Introduction

Trichomonas is a genus of flagellate protozoans that are primarily parasites of vertebrates, including humans, cattle, birds, and cats (1,2). Some species belonging to the genus Trichomonas are already identified worldwide, which can infect humans and animals. In humans, three Trichomonas species (genitourinary T. vaginalis, intestinal T. hominins, and oral T. tenax) are identified in the world, including Iraq (3-6). T. tenax and T. hominis are known to be commensalism species that inhabit the oral and intestinal sites of humans, respectively, where they are considered nonpathogenic (7). In contrast, T. vaginalis is a well-known pathogenic species that cause sexually transmitted diseases in humans and affects over 150 million people worldwide (8). Another important species is T. fetus which commonly causes venereal Trichomonosis in cattle (9). This protozoan is an obligate parasite in cattle and cats' reproductive and gastrointestinal tracts, respectively (10). Interestingly, a study reported for the first time that this species was isolated from the uterus of breeding camels, as well as one preputial washing of a camel bull which showed positive for the infection (11). The disease can cause economic losses in herds due to low pregnancy rates, infertility, endometritis, and abortions in pregnant cows and heifers (12,13). In cattle, the parasite transmission occurs during mating and /or direct contact between infected individuals (14).

In comparison, the fecal-oral route considers a common transmission mode among cats(15,16). In cattle, the parasite is found on the mucosal surfaces of the uterus and vagina of cows, while preputial smegma is considered the favorite place for residue in bulls (17). Vaginitis, cervicitis, endometritis, and infertility are significant pathogenic signs in infected cows. In addition, placental edema, mild lymphocytic and histiocytic chorionitis, and focal necrosis of trophoblasts are also shown as a result of inflammation of the mucosal surfaces of the reproductive tract (18). However, infected bulls that remain healthy are usually parasite carriers without clinical signs (19). In cats, T. fetus has been found in the feces of young cats in the last decades (20), causing diarrhea in domestic cats (15,16,21). Some symptoms can be seen during the infection, including chronic diarrhea associated with blood and mucus, which may be observed as firm or loose in consistency, and suffering from anal irritation and flatulence (22). T. gallinae is the only pathogenic species of trichomonads that causes avian Trichomonosis or is called canker in the gastrointestinal tract of birds in particular; Columbiformes, Falconiformes, Strigiformes, and wild Passeriformes (23,24). Previous studies mentioned that outbreaks of avian Trichomonosis were recorded in wild finches, later in Passeriformes, canaries, and psittacines in Europe and North America, as well as identified in other species of birds in the USA, such as; corvids in California (2,25).

Briefly, the wet mount preparation based on urine and vaginal discharge is routinely used to detect T. vaginalis directly. However,rapid antigen detection and PCR assays have greater sensitivity and accuracy in diagnosing the infection (26-28). In cattle, microscopic examination of bovine preputial and urogenital washes or scrapings can usually be used to detect the parasite. In addition, subsequent culture is also conducted for propagation and detection of the infection in the laboratory (29). Feline Trichomoniasis can be diagnosed by several techniques, including; direct examination of fresh feces smear, fecal culture using specific media, and histopathological examination of intestinal biopsies. Direct microscopy is used to diagnose avian trichomoniasis based on swabbing the oral cavity during clinical examination or necropsy (23), and cultivation tests are also applicable for detecting the infection in birds (30). Furthermore, PCR amplification is commonly used to diagnose the hosts' infection (15,24,30,31).

Indeed, Trichomonas has been documented as a parasite that causes trichomoniasis in mammals and birds for several decades, for instance, in the bovine reproductive tract for about 100 years (32). Interestingly, this parasite has been recently recognized and established in the intestine of cats associated with diarrhea (15,21). Nevertheless, little data is known about the epidemiology and prevalence of this parasite, whether in humans or other animals, including cats in some parts of the world. Thus, this review highlights the distribution and updated prevalence of this parasite in Iraq.

