Co-infection with trichomonas vaginalis increases the risk of cervical intraepithelial neoplasia grade 2-3 among HPV16 positive female: a large population-based study

Prevalence of HPV16 L1 protein in oral biopsies: A diagnostic study from Ecuador

This study was designed to investigate the expression of HPV16 L1-protein in biopsies of oral mucosa samples. The expression of HPV16 L1 protein was investigated in biopsies taken from oral mucosa from patients who required pathological diagnosis of oral lesions. Seventy-two samples were incubated with anti-L1 protein monoclonal antibodies and protein detection was revealed with diaminobenzidine. Expression of L1 protein was performed by a pathologist blinded for tissue diagnosis under light microscopy. Most of the lesions of oral mucosa were present in lining mucosa (75 %) and the most frequent lesion were mucocele (n = 17, 23.6 %), epithelial hyperplasia (n = 6, 8.33 %), fibroma (n = 5, 6.9 %) and inflammatory hyperplasia (n = 5, 6.9 %). L1 protein expression was observed only in five (6.9 %) samples (two squamous cell carcinomas, two epithelial hyperplasia, and one gingival hyperplasia). We concluded that L1 expression in oral biopsies presented a low frequency in oral mucosal biopsies samples.

Vaginal microecology and its role in human papillomavirus infection and human papillomavirus associated cervical lesions

The vaginal microecology comprises the vaginal microbiome, immune microenvironment, vaginal anatomy, and the cervicovaginal fluid, which is rich in metabolites, enzymes, and cytokines. Investigating its role in the female reproductive system holds paramount significance. The advent of next-generation sequencing enabled a more profound investigation into the structure of the vaginal microbial community in relation to the female reproductive system. Human papillomavirus infection is prevalent among women of reproductive age, and persistent oncogenic HPV infection is widely recognized as a factor associated with cervical cancer. Extensive previous research has demonstrated that dysbiosis of vaginal microbiota characterized by a reduction in Lactobacillus species, heightens susceptivity to HPV infection, consequently contributing to persistent HPV infection and the progression of cervical lesion. Likewise, HPV infection can exacerbate dysbiosis. This review aims to provide a comprehensive summary of current literatures and to elucidate potential mechanisms underlying the interaction between vaginal microecology and HPV infection, with the intention of offering valuable insights for future clinical interventions.

Trichomonas vaginalis infection is associated with increased risk of cervical carcinogenesis: A systematic review and meta-analysis of 470 000 patients

BACKGROUND

Trichomonas vaginalis infection is the most prevalent non-viral sexually transmitted infection (STI) in women and has been suggested as a risk factor for developing cervical cancer.

OBJECTIVE

We aimed to investigate the associations between T. vaginalis infection and cervical carcinogenesis.

SEARCH STRATEGY

A comprehensive systematic search was conducted in five databases on 21 October 2021.

SELECTION CRITERIA

Studies assessing the relationship between T. vaginalis infection, HPV co-infections, cervical dysplasia, and cervical cancer were found eligible.

DATA COLLECTION AND ANALYSIS

Summary estimates for pooled odds ratios (ORs) and their 95% confidence intervals (CIs) were calculated with a random-effects model. Statistical heterogeneity was measured with I2 and Cochran's Q tests.

MAIN RESULTS

The 29 articles included 473 740 women, of whom 8518 were T. vaginalis-positive. Our results showed that T. vaginalis-infected women had 1.79 times higher odds of being diagnosed with HPV co-infection (95% CI 1.27-2.53; I2 95%). We also found that T. vaginalis infection was associated with high-grade squamous intraepithelial lesion diagnosis (OR 2.34, 95% CI 1.10-4.95; I2 75%) and cervical cancer (OR 5.23, 95% CI 3.03-9.04; I2 3%).

CONCLUSIONS

Our results showed an association between T. vaginalis and cervical carcinogenesis in sexually active women.

Risk factors for human papillomavirus infection, cervical intraepithelial neoplasia and cervical cancer: an umbrella review and follow-up Mendelian randomisation studies

BACKGROUND

Persistent infection by oncogenic human papillomavirus (HPV) is necessary although not sufficient for development of cervical cancer. Behavioural, environmental, or comorbid exposures may promote or protect against malignant transformation. Randomised evidence is limited and the validity of observational studies describing these associations remains unclear.

