Sexually transmitted diseases of insects: distribution, evolution, ecology and host behaviour

Sexually transmitted diseases (STDs) of insects are known from the mites, nematodes, fungi, protists and viruses. In total 73 species of parasite and pathogen from approximately 182 species of host have been reported. Whereas nearly all vertebrate STDs are viruses or bacteria, the majority of insect STDs are multicellular ectoparasites, protistans or fungi. Insect STDs display a range of transmission modes, with 'pure' sexual transmission only described from ectoparasites, all of which are mites, fungi or nematodes, whereas the microparasitic endo-parasites tend to show vertical as well as sexual transmission. The distribution of STDs within taxa of insect hosts appears to be related to the life histories of the hosts. In particular, STDs will not be able to persist if host adult generations do not overlap unless they are also transmitted by some alternative route. This explains the observation that the Coleoptera seem to suffer from more STDs than other insect orders, since they tend to diapause as adults and are therefore more likely to have overlapping generations of adults in temperate regions. STDs of insects are often highly pathogenic, and are frequently responsible for sterilizing their hosts, a feature which is also found in mammalian STDs. This, combined with high prevalences indicates that STDs can be important in the evolution and ecology of their hosts. Although attempts to demonstrate mate choice for uninfected partners have so far failed it is likely that STDs have other effects on host mating behaviour, and there is evidence from a few systems that they might manipulate their hosts to cause them to mate more frequently. STDs may also play a part in sexual conflict, with males in some systems possibly gaining a selective advantage from transmitting certain STDs to females. STDs may well be important factors in host population dynamics, and some have the potential to be useful biological control agents, but empirical studies on these subjects are lacking.     

Sexually transmitted diseases in polygynous mating systems: prevalence and impact on reproductive success

Studies of disease in relation to animal mating systems have focused on sexual selection and the evolution of sexual reproduction. Relatively little work has examined other aspects of ecological and evolutionary relationships between host social and sexual behaviour, and dynamics and prevalence of infectious diseases; this is particularly evident with respect to sexually transmitted diseases (STDs). Here, we use a simulation approach to investigate rates of STD spread in host mating systems ranging from permanent monogamy to serial polygyny or polyandry and complete promiscuity. The model assumes that one sex (female) is differentially attracted to the other, such that groups of varying size are formed within which mating and disease transmission occur. The results show that equilibrium disease levels are generally higher in females than males and are a function of variance in male mating success and the likelihood of a female switching groups between mating seasons. Moreover, initial rates of disease spread (determining whether an STD establishes in a population) depend on patterns of host movement between groups, variance in male mating success and host life history (e.g. mortality rates). Male reproductive success can be reduced substantially by a sterilizing STD and this reduction is greater in males that are more 'attractive' to females. In contrast, females that associate with more attractive males have lower absolute fitness than females associating with less attractive males. Thus, the potential for STDs to act as a constraint on directional selection processes leading to polygyny (or polyandry) is likely to depend on the details of mate choice and group dynamics.     

SEXUALLY TRANSMITTED DISEASE AND PARASITE-MEDIATED SEXUAL SELECTION

Few studies have investigated the consequences of parasite-mediated sexual selection on the parasites involved. In some cases parasite-mediated sexual selection could lead to increased virulence, but I develop a simple model that shows that, if a parasite is sexually transmitted (i.e., is a sexually transmitted disease, or STD) and if mating success of the host is adversely affected by the parasite, then less virulent STDs will be selected for because transmission of the STD depends on the mating success of the host. This selection for reduced virulence could have important consequences for the role of STDs in sexual selection.     

The role of sexually transmitted diseases in HIV transmission

More than 42 million people worldwide are now infected with HIV, in spite of sustained prevention activities. Although the spread of HIV has been primarily sexual, epidemiological studies have indicated that the efficiency of the spread of HIV is poor, perhaps as infrequently as 1 in every 1,000 episodes of sexual intercourse. However, sexually transmitted diseases (STDs) that cause ulcers or inflammation greatly increase the efficiency of HIV transmission--by increasing both the infectiousness of, and the susceptibility to HIV infection. STDs might be particularly important in the early stages of a localized HIV epidemic, when people with risky sexual behaviour are most likely to become infected. In China, eastern Europe and Russia, there has been a remarkable increase in the incidence of STDs in recent years, and this is reflected in the rapid increase in the spread of HIV in these areas. Targeted STD detection and treatment should have a central role in HIV prevention in these emerging epidemics.     

