Monday, August 17, 2015

What do cats and crocodiles have in common? Three things I learned about saltwater crocodiles

I came across this footprint from a saltwater crocodile on a beach in the Northern Territory.
Actually as soon as I asked that question I could think of multiple answers, such as the fact that they're both magnificent species, they are both partial to a seafood dinner, they can both suffer from fur balls - albeit from different sources), they can both surprise you with a little nip etc. etc., but one thing I wasn’t aware of until last week was this: they both get herpes. Actually most species have their own species-specific herpesviruses, but herpesvirus in crocodiles is a relatively recently described phenomenon.

I learned about it during a fantastic webinar presented by veterinary pathologist Dr Cathy Shilton and hosted by the World AquaticVeterinary Medical Association (WAVMA). The topic was diseases of farmed saltwater crocodiles in Australia.
Crocodiles are distributed in Australia’s tropical north. There are around 14 crocodile farms in Australia, approximately half of which are in the Northern Territory where Dr Shilton works. 

The largest farm holds around 40,000 animals. Around 70,000 eggs are harvested from the wild per year. (Back when I was a veterinary student I participated in one such harvest and was given the unpopular/hair-raising job of climbing onto the nest with an eski actually collecting the eggs from the nest while two big blokes kept lookout for mum).

Crocodiles are farmed primarily for their skins, which are sold into the luxury leather market. The majority of crocodiles are “harvested” from 2-4 years of age.

Saltwater crocodiles on a farm in the Northern Territory.
I learned a lot in the webinar, but if I had to pick three key points they were:
  • Bacterial sepsis is the main cause of mortality, with gram negative pathogens mostly to blame. These include Providencia rettgeri, Morganella morganii, Edwardsiella tarda, and salmonella species (all of which sound like very exotic names for one’s offspring if nothing else). The majority (95 per cent) of mortalities occur in hatchlings. Bacterial sepsis likely occurs secondary to stress, which may be due to inappropriate temperatures (reptiles should always be kept in their preferred optimal temperature zone, and crocodiles like an ambient temperature of around 32 degrees) or other stressors like noise, disruption of the normal routine and so on. Interestingly, Dr Shilton observed that even if they present for sudden death, the stomachs of crocodiles with bacterial sepsis are always empty, i.e. they’ve been off their food for at very least one feed, possibly more. There may be some scope for further honing our skills on assessing the systemic health of reptiles.
  • A herpesvirus is responsible for two distinct syndromes in Aussie salties. It usually affects 6-12 week old hatchlings. The first causes a conjunctivitis-pharyngitis which is a bit similar to the syndrome caused in cats, and apparently tortoises, although it sounds like it’s a bit more severe. That may be because there is a feline herpesvirus vaccine, or possibly because feline herpesvirus is endemic and maybe croc herpesvirus is rather new. Interestingly this syndrome was described in 2006. In 2009 another syndrome was described. This affects juveniles (6-10 months old) and is associated with systemic lymphoid proliferation and non-suppurative encephalitis. Clinically they fail to thrive. They may have splenomegaly or pulmonary oedema. This is more similar to Marek’s disease seen in poultry or bovine malignant catarrhal fever. There are currently no vaccines. Use of drugs such as famciclovir which are used in cats (and people) for herpesvirus signs have not been trialled, probably due to cost being prohibitive.
  • Stress of some kind – possibly maternal stress – seems associated with “runting” or hatchling failure to thrive, which affects 10 to 15 per cent of stock each year. According to Dr Shilton farms have a vested interest in the welfare of animals as their aim is to produce blemish free skin, and stressed crocs tend to get diseases that cause skin lesions, or experience delayed wound healing. Stress is managed to an extent by managing stocking rates (not too low, as crocodiles get territorial, and keeping numbers of females higher than males, but also making stock numbers are excessive in pens). Hatchlings are also graded by size monthly to ensure that they are in pens with animals about their size. Even so, it seems as if welfare assessment of farmed crocodiles is an area where research is lacking.

This was a very well-presented, really informative webinar. WAVMA hosts some excellent webinars, so if you have any interest in creatures that swim, I'd encourage you to join up.