Epidemiology and pathology of Trichomonas gallinae in the common pigeon ( Columba livia )

Pigeons (n=300) were examined during July 2007 to June 2008 in different areas of Mymensingh district. Of the pigeons examined, 202 (67.3%) were infected by Trichomonas gallinae (Rivolta, 1878). Prevalence of Trichomonas gallinae was higher in female pigeon (70.9%) than male pigeon (63.8%). Adult pigeons aged >3 months were comparatively more affected (75%) than the squab aged <30 days (72.1%) and the younger aged between 30 days to 90 days (64.7%). T. gallinae infection was significantly (P<0.01) lower in summer (48.4%) than rainy (69.8%) and winter (69.3%) seasons. Pathological lesions were confined in the crop, proventriculus and liver. There was an accumulation of greenish fluid and/or cheesy material in the crop and proventriculus. At necropsy, yellowish to grayish necrotic lesions were evident in the crop and proventriculus. On the other hand, the liver became congested where congestion of sinusoids and focal accumulation of heterophils in the parenchyma were found. But, no microscopic lesions were seen in the crop and proventriculus although gross lesions were more prominent in these two organs.


Introduction
Among the various types of parasites Trichomonas gallinae is regarded as the largest inhibitor to today's racing pigeon performance in Europe and other countries.T. gallinae a protozoan parasite, which causes the disease in pigeon called as canker mainly affecting the crop, esophagus, liver and lung.Trichomoniasis is cosmopolitan in distribution.In captive birds, the disease has been found in domestic and/or common pigeons, doves, quail, turkeys, chickens, falcons, hawks, various finches, the Java sparrow, and canaries.In wild birds, the disease is found in doves and feral pigeons causing serious threat to these birds (Bon Durant and Honigberg, 1994).In young birds, the infection is severe and even fatal where mortality can reaches up to 80-90% or more in squabs (Soulsby, 1982).With virulent strains, mortality may be as high as 50% in adults before sufficient immunity is developed (McDougald, 1992).Pigeons are often associated with transmission of trichomoniasis to turkeys and chickens.Nearly all pigeons are carriers of this organism apparently because of existence of numerous strains (McDougald, 1992).Occurrences of many parasites including trichomoniasis have been reported from neighbouring countries.In Bangladesh, Begum and Shaikh (1987) recorded only helminths of pigeon while Nasrin (2004) reported different parasites from pigeon.But published reports about the parasites of pigeon and specially of protozoan parasites are scanty in Bangladesh.An in-depth study regarding epidemiology (frequency, distribution and risk factor) of T. gallinae is required to institute control strategies.For this purpose proposed investigation were taken to address properly the parasitological and pathological condition of the protozoon.

Materials and Methods
The study was conducted from July 2007 to June 2008.A total of 300 pigeons were purchased from the farmer's households and local markets of different areas of Mymensingh district.Samples collected from the upper digestive tract of domestic pigeon.At first a cotton swab was fluffed up a bit and immersed in distilled water.The excess fluid was removed and the swab was inserted into the crop.All walls of the crop was contacted by using a swirling motion with the swab which was then withdrawn and the fluid hold in the cotton pressed onto a slide with the help of a spatula or blunt knife.The protozoon was seen to move about in a some what jerky wobbling motion observing immediately under light microscope.
Collected samples were preserved and stained by the Giemsa's method as described by Cable (1957) and morphology was studied (Abraham and Honigberg, 1964).Simultaneously severely infected pigeons were slaughtered to find out the lesions produced by protozoa and histopathological studies were carried out.The gross pathological lesions were recorded and the affected organs were collected and preserved with 10% buffered neutral formalin.For histopathological study, suspected tissues were processed, embedded in wax, cut in appropriate thickness and stained with haematoxylin and eosin (Luna, 1968).
The year was divided into three seasons such as monsoon (July-October), winter (November-February) and summer (March-June) seasons.The pigeons were divided into three age categories such as squab (<30 days of age), young pigeons (30 days to 90 days of age) and adult (>3 months of age).In pigeons, sexes were identified by using conventional methods and confirmed through the detection of male and female reproductive system after slaughtering.Age was determined by taking history from the pigeon owner.

Statistical analysis
The data was analyzed statistically by using chi-square test to determine the relation of T. gallinae infection in pigeon with seasons of the year, but to co-relate the prevalence with age and sex of the host t-test were used (Mostafa, 1989).Odds ratio was obtained by the formula according to the Schlesselman (1982).