Lack of parasite-mediated sexual selection in a ladybird/sexually transmitted disease system

Despite the clear potential of sexually transmitted diseases (STDs) to affect host mating behaviour via both host and parasite evolution, there have been few explicit tests of the relationships between STDs and sexual behaviour in animals. We investigated the effect of infection on host sexual behaviour within an invertebrate system. Coccipolipus hippodamiae is a sexually transmitted ectoparasite of Adalia bipunctata, the two-spot ladybird. The parasite feeds on host haemolymph, develops rapidly, and is deleterious to A. bipunctata hosts of both sexes. We examined whether infection affected mating success, and whether males or females showed any preferences with respect to infection status. We observed field mating rates of infected and uninfected ladybirds and carried out controlled laboratory experiments. We did not detect any negative effects of parasite infection on host mating vigour, nor any evidence for the existence of a host mating preference based on infection status. In addition, there was no evidence of parasite-induced changes in behaviour, such as increased promiscuity, which would increase transmission opportunities for the parasite. In summary, contrary to a body of speculation, there was no evidence of any connection between infection and mating rate, in either sex. We discuss possible explanations for these findings.     

The effect of aggregative overwintering on an insect sexually transmitted parasite system

In contrast to the extensively studied sexually transmitted diseases (STDs) of humans, little is known of the ecology or evolutionary biology of sexually transmitted parasites in natural systems. This study of a sexually transmitted parasite on an insect host augments our understanding of both the parasite's population dynamics and virulence effects. The impact of overwintering was assessed on the prevalence of the parasitic mite Coccipolipus hippodamiae on the two-spot ladybird, Adalia bipunctata. First, the effect of infection on host survival was examined during the stressful overwintering period. Box experiments in the field revealed that the infected ladybirds, especially males, are less likely to survive overwintering. The study provides the first evidence that the parasite harms males and suggests revisions of theories on the adaptive virulence of sexually transmitted parasites. It also indicates the importance of using a range of experimental conditions because virulence can be dependent on host condition and sex. Box experiments were also used to examine whether transmission of the parasite occurs within overwintering aggregations. These revealed that substantial transmission does not occur in aggregations and that transmission is predominantly sexual. Overall, the virulence effects and the lack of transmission mean that the overwintering period acts to diminish parasite prevalence and will retard the spring epidemic associated with host reproductive activity.     

Sexually transmitted disease in a promiscuous insect, Adalia bipunctata

Abstract.

• 1 Sexually transmitted diseases (STDs) have rarely been reported in insects and other invertebrates. The majority of those reported involve organisms where sexual transmission is augmented by either vertical (i.e. inherited) transmission, or horizontal transmission, independent of host sexual activity.
• 2 We here demonstrate the existence of an STD in the coccinellid beetle Adalia bipunctata. This species bears a parasitic mite of the genus Coccipolipus. We show that, like many other podapolipid mites, this mite is transmitted between host individuals at a high rate during copulation. It also appears to be transmitted at a low rate between non-copulating individuals.
• 3 We show that infected female A.bipunctata produced eggs at a reduced rate, and that the eggs produced by infected females have highly decreased viability. However, no effect of infection upon host longevity was observed.
• 4 The results are discussed in relation to the incidences of sexually transmitted disease in invertebrates in general, the causes of disease symptoms, and the importance of this disease in the evolution of A.bipunctata.

     

Modeling AIDS as a function of other sexually transmitted disease.

