A systematic review of the immune-modulators Parapoxvirus ovis and Propionibacterium acnes for the prevention of respiratory disease and other infections in the horse.

Inactivated Parapoxvirus ovis (iPPVO) and Propionibacterium acnes (P. acnes) are currently used in equine medicine as immune-modulators for prophylactic treatment or adjunct to conventional therapy in order to improve immune defences, to prevent or treat infectious diseases. Their mode of action relies on a non-antigen specific interaction with the innate and/or adaptive immune responses. iPPVO stimulates and regulates cytokine secretion by leucocytes, while P. acnes acts primarily through the activation of macrophages. This report aims to describe their activity as immune-modulators and to summarise the scientific literature and reports available about their use in horses, particularly in the prevention or treatment of equine respiratory diseases. This systematic review regroups articles published in peer-review journals, clinical trials reports, conference proceedings and other information made available in the last 2 decades.