The reading by Nahmias and Nahmias from earlier this month detailed the wide breadth of influencing factors that played a role in the spread of sexually transmitted infections (STIs) throughout human populations all over the world. Although the connection between sexual activity and disease was established a long time ago, the epidemiology behind STIs continues to be ever multi-faceted, making the development and execution of successful interventions very difficult. The paper also explained how the nature of the transmission allows for interesting trends in the evolutionary paths taken by the infectious agents. Many factors were cited as contributing to the spread of STIs, including travel, ecological change, economic inequality and public health issues, among many others, all of which created a complex web of interrelationships in the disease epidemiology.

The article “Love and Sex Influence Disease Evolution” talks about a study from August 2006 in The American Naturalist that examined in detail one of those particular influences on sexually transmitted pathogens. The scientists that authored the study, Eames and Keeling, concluded that the length of time sexual partners stay together has a significant influence on the evolution of multiple strains of a particular infection. It showed that some strains evolve as better suited for monogamous pairings with little chance of a rapid change in host environment (considered slow strains because they have the ability to persist in a host for a long time), while others are better adapted for short term relationship (considered to be fast strains because they cannot utilize resources in order to persist in one host). The study gives further proof for why different strains of a single infection can exist without selecting against each other.

In our recent discussion, we read about the principles of Hamiltonian medicine and discussed its usefulness in addressing human health problems and disease that are occurring worldwide. One of the domains that the paper mentioned and we talked about throughout the class was the microbe-to-microbe social interaction that affects the health of the human host. The “Pathogen-pathogen Interaction” paper was very interesting since I was able to learn about the impacts of the pathogen-pathogen interaction in human disease patterns and review specific examples of disease interactions.

The paper emphasized that infectious agents often do not act independently but cooperate with other pathogens to modify microbial phenotype to persist in the human host. The identified examples of pathogen-pathogen interaction are amoeba/bacteria interaction, HIV/HCV and HIV/fungal interactions, and tick-borne disease interaction. All of these identified case examples are known to impact the health of human populations in recent years.

Several pathogen-pathogen interactions show that pathogens can have significant impact on each other. Based on the pathways the pathogens interact upon one another, pathogens cause different impacts on the host. For example, one disease can promote the contagiousness of another disease by enabling them to penetrate to vulnerable area of the body. Another type of interactions between pathogens can accelerate the virulence of one another. For example, patients who are co-infected with HIV and HSV have a boosting of HIV load along with the higher providing of a portal for entry and exit of the virus.

Since the interactions between pathogens considerably impact the human health, a disease should not be considered as a distinct entity separate from other diseases. Instead, a health professional should pay attention to the syndemics model, which states that aggregation of diseases can have negative health affects, and recognize that interactions among diseases can influence the severity, transmission, and diffusion of the disease within human population.