Outside-host predation as a biological control against an environmental opportunist disease

Abstract

Environmentally growing opportunist pathogens are a common threat to human health and food production. Due to environmental growth of the pathogen, these diseases are difficult to control with disinfectants and antibiotics. Thus, there is a need for sustainable and effective control methods against environmentally growing opportunist diseases. Predation is often a major limiting factor in the outside host environment. Here we propose that it could be used in the biological control of these diseases.We introduce a novel epidemiological model for environmentally growing opportunists combining pathogen growth within-host (SI model) and outside-host into classical predator-prey model. We ask how the predation of the pathogens affects epidemiological dynamics, and whether outside-host predators can be used to control the epidemics. The model structure and parameterization are based on the columnaris disease that induces significant economical losses to aquaculture worldwide. The model is also suitable for other environmentally growing opportunist diseases.In line with the classical predator-prey theory, increasing predation of the pathogen can produce cyclic dynamics (outbreaks). Predation can also clear the infection out of the host population and thereafter lead to the extinction of the pathogen. However, when using predators with poor ability to suppress the pathogen population and low inflow rate, the biological control of the disease might fail or counterintuitively lead to an increase in the density of infected individuals. The model demonstrates that environmentally growing opportunist pathogens can be heavily influenced by outside-host predation and this can effectively be utilized in biological control of infectious diseases.