Modeling schistosomiasis and HIV/AIDS codynamics

Modeling schistosomiasis transmission: the importance of snail population structure

Background

Schistosomiasis is a neglected tropical disease endemic in 54 countries. A major Schistosoma species, Schistosoma mansoni, is sustained via a life cycle that includes both human and snail hosts. Mathematical models of S. mansoni transmission, used to elucidate the complexities of the transmission cycle and estimate the impact of intervention efforts, often focus primarily on the human host. However, S. mansoni incurs physiological costs in snails that vary with the age of the snail when first infected. Snail demography and the age of snail infection could thus affect the force of infection experienced by humans, which is frequently used to predict the impact of various control strategies.

Methods

To address how these snail host and parasite interactions influence model predictions, we developed deterministic models of schistosomiasis transmission that include varying complexity in the snail population age structure. Specifically, we examined how model outputs, such as schistosome prevalence in human and snail populations, respond to the inclusion of snail age structure.

Results

Our models suggest that snail population age structure modifies the force of infection experienced by humans and the relationship between snail infection prevalence and corresponding human infection prevalence. There are significant differences in estimated snail infection, cercarial density and mean worm burden between models without snail population dynamics and those with snail populations, and between models with a homogeneous snail population and those with age stratification. The variation between finely age-stratified snail populations and those grouped into only juvenile and adult life stages is, however, minimal.

Conclusions

These results indicate that including snails and snail age structure in a schistosomiasis transmission model alters the relationship between snail and human infection prevalence. This highlights the importance of accounting for a heterogeneous intermediate host population in models of schistosomiasis transmission where the impact of proposed control measures is being considered.

Beyond the barrier: Female Genital Schistosomiasis as a potential risk factor for HIV-1 acquisition

Female genital schistosomiasis (FGS) results from egg-deposition in the female reproductive tract primarily by the waterborne parasite Schistosoma (S.) haematobium, and less commonly by Schistosoma (S.) mansoni. FGS affects an estimated 20-56 million women worldwide, mostly in sub-Saharan Africa. There is cross-sectional evidence of increased HIV-1 prevalence in schistosomiasis-infected women, but a causal relationship between FGS and either HIV-1 acquisition or transmission has not been fully established. Beyond the pathognomonic breach in the cervicovaginal barrier caused by FGS, this narrative review explores potential mechanisms for a synergistic relationship between S. haematobium infection, FGS, and HIV-1 acquisition through vaginal inflammation and target cell recruitment.

ON THE DYNAMICS MALARIA-DYSENTERY CO-INFECTION MODEL

In this paper, a mathematical model for malaria-dysentery co-infection was formulated in order to study and examine its dynamic relationship in the presence of malaria and dysentery preventive and treatment measures. First, analysis of the single infection steady states was done and then the basic reproduction number was obtained. Furthermore, investigation into the existence and stability of equilibria carried out. The single infection models were found to exhibit the possibility of backward bifurcation. Thereafter, the impact of malaria on the dynamics of dysentery is further investigated. Second, incorporating time-dependent controls, using Pontryagin’s Maximum Principle, the necessary conditions for the optimal control of the disease was derived. It is found that malaria infection may be associated with an increased risk of dysentery. Also, that dysentery infection may be associated with an increased risk for malaria. Therefore, to effectively control malaria, the malaria intervention strategies by policy makers must at the same time it also includes effective prevention and control measures for dysentery. Policy makers should take efforts on preventive strategies in combating dysentery and malaria.

Interactions of Schistosoma and HIV in Sub-Saharan Africa: A Systematic Review

Schistosomiasis is an acute and chronic parasitic disease caused by blood flukes of the genus Schistosoma. More than 220 million people worldwide were estimated to have active schistosomiasis in 2017, 90% of whom live on the African continent, but only 102 million were reported to have received treatment. Africa is also disproportionately burdened by HIV, with an estimated 26 million people living with HIV in 2017. Given these overlapping epidemics, we conducted a systematic review to ascertain the contribution of schistosomes to HIV acquisition risk, the contribution of HIV to schistosome acquisition, the impact of HIV on schistosomiasis-related morbidity, the impact of schistosomes on HIV disease progression and immune response, the impact of HIV on the efficacy of praziquantel treatment, and the impact of HIV on egg shedding. We reviewed studies of people living in sub-Saharan Africa coinfected with HIV and Schistosoma spp. between January 1996 and July 2018. We found that 1) infection with Schistosoma haematobium increases the risk of HIV acquisition, 2) there is currently a lack of data on whether HIV infection increases the risk of Schistosoma acquisition, 3a) HIV coinfection was not an accelerating factor for adverse Schistosoma outcomes, 3b) schistosomiasis may be an important contributor to immune activation in HIV coinfected people, 4) praziquantel use in coinfected people may improve immune reconstitution on antiretroviral therapy for HIV, and 5) there is evidence that HIV infection reduces egg excretion in individuals infected with Schistosoma mansoni.

