Trichomonas tenax: The Mouth Flagellate

Trichomonas tenax is a single-celled parasite that lives in the human mouth, in dental plaque and in the pockets that open between teeth and inflamed gums. It is a flagellate, a cell that swims by beating whip-like tails called flagella, and a close relative of Trichomonas vaginalis, a parasite that causes disease in people [1]. A 2021 review of 65 studies estimated that 17% of people worldwide carry it [2]. A 1985 review described it as “usually regarded as a harmless commensal of the human mouth”: a resident that lives on its host without causing harm [3]. Yet it is found more often in people with gum disease than in people with healthy gums [4], and researchers have not settled whether it helps cause gum disease [5], though some reviews conclude that it may [6].

This page follows the flagellate through the published research, from its home in the gums and in pets to the rare chest infections it has caused after being breathed into the lungs. Its neighbor in the gum pocket, the amoeba Entamoeba gingivalis, has its own page: Entamoeba gingivalis: The Gum Amoeba.

Table of Contents

  1. What Trichomonas tenax Is
  2. Where It Lives
  3. How Common It Is
  4. The Link With Gum Disease
  5. How It May Harm Gum Tissue
  6. Infections Beyond the Mouth
  7. How It Is Detected
  8. Treatment Research
  9. Ivermectin and the Mouth Flagellate
  10. Key Research Papers
  11. Connections
  12. Featured Videos

What Trichomonas tenax Is

The mouth flagellate is a protozoan: a single-celled organism, larger and more complex than a bacterium. It belongs to the trichomonads, a group of flagellates, and it is found in the mouths of both humans and animals [1]. It is anaerobic, meaning it lives without oxygen, and it is commensal in the human mouth, living on its host usually without causing harm [7].

A close relative of Trichomonas vaginalis

Its best-known relative is Trichomonas vaginalis, the sexually transmitted parasite and the most studied of the trichomonads [8]. A 2023 scoping review (a broad survey of the research) included 87 articles and called the mouth flagellate a “neglected” parasite, noting how little has been written about it compared with its closely related cousin [1].

In 2022, researchers published a draft sequence of the genome (the full set of genes) of a laboratory strain called Hs-4:NIH [9]. A 2024 study labeled the genes in two draft genomes of that strain and compared them with those of Trichomonas vaginalis. It found candidate virulence factors (molecules that may help a germ cause disease): surface proteins, secreted proteins and enzymes that could interact with human cells and with the bacteria of the mouth. It also found a broad range of families of glycoside hydrolases, enzymes that cut sugar chains, most of them shared by the two species. These findings come from computer analysis of genome sequences, not from experiments with the living flagellate. The authors concluded that the genes support a model in which the flagellate’s interactions with human cells and with the mouth’s microbes could together add to the damaging inflammation of periodontitis (advanced gum disease that destroys the tissue and bone holding the teeth), “supporting a causal link” between the two [8].

Where It Lives

The flagellate lives in dental plaque (the sticky film of microbes on the teeth, also called dental biofilm) and in the gum pockets around the teeth. Around a healthy tooth the gum forms a shallow groove; in periodontitis the gum’s attachment to the tooth breaks down and the groove deepens into a pocket where plaque gathers. A 2019 systematic review (a review that gathers every study meeting set criteria) found the flagellate more often in dental biofilm from sites with periodontitis than from healthy sites [5]. Studies collect it from samples of plaque taken around the teeth [10][11]. It is frequently found in people with poor oral hygiene, as a 1985 review noted [3], and a 2018 study described it as found in people with poor oral hygiene and advanced gum disease [12].

The mouth is not its only home. A 2025 article on how the flagellate spreads lists findings in the lungs and in the urogenital tract (the urinary and genital organs), and in dogs, cats, horses and birds as well as humans [13]. The lung findings are described under Infections Beyond the Mouth.

In dogs, cats and horses

The flagellate was long considered specific to humans [12]. Several studies have now found it in pets:

A 2023 review describes the mouth flagellate as zoonotic, meaning it can pass between animals and people [1].