Scientific classification of Trichomonas

The taxonomic tree indicates that this protozoan belongs to Kingdom: Protista, Phylum: Protozoa, Subphylum: Sarcomastigophora, Order: Trichomonadida, Family: Trichomonadidae, Genus: Trichomonas, Species: T. vaginalis, T. fetus, T. gallinae. These common species cause a disease called trichomoniasis, where T. vaginalis resides in the female lower genital tract and the male urethra and prostate of humans (33), and T. fetus commonly causes a disease called bovine venereal Trichomonosis in cattle or feline Trichomonosis in cats (19). at the same time, T. gallinae causes avian Trichomonosis in the upper gastrointestinal tract of birds (23).

Morphological characteristics of Trichomonas

Although species of the genus Trichomonas tend to be similar in terms of external appearance, each species has some specific characteristic features, particularly the number and shape of flagella. T. vaginalis is oval or pear in shape, measuring 9 × 7 μm, and has five flagella, four anterior, while the fifth flagellum is a recurrent flagellum with an undulating membrane that extends backward of the body (34). Regarding the nonpathogenic Trichomonas species, the trophozoite of T. tenax measures 5-14 µm long and 6-9 µm wide, which has four anterior flagella and the fifth flagellum that raises an undulating membrane that is two-thirds the length of the body (35). T. hominins, this species does not have a cystic stage while it has the trophozoite stage, which is pyriform in shape, measuring 8-20 μm long by 3-14 μm wide and bearing 3-5 anterior flagella (36) While, whereas T. fetus only has a trophozoite stage which is about 5-25 µm in length and 3-15 µm in width, this stage is a pear-like shape, one nucleus, three anterior flagella, and a posterior flagellum (37-39). For T. gallinae, the trophozoite has an ovoidal to pyriform shape with a size of about 7-11 μm. This trophozoite also has four free anterior flagella and a fifth recurrent one, which does not extend outside the posterior pole (40). The life cycle is a simple asexual cycle without a cyst stage, where trophozoites replicate simply by binary fission (41).

Transmission of Trichomonas spp.

T. vaginalis is a species that causes a sexually transmitted disease in humans. Therefore, sexual intercourse is the main route of transmission among humans (42). The oral species, T. Tenax, is transmitted via saliva, droplet spray, kissing, and contaminated drinking water (43,44), and the intestinal T. hominis can be transmitted via the fecal-oral route (45). In comparison, the transmission of T. fetus is one of the primary steps that influence the distribution of the infection among animals. Cow-to-bull or/and bull-to-cow during coitus consider primary routes to transmit the parasite from a host to others, where cows usually get infected by infected bulls through natural or artificial insemination (46,47). Nevertheless, parasites in frozen samples can be killed through drying or high temperatures of the artificial insemination process. Therefore, direct contact between a host and another is a common mode for transmitting the parasite among cattle (48).

In feline trichomoniasis, the parasite is transmitted through the fecal-oral route and can be survived for days in moisture environments, shared litter boxes, and mutual grooming (19). More importantly, this parasite can remain infectious for 24hr in feed containers, dry areas, and water (26). In avian trichomoniasis, the upper digestive tract, including the mouth, pharynx, esophagus, and crop, is the favorite site for T. gallinae. Therefore, the most common route to transmit the infection is direct contact via the crop milk from infected parent birds to the nestlings during feeding (49). Additionally, it is believed that this parasite can infect turkeys and chickens through drinking water (50).

T. vaginalis in humans

According to updated global data, 156 million cases per year are infected by T. vaginalis, where the prevalence in women between 15-49 years old is 5.3%, while in men is 0.6% (51,52). It is known that the infection in women may be asymptomatic or have vaginal discharge, pruritus, dysuria, vaginitis, and cervicitis (53-55). Infected men are also asymptomatic, although urethritis may be shown in some cases (56). Although the epidemiology of the infection in men is still incompletely known, the severity and epidemiology of it in women rely on some risk factors, including lower socioeconomic status, older age, more sexual partners, and the black race (57,58). The prevalence of infection among women also differs according to geographical areas, where the percentage in Asia is 0.8% compared to 17-20% in Africa (58,59,60). In Arabic countries, a previous study using clinical and wet-mount examination was conducted to investigate the Trichomonas infection in 2,450 women in Benghazi City, Libya, from 2000 to 2001. The findings showed that 29 out of 2450 (1.2%) were infected with symptomatic clinical signs, including vaginitis discharge, burning, vulvar pruritus, dyspareunia, dysuria, and strawberry appearance (61). Another descriptive study was conducted among 430 pregnant women in Gaza, Palestine; its results found that 77 out of 423 women 18.2% were favorable to T. vaginalis infection (62).