A systematic review and meta-analysis to assess the association between urogenital schistosomiasis and HIV/AIDS infection

Background

Urogenital schistosomiasis and HIV/AIDS infections are widespread in sub-Saharan Africa (SSA) leading to substantial morbidity and mortality. The co-occurrence of both diseases has led to the possible hypothesis that urogenital schistosomiasis leads to increased risk of acquiring HIV infection. However, the available evidence concerning this association is inconsistent. The aim of this study was to systematically review and quantitatively synthesize studies that investigated the association between urogenital schistosomiasis and HIV/AIDS infection.

Methods

A systematic review basing on PRISMA guidelines was conducted. It is registered with PROSPERO, number CRD42018116648. We searched four databases, MEDLINE, EMBASE, Global Health and Global Index Medicus for studies investigating the association between urogenital schistosomiasis and HIV infection. Only studies published in English were considered. Results of the association were summarised by gender. A meta-analysis was performed for studies on females using random-effects model and a pooled OR with 95% confidence interval was reported.

Results

Of the 993 studies screened, only eight observational studies met the inclusion criteria. Across all studies, the reported unadjusted OR ranged from 0.78 to 3.76. The pooled estimate of unadjusted OR among females was 1.31 (95% CI: 0.87–1.99). Only four of the eight studies reported an adjusted OR. A separate meta-analysis done in the three studies among females that reported an adjusted OR showed that the pooled estimate was 1.85 (95% CI: 1.17–2.92). There were insufficient data to pool results for association between urogenital schistosomiasis and HIV infection in the males.

Conclusion

Our investigation supports the hypothesis of an association between urogenital schistosomiasis with HIV/AIDS infection in females. Due to insufficient evidence, no conclusion could be drawn in males with urogenital schistosomiasis. Large-scale prospective studies are needed in future.

Urogenital schistosomiasis, caused by parasitic trematode Schistosoma haematobium is a significant source of morbidity in sub Saharan Africa. HIV infection caused by a retrovirus is of two subtypes HIV 1 and HIV 2, with subtype HIV 1 being found worldwide and more aggressive, leading to HIV/AIDS. Research on both of these diseases in the same settings, has shown that these diseases cross paths. This has led to the suggestion that there could be a possible association between the two. Here we describe a systematic review that was carried out to determine if there is an association between UGS and HIV/AIDS infections. We searched all published articles available in MEDLINE, EMBASE, Global Health (CABI), and Global Index Medicus before 28^th January 2020. We found eight observational studies eligible to be included in the systematic review and no intervention study. Six of these studies were included in the meta-analysis. A summarized meta-analysis of the study findings with adjusted OR showed that there was a likely association between urogenital schistosomiasis and HIV/AIDS infections in females. However, due to limited papers in males, no conclusion could be drawn.

Female Genital Schistosomiasis and HIV: Research Urgently Needed to Improve Understanding of the Health Impacts of This Important Coinfection

Evidence suggests that there are important interactions between HIV and female genital schistosomiasis (FGS) that may have significant effects on individual and population health. However, the exact way they interact and the health impacts of the interactions are not well understood. In this article, we discuss what is known about the interactions between FGS and HIV, and the potential impact of the interactions. This includes the likelihood that FGS is an important health problem for HIV-positive women in Schistosoma-endemic areas potentially associated with an increased risk of mortality, cancer, and infertility. In addition, it may be significantly impacting the HIV epidemic in sub-Saharan Africa by making young women more susceptible to HIV. We call for immediate action and argue that research is urgently required to address these knowledge gaps and propose a research agenda to achieve this.

Optimal control applied to a temperature dependent schistosomiasis model

Schistosomiasis, the most common water-borne infection worldwide, continues to pose a serious public health challenge in developing nations and to travellers who visit these endemic regions. We apply optimal control on a temperature dependent schistosomiasis model. Our optimal control aims to minimize the pre-patent and patent human population at minimal costs. Our analysis and results throughout the paper highlight the impact of optimal control shaping the future patterns of the disease. Our results show that optimal control can significantly reduce the schistosomiasis burden in the community and in some instance by more than three-fold. In addition, our results show that with low costs the optimal strategy will be carried out at or close to its maximum strength for a sufficiently long period of time, so as minimize the exposure and infection. With high costs, however, the control have to be implemented with reduced or even minimum, strength, to achieve an optimal balance between the costs and effects of control. Our findings suggest that optimal control theory can be useful on minimizing the infected host and vector. The study and its findings can provide a useful framework for designing cost-effective control for schistosomiasis.

Optimal control analysis of malaria-schistosomiasis co-infection dynamics

This paper presents a mathematical model for malaria--schistosomiasis co-infection in order to investigate their synergistic relationship in the presence of treatment. We first analyse the single infection steady states, then investigate the existence and stability of equilibria and then calculate the basic reproduction numbers. Both the single-infection models and the co-infection model exhibit backward bifurcations. We carrying out a sensitivity analysis of the co-infection model and show that schistosomiasis infection may not be associated with an increased risk of malaria. Conversely, malaria infection may be associated with an increased risk of schistosomiasis. Furthermore, we found that effective treatment and prevention of schistosomiasis infection would also assist in the effective control and eradication of malaria. Finally, we apply Pontryagin's Maximum Principle to the model in order to determine optimal strategies for control of both diseases.

