Viral and Fungal Diseases of the Skin

what does papillomavirus infection result in (generally)?

development of warts in dogs, cattle and horses

what are warts?

hyperplastic lesions that commonly occur in young animals and almost invariably spontaneously resolve

what does papillomavirus infection in cattle result in?

young cattle will develop warts on the skin (especially around the head and neck), on the teats (which can predispose to mastitis) and on the penis (which can interfere with mating)

what does papillomavirus infection in horses result in?

warts, generally seen on the legs or around the face → may be referred to as ‘grass warts’ caused by equine papillomavirus type 1

development of large warts on the penis and prepuce (can progress to SCCs) caused by equine papillomavirus type 2

what are equine sarcoids

most common skin neoplasm of horses though to be caused by cross-species infection by bovine papillomavirus results in proliferation of fibroblasts within the dermis

often develop on the limbs or around the head

how do you diagnose equine sarcoids?

often by clinical examinations, although histology can be used to confirm

in case where histology is inconclusive, detection of bovine papillomavirus DNA by PCR is considered good evidence

what does papillomavirus infection of dogs result in?

warts, which frequently develop in the mucosa of the oral cavity and skin around the mouth of young dogs; can also develop on the feet and around the ears

frequently caused by canine papillomavirus type 1

what do canine warts look like?

nodular, exophytic lesions that may have a roughened surface or be covered by grey keratin

what are canine pigmented plaques?

papillomaviruses cause flat pigmented lesions most commonly on the medial surface of the hind limbs and the ventrum

there is a breed predisposition in pugs and Vizslas

what are feline sarcoids?

caused by cross-species infection by bovine papillomavrius and develop most often around the lips and nose

what do feline papillomaviruses cause?

squamous cell carcinomas, especially in darkly pigmented, haired skin

what diseases are caused by parapoxviruses?

contagious ecthyma, pseudocowpox and bovine pustular stomatitis

what is contagious ecythma?

aka orf, scabby mouth, contagious pustular dermatitis

disease of sheep and goats that are infected through abrasions on the skin often due to eating rough spiky plants

affected animals develop proliferative crusting or ulcerative lesions that are painful, and animals are often reluctant to eat because of it

what clinical signs are associated with contagious ecthyma?

incubation period is 4-5 days; localized skin lesions on the muzzle, gums, tongue, lips, eyelids, feet, teats; lesions heal in 10 days to ~8 weeks; morbidity is high, mortality is low

how does contagious erthyma spread?

scabs containing the orf virus contaminate the pasture, trughs, etc where it remains infectious for months to even years

are there any control measures for scabby mouth?

live, fully-virulent virus vaccine scarified on the inside of the thigh of lambs can be used; lambs are checked for vaccine ‘take’ (presence of scabs) 1-2 weeks later

what is pseudocowpox?

the virus causes lesions on the teats and udder of milking cows

start as small red papules, which scab rapidly, but small vesicles and pustules may also be present

it is zoonotic and is often transferred to the hands of milking staff resulting in “milking nodules” which are itchy but not painful and disappear within several weeks

what is bovine papular stomatitis?

similar to pseudocowpox virus but tends to cause nodular proliferative lesions on the muzzle and within the mouth of calves and young cattle

what diseases are caused by orthopoxviruses?

cowpox and avipoxviruses

what is cowpox?

has a very broad host range, mainly rodents!

can cause localized skin lesions but also spread systemiclly in immunocompromised individuals

the teat lesions in milking cows progress from a papulae to vesicle, ulcer and scab

what are avipoxviruses?

most bird species have their own poxviruses, which are highly species specific

fowlpox of chickens is an important disease worldwide

prevention by vaccination

what is the cutaneous form of avipoxviruses?

characterized by nodular lesions on various parts of unfeathered skin

virus enters the skin through local trauma, followed by viremic spread and secondary lesions on the comb, wattle, feet and cloaca

this form has low mortality but can cause economic losses due to weight loss and decreased egg production

what is the diphtheritic form of avipoxviruses?

characterized by lesions on the mucosal surfaces of the mouth, esophagus, pharynx, larynx or trachea

infection usually by inhalation

this form has high mortality and birds typically die of asphyxiation

what is equine coital exanthema?

venereal skin disease caused by equine herpesvirus type 3 (EHV-3)

uncommon in NZ

what is the characteristic clinical appearance of equine coital exanthema?

lesions on the penis, prepuce, vulva and vagina but typically has no effect on reproductive performance

what is bovine mammilitis?

caused by infection with bovine herpesvirus type 2 and can present in two forms:

• lesions on the teat/udder only (seen in NZ)

• generalized skin disease called pseudo lumpyskin disease because it resembles lumpyskin disease caused by a poxvirus (not seen in NZ)

Which two viruses are most likely to be associated with teat lesions in milking cows in NZ?

bovine mammilitis and pseudocowpox virus

what fungal infections are common in domestic animals?

ringworm and malassezia

what is ringworm?

a disease of young animals; the fungus uses the keratin of the hair shaft as food, damaging the hair shaft and causing alopecia

infection also causes inflammation and lesions are reddened and crusting in appearance

in severe cases or when secondary bacterial infection occurs, rupture of the hair follicle can cause furunculosis and a secondary pyoderma

what lesions are seen in cats with ringworm?

lesions often develop over the face and ears and appear as areas of alopecia, often covered by serocellular crust

lesions usually fluoresce under UV light (a Wood’s lamp)

they don’t show clinical signs of disease, but act as disease reservoirs

what lesions are seen in dogs with ringworm?

variable distribution, but usually appear as single or multiple 1-2cm diameter foci of alopecia and crustin

~50% of lesions will flouresce

what lesions are seen in cattle with ringworm?

lesions can become extensive and are most common around the head and neck

can appear more proliferative with thicker crusts covering the lesions

can appear similar in appearance to dermatophilosis

what is malassezia dermatitis?

ear and skin infection due to this yeast; only seen regularly in dogs

part of normal flora but when defenses are impaired, the yeasts can proliferate and cause disease

what breed is predisposed to malassezia

west highland white terriers, although there is uncertainty whether this is simply due to the predisposition to atopy in this breed or due to other factors

how is malassezia dermatitis diagnosed?

by smell! as yeasts break down the keratin on the surface of the skin, they emit a very unpleasant ‘doggy’ smell

sellotape swabs can be done to look for the presence of yeasts, although the primary treatment strategy is restoring the normal keratin layer, so definitively differentiating between overgrowth of skin bacteria and overgrowth of skin yeasts may not always be necessary