METHODS

In this umbrella review, we searched electronic databases to identify meta-analyses of observational studies that evaluated risk or protective factors and the incidence of HPV infection, cervical intra-epithelial neoplasia (CIN), cervical cancer incidence and mortality. Following re-analysis, evidence was classified and graded based on a pre-defined set of statistical criteria. Quality was assessed with AMSTAR-2. For all associations graded as weak evidence or above, with available genetic instruments, we also performed Mendelian randomisation to examine the potential causal effect of modifiable exposures with risk of cervical cancer. The protocol for this study was registered on PROSPERO (CRD42020189995).

RESULTS

We included 171 meta-analyses of different exposure contrasts from 50 studies. Systemic immunosuppression including HIV infection (RR = 2.20 (95% CI = 1.89-2.54)) and immunosuppressive medications for inflammatory bowel disease (RR = 1.33 (95% CI = 1.27-1.39)), as well as an altered vaginal microbiome (RR = 1.59 (95% CI = 1.40-1.81)), were supported by strong and highly suggestive evidence for an association with HPV persistence, CIN or cervical cancer. Smoking, number of sexual partners and young age at first pregnancy were supported by highly suggestive evidence and confirmed by Mendelian randomisation.

CONCLUSIONS

Our main analysis supported the association of systemic (HIV infection, immunosuppressive medications) and local immunosuppression (altered vaginal microbiota) with increased risk for worse HPV and cervical disease outcomes. Mendelian randomisation confirmed the link for genetically predicted lifetime smoking index, and young age at first pregnancy with cervical cancer, highlighting also that observational evidence can hide different inherent biases. This evidence strengthens the need for more frequent HPV screening in people with immunosuppression, further investigation of the vaginal microbiome and access to sexual health services.

Trichomonas vaginalis infection and risk of cervical neoplasia: A systematic review and meta-analysis

OBJECTIVES

The evidence in the literature regarding the relationship between Trichomonas vaginalis (TV) infection and cervical neoplasia is conflicting. The main aim of this study was to evaluate the magnitude of the risk of cervical neoplasia associated with TV infection.

METHODS

A meta-analysis of observational studies, which provided raw data on the association of TV infection with cervical neoplasia, was performed. For this aim, we searched scientific databases (PubMed/Medline, Scopus, the Web of Sciences, and Embase) from inception to March 15, 2023. A random-effects model was applied by Stata 17.0 to calculate the pooled and adjusted odds ratios (ORs) with 95% confidence intervals (CI), including subgroup, sensitivity, and cumulative analyses to explore sources of heterogeneity.

RESULTS

Of the 2584 records initially identified, 35 eligible studies contributed data for 67,856 women with cervical neoplasia, and 933,697 healthy controls from 14 countries were included. The pooled (2.15; 1.61-2.87; I2 = 87.7%) and adjusted (2.17; 1.82-2.60; I2 = 31.27%) ORs indicated a significant positive association between TV infection and the development of cervical neoplasia. There was no significant change in pooled and adjusted ORs by applying sensitivity and cumulative analyses, indicating the robustness of our findings. The pooled OR was significant in most sub-group analyses. There was no publication bias in the included studies.

CONCLUSION

Our findings indicated that women with a TV infection are at significantly greater risk of cervical neoplasia. Future research, particularly longitudinal and experimental studies, should be done to better understand the various aspects of this association.

Human Papillomavirus Vaccine

Cervical cancer is the fourth most common cancer in women worldwide with immense associated morbidity and mortality. Although most of the cervical cancer cases are caused by the human papillomavirus (HPV) and can effectively be prevented by HPV vaccination, vaccination unfortunately remains underused on a global scale with vast inequities in distribution. A vaccine as a tool to prevent cancer, cervical and others, is largely unprecedented. Then why do HPV vaccination rates globally remain so low? This article explores the burden of disease, development of the vaccine and its subsequent uptake, cost-effectiveness, and associated equity issues.

Is Candida albicans a contributor to cancer? A critical review based on the current evidence

The association between Candida albicans (C. albicans) and cancer has been noticed for decades. Whether C. albicans infection is a complication of cancer status or as a contributor to cancer development remains to be discussed. This review systematically summarized the up-to-date knowledge about associations between C. albicans and various types of cancer, and discussed the role of C. albicans in cancer development. Most of the current clinical and animal evidence support the relationship between C. albicans and oral cancer development. However, there is insufficient evidence to demonstrate the role of C. albicans in other types of cancer. Moreover, this review explored the underlying mechanisms for C. albicans promoting cancer. It was hypothesized that C. albicans may promote cancer progression by producing carcinogenic metabolites, inducing chronic inflammation, remodeling immune microenvironment, activating pro-cancer signals, and synergizing with bacteria.

