Dioecious species that reproduce by internal fertilization typically carry an associated risk of exposure to sexually transmitted parasites and pathogens. When hosts intermingle for procreation, certain protist and helminth parasites, for example, transfer successfully between individuals and then navigate across various life history traits of their hosts, often probing dimensions in both sex and gender, respectively. In humans, there are many sexually transmitted infections as well as sexually transmitted diseases. A well-known sexually transmitted infection is the flagellated protist Trichomonas vaginalis that causes trichomoniasis, with over 150 million new cases reported annually. By contrast, the schistosome blood fluke Schistosoma haematobium, though not a sexually transmitted infection, causes significant damage to the male and female genital tracts. Such overt damage raises risks of spreading and acquiring Human Immunodeficiency Virus and Human Papilloma Virus. In Africa, over 50 million women continue to suffer from female genital schistosomiasis, alongside a poorly quantified global burden of travel-related infections. In conjunction with male genital schistosomiasis, urogenital schistosomiasis causes much suffering, within and between afflicted households, inclusive of stigmatization. Both trichomoniasis and schistosomiasis expose several public health needs currently addressed inadequately by routine sexual and reproductive health services. This preface to the Parasitology Special Issue entitled ‘Parasites of the genital tract: short- and long-term consequences’, introduces 19 papers that explore the short – and long-term impacts of parasitic infections within the genital tract. While current parasitological research is weighted towards human medicine, we encourage future studies that explore veterinary contexts and analogous parasitic diseases within wildlife.

Trichomonas vaginalis causes trichomoniasis, an inflammatory process related to an increased rate of HIV transmission. In order to study T. vaginalis infection response in a microorganism-free environment, an infection model was established providing a host–parasite interaction system useful to study the interplay between immune cells and the parasite. Infected mice peritoneal cells were immunophenotyped at different times after infection using flow cytometry. Neutrophils and macrophages showed the most relevant increase from third to 12th day post-infection. A high number of B lymphocytes were present on 15th day post-infection, and an increase in memory T cells was observed on sixth day post-infection. The levels of NO increased at day 10 post-infection; no significant influence was observed on T. vaginalis clearance. Increased viability of T. vaginalis was observed when the NETs inhibitors, metformin and Cl− amidine, were administrated, highlighting the importance of this mechanism to control parasite infection (43 and 86%, respectively). This report presents a comprehensive cell count of the immune cells participating against trichomoniasis in an in vivo interaction system. These data highlight the relevance of innate mechanisms such as specific population changes of innate immune cells and their impact on the T. vaginalis viability.

Trichomonas vaginalis is a protozoan parasite that causes trichomoniasis in humans, the most prevalent non-viral sexually transmitted disease (STD). Imidazole compounds are used for the treatment of trichomoniasis, and metronidazole is the most commonly prescribed. However, these compounds can lead to parasite resistance and unwanted side effects. Therefore, there is a need for an alternative treatment for this disease. Here, we explored the potential of clotrimazole (CTZ) and zinc compounds, as well as CTZ complexed with zinc salts ([1] acetate [Zn(CTZ)2(Ac)2] and [2] a chloride [Zn(CTZ)2Cl2] complexes) against T. vaginalis. We synthesized the zinc complexed CTZ compounds and determined their concentration values that inhibited parasite growth by 50% (IC50). We used scanning and transmission electron microscopy to visualize the ultrastructural alterations induced by CTZ and their zinc complexes. The incubation of the parasites with [Zn(CTZ)2(Ac)2] complex inhibited their growth, yielding an IC50 of 4.9 µm. Moreover, there were changes in the shape of treated parasites, including the formation of surface projections that subsequently detached from the cell, in addition to changes in the hydrogenosomes, endoplasmic reticulum and Golgi complex. We found [Zn(CTZ)2(Ac)2] to be a highly effective compound against T. vaginalis in vitro, suggesting its potential utility as an alternative chemotherapy for trichomoniasis.