The spread of AIDS, as with any sexually transmitted disease, will depend on the pattern of sexual activity. Both the proportion of the population who have high partner exchange rates and the extent to which that proportion interacts with the remainder of the population are likely to be important determinants of the AIDS epidemic. However, it does not seem likely that surveys could obtain sufficiently reliable information of this nature for use in an accurate model of the AIDS epidemic. On the other hand, such information is implicitly contained in the epidemiology of other sexually transmitted diseases (STDs). Therefore a method is suggested of calculating the parameters of a model of the AIDS epidemic by comparing it with the epidemiology of another STD. The result is a model that predicts the likelihood of infection by the AIDS virus as a function of time and an individual's history of STD. It is suggested that further work along these lines may lead to a quantitative approach to assessing the importance of various STDs as cofactors in the spread of AIDS.     

Prevention de l’infertilite d’origine infectieuse chez l’adolescent

Some causes of infertility can be prevented, as is the case for infertility of infectious origin. Genital infections represent a major source of infertility. Prostato-epididymitis consecutive to an urinary infection can be prevented by identifying and treating prostatic localizations at an early stage of urinary infection. The prevention of sexually transmitted diseases (STD), which cause male and female infertility, is, at the moment, accomplished by the prevention of the sexual transmission of the HIV. Teenagers represent a target of choice for the educational campaigns promoting condom use. The role of physicians, especially when teenagers are asking for a contraception, must be complementary to the public health campaign to decrease the spread of HIV and other STDs.     

Prevention de l’infertilite d’origine infectieuse chez l’adolescent

Some causes of infertility can be prevented, as is the case for infertility of infectious origin. Genital infections represent a major source of infertility. Prostato-epididymitis consecutive to an urinary infection can be prevented by identifying and treating prostatic localizations at an early stage of urinary infection. The prevention of sexually transmitted diseases (STD), which cause male and female infertility, is, at the moment, accomplished by the prevention of the sexual transmission of the HIV. Teenagers represent a target of choice for the educational campaigns promoting condom use. The role of physicians, especially when teenagers are asking for a contraception, must be complementary to the public health campaign to decrease the spread of HIV and other STDs.     

How often is genital yeast infection sexually transmitted?

We analysed data from a computer-based bank of clinical records of patients seen in a clinic for sexually transmitted diseases over a three-year period to investigate the association between genital yeast infections and sexually transmitted diseases (STDs). We classified STDs as primary and secondary syphilis; gonorrhoea; lymphogranuloma venereum; trichomoniasis; scabies; pediculosis; genital herpes; warts; and molluscum contagiosum. Of a total of 2984 disease episodes among women, 1054 (35-3%) included yeast infections, whereas only 382 (6-9%) of 5501 episodes in heterosexual men were associated with yeast infections, We found a significant association between yeast infection and STD and non-specific genital infection (non-specific urethritis (NSU) and procitis in men, and female contacts of men with NSU), which suggested that yeast infection was sexually acquired in 414 out of 1054 disease episodes in women (39%) and 110 out of 382 episodes in heterosexual men (29%). We conclude that sexually active patients with genital yeast infections should be screened for other STDs particularly non-specific genital infection.     

Design of a "microbicide" for prevention of sexually transmitted diseases using "inactive" pharmaceutical excipients.

The human immunodeficiency virus (HIV-1) pandemic has been driven primarily by the sexual transmission of the virus, and facilitated by prior infections with other sexually transmitted disease (STD) pathogens. Although treatment of these STDs has been proposed as a means to decrease the rate of HIV-1 sexual transmission, preventive measures effective against both HIV-1 and other STD pathogens are expected to have a larger impact. These measures include topically applied mechanical and chemical (i.e. microbicidal) barriers. Microbicides of preference should have a broad specificity against diverse STD pathogens and a well established safety record, considering their repeated use over decades. Here, we report that cellulose acetate phthalate (CAP), an "inactive" pharmaceutical excipient, commonly used in the production of enteric tablets and capsules: (1) has antiviral activity against HIV-1 and several herpesviruses (HSV); and (2) when appropriately formulated, in micronized form, inactivates HIV-1, HSV-1, HSV-2, cytomegalovirus, Neisseria gonorrhoeae, Trichomonas vaginalis, Haemophilus ducreyi and Chlamydia trachomatis but does not affect Lactobacilli, components of the natural vaginal flora contributing to resistance against STDs. Thus, the CAP formulations meet the criteria for preferred microbicides and warrant further evaluation in vivo in humans.     