In Iraq, several studies are already conducted to detect this infection in humans, particularly symptomatic women. This may be an indicator that trichomoniasis considers an endemic disease in Iraqi populations. For instance, A study in Basra province used wet preparation and culture methods to examine 300 females to detect this parasite. The results show that 34 females 11.3% suffering from vaginal discharge were favorable to the infection (63). In 2010, 600 women who attended the gynecological outpatient clinic and hospitals in Sulaimania were examined for T. vaginalis infection. The infection rates are 1.66% and 5% based on direct wet mount examination and culture techniques (64). In Dohuk city, 425 vaginal swabs were collected from women with vaginal discharge associated with vaginitis, cervicitis, and pelvic inflammatory disease. The finding appeared that the infection was positive in 10(2.4%), 15(3.5%), 17(4.0%), 23(‎5.4%)‎ swabs by wet smear preparation, hematoxylin-eosin-stained smear, Papanicolaou stain, and Diamond modified culture, respectively. This study also found that young women aged 20-25 showed the highest infection rate 7.6% compared to other ages (65). In Babylon province, A study investigated 250 samples of cervical swap for detecting the parasite, and its results appear that the infection rate is 20% by mediated wet swab and 22% by mediated centrifuge (66). Epidemiological research was also carried out for screening for trichomoniasis in 440 women ages (16-60 years old) in Erbil city. The results showed that 14 (3.18%) were positive using the culture technique, while 12 (2.73%) were infected using the direct wet mount technique. Additionally, the age group of 16-26 years recorded the highest infection rate 4% compared to other age groups of 16-26 years and 27-37 years, who recorded 3.3% and 3.1%, respectively (67). A recent study on wet mount and polymerase chain reaction was also conducted to detect the infection in symptomatic women in Babylon city. The results demonstrated that (19.1%) was positive for wet mount and (27.6%) for PCR technique. This study also found that the highest infection rates were recorded in women in the age group 30-40 years (68).

Furthermore, a molecular study using the multilocus sequence typing (MLST) method was conducted to examine 154 Iraqi women in Baghdad province. This study finds that 53 women (34.41%) are positive for T. vaginalis infection (69). Recently, a study in the north of Iraq was conducted to assess serum levels of interferon-gamma (IFN-γ), Interleukin 10 (IL-10), C-reactive protein, and antiphospholipid, anticardiolipin antibodies with eosinophil count in response to T.vaginalis infection. The observation of this study appeared that serum IFN-γ levels and antiphospholipid immunoglobulin G (IgG) antibodies were significantly increased in infected women (70). A comparative study was carried out to compare ELISA and wet mount preparation for the detection of T. vaginalis infection, and its findings reveal that these two techniques recorded 65.5% and 57.2%, respectively (71). More recently, research was conducted on 160 non-pregnant married women who attended private clinics and public hospitals in Baghdad to detect T. vaginalis using serological techniques, recording 14.37% as the total infection rate (72). Notably, a serological study based on ELISA examined 240 serum samples collected from 120 couples between 18-43 years old to diagnose this species. The results demonstrate that the infection rates in women are higher than in men, which were 31.7% and 24.2%, respectively (73). Another recent research was done in Baghdad city targeting pro-inflammatory cytokines in the serum of infected women with T. vaginalis, showing that this parasite's IL-8 and IL-12 may alter during infection (74). In Al-Diwaniya city, direct wet mount microscopy and culture were used to detect this parasite in vaginal swabs collected from female pregnant patients. The results of this study explain that 12 out of 200 (6%) pregnant women are favorable to infection (75). A more recent study was conducted in Mosul city to investigate this species in outpatient women (18-45 years) at a Maternity hospital using microscopic and molecular techniques, explaining the high sensitivity of molecular techniques in the detection of the parasite compared to routine methods (76).