Trichomoniasis

Trichomoniasis is the most common nonviral sexually transmitted infection worldwide. It has been associated with a variety of adverse sexual and reproductive health outcomes for both men and women. In this review, the authors discuss updates in its epidemiology, pathophysiology, clinical significance, diagnosis, and treatment.

Prevention Strategies and Early Diagnosis of Cervical Cancer: Current State and Prospects

Cervical cancer ranks third among all new cancer cases and causes of cancer deaths in females. The paper provides an overview of cervical cancer prevention strategies employed in different regions, with incidence and mortality rates ranging from high to low. It assesses the effectiveness of approaches proposed by national healthcare systems by analysing data published in the National Library of Medicine (Pubmed) since 2018 featuring the following keywords: "cervical cancer prevention", "cervical cancer screening", "barriers to cervical cancer prevention", "premalignant cervical lesions" and "current strategies". WHO's 90-70-90 global strategy for cervical cancer prevention and early screening has proven effective in different countries in both mathematical models and clinical practice. The data analysis carried out within this study identified promising approaches to cervical cancer screening and prevention, which can further enhance the effectiveness of the existing WHO strategy and national healthcare systems. One such approach is the application of AI technologies for detecting precancerous cervical lesions and choosing treatment strategies. As such studies show, the use of AI can not only increase detection accuracy but also ease the burden on primary care.

Meta-analysis of the correlation between vaginal microenvironment and HPV infection

PURPOSE

To study the correlation between the vaginal microenvironment and human papillomavirus (HPV) infection by meta-analysis.

METHODS

Databases including the Chinese Journal Full-text Database, China Science and Technology Journal, Wanfang, PubMed, Embase, Cochrane, and Web of Science were used to comprehensively retrieve published clinical studies on the correlation between the vaginal microenvironment and HPV infection. The retrieval was performed according to the inclusion and exclusion criteria, then qualified clinical studies were included for quality evaluation and data extraction. Revman 5.3 software was used for meta-analysis. The correlation between the vaginal microenvironment and HPV infection was assessed. The statistical results were shown by forest plots. Publication bias was tested by funnel plot.

RESULTS

Ten independent studies were included in this study, involving 11,649 patients. The meta-analysis results showed that compared with the HPV-negative group, the HPV-positive group had a significant increase in the aerobic vaginitis (OR = 1.73, 95% CI: 1.19-2.50, P = 0.004), bacterial vaginosis (OR = 2.52, 95% CI: 1.78-3.57, P < 0.001) and trichomonal vaginitis (OR = 1.60, 95% CI: 1.27-2.02, P < 0.001) infection rates, while there was no substantial difference in the vulvovaginal candidiasis infection rate between two groups (OR = 1.48, 95% CI: 0.99-2.23, P = 0.06).

CONCLUSION

The vaginal microenvironment is closely related to HPV infection, especially aerobic vaginitis, bacterial vaginosis and trichomonal vaginitis are high-risk factors for HPV infection.

The Risk Factors for Cervical Cytological Abnormalities Among Women Infected With Non-16/18 High-Risk Human Papillomavirus: Cross-sectional Study

BACKGROUND

High-risk human papillomavirus (hrHPV) infection is a necessary cause of almost all cervical cancers. Relative to hrHPV 16/18 infection, non-16/18 hrHPV infection is of less concern. However, the increasing prevalence of non-16/18 hrHPV infections has become an important public health issue. The early identification and treatment of cervical cytological abnormalities in women infected with non-16/18 hrHPV reduces the incidence of cervical cancer. To date, no study has examined the risk factors for cytological abnormalities in this high-risk population.

OBJECTIVE

This population-based, cross-sectional study aimed to identify the risk factors for cervical cytological abnormalities in women infected with non-16/18 hrHPV.