How it spreads

Research on how the flagellate passes from one host to another is scarce. A 2025 article judged that it is very likely spread through kissing, shared saliva, contaminated utensils and water, and that direct spread between hosts plays an important role, while spread through objects or water has yet to be scientifically proven. It lists influences on its spread: temperature, age, income, smoking, public awareness, poor oral hygiene and diseases elsewhere in the body [13].

How Common It Is

A 2021 review pooled 65 studies and estimated that 17% of people worldwide carry the flagellate, with the true figure likely between 14% and 22% (the 95% confidence interval). The highest pooled rate was 56%, in Chile, and the lowest 3%, in Kenya. In subgroups, the pooled rate was 21% in people with gingivitis, 27% in people with periodontitis and 22% in people with candidiasis (a yeast infection) [2].

Earlier estimates varied just as widely. A 1985 review put the flagellate’s prevalence (the share of people carrying it) between 4% and 53%, and noted that in adult women it may be more common than vaginal infection with Trichomonas vaginalis [3]. A 2017 review of 47 studies found rates in diseased gums ranging from 0 to 94.1%, and linked this wide spread to differences in the people screened (age, sex, other diseases) and in the methods used to detect the flagellate [4].

Studies around the world

Single studies give very different figures, depending on where they were done, who was tested and how:

Gum disease develops in stages. In gingivitis, plaque inflames the gums; in periodontitis, the inflammation destroys the fibers and bone that hold the teeth in place. A 2017 review describes both as the result of a disruption in the balance between the body and the microbes of the mouth. The role of some bacteria is well documented, the review notes, while the part parasites play “is still under debate” [4].

The 2017 review

The review gathered data from 47 studies. It found mouth protozoa far more common in people with gum disease than in people with healthy gums, and concluded that the flagellate’s presence “was clearly correlated with periodontal disease” and that it “seems to have the capacity to be involved in the inflammatory process of gum disease”. Most of the studies had looked for it by direct microscopy. The authors called for animal experiments, using models of periodontitis, to find out whether the flagellate can cause the disease or make it worse [4].

The 2019 systematic review

The 2019 systematic review judged the evidence against Koch’s postulates, the classic criteria for proving that a germ causes a disease, in the form revisited by Socransky. Of 376 studies identified, 25 met its criteria; most were laboratory studies of possible virulence factors, and the rest were clinical studies and case reports. The review found that the flagellate is detected more often in plaque from periodontitis sites than from healthy sites. It concluded that the data “do not meet all the postulates” and are “not enough to provide firm conclusions” about the flagellate’s role in causing periodontitis [5].

Pooled analyses

The 2021 Jordan study

The 2021 study in Jordan tested 237 people by polymerase chain reaction. People carrying the flagellate had 4.7 times the odds of periodontitis compared with healthy people. It was found only in people whose periodontal disease was generalized (spread through the mouth), in 19.6% of them, and in none of those whose disease was localized. Both mouth parasites together were found in 11.0% of participants. The authors concluded that the higher rates of the parasites in gum disease appear “to be more than a mere marker for the disease” and may be linked to how severe it is and how likely it is to progress, and that the view of these parasites as harmless commensals “needs to be re-evaluated” [18].

Different readings of the evidence

Some researchers read the evidence strongly. The 2024 genome study describes the flagellate as increasingly seen as a likely contributor to periodontitis in humans and domestic animals, “strongly associated with its worst prognosis” [8]. A 2023 review concluded that both mouth parasites are potential pathogens that “may cause periodontal disease” [6]. A 2024 article summarizes observational studies as showing a significant statistical correlation between carrying the flagellate and the progression of periodontal disease [22]. The 2026 study of people and pets concluded that the gum amoeba likely acts as a commensal, whereas the flagellate is linked to age and periodontal disease [16].

Others are more cautious, like the 2017 and 2019 reviews above [4][5]. The Nigerian study, which found the flagellate in fewer than one in a hundred people with gum disease, concluded that the two mouth parasites “may not be of etiologic importance” (may not be a cause) in gum disease [10]. Finding a germ more often in diseased gums shows an association; on its own it does not show whether the germ causes the disease or simply thrives in the pockets the disease creates.