Frequency-dependent incidence in models of sexually transmitted diseases: portrayal of pair-based transmission and effects of illness on contact behaviour

We explore the transmission process for sexually transmitted diseases (STDs). We derive the classical frequency-dependent incidence mechanistically from a pair-formation model, using an approximation that applies to populations with rapid pairing dynamics (such as core groups or non-pair-bonding animals). This mechanistic derivation provides a framework to assess how accurately frequency-dependent incidence portrays the pair-based transmission known to underlie STD dynamics. This accuracy depends strongly on the disease being studied: frequency-dependent formulations are more suitable for chronic less-transmissible infections than for transient highly transmissible infections. Our results thus support earlier proposals to divide STDs into these two functional classes, and we suggest guidelines to help assess under what conditions each class can be appropriately modelled using frequency-dependent incidence. We then extend the derivation to include situations where infected individuals exhibit altered pairing behaviour. For four cases of increasing behavioural complexity, analytic expressions are presented for the generalized frequency-dependent incidence rate, basic reproductive number (R0) and steady-state prevalence (i infinity) of an epidemic. The expression for R0 is identical for all cases, giving refined insights into determinants of invasibility of STDs. Potentially significant effects of infection-induced changes in contact behaviour are illustrated by simulating epidemics of bacterial and viral STDs. We discuss the application of our results to STDs (in humans and animals) and other infectious diseases.     

Recent change in the annual pattern of sexually transmitted diseases in the United States

This study analyzed the 1999 to 2003 database of the Center for Disease Control and Prevention (CDC) for seasonal and longer-term time trends in the sexually transmitted diseases (STDs) of chlamydia, gonorrhea, and syphilis in the United States. Linear regression was used to ascertain time trends, and a linear mixed auto-regression model was applied to determine the statistical significance of the major peaks relative to the annualized time series mean. A statistically significant increasing trend during the 5 yr span was documented only in the incidence of chlamydia. No clear annual periodicity was detected in any of the STDs; instead, significant three-month cycles were documented in all the STDs, with prominent peaks evident in March, May, August, and November. The March and May peaks could be associated with the sexual activities of young adults during spring break, which for different colleges and universities, commences as early as mid- to late-February and concludes as late as early- to mid-April, when huge numbers of sexually active youth congregate at beach resort settings. We propose the August peak is representative of summer sexual activity, in particular, of youths during school recess when adult supervision is poor. Finally, the autumn peak seems to be an expression of an endogenous annual rhythm in human reproductive biology, exemplified by elevated levels of testosterone in young males and sexual activity at this time of the year.     

The host selects mucosal and luminal associations of coevolved gut microorganisms: a novel concept

Along the human gastrointestinal tract, microorganisms are confronted with multiple barriers. Besides selective physical conditions, the epithelium is regularly replaced and covered with a protective mucus layer trapping immune molecules. Recent insights into host defense strategies show that the host selects the intestinal microbiota, particularly the mucosa-associated microbial community. In this context, humans coevolved with thousands of intestinal microbial species that have adapted to provide host benefits, while avoiding pathogenic behavior that might destabilize their host interaction. While mucosal microorganisms would be crucial for immunological priming, luminal microorganisms would be important for nutrient digestion. Further, we propose that the intestinal microorganisms also coevolved with each other, leading to coherently organized, resilient microbial associations. During disturbances, functionally redundant members become more abundant and are crucial for preserving community functionality. The outside of the mucus layer, where host defense molecules are more diluted, could serve as an environment where microorganisms are protected from disturbances in the lumen and from where they can recolonize the lumen after perturbations. This might explain the remarkable temporal stability of microbial communities. Finally, commensals that become renegade or a decreased exposure to essential coevolved microorganisms may cause particular health problems such as inflammatory bowel diseases, obesity or allergies.     

