Scabies is a skin disease caused by a mite known as Sarcoptes scabiei. It is a parasitic arthropod that is found in nearly all parts of the world. Otherwise known as the ‘itch mite’, this parasite is able to infect a wide range of hosts including humans, cats, dogs, great apes, koalas, and other mammals. It has been documented to affect over a 100 species in total throughout the world. The mite variant that infects canines is known as Sarcoptes scabiei canis. When the mite infects canines, it causes a specific type of scabies called sarcoptic mange. This phrase originates from the Greek root ‘sark’ meaning flesh and the Latin root ‘manducare’ meaning to chew. Its literal translation is ‘flesh eating’. The mite variant that infects canines is known as Sarcoptes scabiei canis.
Mites were first discovered as the cause for scabies in 1687. Pregnant female mites burrow under the skin of hosts and lay their eggs. The eggs hatch within three to ten (3-10) days and the larvae seek out hair follicles to feed and moult in, causing loss of hair and fur on the host. They then grow into adult mites and can live up to three to four (3-4) weeks in a host. If opposite sex are present in the host then the mites can mate and produce further generations of mites. The movement of the mites under the skin creates an itching sensation that cannot be relieved by scratching. This leads to dermatitis of the skin on the host. The immune system within the host mounts a response similar to an allergic reaction against the mites and the eggs which further compounds the problem since the reaction results in increased itching.
The mites can be transmitted via direct or indirect contact. Since they are present on the skin of a host, they are able to jump from to a new host upon direct skin-to-skin contact. Mites may fall off of a host and then can climb onto a new host. This can happen when sharing same food sources, at a watering hole, or when being in close proximity with one another. Mites also have the capability of surviving away from a host for a few days. Therefore, it can be transmitted from dead carcasses of infected animals.
Mange does not directly result in death of the host specie. A combination of factors including loss of hair, damaged skin, infection of open wounds, improper function of immune system, and general weakness debilitates the host. In the long run, the host can become dehydrated, easily develop hypothermia from exposure to the elements, and starve. If not treated in a timely manner the host will die.
Ivermectin is the current medication prescribed for mange. Individuals can be captured and treated for the infection. However, due to the nature of transmission of the disease, it is highly likely that an animal can contract it again once released back into the wild. Therefore, all members of a population have to be treated at the same time in order to eradicate the disease completely from an area. This is not possible in large populations because even if one individual is overlooked then it can reinfect the treated animals upon release. There have been no observed long-term effects on population size from mange and it also appears to occur normally in animals. In small population, on the other hand, the disease can be devastating. It could potentially wipe out the entire population if the number of hosts are small enough. This is a scenario when all the animals have to be captured and treated. Mange is believed to be the main cause for the extinction of the red foxes on Bornholm, Denmark. It has also been observed to cause mass casualties in European chamois and ibex populations. There have been instances where sarcoptic mange had a mortality rate of greater than 80% within a population.
Research is being done currently to identify alternative treatment methods for this disease. A more effective treatment would be one that can be used on large populations, prevent reinfections, and help eradicate the disease. Moxidectin, an anthelmintic drug, that is currently used to treat parasites in animals is being looked at as an alternative for ivermectin. Moxidectin appears to have longer lasting effects which will reduce the chances of immediate reinfection.
Sarcoptic mange is a disease that has a large number of hosts including humans. I believe that for this reason alone treatment methods have to be discovered to fight against mites. It is not a microbe so develop a vaccine is difficult, but perhaps medication that can help the immune system fight against the mites is an avenue to pursue. The immune system clearly recognizes that a parasite is present, but it is not able to mount an efficient defense. Another idea for future research can be a better medication distribution system for large populations. This will overcome the hurdle of not being able to treat individuals who are part of large groups.
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