How It May Harm Gum Tissue

Most of what is known about how the flagellate might harm the gums comes from laboratory experiments with cells grown in dishes, and from its genes; most of the studies in the 2019 systematic review were laboratory studies of this kind [5]. Mechanisms proposed in the 2024 article include enzymes that damage tissue, triggering apoptosis (programmed cell death) in human cells, and dysbiosis, an upset in the balance of the microbes living in the mouth [22].

Enzymes and attachment to cells

The 2019 systematic review found that the living flagellate seems able to produce diverse enzymes that could take part in the breakdown of gum tissue, and that it can adhere (stick) to epithelial cells, the cells that form the body’s linings and surfaces [5]. The 2023 scoping review notes studies showing that it can damage mammalian cells and that it secretes proteins linked to its ability to cause disease [1]. The 2024 genome study found genes for candidate surface proteins, secreted proteins and enzymes that could mediate contact with human cells or with the bacteria of the mouth [8].

Breaking the seal between gum cells

In a 2023 laboratory study, the flagellate damaged gum epithelial cells by disrupting their cell junctions, the connections that hold neighboring cells together and keep the surface of the gum sealed. It caused hardly any damage to two kinds of lung cells tested the same way. The authors cite an earlier study in which the flagellate damaged cells and engulfed (swallowed) human epithelial cells [7].

Inflammation signals

In the same 2023 study, the flagellate raised the production of interleukin 6, a signaling molecule that drives inflammation, in gum cells and in both kinds of lung cells, even at a low ratio of flagellates to cells [7]. The 2019 systematic review reports that the flagellate’s broken-up (lysed) form could make macrophage cell lines produce interleukin 8, a signal that draws white blood cells into tissue; macrophages are immune cells that swallow germs and debris [5]. A 2023 review concluded that both mouth parasites can bring on inflammation in gum tissue by raising inflammatory molecules and recruiting neutrophils, the white blood cells that attack microbes [6].

An earlier finding of no harm

Not every study found harm. A 1985 laboratory study of Trichomonas vaginalis used the mouth flagellate for comparison and described it as “avirulent” (unable to cause disease): it did not stick to layers of human cells and did not damage them, while strains of Trichomonas vaginalis did both [23]. Later studies, described above, report that the mouth flagellate can stick to cells and damage them [5][7].

Infections Beyond the Mouth

The flagellate has also been found in the chest. A 1985 review explained that pulmonary trichomoniasis (trichomonad infection of the lungs) is usually caused by Trichomonas tenax that has been aspirated, meaning breathed into the lungs from the mouth. The review counted sixty-eight patients described until then, usually adult men with chronic lung disease in which pus forms or tissue dies. It cited a Russian study that found pulmonary trichomoniasis in 19 of 112 patients (17%), mostly people with lung cancer, a lung abscess (a pus-filled cavity in the lung) or bronchiectasis (permanently widened, damaged airways). The review described the infection as opportunistic: it takes hold in a body already weakened by other disease [3].

Case reports

Case reports describe these infections:

The 2002 report noted that the flagellate is part of the normal flora of the mouth and may at times colonize the airways. It can then become involved in aspiration pneumonia (lung infection from inhaled material) or cause infection around the lung after a lung abscess bursts. Such infection tends to occur alongside other lung disease or a weakened immune system, and the report called the meaning of finding the flagellate in the airways unclear [25]. The 2003 report described empyema caused by trichomonads as very rare, occurring in predisposed people, with Trichomonas tenax apparently the most common cause [26].

The 2023 laboratory study described above was designed partly with these chest cases in mind: the flagellate barely damaged lung cells but raised their production of interleukin 6, and the authors note that in the reported cases it may have been aspirated from the mouth [7].

How It Is Detected

Samples are taken from the plaque and gum pockets around the teeth with a curette (a small scraping instrument) or a probe, and some studies also test saliva [10][18]. Three kinds of test are used: microscopy, culture and genetic tests.

