This paper is a study on sarcoids and its epidemiology. The paper discusses the types of sarcoids, the probable cause of such disease, its mode of transmission, its treatment and its possible prevention.
Sarcoid is a disease of the skin more common to horses and donkeys. It is actually a tumor that occurs in several different forms: verrucous, occult, nodular, mixed and malevolent. It can occur as single or multiple lesions all over the body but show sites of preference particularly in the paragenital region, the thorax-abdomen and head and frequently occur on parts of the body that was previously injured and scarring ( 1994).
They can also occur in parts that are difficult to treat such as the ears, around the eyes, the mouth, tailhead, legs and ventral trunk or any sites that have been previously injured (1999). It is not a contagious disease but occasionally occur in group of horse. In veterinary dermatopathology, it is also termed as fibroma or fibrosarcoma ( 2003).
The verrucous type of sarcoid has a dry wart-like appearance with grey crusty surface and usually flat and small. It is usually found on the head, neck, brisket or groin. In years, it may remain unchanged but can develop into a more aggressive fibroplastic type ( 1999). Fibrolastic type is an aggressive ulcerated mass often appears at the site of previous wounds or results from one of the less aggressive forms of sarcoid being damaged accidentally or by surgery ( 2006). Nodular types of sarcoids often appear around the eyes or in the groin. They appear as a firm nodule underneath the skin. When the overlaying skin is damaged, it may become more aggressive and may transform into the fibroplastic form. The mixed types of sarcoids are a combination of any other types and also leas to the fibrolastic type. The rarest from of sarcoids are the malevolent forms. They occur on the face, inside the thigh and at the elbow consisting of nodular or fibroplastic sarcoids which affect the lymphatic vessels.
Many clinical studies show that the probable cause of sarcoids is a papilloma virus. A high proportion of sarcoids contain genetic material that is found identical or very closely related to bovine papilloma virus, BPV. Papilloma viruses are small, double-stranded DNA viruses of the Papillomavaviridae family ( 2006). The Pappilliomavaviridae is a large family of animal and human viruses that normally infect epithelial cells causing hyperproliferative lesions known as warts, papillomas or condylomas ( 2003). Some mammals have distinct papilloma viruses. Humans may have greater than 20 papilloma viruses; cattle may have 6 and dogs may have 3 (2006). Early studies detected BPV DNA in sarcoids from horses and donkeys using DNA hybridization techniques (1979).
There are also studies that link the development of sarcoids with genetics. The frequency of sarcoids in standardbred horses was less than half that of thoroughbreds (1988) and major studies in the USA showed that the frequency of sarcoids in the quarter horses was almost twice that of thoroughbreds ( 2003). However, these studies need further investigation to establish more reliable theories.
With so many studies about sarcoids, there is strong evidence that BPV types 1 and 2 are the principal cause of sarcoids and genes and bred type also play role in having sarcoids. However the mode of transmission has no established evidence yet. There were proposals that this may be due to flies acting as a vector as they move between sites from one horse to another (2003).
There was a reported study on the detection of BPV viral DNA sequences in flies which are commonly seen around wounds and which tend to frequent the head and neck area which are the most common areas in which sarcoids occur (2000). There were also the same viral DNA sequences detected in the horses from which flies were removed ( 2003). Other possible mode of tranmsmission are due to stable management practices like sharing of contaminated tack, or passed into existing wounds from contaminated pasture ( 2003).
The risk factors of sarcoids are still unclear. Aside from the studies that occurrence of sarcoids may be due to breed, stable management and the environment of hoses where flies carrying BPV are present, other possible risk factors are not clearly stated. Also, there are still currently no effective treatments for sarcoids. If treated surgically, there is more possibility for recurrence. Other commonly employed treatments include cryotherapy, excision and local immune modulation ( 1998).
There are some vaccines that can somehow make the hosts which are the horses or donkeys, be immune to sarcoids, such autogenous vaccine and BCG which is originally used to protect people from tuberculosis and acts as an immune stimulant that works well for some nodular sarcoids and some fibroplastic sarcoids.
Since the mode of transmission and origin of the virus that causes sarcoids is still not established, there is still no definite solution on how the virus can be made less active aside from the above mentioned vaccines. Even if sarcoids were removed, there is still a possibility for their recurrence which could mean that the virus is strong. However, there are ways to make the environment less susceptive to sarcoids such as implementing cleanliness to the surroundings of horses, good stable management practice and being aware of breed that are more likely have sarcoids so that it may not infect other breeds which do not have the disease.
Credit:ivythesis.typepad.com
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