Treating cofactors can reverse the expansion of a primary disease epidemic

Abstract

BackgroundCofactors, "nuisance" conditions or pathogens that affect the spread of a primary disease, are likely to be the norm rather than the exception in disease dynamics. Here we present a "simplest possible" demographic model that incorporates two distinct effects of cofactors: that on the transmission of the primary disease from an infected host bearing the cofactor, and that on the acquisition of the primary disease by an individual that is not infected with the primary disease but carries the cofactor.MethodsWe constructed and analyzed a four-patch compartment model that accommodates a cofactor. We applied the model to HIV spread in the presence of the causal agent of genital schistosomiasis, Schistosoma hematobium, a pathogen commonly co-occurring with HIV in sub-Saharan Africa.ResultsWe found that cofactors can have a range of effects on primary disease dynamics, including shifting the primary disease from non-endemic to endemic, increasing the prevalence of the primary disease, and reversing demographic growth when the host population bears only the primary disease to demographic decline. We show that under parameter values based on the biology of the HIV/S. haematobium system, reduction of the schistosome-bearing subpopulations (e.g. through periodic use of antihelminths) can slow and even reverse the spread of HIV through the host population.ConclusionsTypical single-disease models provide estimates of future conditions and guidance for direct intervention efforts relating only to the modeled primary disease. Our results suggest that, in circumstances under which a cofactor affects the disease dynamics, the most effective intervention effort might not be one focused on direct treatment of the primary disease alone. The cofactor model presented here can be used to estimate the impact of the cofactor in a particular disease/cofactor system without requiring the development of a more complicated model which incorporates many other specific aspects of the chosen disease/cofactor pair. Simulation results for the HIV/S. haematobium system have profound implications for disease management in developing areas, in that they provide evidence that in some cases treating cofactors may be the most successful and cost-effective way to slow the spread of primary diseases.

An integrated study of human and animal infectious disease in the Lake Victoria crescent small-holder crop-livestock production system, Kenya

“…The wide range of pathogens considered here provides a rich data set for exploration of such relationships. In particular, by considering infection with the ‘big 3’ infectious diseases (HIV, TB and malaria), in addition to a number of neglected zoonotic and tropical diseases, these data can potentially contribute to the growing evidence base on the effects of immunological interactions between these pathogens on within community transmission dynamics [ 18 , 42 , 43 ].…”

“…East Coast fever (ECF), helminthiasis, trypanosomiasis, bovine tuberculosis). These ‘co-factors” may exacerbate susceptibility to zoonotic agents in individuals or result in enhanced spread at a community level [ 18 ]. To further explore this dual burden, we also quantified the prevalence of a wide range of endemic, non-zoonotic infectious agents in both people and animals within the study population.…”

The Effect of Anthelmintic Treatment During Pregnancy on HIV Plasma Viral Load

“…An association between S. haematobium infection and HIV prevalence has been documented 36,37 , suggesting a role for this helminth species in HIV transmission dynamics 38 . We could not examine this possibility since S. haematobium was not prevalent in the study area; similar studies conducted in regions where S. haematobium infection is endemic are required to elucidate this relationship.…”

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

“…In addition to its role in schistosomiasis morbidity reduction, mathematical modelling suggests that PZQ treatment of women and school-aged children in S. haematobium high-risk communities could reduce HIV-1 prevalence ( Gibson et al., 2010 ; Mushayabasa and Bhunu 2011 ; Ndeffo Mbah et al., 2013 ; Ndeffo Mbah et al., 2014 ). This finding highlights the need for further research into the use of PZQ for HIV-1 prevention.…”