Microscopy

The oldest method is to look for the moving flagellate in a fresh, wet sample under the microscope. In the 2023 Quetta study, each plaque sample was mixed with a drop of saline on a glass slide and examined at once for moving amoebae or flagellates; the authors suggested that future research use more advanced and reliable techniques, such as polymerase chain reaction and electron microscopy [11]. Most of the studies in the 2017 review had relied on direct microscopy [4]. Identification by eye is difficult. Trichomonads from people and animals vary in shape and look very much alike, which complicates telling the species apart with the microscope and other standard techniques [12]. The new species found in dogs and cats, Trichomonas brixi, looks very similar to Trichomonas tenax [14].

Culture

Culture means growing the flagellate in the laboratory. A 1985 review judged culture superior to examining wet smears or slides stained with the Gram or Papanicolaou stains (the stain used for Pap smears) [3], and a 2023 review judged culture and molecular (DNA-based) tests the best tools for detecting both mouth parasites [6]. Across the 65 studies in the 2021 worldwide review, the pooled rate was 21% with culture, 19% with molecular tests and 17% with direct examination [2]. One laboratory strain, Hs-4:NIH, can be grown on its own, without other microbes (axenic culture), and its genome has been sequenced [8][9].

Genetic tests

Polymerase chain reaction detects the flagellate’s DNA, and was used in the Jordan and Nigeria studies [18][10]. To tell Trichomonas tenax apart from look-alike species, studies of pets copy and read the sequence of a stretch of DNA that differs from one trichomonad species to another; this is how Trichomonas brixi was recognized as a separate species [14][12].

Treatment Research

No treatment trial against the flagellate in the mouth was found among the studies gathered for this page. The 2019 systematic review notes that the effect of non-surgical gum treatment (deep cleaning of the teeth and roots) on the flagellate has not been thoroughly evaluated [5], and the 2023 scoping review calls for more studies to help develop effective drugs to control it [1].

Metronidazole

Metronidazole is a medicine used to treat infections caused by protozoa [28]. In the chest infection cases above, it eliminated the flagellates in the 1998 case [24] and, given with the antifungal voriconazole, in the 2021 case [27]; the patient in the 2002 case died despite treatment that included it [25]. For aspirated lung infection with the flagellate, the 1985 review advised giving metronidazole until the question of whether the flagellate causes disease is resolved, along with vigorous treatment of the underlying lung disease [3].

Mouth rinses in the laboratory

A 2019 laboratory study tested standard reference strains of Trichomonas tenax and the gum amoeba against metronidazole and fourteen mouth-rinse agents: 20% benzocaine (a numbing medicine), 0.2% chlorhexidine (an antiseptic) and 12 commercially sold rinses. The protozoa were counted under the microscope after 1, 10 and 30 minutes, and a cell was counted as dead when it stopped moving and changed shape or broke apart. Used undiluted, every rinse killed both protozoa. Chlorhexidine “confirmed its high efficiency”, and the authors wrote that benzocaine has properties that could support anti-protozoal treatment, and that mouth rinses are an important complement to other oral-hygiene measures [28]. The test was on protozoa in laboratory culture, not in people’s gum pockets.

Plant compounds

The 2024 article on plant compounds and the flagellate proposes that, for patients who cannot take metronidazole, phytochemicals (natural chemicals made by plants) may offer an alternative way to control it. The evidence it points to comes from laboratory work on other trichomonads: various plant extracts have shown promising activity against Trichomonas vaginalis and Tritrichomonas foetus in laboratory tests [22].

Ivermectin and the Mouth Flagellate

Ivermectin is an antiparasitic medicine. In online chat groups, members describe putting ivermectin paste, the oral paste made for horses, directly on their gums, on the theory that gum disease is driven by parasites living in the gum tissue. Those accounts, and published case reports of ivermectin used against other parasites in the tissues of the mouth, are collected on Ivermectin for Gum Disease. The history of treating gum disease as an amoeba infection is told on Amoebic Pyorrhea and Emetine.

No laboratory, animal or human study testing ivermectin against Trichomonas tenax was found in the published record. None of the studies described on this page used ivermectin, so they say nothing either way about whether it affects this flagellate. The substances tested or used against the flagellate in these studies are metronidazole, in the chest infection cases [24][27], and mouth rinses, in the laboratory [28]; plant compounds have been proposed as an alternative [22]. The research on ivermectin and other single-celled parasites is gathered on Ivermectin and Single-Celled Parasites.