Avian trichomonosis is an architypal disease of wild columbids and those birds that predate them. Increasingly though, it has been reported in passerines; a recent and ongoing epidemic in the chaffinches and greenfinches of Europe and outbreaks amongst house finches, American goldfinches and purple finches in North America. The parasite, Trichomonas gallinae, causes lesions in the upper respiratory tract which can cause mortality associated with dehydration and emaciation. This paper reports for the first time, the widespread, endemic and often asymptomatic infection of common mynah (Acridotheres tristis) around the Faisalabad District, Pakistan. Parasite typing was used to investigate the potential for transmission among the frequently sympatric species. Type C parasites were found in mynah, and while this is analagous to the pandemic finch strain which is Type A, it is the first known example of passerine infections of this parasite genotype. Subtype analysis showed the strain to be C4 a subtype which has a widespread distribution in columbids.

Avian trichomonosis, caused by the flagellated protozoan Trichomonas gallinae, is a recently emerged infectious disease of British passerines. The aetiological agent, a clonal epidemic strain of the parasite, has caused unprecedented finch mortality and population-level declines in Britain and has since spread to continental Europe. To better understand the potential origin of this epidemic and to further investigate its host range, T. gallinae DNA extracts were collected from parasite culture and tissue samples from a range of avian species in Britain. Sequence typing at the ITS1/5.8S rRNA/ITS2 region resolved three distinct ITS region types circulating in free-ranging British birds. Subtyping by sequence analyses at the Fe-hydrogenase gene demonstrated further strain variation within these ITS region types. The UK finch epidemic strain was preponderant amongst columbids sampled, however, wide strain diversity was encountered in isolates from a relatively small number of pigeons, suggesting further strains present in columbid populations across the UK are yet to be identified. Fe-hydrogenase gene sequence data in isolates from birds of prey with disease were predominantly identical to the UK finch epidemic strain, demonstrating its presence as a virulent strain in UK birds of prey since at least 2009.

Immunoprecipitation combined with electrophoresis in gelatin-polyacrylamide gels was successfully used for detection of antibodies against numerous proteinases of Trichomonas vaginalis in infected patients. The method proved to be highly specific as anti-proteinase antibodies were absent in women with negative cultivation of T. vaginalis and no history of trichomoniasis. Sera of 71% and vaginal washes of 86% patients with trichomoniasis were positive for these antibodies. In vaginal washes, but not in sera, antibodies were partly complexed with proteinases, possibly of trichomonad origin. It was also shown that serum antibodies as well as local anti-proteinase antibodies persisted for weeks after patients had been cured.

The clinical spectrum of Trichomonas vaginalis infection varies from asymptomatic to mild, moderate or severe vaginitis. Nitric oxide and other reactive nitrogen radicals produced by immune effector cells are important cytotoxic and cytostatic mediators against several microorganisms including parasites. In the present study, inducible nitric oxide synthase (iNOS) and reactive nitrogen intermediates (RNI) were determined in leucocyte cultures (stimulated with T. vaginalis in vitro) and vaginal washes (VWs) of 22 symptomatic and 20 asymptomatic T. vaginalis-infected and 20 healthy women by immunoblotting and Griess method respectively. The iNOS protein was detected in leucocytes and VWs of all the symptomatic and asymptomatic women, but was not detected in any of the samples from healthy women. Mean iNOS protein band intensity was significantly higher in leucocytes as compared to VWs (P<0·001) of both symptomatic and asymptomatic women and was also higher in leucocytes of asymptomatic as compared to symptomatic women (P<0·05). Mean RNI concentration was also significantly higher in leucocytes (P<0·01) and VWs (P<0·05) of asymptomatic as compared to symptomatic women, and was also higher in samples of infected as compared to healthy women (P<0·001). These results suggest that reactive nitrogen radicals may have a role in limiting T. vaginalis infection in asymptomatic women.