Water Deer Parasites & Diseases - An Introduction
All animals carry parasites, both inside their bodies (endoparasites) and on the surface of their skin or hair (ectoparasites). In the introduction to his fascinating review of the history of human parasitology, published in Clinical Microbiology Reviews in 2002, Frank Cox of the London School of Hygiene and Tropical Medicine noted that during our relatively short history on Earth, humans have acquired an remarkable number of parasites – around 300 species of helminth worms and over 70 species of protozoa. While many of these are rare or accidental, around 90 relatively common species are still regularly harboured. Cox is quick to point out, however, that this is not necessarily cause for concern. The thought of mites or lice on our skin, or worms in our digestive tract, may repulse us, but the odd one or two is no cause for alarm. Only a very small proportion of the species known to infect us cause serious problems, and more common species become an issue only when other stresses allow their populations to get out of hand. Indeed, there is growing evidence that some parasites with which we have co-evolved (helminths in particular) may quietly bolster our immune systems.
I raise this here simply to emphasise that the presence of certain parasites in water deer, or even a long list of parasitic species, is not necessarily cause for concern, nor does it imply the animals are inherently unhealthy. What follows is a summary of some of the species recorded on and in water deer. No single animal will harbour all of them, and in most cases those it does carry are unlikely to affect its overall health or survival. For simplicity, the list is divided broadly into endoparasites and ectoparasites; where no specific pathogen was identified, it is noted as "miscellaneous disease". This should not be considered a comprehensive list.
It is also worth noting that Britain's deer do not appear to be particularly unhealthy. As Arnold Cooke points out in Muntjac and Water Deer, British Deer Society vet Peter Green has observed that around 20% of our deer population is culled by people trained or experienced in recognising when something is amiss; providing a degree of ongoing health surveillance. While relatively little is known about the immune responses of water deer specifically, a 2018 study by Elena Artemeva of the Research Institute of Veterinary Science of Eastern Siberia, published in the Basrah Journal of Veterinary Research, was the first to record haemolymph nodes (HLNs) in the species. This is significant on two counts: it reinforces the taxonomic placement of water deer, and it points to the species possessing an internal immune architecture as sophisticated as that of modern livestock and other deer. Haemolymph nodes share characteristics of both lymph nodes and the spleen – they function, in effect, as miniature spleens distributed throughout the body. Artemeva observed HLNs along the trachea and jugular veins in the neck, near the aortic arch and pericardium in the chest, and along the abdominal aorta and caudal vena cava in the abdomen. She also identified two distinct node types -- haemolymphatic and venous haemal nodes -- indicating that water deer possess a highly specialised immune system capable of responding to both blood-borne and lymph-borne pathogens.
Bibliography
Artemeva, E.A. 2018.
Histomorphology of Haemolymph Nodes of Water Deer (Hydropotes inermis argyropus): Novel Study.
Basrah Journal of Veterinary Research. 17(1): 315-325.
Cox, F.E.G. 2002.
History of Human Parasitology.
Clinical Microbiology Reviews. 15(4): 515-612.
Cooke, A.S. 2019.
Muntjac and Water Deer: Natural History, Environmental Impact and Management.
Pelagic Publishing. ISBN: 978-1784271909