Introduction

The scientific and medical community are increasingly recognizing both sex and gender as important determinants of health (Tannenbaum et al., Reference Tannenbaum, Ellis, Eyssel, Zou and Schiebinger2019). Briefly, sex is a biological variable determined by chromosomes, anatomy and hormones and typically classifies individuals as male, female or intersex. Most animal species and some plant species have biological sex, though not all (Johnson et al., Reference Johnson, Greaves and Repta2007). Gender, on the other hand, is a social construct defined by the roles, norms, behaviours and presentations typically viewed as ‘masculine’ or ‘feminine’ by a society. Gender encompasses an individual level in terms of how a person identifies themselves and the roles they occupy (gender identity and gender roles), as well as an interpersonal level in terms of how individuals interact with each other based on gender (gender relations), and a population level in terms of how a society is structured to enforce expectations and norms for men and women (institutionalized gender) (Johnson et al., Reference Johnson, Greaves and Repta2007). Definitions can therefore vary considerably by culture, and gender falls along a much wider spectrum than sex, though often is used to classify individuals as men/boys, women/girls or non-binary. As such, this term is typically only relevant to humans, for which a more in-depth understanding of culture and social norms is possible.

Both sex and gender impact an individual’s general lived experience in a myriad of ways, including risk and outcomes of communicable and noncommunicable disease, accidental injury, mental health or personal safety. In terms of factors relevant to parasitological research, sex hormones are known to impact host immunity (Taneja, Reference Taneja2018), resulting in differences between males and females in both prevalence and severity of a broad range of parasitic infections (Córdoba-Aguilar and Munguía-Steyer, Reference Córdoba-Aguilar and Munguía-Steyer2013; Schmid-Hempel, Reference Schmid-Hempel2021; Sellau et al., Reference Sellau, Hansen, Gálvez, Linnemann, Honecker and Lotter2024). Sex-related biological variables may also influence a host’s response to pharmaceutical interventions (Spoletini et al., Reference Spoletini, Vitale, Malorni, Rosano and Regitz-Zagrosek2012; Madla et al., Reference Madla, Gavins, Merchant, Orlu, Murdan and Basit2021). For parasites which have biological sex, sex may also influence their infectivity or virulence (Boissier et al., Reference Boissier, Morand and Moné1999) or resistance to drugs (Delves Michael et al., Reference Delves Michael, Ruecker, Straschil, Lelièvre, Marques, López-Barragán María, Herreros and Sinden Robert2013; Koopman et al., Reference Koopman, Houlder, Janse, Casacuberta-Partal, Lamers, Sijtsma, de Dood, Hilt, Ozir-Fazalalikhan, Kuiper, Roozen, de Bes-roeleveld, Kruize, Wammes, Smits, van Lieshout, van Dam, van Amerongen-westra, Meij, Corstjens, Jochems, van Diepen, Yazdanbakhsh, Hokke and Roestenberg2023).

