All animals carry parasites, both inside their bodies (called endoparasites) and on the surface of their skin and/or hair (ectoparasites). In the introduction to his fascinating review on the history of human parasitology, published in Clinical Microbiology Reviews in 2002, London School of Hygiene and Tropical Medicine biologist Frank Cox noted that:
“During our relatively short history on Earth, humans have acquired an amazing number of parasites, about 300 species of helminth worms and over 70 species of protozoa.”
While many of these are rare or accidental parasites, there are still 90 or so relatively common species that we harbour. Cox is quick to point out, however, that it's not necessarily a bad thing. So, while the thought of mites or lice on our skin or worms in our digestive tract might repulse us, the odd one or two is no cause for alarm. Only a very small proportion of the species known to infect us cause any serious problems, while more common species are only an issue when other stresses allow their populations to get out of check. Indeed, we're now starting to think that some parasites with which we've evolved, particularly helminths (i.e. parasitic worms), may have actually been quietly boosting our immune systems.
I mention this here simply to highlight how the presence of certain parasites, or even a long list of parasitic species, in water deer is not necessarily a cause for concern, nor does it imply they are inherently unhealthy. That which follows is merely a summary of some of the species that have been found on and in water deer. No single water deer will have all of these and, in most cases, those they do have are unlikely to affect the overall health or survival of the animal. For simplicity, I have split the list broadly into endoparasites and ectoparasites, and where no specific pathogen was identified it is mentioned as “miscellaneous disease”. This should not be considered a comprehensive list. It is also worth mentioning at this juncture, that Britain's deer don't appear to be particularly unhealthy and, as Arnold Cooke points out in Muntjac and Water Deer, British Deer Society vet Peter Green has previously commented on how some 20% of our deer population is culled by people who are trained or experienced in recognising when something's amiss.