Epidemiological aspects of Trichomonas gallinae in pigeon
Overall prevalence of Trichomonas gallinae: During this study (July 2007 to June 2008) 67.3% pigeons (n=202) were infected with T. gallinae which supported the findings of McKeon et al. (1997) andDe Carli et al. (1979), who recorded 59.0% and 62.3% prevalence of T. gallinae in pigeons in Australia and Brazil, respectively.But, the present finding is found higher prevalent rate than that of Catelli et al. (1999), Tasca and Carli (1999) and Toro et al. (1999), who reported 32%, 26.5% and 11% T. gallinae infection in pigeon in Italy, Brazil and Chile, respectively.Dorrestein et al. (1990) reported the lower prevalence rate in Germany and Netherlands.They recorded 27% of Munich and 46% of the Dutch pigeons.This disparity among the findings might be due the variations in the method of study, geo-climatic condition of the research and husbandry practices of the pigeons.
Sex related prevalence: Prevalence of T. gallinae infection varied in relation to sex.Although not statistically significant but higher rate of infection was detected in female pigeons (70.9%) than the male (63.8%) pigeons.Female pigeons were 1.4 times more susceptible to T. gallinae infection than males (Table 1).The cause of higher prevalence of T. gallinae infection can not be explained exactly but it is supposed due to female sex hormones that make the individual more susceptible to any infection (Lloyd, 1983).Age related prevalence: Age of the host had an effect on the prevalence of Trichomonas gallinae in pigeons.Prevalence of T. gallinae was lower (64.7%) in young aged between 30 to 90 days than in squabs aged <30 days (72.1%) and in adult pigeons aged >90 days (75%; Table 2), which supported the findings of Hinshaw (1965) and Nasrin (2004).Hinshaw (1965) reported the major inroads of the T. gallinae occurred at 16-30 weeks of age in turkey.Nasrin (2004) reported the overall helminths incidence was higher in adult pigeons than in squabs.But, Soulsby (1982) reported 80-90% or more of the adult pigeons were infected with T. gallinae.Calculated odd ratio implied that squabs were 1.4 times more susceptible to young, but the adult pigeons were 1.6 times more susceptible than young pigeons.On the other hand, adult pigeons and squabs were almost equally (odds ratio1.2) susceptible to T. gallinae infection.Seasonal prevalence: It was observed that seasons of the year had a profound effect on the prevalence of T. gallinae in pigeons.Prevalence of T. gallinae was the highest in the rainy season (69.8%) followed by winter (69.3%) and summer (48.4%) seasons (Table 3).But, different finding was recorded in turkey, where Hinshaw (1965) reported the major inroads of the T. gallinae occurred during midsummer and later.This difference might be due to the species variation, hormonal influence and methods of husbandry in the pigeon.It was revealed that pigeons were 2.5 times more susceptible to T. gallinae infection in rainy season than in summer season.But in winter season, pigeons were 2.4 times vulnerable to T. gallinae infection than summer.On the other hand, in the rainy season and in winter pigeons were almost equally (odds ratio1.02)susceptible to T. gallinae infection.

Lesions produced by T. gallinae in different organs of pigeons
Obviously the course of the disease in pigeon varies with the strain of T. gallinae (Stabler, 1947;Stabler and Herman, 1951).Pathological lesions were confined in the crop, proventriculus and liver.There was an accumulation of greenish fluid and/or cheesy material in the crop and proventriculus.On post mortem examination, yellowish to grayish necrotic lesions were evident in the crop and proventriculus.These findings confirmed the findings of Soulsby (1982) who reported the similar lesions in mouth, crop and esophagus.The author reported the small yellowish circumscribed areas in the mouth cavity, esophagus, crop and proventriculus.The esophageal portion of proventriculus is mostly affected (Fig. 3), which supported the findings of Hinshaw (1965).No microscopic lesions were seen in the crop and proventriculus although gross lesions were more prominent in these two organs.
That might be due to the presence of avirulent strains, which did not cause any lesions or the lesion might be in subclinical form or the lesion was in early stages.Grossly the liver became congested.Soulsby (1982) also reported the similar liver lesions with T. gallinae infection.
Microscopically congestion of sinusoids (Fig. 1) and focal accumulation of heterophils in the parenchyma of liver (Fig. 2) were observed, which confirmed the findings of Perez Mesa et al. (1961) who reported the focal necrotic abscesses in al zones of lobules of liver with an inflammatory reaction characterized by mononuclear cells and heterophils.Soulsby (1982) and McDougald (1992) never reported the lesions due to T. gallinae in the digestive tract below the proventriculus but in the present study both gross (Fig. 4) and microscopic lesions were found in the gizzard.Grossly the lesions were similar to that of crop and proventriculus but different microscopic lesions were observed.The muscle layer was thickened and there was formation of granulomatous type of reaction (Fig. 5).The granuloma was mainly formed by the mononuclear cells (Fig. 6).But these were not confirmed whether the lesion was due to T. gallinae or other organisms.As the gross lesion of both proventriculus and gizzard was similar so the authors suggested that the lesions might be due to T. gallinae.Further research should be conducted to solve the question.
The present study suggests that pigeons commonly reared in Bangladesh are very much susceptible to T. gallinae infection irrespective to age and sex of pigeons and seasons of the year.So proper treatment against this protozoon is essential.Further research may be implicated towards economic aspects of Trichomonas gallinae in domestic pigeon as well as to develop its preventive measures.