Gender, on the other hand, may play a role in an individual’s likelihood of exposure to an infectious disease agent, or their ability to treat infection, due to differences in roles and norms which impact an individual’s behaviour. For example, employment in healthcare or service as well as domestic and caregiving responsibilities, which tend to be dominated by women, may make women more likely to be exposed to some infectious diseases or parasites (Sevilimedu et al., Reference Sevilimedu, Pressley, Snook, Hogges, Politis, Sexton, Duke, Smith, Swander, Baker, Gambhir and Fung2016; Heise et al., Reference Heise, Greene, Opper, Stavropoulou, Harper, Nascimento, Zewdie, Darmstadt, Greene, Hawkes, Heise, Henry, Heymann, Klugman, Levine, Raj and Rao Gupta2019; Lewandowski et al., Reference Lewandowski, Katarzyna and Magda2021), while outdoor or agricultural work may make men more likely to be exposed to others (Tolhurst et al., Reference Tolhurst, De Koning, Price, Kemp, Theobald and Squire2002; Heise et al., Reference Heise, Greene, Opper, Stavropoulou, Harper, Nascimento, Zewdie, Darmstadt, Greene, Hawkes, Heise, Henry, Heymann, Klugman, Levine, Raj and Rao Gupta2019). It has also been documented that men exhibit more risk-seeking behaviours and are less likely to adopt precautions around infection prevention such as handwashing, use of personal protective equipment, and others (Heise et al., Reference Heise, Greene, Opper, Stavropoulou, Harper, Nascimento, Zewdie, Darmstadt, Greene, Hawkes, Heise, Henry, Heymann, Klugman, Levine, Raj and Rao Gupta2019; Urbán et al., Reference Urbán, Paksi, Miklósi, Saunders and Demetrovics2021; Dias Sara et al., Reference Dias Sara, Brouwer Matthijs and van de Beek2022; Yan et al., Reference Yan, Howden, Mahar, Glidden, Garland and Oberoi2022). Once infected, women are often more proactive in health-seeking behaviour than men (Pinkhasov et al., Reference Pinkhasov, Wong, Kashanian, Lee, Samadi, Pinkhasov and Shabsigh2010; Thompson et al., Reference Thompson, Anisimowicz, Miedema, Hogg, Wodchis and Aubrey-Bassler2016), which may improve their outcomes by receiving treatment earlier, though this may not be the case in settings where women have less agency over seeking medical treatment, or experience greater shame or stigma around infections (Tolhurst et al., Reference Tolhurst, De Koning, Price, Kemp, Theobald and Squire2002; Heise et al., Reference Heise, Greene, Opper, Stavropoulou, Harper, Nascimento, Zewdie, Darmstadt, Greene, Hawkes, Heise, Henry, Heymann, Klugman, Levine, Raj and Rao Gupta2019). It has also been documented in some cases that women have poorer access to healthcare than men (Wagner et al., Reference Wagner, Graves, Fan, Walker, Zhang and Ross-Degnan2013; Heise et al., Reference Heise, Greene, Opper, Stavropoulou, Harper, Nascimento, Zewdie, Darmstadt, Greene, Hawkes, Heise, Henry, Heymann, Klugman, Levine, Raj and Rao Gupta2019; Tadiri et al., Reference Tadiri, Gisinger, Kautzky-Willer, Kublickiene, Herrero, Norris, Raparelli and Pilote2021a) and that due to unconscious bias medical providers often take women’s complaints less seriously than those of men, or have only been trained to recognize diseases in men, meaning women may be less likely to receive diagnoses or treatment (Govender and Penn-Kekana, Reference Govender and Penn-Kekana2008; Heise et al., Reference Heise, Greene, Opper, Stavropoulou, Harper, Nascimento, Zewdie, Darmstadt, Greene, Hawkes, Heise, Henry, Heymann, Klugman, Levine, Raj and Rao Gupta2019; Meidert et al., Reference Meidert, Dönnges, Bucher, Wieber and Gerber-Grote2023). For non-binary and other gender-diverse individuals, there is very little information about how gender and sex intersect to shape their risks and outcomes of infectious diseases, as most studies have used a binary definition of gender and these individuals are underrepresented in research. These complexities are why it is important to deepen our understanding of how gender-related and other social variables influence infection risk and outcomes when studying any parasite.