Key Research Papers

  1. Matthew MA, Yang N, Ketzis J, Mukaratirwa S, Yao C. Trichomonas tenax: A Neglected Protozoan Infection in the Oral Cavities of Humans and Dogs-A Scoping Review. Trop Med Infect Dis. 2023;8(1). PubMed PMID: 36668967
  2. Eslahi AV, Olfatifar M, Abdoli A, Houshmand E, Johkool MG, Zarabadipour M, et al. The Neglected Role of Trichomonas tenax in Oral Diseases: A Systematic Review and Meta-analysis. Acta Parasitol. 2021;66(3):715-732. PubMed PMID: 33595770
  3. Hersh SM. Pulmonary trichomoniasis and Trichomonas tenax. J Med Microbiol. 1985;20(1):1-10. PubMed PMID: 3894667
  4. Marty M, Lemaitre M, Kémoun P, Morrier JJ, Monsarrat P. Trichomonas tenax and periodontal diseases: a concise review. Parasitology. 2017;144(11):1417-1425. PubMed PMID: 28583214
  5. Bisson C, Dridi SM, Machouart M. Assessment of the role of Trichomonas tenax in the etiopathogenesis of human periodontitis: A systematic review. PLoS One. 2019;14(12):e0226266. PubMed PMID: 31846467
  6. Santos JO, Roldán WH. Entamoeba gingivalis and Trichomonas tenax: Protozoa parasites living in the mouth. Arch Oral Biol. 2023;147:105631. PubMed PMID: 36764082
  7. Hong ZB, Lai YT, Chen CH, Chen YJ, Chen CC, Lin WC. Trichomonas tenax induces barrier defects and modulates the inflammatory cytotoxicity of gingival and pulmonary epithelial cells. Parasite. 2023;30:7. PubMed PMID: 36971465
  8. Mpeyako LA, Hart AJ, Bailey NP, Carlton JM, Henrissat B, Sullivan SA, et al. Comparative genomics between Trichomonas tenax and Trichomonas vaginalis: CAZymes and candidate virulence factors. Front Microbiol. 2024;15:1437572. PubMed PMID: 39086644
  9. Yang N, Christie J, Keen HL, Matthew MA, Yao C. Draft Genome Sequence of Trichomonas tenax Strain Hs-4:NIH. Microbiol Resour Announc. 2022;11(7):e0015722. PubMed PMID: 35861552
  10. Oladokun AO, Ogboru P, Opeodu OI, Lawal AO, Falade MO. Prevalence of Entamoeba gingivalis and Trichomonas tenax among patients with periodontal disease attending Dental Clinic, University College Hospital, Ibadan. Trop Parasitol. 2023;13(2):107-113. PubMed PMID: 37860615
  11. Gichki AS, Mooen M, Hasni MT, Ghilzi D. Oral Protozoa Entamoeba Gingivalis And Trichomonas Tenax Among Periodontitis And Gingivitis Patients In Periodontology Department Dental Section Quetta. J Ayub Med Coll Abbottabad. 2023;35(Suppl 1)(4):S732-S739. PubMed PMID: 38406902
  12. Dybicz M, Perkowski K, Baltaza W, Padzik M, Sędzikowska A, Chomicz L. Molecular identification of Trichomonas tenax in the oral environment of domesticated animals in Poland - potential effects of host diversity for human health. Ann Agric Environ Med. 2018;25(3):464-468. PubMed PMID: 30260189
  13. Matthew M, Ketzis J, Mukaratirwa S, Yao C. Transmission Dynamics of Trichomonas tenax: Host and Site Specificity, Zoonotic Potential, and Environmental Factors. Microorganisms. 2025;13(7). PubMed PMID: 40731985
  14. Kellerová P, Tachezy J. Zoonotic Trichomonas tenax and a new trichomonad species, Trichomonas brixi n. sp., from the oral cavities of dogs and cats. Int J Parasitol. 2017;47(5):247-255. PubMed PMID: 28238869
  15. Gui LQ, Wu XH, Shi SL, Liu CC, Li MT, Ge XL, et al. First Report of the Molecular Prevalence of Trichomonads from Oral Cavities in Household Dogs and Cats in East China. Acta Parasitol. 2025;70(3):136. PubMed PMID: 40506568