To conclude the above data, it is evident that the infection by T. vaginalis in Iraq is common and well investigated in most cities, showing the importance of this parasite and its effects on public health. Thus, awareness and advice should always be given to people, particularly women, about the risk of this infection.

T. tenax and T. hominis (synonym: PentaTrichomonas hominis) in human

Despite these two species being initially known as nonpathogenic or commensal species in the host (36,77), some recent studies suggest that they are associated with some diseases and symptoms (35,78-81).

In Iraq, some local studies were conducted on humans to investigate the infection by T. tenax and T. hominins, showing various infection rates. For instance, a study in Basrah, Iraq, examined 100, 104, 110, and 100 samples of the general population, primary school, secondary school, and university students, respectively, during a period of (October-December) based on the direct wet smear method to detect T. tenax, the rates of the infection were 11% in the general population, 6.7% in primary school children, 3.6% in secondary school children, 1% in university students (3). T. tenax was recorded in patients who attended clinics periodontics in Babylon province. The results demonstrated that 64 out of 310 (20.6 %) patients were positive (40.2% periodontitis, 14.2 % gingivitis) according to wet preparation and Giemsa staining (82). Another study in Babylon province done from September 2011 to May 2012 used the direct smear method and wet preparation method to examine 653 sputum, and 653 saliva samples collected from hospitals, medical centers, and special clinics showed that the total infection rate of T. tenax is 1.99 % and 7.81% in sputum and saliva samples, respectively (5). Furthermore, the distribution of oral T. Tenax in patients in Karbala city was determined by a random examination of 199 samples taken from 160 patients using PCR, where the parasite was found in 25% out of examined patients (83). Another recent study in Karbala city investigated 383 samples collected from specialized dental centers and some health centers to detect T. tenaxfrom September 2017 to May 2018 using the microscopic examination. The findings of this study recorded that the total infection rate is 8.09% (84). A molecular study was conducted in Duhok to detect T. Tenax using PCR based on 18s rRNA gene-specific, showing that 8 out of 184 (4.32%) are only positive (85).

Regarding T. hominins, little data is found about the presence and epidemiology of this species in Iraqi cities. Nevertheless, a study in Karbala city examined 277 diarrhea cases in children under five, recording the infection rate at 1.1% (86). In the Kurdistan region, particularly in Erbil province, a microscopic study found 2 cases (0.19%) out of 332 children are infected by T. hominins (87). Recently, a study was conducted in Ramadi / Iraq from May 2019 to May 2020 to diagnose T. hominins in 200 fecal samples based on microscopic examination, where the infection rate is % 2.06 (6). Although some studies suggest that these species can cause host symptoms, their pathological role and effects on hosts are still unclear and /or incompletely understood (6,88). Thus, Further studies can explain more information regarding their epidemiology and pathogenicity.

T. fetus in cattle

In 1932, Trichomonosis was reported for the first time in Pennsylvanian cattle (89). Importantly,it has been shown that the prevalence of infection differs from region to region in the world, where the prevalence of infection is limited in countries that use artificial insemination as the common methodof cattle reproduction (19). A study in the northwest USA investigating 450 bulls revealed no infections recorded in these animals (90). However, T. fetus was reported in Florida, where 1984 beef bulls in 59 herds were examined, and the overall prevalence was 6.0%, suggesting that the percentage of infection is associated with some bulls factors, such as age, breed, herd, and herd management practices (91). Other studies also reported disease prevalence in different parts of the world. In Argentina and Brazil, the prevalence was 3.5% and 3.7%, respectively (92,93). Another study recorded 18.4% of cows and 7.2% of bulls in Costa Rica (94). In Africa, the prevalence of T. fetus infection was 10.4% in the north-western part, while 26.4% was in examined animals of South Africa (95). However, a recent molecular study did not detect T. fetus infection in 360 dairy cows in Algeria (96). In Australia, the percentage significantly increased between 1985 and 1986 in the Victoria River district (VDR) of the Northern Territory, where 65.6% of bulls were infected with trichomoniasis, explaining this percentage to the lack of trichomoniasis control measures in the VRD management situation (97). Although the prevalence of Trichomonosis tends to be zero in some European countries due to using control programs, such as artificial insemination, the percentage of 32% was documented in tested bulls of Spain in 2011(98). Recently, two molecular techniques were used to investigate T. fetus in 172 pigs, 236 wild boars, and 180 cattle in Poland. The findings showed that pigs were infected with a percentage of 16.28%, while no positive cases in cattle and wild boar (99). Therefore, more research is helpful to understand the epidemiology of this parasite and whether other factors may significantly impact the disease's distribution. In Turkey, cows with various clinical signs were examined to detect T. fetus infection. The findings revealed that the percentage of infection was 8.53%, and these cows suffered from vaginal discharge, metritis, and abortion (14). Another study reported that T. fetus was found in aborted fetuses from the Eastern Anatolian Region of Turkey by staining, culture, and PCR methods, suggesting that further investigation is needed to study the epidemiology of the parasite in the region (100).