Female genital schistosomiasis (FGS): from case reports to a call for concerted action against this neglected gynaecological disease

In recent years, control of neglected tropical diseases has been increasingly gaining momentum and interventions against schistosomiasis are being progressively scaled-up through expansion of donated praziquantel and preventive chemotherapy campaigns. However, the public health importance of female genital schistosomiasis is not fully recognised nor its control is adequately addressed. Taking a clinical and anatomopathological perspective, we evaluated the available literature to highlight the importance of female genital schistosomiasis and its connections with two sexually transmitted infections of global importance, Human Immunodeficiency Virus (HIV) and Human Papilloma Virus. Outside the long list of clinical descriptive reports beginning in 1899, there is presently a shocking gap in epidemiological assessment and a significant underestimation of the burden of FGS remains. The scarcity of integrated approaches to address female genital schistosomiasis calls for more concerted action in its detection, treatment and prevention alongside other concomitant women's health issues, otherwise female genital schistosomiasis will remain a neglected gynaecological disease.

A co-infection model of malaria and cholera diseases with optimal control

In this paper we formulate a mathematical model for malaria-cholera co-infection in order to investigate their synergistic relationship in the presence of treatments. We first analyze the single infection steady states, calculate the basic reproduction number and then investigate the existence and stability of equilibria. We then analyze the co-infection model, which is found to exhibit backward bifurcation. The impact of malaria and its treatment on the dynamics of cholera is further investigated. Secondly, we incorporate time dependent controls, using Pontryagin's Maximum Principle to derive necessary conditions for the optimal control of the disease. We found that malaria infection may be associated with an increased risk of cholera but however, cholera infection is not associated with an increased risk for malaria. Therefore, to effectively control malaria, the malaria intervention strategies by policy makers must at the same time also include cholera control.

Measuring and modelling concurrency

This article explores three critical topics discussed in the recent debate over concurrency (overlapping sexual partnerships): measurement of the prevalence of concurrency, mathematical modelling of concurrency and HIV epidemic dynamics, and measuring the correlation between HIV and concurrency. The focus of the article is the concurrency hypothesis - the proposition that presumed high prevalence of concurrency explains sub-Saharan Africa's exceptionally high HIV prevalence. Recent surveys using improved questionnaire design show reported concurrency ranging from 0.8% to 7.6% in the region. Even after adjusting for plausible levels of reporting errors, appropriately parameterized sexual network models of HIV epidemics do not generate sustainable epidemic trajectories (avoid epidemic extinction) at levels of concurrency found in recent surveys in sub-Saharan Africa. Efforts to support the concurrency hypothesis with a statistical correlation between HIV incidence and concurrency prevalence are not yet successful. Two decades of efforts to find evidence in support of the concurrency hypothesis have failed to build a convincing case.

Epidemiology and immunology of helminth-HIV interactions

PURPOSE OF REVIEW

Helminths and HIV-1 use multiple mechanisms to avoid or deviate immune responses, and these mechanisms may interact with important consequences for the epidemiology of each infection. In this review, we summarize recent immunological and epidemiological advances in the understanding of HIV-1-helminth co-infections.

RECENT FINDINGS

Considering the extent of geographical overlap of these chronic infections, there has been so far surprisingly limited and inconsistent evidence of important interactive effects, either from epidemiological studies examining associations between helminth infection indicators and HIV disease parameters, or from studies that have dissected the immune mechanisms triggered by each pathogen in isolation and investigated their interaction. Systematic reviews have found inconsistent evidence for a beneficial effect of anthelmintic treatment of helminth-HIV-1 co-infected individuals on viral load or CD4 cell counts. It is not certain that co-infection with HIV-1 and helminths will always be more detrimental to the host than either single infection alone, or that intervening against co-infections will have only beneficial effects.

SUMMARY

A consensus on the implications of co-infection on de-worming and vaccination policies has not yet emerged. Well powered randomized trials in HIV-1-infected individuals with defined helminth infections are required to determine the benefits of anthelmintic interventions.

The effects of schistosomiasis on HIV/AIDS infection, progression and transmission

PURPOSE OF REVIEW

The recent findings pertaining to the public health impact of schistosomiasis on the epidemiology of HIV/AIDS are summarized.

RECENT FINDINGS

Both empiric data and mathematical models support the hypothesis that schistosome infections lead to increased susceptibility to infection with HIV-1, a more rapid progression to disease through more vigorous viral replication and immunosuppression, and a higher likelihood of transmitting the infection to others through both vertical and horizontal routes. Different species of schistosome infection vary in the magnitude of their effects on these mechanisms with Schistosoma haematobium playing a greater role for increased susceptibility and transmission because of its association with urogenital disease.

SUMMARY

Schistosomiasis appears to be a cofactor in the spread and progression of HIV/AIDS in areas wherein both diseases are endemic; increased emphasis on treatment of schistosome infections in persons at risk of HIV/AIDS should be pursued.