  16. Luo B, Yin Z, Liang S, She X, Otranto D, Fang F. High prevalence and cross-species transmission potential of Entamoeba gingivalis and Trichomonas tenax in humans, dogs, and cats in Guangxi, China. Acta Trop. 2026;280:108198. PubMed PMID: 42323966
  17. Piekara-Stępińska A, Czerski A, Szczepankiewicz B, Lachowicz-Wolak A, Gorczykowski M, Piekarska J. Trichomonads in the oral cavity of dogs and cats: species composition and relationship with animal age and oral hygiene status. Vet Res Commun. 2026;50(6). PubMed PMID: 42842143
  18. Yaseen A, Mahafzah A, Dababseh D, Taim D, Hamdan AA, Al-Fraihat E, et al. Oral Colonization by Entamoeba gingivalis and Trichomonas tenax: A PCR-Based Study in Health, Gingivitis, and Periodontitis. Front Cell Infect Microbiol. 2021;11:782805. PubMed PMID: 34950608
  19. Aciöz M, Ak G, Bozkaya F. Investigation of Entamoeba gingivalis and Trichomonas tenax in gingivitis and periodontitis patients. BMC Oral Health. 2025;25(1):1105. PubMed PMID: 40618059
  20. Martin-Garcia DF, Sallam M, Garcia G, Santi-Rocca J. Parasites in Periodontal Health and Disease: A Systematic Review and Meta-analysis. Adv Exp Med Biol. 2022;1373:95-111. PubMed PMID: 35612794
  21. Moosazadeh M, Sabeti MA, Hashemi SM, Ghazalgoo A, Mousavi T, Mahdavi S, et al. The Relationship Between Entamoeba gingivalis and Trichomonas tenax With Periodontitis and Gingivitis: A Systematic Review, Meta-Analysis, and Meta-Regression. J Evid Based Dent Pract. 2025;25(3):102141. PubMed PMID: 40716826
  22. Stuart MK, Motes HC, Hudman DA. Effect of Phytochemical Compounds on Trichomonas tenax, an Oral Protozoan. Altern Ther Health Med. 2024;30(3):6-8. PubMed PMID: 38518169
  23. Alderete JF, Garza GE. Specific nature of Trichomonas vaginalis parasitism of host cell surfaces. Infect Immun. 1985;50(3):701-8. PubMed PMID: 3877690
  24. Shiota T, Arizono N, Morimoto T, Shimatsu A, Nakao K. Trichomonas tenax empyema in an immunocompromised patient with advanced cancer. Parasite. 1998;5(4):375-7. PubMed PMID: 9879561
  25. Porcheret H, Maisonneuve L, Estève V, Jagot JL, Le Pennec MP. [Pleural trichomoniasis due to trichomonas tenax]. Rev Mal Respir. 2002;19(1):97-9. PubMed PMID: 17546821
  26. Lewis KL, Doherty DE, Ribes J, Seabolt JP, Bensadoun ES. Empyema caused by trichomonas. Chest. 2003;123(1):291-2. PubMed PMID: 12527635
  27. Wu Y, Ye Y, Yang Y, Yang W, Lin J, Cao K. Pyopneumothorax from coinfection by Trichomonas tenax and Geotrichum capitatum in a child from China: a case report. BMC Infect Dis. 2021;21(1):842. PubMed PMID: 34416850
  28. Moroz J, Kurnatowska AJ, Kurnatowski P. The in vitro activity of selected mouthrinses on the reference strains of Trichomonas tenax and Entamoeba gingivalis. Ann Parasitol. 2019;65(3):257-265. PubMed PMID: 31599542

PubMed Topic Searches

  1. PubMed: Trichomonas tenax and periodontitis
  2. PubMed: Trichomonas tenax prevalence
  3. PubMed: Trichomonas tenax in dogs and cats
  4. PubMed: Trichomonas tenax and empyema
  5. PubMed: Trichomonas tenax genome
  6. PubMed: Trichomonas tenax and metronidazole

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