Furthermore, a study documented for the first time that T. fetus was detected in the ileum, cecum, and colon of cats suffering from diarrhea (101). In Iran, the nested PCR technique demonstrated that the parasite is detected in cattle in Isfahan city, where 6 Bulls (8.2%) and 2 Cows (7.4%) isolates are positive (102). It is also reported for the first time in Iran that a cat with chronic diarrhea is found to be infected by a T. fetus (103).

As mentioned above, venereal Trichmoniasis is found in various parts of the world, indicating the importance of the disease and its effect on the health of animals, particularly cattle and cats. However, it is still incompletely investigated in some parts of Asia, such as; Iraq. More recently, the parasite was found in the preputial fluid of the bull's penis of Basra, Iraq, showing that 2 out of 100 samples are positive using microscopic examination of slide smear stained with Giemsa stain (104). Furthermore, T. fetus is found in the vaginal mucus of infected cows in Nineveh province, Iraq, where the infection percentage is 11 out of 87 cows (12.6 %) using the conventional polymerase chain reaction technique (105). Previous studies explain that the epidemiology of T. fetus infection in animals is incompletely studied yet in this region. Thus, it is suggested that priority would be given to investigating the infection in animals to understand whether this disease is endemic or not in Iraq.

T. fetus in cats

In 1996, Trichomonosis in cats was identified for the first time, and it has been considered one of the common gastrointestinal tract disorders in cats globally (106). Some studies carried out in the USA showed positive cases among examined cats. For example, 27out of 68 (39%) of cats suffering from diarrhea were positive for T. foetus (107). Another study conducted in the USA demonstrated 31% positive results among 117 cats (20). In addition, the percentage of infection in cats in Australia and New Zealand was 42.4% and 81.8%, respectively (108,109). According to studies conducted on the European cat population, the disease has been recorded in different European countries, where the percentage of infection was about 2-30% (80,110). More recently, T. fetus was also found in cats of Poland in a percentage of 20.51% (96). In Asia, the infection percentage was 8.8% in cats found in Japanese hospitals (111), while 86% of the prevalence of the disease was in young cats between 2009 and 2014 in China (112). Undoubtedly, further investigation could provide a further understanding of the epidemiology and prevalence of this disease in cats. According to current research, the infection of T. fetus in Iraqi cats is not recorded yet. Thus, survey studies are needed to investigate and understand the epidemiology of this species in cats.

