Ebola virus (EBOV) infection usually leads to highly lethal EBOV disease (EVD) with associated viraemia. Viraemia is cleared in those that do survive, however, EBOV may remain hidden in the testes and other immune privileged niches (IPNs) where it can persist for years during asymptomatic convalescence. Viral shedding into seminal fluid may result in sexual transmission to naive contacts years after EBOV outbreaks have been declared over. This leads to flare-ups of cases, redefining our understanding of the shaping and origin of EBOV outbreaks. Such delayed sexual transmission eliminates the geographical boundaries which typically constrain EBOV outbreaks, thus posing a significant global health security threat. Despite hints of EBOV persistence dating over half a century, it was only until the unprecedented scale of the 2013–2016 Western Africa EBOV epidemic that the true importance of this phenomenon was revealed to scientists, public health officials and policy makers alike. This review summarises the evidence for EBOV persistence, suggests the possible underlying molecular mechanisms and proposes future directions for research in the field. A meta-analysis is presented to further investigate the duration of EBOV shedding in seminal fluid. The ultimate aim is to develop therapeutics that clear sites of persistence. Such therapeutics could prevent the re-emergence of the persistent virus, eliminating the chance of new outbreaks whilst alleviating the severe stigmatisation facing the EBOV survivor population.

Vaccines are typically designed either for human or veterinary use. Using One Health principles it would be more efficient to develop a single vaccine to cover all animal and human species at threat from a specific pathogen. A major issue for designing One Health vaccines is that some commonly used human adjuvants such as aluminium salts are not suitable for some animal species, such as felines, where they can cause injection site sarcomas. Conversely, some commonly used animal adjuvants such as mineral oil emulsions are too reactogenic to be used in humans. In addition, species-specific differences in innate immune receptors such as Toll-like receptors (TLR) may mean an adjuvant that works in one species does not work in another. This review presents an overview of human and veterinary adjuvants in use and from this list identifies those that might be most suitable for use in a One Health vaccine strategy. Two notable adjuvant candidates already supported by both human and animal data are squalene oil emulsions and delta inulin-CpG combination adjuvant known as Advax-CpG55.2. These two adjuvants have already been shown to be safe and effective across multiple species including when formulated in influenza vaccines. This could be highly relevant to adjuvant selection for vaccines in development against the current North American bovine H5N1 avian influenza outbreak with the potential need to cover multiple susceptible species including birds, cattle and cats in addition to humans. Additional considerations for One Health adjuvants would be suitable administration routes and dosing across species of widely varying size, physiology and genetics. The availability of adjuvants such as squalene emulsions and Advax-CpG55.2 with broad species activity and safety, including in humans, should make One Health vaccine approaches more common in the future.

Within group A Streptococcus (GAS), only Streptococcus pyogenes exhibits clinical significance. GAS is typed serologically based on unique surface proteins and critical virulence factors, such as a hyaluronic acid capsule that shields GAS from phagocytosis. The burden of GAS was estimated in the last five years as 14,000 to 25,000 cases of the invasive group A streptococcal disease in the USA with an estimated death from 1,500 to 2,300 cases per year. Early in the summer of 2022 in England, there was more scarlet fever than was anticipated. Early in the current season, the number of notifications rose to unusual heights. The analysis of invasive GAS (iGAS) isolate typing data shows that this season has seen a wide variety of encoding mature M protein (emm) gene sequence types found. Therefore, public health authorities should think about initiatives to increase clinicians’ and the general public’s awareness of GAS infections and to promote their quick diagnosis, molecular testing and antibiotic susceptibility testing, and standard treatment.