There are two types of mange seen in swine. The first is demodectic mange, and is caused by the mite Demodex phylloides. This mite is not uncommon, but this form of mange is relatively unimportant in swine. The second, and more important, form is sarcoptic mange. Caused by the burrowing mite Sarcoptes scabiei var. suis, sarcoptic mange is also known as scabies. Scabies can be of great economic importance to pork production because it results in reduced growth rates, reduced feed efficiency, and decreased fertility in sows. However, it is mostly eliminated from US herds.
Etiology and Transmission
A full grown adult Sarcoptes mite is approximately 0.4 to 0.6 mm in length and has four pairs of stubby legs. Sarcoptes scabiei feeds via the sucking organ at the end of a pedicle on two of the legs. The entire life cycle of the mite is spent on and in the skin of the host pig. It takes 10 to 20 days for an egg to turn into a fertilized female. The females burrow into the epidermis after mating and lay about 50 eggs there before dying. Sows transmit the mite to other swine by direct contact, horizontally via huddling or vertically via nursing of suckling pigs. As a result, the higher the stocking density the faster the rate of transmission. The mites are permanent parasites of the pig and are not viable away from the host. They are sensitive to desiccation; therefore, environmental contamination is of little concern, unless pigs are being placed into a pen immediately after an infested group has been removed. Scabies mites are species-specific and no other host has been identified.
How is sarcoptic mange most commonly transmitted between pigs?
- By direct contact through huddling or nursing
- Indirectly through an infected environment
- It is a commensal bacteria of the pig
The most common symptom of mange is pruritus, occurring between 2 and 11 weeks post-infection. Its intensity is directly correlated with the number of mites. Growing pigs flap their ears and scratch against the crates or the walls. The infested pigs will also exhibit reduced feed efficiency and growth rate. The skin can also thicken, requiring it to be removed during pork processing, downgrading the meat.
Infested pigs first develop encrusted lesions on the skin where mites have been feeding, especially on the inner surface of the ears. The crusts are raised and thick, dark brown in aspect and give the impression of dirty ears. When these lesions subside, multifocal punctiform erythematous papules can be seen on the rear end of the pigs all the way to the flanks.
Examining the encrusted lesions of the inner ears under the microscope will show the presence of mites. However, the papules display signs of hypersensitivity lesions such as a large number of lymphocytes, mast cells, and eosinophils.
What is the most common sign of sarcoptic mange?
- Coarse hair
- Exudative skin lesion
The most common sign of scabies in growing pigs is pruritus. However, rubbing is non-specific and can occur for multiple reasons. Skin scrapings of the inner ear can confirm the diagnosis, but mites can be difficult to find, one must be mindful of false negatives. Mites can also be seen with a magnifying glass when encrusted lesions are set on a dark background. An ELISA test is available to detect S. scabiei antibodies in the serum.
Differential diagnosis includes parakeratosis and exudative epidermitis for the encrusted lesions and swinepox, dermatomycosis, and insect bites for the extended skin papules.
Treatment, Prevention and Control
Sarcoptic mange can effectively be treated with acaricides such as amitraz or ivermectin. It is important to notice whether or not there is an ovicide action in your chosen treatment. If not, the pigs need to be treated twice at around 14 days interval to kill any mites that may have hatched since the first treatment. Control of scabies is rather difficult, as it requires quick identification and treatment of animals with chronic infestation to prevent spread to young pigs. Eradication by treatment of the entire herd at once and introduction of naive breeding stock is the preferred option. All-in, all-out management of the pigs in the nursery and finishing sites
Treatment against scrabies needs to be repeated once, 14 days after the first one because:
- Sarcoptic eggs can survive for a long time in the environment.
- It is the time needed for an egg to become a fully developed adult
- Some sarcoptic species are resistant to acaricides.