Parasites of the genital tract particularly highlight how both sex and gender interact to shape the risks and outcomes of an infectious disease. For example, Schistosomiasis haematobium, which causes urogenital schistosomiasis, infects both males and females and significantly contributes to the burden of disease in the tropics, particularly sub-Saharan Africa. Risk of contracting the disease may differ between men and women or boys and girls due to gender norms around contact with water. For example, in some cultures girls are more likely to be prevented from playing outside, particularly swimming or bathing, decreasing their risk of exposure compared to boys who participate in many activities including swimming, washing animals and fishing, which prolongs their contact with water (Senghor et al., Reference Senghor, Diallo, Sylla, Doucouré, Ndiath, Gaayeb, Djuikwo-Teukeng, Bâ and Sokhna2014). Similarly, women may be more likely to be responsible for household duties rather than fishing or farming, which are considered more masculine occupations, thus increasing the risk of exposure for men (Ayabina et al., Reference Ayabina, Clark, Bayley, Lamberton, Toor and Hollingsworth2021). However in areas without running water, the need to collect water as part of household duties may increase the risk for women (Senghor et al., Reference Senghor, Diallo, Sylla, Doucouré, Ndiath, Gaayeb, Djuikwo-Teukeng, Bâ and Sokhna2014). Pathology and symptoms differ by sex because this parasite infect the genitals. Infections lead to lesions caused by S. haematobium ova which are not excreted, and have been observed primarily in the seminal vesicles, prostate, testes and bladder in males, and causing haemospermia and haematuria (Kayuni et al., Reference Kayuni, Lampiao, Makaula, Juziwelo, Lacourse, Reinhard-Rupp, Leutscher and Stothard2019). In females, granuloma due to schistosome ova infections are often seen on the cervix, fallopian tubes and vagina, and other symptoms include itchiness, pain and abnormal vaginal discharge (Kjetland et al., Reference Kjetland, Kurewa, Ndhlovu, Midzi, Gwanzura, Mason, Gomo, Sandvik, Mduluza, Friis and Gundersen2008). It has additionally been shown that females infected with genital schistosomiasis may increase their risk of contracting HIV and other infections (Kjetland et al., Reference Kjetland, Leutscher and Ndhlovu2012), including other parasites of the genital tract, such as Trichomonas vaginalis (Aribodor et al., Reference Aribodor, Azugo, Jacob, Ngenegbo, Onwusulu, Obika, Obikwelu and Nebe2024). Delaying care can lead to more severe symptoms including infertility and bladder cancer (Kjetland et al., Reference Kjetland, Leutscher and Ndhlovu2012; Santos et al., Reference Santos, Santos, Gouveia, Bernardo, Lopes, Rinaldi, Brindley and Costa2021). Gender may also influence whether an individual seeks treatment due to attitudes and stigmas about the genitals. For example, girls were less likely to self-report infections with schistosomiasis, despite showing similar prevalence through microscopy to boys (Clements et al., Reference Clements, Barnett, Nyandindi, Lwambo, Kihamia and Blair2008). On the other hand, haemosperia in males may be overlooked as some cultures see this as a sign of maturity, rather than a symptom of infection (Kayuni et al., Reference Kayuni, Lampiao, Makaula, Juziwelo, Lacourse, Reinhard-Rupp, Leutscher and Stothard2019; Ayabina et al., Reference Ayabina, Clark, Bayley, Lamberton, Toor and Hollingsworth2021). Women may also live with infection for a long time without seeking care due to shame and similarities of symptoms to sexually transmitted infections (Kjetland et al., Reference Kjetland, Kurewa, Ndhlovu, Midzi, Gwanzura, Mason, Gomo, Sandvik, Mduluza, Friis and Gundersen2008, Reference Kjetland, Leutscher and Ndhlovu2012), and some people misunderstanding it as an STI (Mazigo et al., Reference Mazigo, Samson, Lambert, Kosia, Ngoma, Murphy and Matungwa2021). Low awareness of female genital schistosomiasis in some endemic communities may also prevent women from accessing appropriate care through misdiagnosis (Mazigo et al., Reference Mazigo, Samson, Lambert, Kosia, Ngoma, Murphy and Matungwa2021). Clearly, parasites of the genital tract exemplify why a sex and gender-based approach and an awareness and sensitivity to these factors is necessary for understanding and treating infectious diseases.

Many large funding bodies also now require applicants to specifically incorporate both the sex and gender dimension into their research (European Commission Decision, 2024). However, many if not most grant application calls include this requirement without providing the above definitions or much guidance for applicants on how to appropriately incorporate this dimension in their projects, or for evaluators to assess whether it has been accurately considered, with a notable exception being the Canadian Institute for Health Research (Canadian Institutes of Health Research, Reference Research2019). There is also little oversight or standardization in how this dimension is incorporated into studies or manuscripts, often resulting in confusion among researchers over this terminology, particularly around the definition of term ‘gender’ as distinct from sex (Tadiri et al., Reference Tadiri, Raparelli, Abrahamowicz, Kautzy-Willer, Kublickiene, Herrero, Norris and Pilote2021b). Due to the increasing recognition of the importance of incorporating the gender dimension into parasitological research, and this topic’s relevance to the current Parasitology special issue on parasites of the genital tract, a review of how the gender dimension has been incorporated into research in Parasitology thus far is timely. The purpose of this commentary is to provide an overview of where parasitologists, particularly those publishing in Parasitology, are in terms of incorporating the gender dimension into their research, and to provide further clarity to parasitologists on best practice moving forward.