Recent Change in the Annual Pattern of Sexually Transmitted Diseases in the United States

This study analyzed the 1999 to 2003 database of the Center for Disease Control and Prevention (CDC) for seasonal and longer‐term time trends in the sexually transmitted diseases (STDs) of chlamydia, gonorrhea, and syphilis in the United States. Linear regression was used to ascertain time trends, and a linear mixed auto‐regression model was applied to determine the statistical significance of the major peaks relative to the annualized time series mean. A statistically significant increasing trend during the 5 yr span was documented only in the incidence of chlamydia. No clear annual periodicity was detected in any of the STDs; instead, significant three‐month cycles were documented in all the STDs, with prominent peaks evident in March, May, August, and November. The March and May peaks could be associated with the sexual activities of young adults during spring break, which for different colleges and universities, commences as early as mid‐ to late‐February and concludes as late as early‐ to mid‐April, when huge numbers of sexually active youth congregate at beach resort settings. We propose the August peak is representative of summer sexual activity, in particular, of youths during school recess when adult supervision is poor. Finally, the autumn peak seems to be an expression of an endogenous annual rhythm in human reproductive biology, exemplified by elevated levels of testosterone in young males and sexual activity at this time of the year.     

The effect of combat exposure on sexually transmitted diseases

Traumatic exposures can affect beliefs and behaviors related to the spread of sexually transmitted diseases (STDs), a persistent public health problem. I leverage a natural experiment created by variation in US military deployment location assignments to estimate how combat exposure changes a surviving deployed male veteran’s probability of acquiring a sexually transmitted disease. I analyze longitudinal data from 1994 to 2008 on 485 deployed veterans with information theoretic methods to reduce the sensitivity of estimates to small samples, an infrequently observed outcome, and highly correlated covariates. For veterans assigned to a combat zone, I estimate combat exposure results in a 5.4 percentage point increase in the probability of acquiring an STD. Additional estimations provide evidence suggesting risky behaviors involving substance use or multiple sexual partners may serve as pathways from combat exposure to STDs. My results are relevant to discussions regarding STD screening and care needs for trauma exposed individuals.     

性病后慢性前列腺炎病原微生物分析

本文对性病后慢性前列腺炎病原微生物进行了研究。９０例患者前列腺液支原体检出率为２４．４４％（２２／９０）,其中解脲支原体为２２．００％（１８／９０）,人型支原体为４．４４％（４／９０）。另一组２３２例患者进行前列腺液细菌培养鉴定,总检出率为４２．７％（９９／２３２）,以金黄色葡萄球菌为主２４．５％（５７／２３２）,其它菌依次为表皮葡萄球菌７．３％（１７／２３２）,肠球菌４．３％（１０／２３２）,非发酵菌２．６％（６／２３２）,肠杆菌科细菌２．２％（５／２３２）和Ａ群链球菌１．７％（４／２３２）。作者认为,性病后慢性前列腺炎可能为急性尿道炎期,由于治疗不彻底或忽略非特异性性病病原菌的治疗而使条件致病菌上行感染所致。     

New principles and criteria in assessing pathogenic and opportunistic microorganisms

Using the ecological and natural-science approaches, the authors have come to the conclusion that microorganisms, pathogenic for humans (animals), are their parasites for whom the disease of their biological host is the necessary condition of their existence as a biological species. And accordingly, microorganisms, opportunistic in humans (animals) are their parasites and commensals, as well as saprophytes, for whom the disease of their host is not the necessary condition of their existence in nature. The biological host is a symbion necessary for the existence of pathogenic and most opportunistic microorganisms, but for a pathogenic microorganism the disease of the host is the result of symbiotic relationships, while for an opportunistic microorganism the disease of the host is the consequence of disturbances in symbiotic relationships. Such view of pathogenicity is important for creating a scientifically grounded theory of the liquidation of human infectious diseases.     

Conquering sexually transmitted diseases

Sexually transmitted diseases (STDs) are a major public-health problem and also a significant financial burden on the economy. Past and ongoing attempts to create vaccines against sexually transmitted pathogens have met with varying success. This article highlights some of the public-health and social problems that are associated with STDs and the technical and ethical challenges in treating them, and raises several questions that need to be addressed if STDs are to be conquered.