Author: Stephen J.Divers BSc(Hons), CBioI. MIBiol, BVetMed, MRCVS
Parasitic mites are small invertebrates which feed off the host’s blood or other tissues. Mites have been recorded to parasitize members of all the major reptile orders and suborders, but few are as infamous as the common snake mite.
The snake mite (Ophionyssus natricis) is probably the most important ectoparasite of captive snakes world-wide. It is a relatively fast moving arachnid invertebrate which spends most of its time wandering throughout the environment rather than being permanently attached to the snake host. The snake mite feeds by penetrating the snake’s skin with modified mouth parts and sucking the blood from superficial capillaries.
The results of their feeding habits include discomfort, restlessness, poor or incomplete shedding (dysecdysis) and local skin damage (dermatitis). In more severe cases, extensive skin damage and secondary infection can lead to septicaemia while excessive blood loss can cause anemia and lethargy. Fatalities due to mite infestations are not uncommon and usually related to the spread of certain bacteria (e.g. Aemmonas hydrophilia) causing haemorrhagic septicaemia. These mites have been documented to cause skin disease in humans (popular vesiculobullous dermatitis).
The snake mite, Ophionyssus natricis, is a mite of average size, measuring 0.75-1.5mm in total length depending upon the degree of blood engorgement. Although commonly black, these oval-shaped mites can vary in colouration from brown to black. Each adult mite is sparsely covered with hair, has two dorsal shields and eight long legs.
Distribution and life-cycle
This mite is a parasite of snakes, although it has rarely been seen on lizards. Wild reptiles are rarely parasitized, the vast majority of affected snakes being found in captive collections. Collections that become infected with mites are likely to have received the infection from captive rather than wild caught additions to the collection.
The mites are extremely prolific breeders and under ideal conditions of 30C and 95% humidity, a single female could produce 60-80 mature offspring in 3 weeks. The adult female can lay 60-80 fertile eggs without the need for a male mate both on the snake while feeding and also in the environment. The majority of eggs are laid in the environment, that is, in the vivarium, on the vivarium, and in the snake room (walls, carpet, furniture etc.). The eggs hatch into 6 legged larvae which live in the environment but do not feed off snakes. The larvae moult to form 8- legged protonymphs which begin to feed on the snake(s). The protonymph then undergoes two more moults before finally becoming an adult mite, which also feeds on the snake(s).
There has been a great deal of speculation that this mite is not a natural snake parasite, Ophionyssus natricis behaves as a ‘nest parasite’, spending most of its time off the host and in the immediate environment, returning to the host to feed. Snakes do not generally have nests which they regularly return to and so in the wild it is unlikely that this parasite could complete its life cycle and survive. It is more likely that this parasite is a captivity induced problem, as the snake hosts are unnaturally restricted to one small area. The natural host for these mites is unknown but birds and rodents may be infected or at least act as transport hosts and therefore great care must be exercised when feeding fresh prey items, to avoid parasitic spread. Freezing bird and rodent prey before feeding will reduce their parasite burdens (both external and internal parasites) and make snake infection less likely.
The mites can often be seen as small black dots roaming across the snake’s skin. They may congregate under scales, in skin folds, in rostral pits, and around the eyes. Mite faecal material can often be observed as white deposits on the skin of the infected snake and may be used to diagnose the condition in the early stages before the mites grow and become more numerous and more obvious. Affected snakes become irritated, anorexic and lethargic. In an attempt to ease the irritation, most snakes will attempt to bathe for extended periods of time, which will result in many mites drowning and being visible as black specks at the bottom of the water bowl.
Diseases and problems caused by mites
The diseases that mites cause can be summarised into three categories;
C. Spread of blood-borne diseases.
During the feeding process, the mite produces a special saliva which prevents the blood from clotting. This saliva is likely to be irritating, causing localized inflammation and hemorrhage. It is for this reason that affected snakes may twitch or shake their heads, and bathe for extended periods. A secondary infection of the skin is also possible once the skin barrier has been breached, which will result in poor shedding.
The main effect of blood-sucking mites is blood-loss resulting in anemia. Anemic animals are often anorexic, lethargic and debilitated, leading to weight loss, breeding failure and recurrent secondary infections such as pneumonia and abscessation.
The greatest concern about blood sucking mites is that they act as vectors for blood borne diseases. Their sucking mouth- parts act as tiny needles, inoculating each host with a disease that was picked up from an infected snake that was previously fed upon. Aeromonas hydrophila is a gram-negative bacterium which causes haemorrhagic septicaemia. It has been demonstrated that mites can transmit these bacteria, through their feeding habits, from infected to previously uninfected snakes.
Boid inclusion body virus and possibly ophidian paramyxovirus are two viruses that could also be spread by mites. Various other bacteria and protozoa could also be spread by mites. All in all, mites pose a serious threat to any reptile collection and their eradication should be attempted.
Control and treatment
There is no single control strategy that is universally accepted. It is important not only to treat the snake and kill the mites that are currently feeding, but also to address the problems of the unhatched eggs, immature larvae and mature mites roaming the environment.There is no single action that will accomplish all these requirements. A snake and environmental control strategy is what is required.
- Reduce the number of crevices, cracks and pieces of bark in the vivarium. Use newspaper on the floor and disposable cardboard boxes as hide-outs.
- Remove all shed skins as soon as possible
- Provide water bowls containing clean water that are large enough for the snake(s) to bathe and be completely immersed.
- Infested snakes and vivaria should be isolated well away from the rest of the collection
- Hoover the snake room (carpets, curtains and furniture) to remove eggs, larvae and adult mites.
To quickly kill most mites, use an environmental acaricide such as Acclaim Plus spray (Vet-kem) over the carpet and external vivarium surfaces. However, these sprays are potentially toxic so ensure that all animals are removed from the vicinity before spraying the room and are not replaced until the room has been thoroughly aired. Alternatively, hang a whole Vapona device in the centre of an average-sized room for at least two months. Very small or large snake rooms will need appropriate changes to the Vapona dose, but as a guide do not exceed 6mm of Vapona strip per cubic meter.
I keep a Vapona device permanently in my snake room and have seen no side-effects in boas or pythons. However, many authorities recommend its use for only four days at a time, and there have been reports of paralysis in lizards. It is ill-advised to place Vapona inside the vivarium, treat the room not just the snake.
Isolate any affected snake in a clean vivarium and treat the empty, infested vivarium with Acclaim Plus or a high dose of Vapona for at least 4 weeks. Keep the vivarium heated during treatment. If infection has spread to other vivaria, treat the entire snake room as outlined above.
Take the snake to a veterinary surgeon for treatment. There are two modern treatments for snake mite infections that are commonly employed. The first is an injection of ivermectin, which kills the mites as they ingest blood containing the drug. However, as the eggs and immature larvae are not killed using this method, it is often necessary to repeat the injection every 7- 14 days until all eggs have hatched and matured, usually 2-4 injections.
The second treatment involves a new spray called Frontline. This new spray is much less toxic than the widely available organophosphorus compounds and has the advantage that it can be sprayed directly onto the snake(s) and the inside of the vivarium. This spray lasts for 2-3 months in mammals because the active ingredient is stored in the lipid layer of the skin produced by the sebaceous glands. Reptiles do not have these glands and therefore it is unlikely that there is much of a residual effect. Therefore, repeat spraying every 10- 14 days may be required.
The common snake mite is a constant thorn in the side of many herpetologists, especially those with larger breeding collections. Some suggest that it may be impossible to eradicate in a large collection once infestation takes hold and when you consider the problems that mites can cause, early and effective treatment remains the best option.
Published with permission from The Reptillian Magazine