Cerebrospinal nematodiasis is an invasion of the central nervous system by nematode (roundworm) larvae and a cause of neurological disease in rabbits that have access to the outdoors. Infected rabbits may show a variety of clinical signs. These can also be attributed to many other disease processes.
Cerebrospinal nematodiasis occurs when rabbit ingest material, e.g. grass, that is contaminated with faeces containing the eggs from Toxacara canis (canine roundworm) or Baylisascaris spp eggs.
When the eggs are ingested they migrate through the central nervous system and damage surrounding tissues, causing encephalomalacia, a degenerative disease of the brain which causes softening of brain tissues. The eggs can remain dormant in the environment for months or years at a time before being ingested.
Signs can vary and may have a slow onset (chronic) or be acute (have a sudden onset). The signs will vary depending on the level of infection, the damage done and the route which the larval migration takes.
Clinical signs may include:
- behavioural changes
- torticollis (head tilt)
- vertical nystagmus (eye flicking/twitching)
- falling over
- ataxia (loss of co-ordination).
There seems to be no evidence that sex, breed or age of the rabbit makes it more predisposed to the effects of the parasite.
Diagnosis is made on blood sampling. Toxoplasma serology and examination of the rabbit’s faeces are the normal way that a diagnosis is made. Samples for these tests will normally have to be sent to an external laboratory.
Anti-parasitic medications, such as albendazole or fenbendazole, together with anti-inflammatory medications, to help inflammation is the usual treatment of choice.
Rabbits that are not eating well will also require supportive feeding, intravenous fluids and prokinetic (improves gastrointestinal motility) medication to ensure they do not go into gastrointestinal stasis.
The prognosis for successful recovery is poor, although some rabbits may have a resolution of clinical signs. Treatment can be expensive and on-going so cost considerations should be discussed with your vet.
Rabbits act as the end host for the parasite and do not shed the parasite in their faeces. However, if the rabbit contracted the parasite from an infected host in an environment shared by humans, then there is a risk that humans could contract the infection from a similar means, although not directly from the rabbit. Therefore, cerebrospinal nematodiasis is classed as a zoonotic risk to humans.
If an infected rabbit is eaten after death, the risk to predators consuming the rabbit (potentially humans), and other vertebrate predators who may therefore contract and spread the infection, is a serious risk.