Hafidth et al., (2011), Begum et al., (2008), however reported non significantly highest prevalence of
T. gallinae in adult followed by squabs and young birds. The highest prevalence in squabs followed by young and least in adults as observed in the present study might be related to the resistance status that reflects the age of the host to have an effect on the prevalence of
T. gallinae in pigeons.
Prevalence of Trichomonas gallinae infection according to sex of pigeon
Sex wise, 53 out of 158 samples examined from female birds were positive (33.54%) while in males, the corresponding value was 20.48% (Table 2). Comparatively higher prevalence was observed in female than in male birds and this variation was also found statistically significant (P<0.05). Similar finding was also shown by
Begum et al., (2008). However, Al- Sadi and Hamodi (2011) and
Hafidth et al., (2011) recorded higher infection in male than in female pigeons.
Villanua et al., (2006) on the other hand reported non significant difference in prevalence of
T. gallinae according to sex. The cause of higher prevalence in females could not be justified although Lloyd (1983) assumed that female sex hormones might play a role making the individual more susceptible to any infection.
Seasonal prevalence of Trichomonas gallinae in pigeon
Clinical and subclinical illness in pigeons were recorded throughout the year. Season wise, prevalence was found highest in winter (34.0%) followed by Pre-monsoon (25.55%), Monsoon (23.07%) and Post-monsoon (21.44%) showing no significant difference (Table 3). However,
Begum et al., (2008) recorded higher prevalence in rainy and winter seasons than in summer. Thus, wide variation could be noticed in different studies on the prevalence of
T. gallinae depending on season, host factor and other epidemiological factors such as climate, geographical region, host resistance and living status of birds as opined by other workers
(Saleem et al., 2008; Hafidth et al., 2011; Amin et al., 2014).
Gross pathological findings
In the present study trichomoniosis was diagnosed in 14 out of 55 carcasses at post mortem examination. External findings included emaciated body with ruffled feather, swollen beaks, puffed up appearance of mouth, exudation of foul smelling fluid through mouth with the beaks wide apart. In some cases lesions around the eyes were seen with appearance of a whitish membrane partially covering the eyes (Fig 2a). Further examination of carcasses revealed presence of yellowish white caseated masses with lesions in the oral cavity (Fig 2b-c), oesophagus, crop (Fig 2e) and proventriculus while the gizzard had yellowish to greenish areas of necrosis. In the liver circumscribed areas of necrosis were seen (Fig 2d). Our findings confirmed the observations made by several workers
(Begum et al., 2008; Sansano-
Maestre et al., 2009; Borji et al., 2011; Al-Sadi and Hamdi 2011). According to
Neimanis et al., (2010) presence of gross lesions is a primary diagnostic feature of this disease. The lesions in different organs were basically inflammatory, ulcerative and necrotic in nature as similar to those observed in experimentally induced trichomoniosis (McDougold 2003 and
Hafidth et al., 2011) reported absence of a secondary disease as a pre-requisite for the occurrence of
Trichomonas infection. Isolation of facultative bacterial pathogens from natural cases of trichomoniosis with caseated lesions rather revealed association of secondary infection
(Mohamed et al., 2009) that produced caseative necrosis with drooling of offensive odour fluid from mouth under the stress of trichomoniosis. Although no attempt was made to isolate bacterial pathogens in the present study, similar observation on the presence of caseated mass inside oral cavity and drooling of offensive exudate through mouth might suggest secondary bacterial infection as was reported in earlier studies
(Mohamed et al., 2009). Observation of grossly visible lesions in the eyes of affected pigeons agreed with Bondurant and Honingberg (1994) who reported that the parasite could invade the brain and the eye region with release of organism in tears.
Histopathological findings
Microscopically, histopathological lesions were observed in the crop, oesophagus, gizzard, liver, heart, trachea and lungs (Fig 3 a, b, c, d). Crop showed moderate haemorrhage and congestion. In the oesophagus submucosal glands were swollen. Gizzard showed separation of mucosal layer from muscular layer and separation of muscle. Sinusoidal congestion and kupffer cell hyperplasia also observed in the liver. Myocardium of heart showed congestion and focal areas of haemorrhages. Sloughing of mucosal layer observed in trachea. Lung showed infiltration of polymorphonuclear cells in the thickened inter alveolar space. Similar lesions were described by McDougald (2003) and Al-Sadi and Hamodi (2011) in naturally occurring and experimentally induced trichomoniasis in pigeons, thus conforming our findings. Contrary to our report,
Begum et al., (2008) did not observe microscopic lesions in the crop and proventriculus despite the presence of predominant gross lesions. According to
Villanua et al., (2006), variation in pathologic changes was due to heterogeneity and variations in the virulence of strains involved. Presence of avirulent strains might have contributed to absence of any lesions or the lesion might be in subclinical form. The histopathological alterations in the lungs as thickening of alveolar epithelium, infiltration of polymorphonuclear cells, congestion of the blood vessels, prominent areas of haemorrhages and focal areas of necrosis were in conformation to reports of
Borji et al., (2011). Similarly, Stoute
et al. (2009) observed pulmonary lesion, characterized by caseonecrotic debris and infiltration of heterophils, lymphocytes and plasma cells. However, McDougald (1992) never reported lesions caused by
T. gallinae in the digestive tract below the proventriculus. The present microscopical changes in liver are similar to those reported by Soulsby (2012) and
Borji et al., (2011) who additionally recorded hyperemia and bile duct hyperplasia in moderately infected pigeons. Presence of focal abscesses in the liver, with an inflammatory reaction characterized by mononuclear cells and heterophils, was also reported by
Begum et al., (2008).