METHODS

A total of 314,587 women from the general population were recruited for cervical cancer screening at 136 primary care hospitals in Xiangyang, China. Of these, 311,604 women underwent HPV genotyping, and 17,523 non-16/18 hrHPV-positive women were referred for cytological screening according to the screening program. A logistic regression model was used to assess the risk factors for cytological abnormalities among these non-16/18 hrHPV-positive women. A separate analysis was performed to determine the factors influencing high-grade cytological abnormalities.

RESULTS

The non-16/18 hrHPV infection rate was 5.88% (18,323/311,604), which was 3-fold higher than that of hrHPV 16/18 (6068/311,604, 1.95%). Among the non-16/18 hrHPV-positive women who underwent ThinPrep cytologic test, the overall prevalence rates of cervical cytological abnormalities and high-grade cytological abnormalities were 13.46% (2359/17,523) and 1.18% (206/17,523), respectively. Multivariate logistic regression analysis revealed that women with middle or high school educational attainment were at a higher risk of having cytological abnormalities than those who received primary education (odds ratio [OR] 1.31, 95% CI 1.17-1.45; P<.001, and OR 1.32, 95% CI 1.14-1.53; P<.001, respectively). Living in rural areas (OR 2.58, 95% CI 2.29-2.90; P<.001), gravidity ≥3 (OR 2.77, 95% CI 1.19-6.45; P=.02), cervix abnormalities detected in pelvic examination (OR 1.22, 95% CI 1.11-1.34; P<.001), and having a cervical cancer screening 3 years ago (OR 0.79, 95% CI 0.62-1.00; P=.048) were associated with cytological abnormalities. The risk factors for high-grade cytological abnormalities included middle school education (OR 1.45, 95% CI 1.07-1.98; P=.02), living in rural regions (OR 1.52, 95% CI 1.10-2.10; P=.01), and cervix abnormality (OR 1.72, 95% CI 1.30-2.26; P<.001).

CONCLUSIONS

The dominant epidemic of non-16/18 hrHPV infection is revealed in Chinese women. Multiple risk factors for cervical cytological abnormalities have been identified in women infected with non-16/18 hrHPV. These findings can provide important information for clinically actionable decisions for the screening, early diagnosis, intervention, and prevention of cervical cancer in non-16/18 hrHPV-positive women.

Sexually transmitted infections and female reproductive health

Women are disproportionately affected by sexually transmitted infections (STIs) throughout life. In addition to their high prevalence in women, STIs have debilitating effects on female reproductive health due to female urogenital anatomy, socio-cultural and economic factors. In this Review, we discuss the prevalence and impact of non-HIV bacterial, viral and parasitic STIs on the reproductive and sexual health of cisgender women worldwide. We analyse factors affecting STI prevalence among transgender women and women in low-income settings, and describe the specific challenges and barriers to improved sexual health faced by these population groups. We also synthesize the latest advances in diagnosis, treatment and prevention of STIs.

Women are more affected by sexually transmitted infections than men. This Review examines the impact of non-HIV STIs on women’s health, and discusses recent advances and current challenges in the treatment and prevention of STIs.

Association between common vaginal and HPV infections and results of cytology test in the Zhoupu District, Shanghai City, China, from 2014 to 2019

Background

HPV (human papillomavirus) is an important cause of cervical cancer. Cervical-vaginal infection with pathogens, such as herpes simplex virus (HSV), bacterial vaginosis Trichomonas vaginalis and vaginal candidiasis could be a cofactor. This study aimed to assess the relationship between vaginal infection with HPV genotype and cytology test results and analyze the relationship between vaginal and HPV infections and cervical cancer.

Methods

We performed a district-based study to elucidate the relationship among the vaginal and HPV infections and cervical cancer. We collected the cervical exfoliation data of 23,724 women admitted to the Shanghai Zhoupu Hospital and received ThinPrep cytology test (TCT) and HPV detection between 2014 and 2019.

Results

Total vaginal infection rate was 5.3%, and the HPV-positive group had a slightly higher vaginal infection rate than the HPV-negative group (P < 0.01). The incidence rate of cervical intraepithelial neoplasia or cervical cancer with vaginal infection was higher than without vaginal infection (P < 0.001).

Conclusion

HPV/vaginal infection-positive women tended to have abnormal results of TCT. Women with vaginal infection were more likely to develop HPV infection. HSV combined with HPV infection was noted as a causal factor for HSIL.

Supplementary Information

The online version contains supplementary material available at 10.1186/s12985-022-01850-x.