 T. gallinae in birds

Since the 19^th century, T. gallinae has been reported as a significant protozoan parasite that causes avian trichomoniasis in birds worldwide (23). This disease is endemic to columbid (pigeon and dove) species and has recently been an emerging infectious disease (EID) among European birds called fringillid species (113,114). It is mentioned that different strains of this species cause various morbidity and mortality in pigeons, whereas virulent strains can lead to mortality of 50% and 90% in adults and squabs, respectively (115). A recent molecular study documents that genotypic diversity is found among domestic and wild pigeons where a variety of strains are identified in the birds of Saudi Arabia, confirming that infection is significantly higher in domestic pigeons and genotypes of ribotypes A and C are predominant (116). Another recent study confirms this genetic diversity, showing that four strains of T. gallinae A, C, II, and KSA11 are recorded in falcon of Saudi Arabia (117). Several epidemiological studies recorded the prevalence of avian trichomoniasis in birds. For instance, a microscopic examination study in India revealed a prevalence of 26.85% of T. gallinae in Domestic Pigeon (118). In Iran, a recent wet mount preparation and light microscopy study examined the oropharyngeal cavity, crop/esophagus, droppings/cloaca, and conjunctival swabs of several types of birds belonging to different orders throughout a year. The findings detect that the total positive samples are 23.7%, distributed from the upper gastrointestinal tract to the ophthalmic and respiratory systems (119).

In Iraq, several studies in most Iraqi cities were also conducted to detect avian trichomoniasis, showing various infection rates (120-124). Recently research done in Baghdad from October 2018 to March 2019 found a prevalence of 58 % (106/180) by Giemsa stain microscopy while 85% using PCR product of 370bp of ITS1/1.5.8S./ITS2 rRNA (125). Avain trichomoniasis was also recently recorded in Karbala by a comparative study in the three types of birds (Bird toilet decorations, Bird pigeon, Broiler bath decorations) based on a culture method of oral swabs where the total rate of infection is 14.7% (126). Another study from March 2020 to January 2021 in Samawah, Al-Muthanna province, found that domestic and wild pigeons (Columba livia) are infected with T. gallinae with a prevalence of 4% and 3.2%, respectively, based on clinical and microscopic examination (127). In summary, it is shown that avian trichomoniasis is widespread among birds of Iraq, considering that veterinarians should frequently give awareness campaigns to owners for knowing this infection and its risk to their birds.

Conclusion

It is demonstrated that the genus Trichomonas is one of the common protozoa that infect mammals and birds, causing a disease called Trichomonosis. This genus has essential species, including (T. vaginalis in humans, T. fetus in cattle and cats, and T. gallinae in birds). The name of the disease differs based on its species and the site of infection inside a host. For instance, T. vaginalis causes Trichomonosis, which considers one of the Sexually Transmitted Diseases (STDs) in humans, while T. fetus causes venereal Trichomonosis in cattle and intestinal Trichomonosis in cats. In birds, T. gallinae infects the upper digestive tract, causing avian trichomoniasis, called canker. According to the survey conducted in this article, all these species are classified as pathogenic, leading to significant health disorders in their hosts. It is shown that many studies are carried out to detect and investigate this disease worldwide, including in Iraq. Data collected from the scientific websites suggested that the prevalence of T. vaginalis, T. gallinae, and T. tenax are well investigated, recording different infection rates in most Iraqi cities.

Nevertheless, the observations reveal that the percentage of infection by T. fetus tends to be slight or absent. Only two recent studies in Basra and Nineveh provinces recorded venereal Trichomonosis in cattle. In addition, T. hominis is only found in the middle and northern parts of Iraq, with a small proportion of infection. Furthermore, current research shows intestinal Trichomonosis has not been recorded in Iraq. These findings raise questions about whether the infection by T. fetus is not endemic in this region or the presence of parasite might be limited to other factors, such as the animal breed, climate, or lack of a routine examination. Thus, it is suggested that epidemiological survey studies can be necessary to determine whether the parasite T. fetus is present in cats and cattle of other Iraqi cities.

Acknowledgment

The authors thank the the College of Veterinary Medicine at Al-Qasim Green University for their support and information to complete this research.

Conflict of Interest

The author declares that there is no conflict of interest regarding the publication of this article.

1-    The prevalence of T. vaginalis, T. gallinae, and T. tenax is well investigated and identified in Iraq.

2-    The percentage of infection by T. fetus tends to be slight, where only two recent studies in Basra and Nineveh provinces recorded venereal Trichomonosis in cattle.

3-    T. hominis is only found in the middle and northern parts of Iraq, with a small proportion of infection.

4-    Current research shows that intestinal Trichomonosis has not been recorded in Iraqi cats.

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