PT  - JOURNAL ARTICLE
AU  - Charlotte E. Davies
AU  - Jessica E. Thomas
AU  - Sophie H. Malkin
AU  - Frederico M. Batista
AU  - Andrew F. Rowley
AU  - Christopher J. Coates
TI  - Environment, rather than <em>Hematodinium</em> parasitization, determines collateral disease contraction in a crustacean host
AID  - 10.1101/2021.05.26.445743
DP  - 2021 Jan 01
TA  - bioRxiv
PG  - 2021.05.26.445743
4099  - http://biorxiv.org/content/early/2021/05/27/2021.05.26.445743.short
4100  - http://biorxiv.org/content/early/2021/05/27/2021.05.26.445743.full
AB  - Host, pathogen, and environment are determinants of the disease triangle, the latter being a key driver of disease outcomes and persistence within a community. The dinoflagellate genus Hematodinium is detrimental to crustaceans globally – considered to suppress the innate defences of hosts, making them more susceptible to co-infections. Evidence supporting immune-suppression is largely anecdotal and sourced from diffuse accounts of compromised decapods. We used a population of shore crabs (Carcinus maenas), where Hematodinium sp. is endemic, to determine the extent of collateral infections across two distinct environments (open water, semi- closed dock). Using a multi-resource approach (PCR, histology, haematology, population genetics, eDNA), we identified 162 Hematodinium-positive crabs and size/sex-matched these to 162 Hematodinium-free crabs out of 1,191 analysed. Crabs were interrogated for additional disease-causing agents; haplosporidians, microsporidians, mikrocytids, Vibrio spp., fungi, Sacculina, trematodes, and haemolymph bacterial loads. We found no significant differences in occurrence, severity or composition of collateral infections between Hematodinium-positive and Hematodinium-free crabs at either site, but crucially, we recorded site-restricted blends of pathogens. We found no gross signs of host cell immune reactivity toward Hematodinium in the presence or absence of other pathogens. We contend Hematodinium sp. is an immune-evader rather than immune-suppressor, which suggests an evolutionary drive toward latency in this environmentally plastic host.Competing Interest StatementThe authors have declared no competing interest.