Effect of the Symbiosis with Mycoplasma hominis and Candidatus Mycoplasma Girerdii on Trichomonas vaginalis Metronidazole Susceptibility

Trichomoniasis, the most common non-viral sexually transmitted infection worldwide, is caused by the protozoon Trichomonas vaginalis. The 5- nitroimidazole drugs, of which metronidazole is the most prescribed, are the only effective drugs to treat trichomoniasis. Resistance against metronidazole is increasingly reported among T. vaginalis isolates. T. vaginalis can establish an endosymbiosis with two Mycoplasma species, Mycoplasma hominis and Candidatus Mycoplasma girerdii, whose presence has been demonstrated to influence several aspects of the protozoan pathobiology. The role of M. hominis in T. vaginalis resistance to metronidazole is controversial, while the influence of Ca. M. girerdii has never been investigated. In this work, we investigate the possible correlation between the presence of Ca. M. girerdii and/or M. hominis and the in vitro drug susceptibility in a large group of T. vaginalis isolated in Italy and in Vietnam. We also evaluated, via RNA-seq analysis, the expression of protozoan genes involved in metronidazole resistance in a set of syngenic T. vaginalis strains, differing only for the presence/absence of the two Mycoplasmas. Our results show that the presence of M. hominis significantly increases the sensitivity to metronidazole in T. vaginalis and affects gene expression. On the contrary, the symbiosis with Candidatus Mycoplasma girerdii seems to have no effect on metronidazole resistance in T. vaginalis.

Prevalence and spatial heterogeneity of Trichomonas vaginalis infection among the female population and association with climate in Guangxi Zhuang autonomous region, Southern China

BACKGROUND

Two cervical cancer screening (CCS) projects have been ongoing for years in Guangxi Zhuang autonomous region (Guangxi), and some Trichomonas vaginalis infection (TVI) cases have been found as an opportunistic finding. This study aimed to identify the high-risk population and expound the spatial epidemiological features of TVI in Guangxi.

METHODS

This study was based on CCS from 2012 to 2019. Adjusted odds ratio (AOR), and spatial analyses were used to identify the high-risk subgroups, as well as to depict the spatial epidemiological feature and its relationship with meteorological factors.

RESULTS

The infection rate of TVI was 0.38% in 873,880 samples. Significant association with a high risk of TVI was found in the following: females aged 40-49 years (aOR=4.464; 95% CI, 3.359-5.932; p<0.001), aged 50-59 years (aOR=3.169; 95% CI, 2.370-4.237; p<0.001), from urban (aOR=1.577; 95% CI, 1.471-1.691; p<0.001), from minority areas (aOR=1.183; 95% CI, 1.060-1.320; p=0.003), areas with GPD <41,500 CNY (aOR=1.191; 95% CI, 1.106-1.282; p<0.001), and inland areas (aOR=1.520; 95% CI, 1.339-1.726; p<0.001). Counties with higher infection rate were concentrated in northwest Guangxi's mountainous area (Z-score=3.9656, p<0.001), in the upper reaches of the Hongshui River and Yu River, and with a significant spatial autocorrelation (Moran's I=0.581, p=0.002). Spatial error model showed significantly negative regressions among temperature (B=-0.295, p=0.002), annual temperature range (B=-0.295, p=0.002), and TVI spatial distribution.

CONCLUSION

The spatial clustering and disparity of TVI in northwest Guangxi warrant further study, and meteorological conditions may play an important role in TVI in northwest Guangxi.

Lupeol acetate isolated from Chrysophyllum cainito L. fruit as a template for the synthesis of N-alkyl-arylsulfonamide derivatives and their synergistic effects with metronidazole against Trichomonas vaginalis

Pentacyclic triterpenes are found in a great variety of natural products and constitute an organic template for the development of new derivative compounds with therapeutic applications. In the present work, lupeol acetate isolated from Chrysophyllum cainito L. fruit was used as a template for the synthesis of novel N-alkyl-arylsulfonamide derivatives, and their synergistic effects with metronidazole against strains of Trichomonas vaginalis were tested. A library of 18 derivatives was synthesized. Ten compounds exhibited an IC₅₀ < 100 μM against a metronidazole-sensitive strain of T. vaginalis. Only seven of these compounds (12, 15, 18-22) also showed activity against metronidazole-resistant strains. The compounds 20 (N-cyclohexyl-p-chlorobenzenesulfonamidolupeol acetate) and 22 (N-cyclohexyl-p-nitrobenzenesulfonamidolupeol acetate) exhibited a similar IC₅₀ against both susceptible and resistant T. vaginalis strains and enhanced the efficacy of metronidazole in a partial and total synergistic way, respectively. These data provided evidence of the trichomonicidal effect of N-alkyl-arylsulfonamide derivatives of lupeol acetate, representing highly promising novel antiparasitic agents.

Protozoan-Viral-Bacterial Co-Infections Alter Galectin Levels and Associated Immunity Mediators in the Female Genital Tract

Co-infections with sexually transmittable pathogens are common and more likely in women with disturbed vaginal bacteriome. Among those pathogens, the protozoan parasite Trichomonas vaginalis (TV) is most common after accounting for the highly persistent DNA viruses human papillomavirus (HPV) and genital herpes. The parasitic infection often concurs with the dysbiotic syndrome diagnosed as bacterial vaginosis (BV) and both are associated with risks of superimposed viral infections. Yet, the mechanisms of microbial synergisms in evading host immunity remain elusive. We present clinical and experimental evidence for a new role of galectins, glycan-sensing family of proteins, in mixed infections. We assessed participants of the HIV Epidemiology Research Study (HERS) at each of their incident TV visits (223 case visits) matched to controls who remained TV-negative throughout the study. Matching criteria included age, race, BV (by Nugent score), HIV status, hysterectomy, and contraceptive use. Non-matched variables included BV status at 6 months before the matched visit, and variables examined at baseline, within 6 months of and/or at the matched visit e.g. HSV-2, HPV, and relevant laboratory and socio-demographic parameters. Conditional logistic regression models using generalized estimating equations calculated odds ratios (OR) for incident TV occurrence with each log₁₀ unit higher cervicovaginal concentration of galectins and cytokines. Incident TV was associated with higher levels of galectin-1, galectin-9, IL-1β and chemokines (ORs 1.53 to 2.91, p <0.001). Galectin-9, IL-1β and chemokines were up and galectin-3 down in TV cases with BV or intermediate Nugent versus normal Nugent scores (p <0.001). Galectin-9, IL-1β and chemokines were up in TV-HIV and down in TV-HPV co-infections. In-vitro, TV synergized with its endosymbiont Trichomonasvirus (TVV) and BV bacteria to upregulate galectin-1, galectin-9, and inflammatory cytokines. The BV-bacterium Prevotella bivia alone and together with TV downregulated galectin-3 and synergistically upregulated galectin-1, galectin-9 and IL-1β, mirroring the clinical findings of mixed TV–BV infections. P. bivia also downregulated TVV+TV-induced anti-viral response e.g. IP-10 and RANTES, providing a mechanism for conducing viral persistence in TV-BV co-infections. Collectively, the experimental and clinical data suggest that galectin-mediated immunity may be dysregulated and exploited by viral–protozoan–bacterial synergisms exacerbating inflammatory complications from dysbiosis and sexually transmitted infections.

Paradigms of Protist/Bacteria Symbioses Affecting Human Health: Acanthamoeba species and Trichomonas vaginalis

Ever since the publication of the seminal paper by Lynn Margulis in 1967 proposing the theory of the endosymbiotic origin of organelles, the study of the symbiotic relationships between unicellular eukaryotes and prokaryotes has received ever-growing attention by microbiologists and evolutionists alike. While the evolutionary significance of the endosymbiotic associations within protists has emerged and is intensively studied, the impact of these relationships on human health has been seldom taken into account. Microbial endosymbioses involving human eukaryotic pathogens are not common, and the sexually transmitted obligate parasite Trichomonas vaginalis and the free-living opportunistic pathogen Acanthamoeba represent two unique cases in this regard, to date. The reasons of this peculiarity for T. vaginalis and Acanthamoeba may be due to their lifestyles, characterized by bacteria-rich environments. However, this characteristic does not fully explain the reason why no bacterial endosymbiont has yet been detected in unicellular eukaryotic human pathogens other than in T. vaginalis and Acanthamoeba, albeit sparse and poorly investigated examples of morphological identification of bacteria-like microorganisms associated with Giardia and Entamoeba were reported in the past. In this review article we will present the body of experimental evidences revealing the profound effects of these examples of protist/bacteria symbiosis on the pathogenesis of the microbial species involved, and ultimately their impact on human health.