12 Diseases of the Skin

These are common and normally follow wounds from fighting. They may also lead on from an initial haematoma which then becomes infected by haematogenous spread. A wide variety of bacteria may be isolated. These would include: Streptococcus spp., Staphylococcus spp., Bacteriodes spp. and Arocanobacterium pyogenes. Equally, they are often sterile. They may be seen as swellings anywhere on the body irrespective of age or gender (Fig. 12.1).

Differentiation from haematomata is not straightforward. In theory abscesses should be hard, hot and painful and haematomata should be soft, fluctuating and not really painful. Ultrasonography may be helpful but paracentesis is the ultimate diagnostic tool. It is very important that this is carried out in a sterile manner as haematomata are easily infected to become abscesses. The skin should be carefully cleaned with chlorhexidine as if for a surgical procedure. A new, sterile, 14 gauge × 5 cm needle should be inserted deep into the swelling. If serum or blood comes out, then it should be withdrawn and the area sprayed with an antibiotic spray. If nothing comes out of the needle, a syringe should be attached and suction should be applied. If nothing comes into the syringe, the needle should be carefully withdrawn. If the syringe fills, with the tip of the needle over a slide, a drop of the contents of the abscess should be carefully expelled. If it is obviously pus the clinician can then happily lance the abscess. If required, a smear of the pus can be made and stained appropriately. Haematomata should not be lanced. If pigs are not likely to be slaughtered for human consumption in the near future it is prudent to give a course of antibiotics. If paracentesis reveals an abscess it is essential to provide good drainage. A digital search should be carried out to make sure there is no foreign body. Antibiotics are useful both parenterally and as an aerosol over the incision.

1. The acute-onset febrile disease in growing pigs, where the fever and inappetence precede the appearance of the classical raised, inflamed, diamond areas on the skin (Fig. 12.2).

2. The subacute form in older pigs which are hardly ill but show the classical diamondshaped skin lesions.

3. Polyarthritis in growing pigs, which may occur following either of the first two types of infection.

4. The bacteraemia and endocarditis form, which may cause a peracute fatal disease in adult pigs.

The organism is very sensitive to penicillin. This is an excellent treatment in the first two manifestations which show very fast recovery rates. Pigs showing polyarthritis will recover provided there is no other organism involved. NSAIDs are useful with penicillin to aid recovery.

PDNS is a complex condition which is thought to be a hypersensitivity reaction to a severe bacteriological infection. The exact cause is still not known. It is invariably fatal and the clinical manifestation might be confused with CSF, as it is so acute. Affected pigs are severely depressed and totally anorexic. It is normally found in older growing pigs, particularly pigs close to slaughter weight. Mortality rates can be as high as 25% but are normally less. It is extremely rare for the disease to occur in adults. It also might be confused with thrombocytopaenic purpura. The skin lesions are seen over the chest and abdomen together with all four upper legs. The dermatitis is manifest as large purple lumps. There is no specific test for the disease. On post-mortem the kidneys will be enlarged with a mottled appearance due to multiple small haemorrhages (see Chapter 10). The lymph nodes are also enlarged and haemorrhagic. There is no treatment.

Staphylococcal folliculitis

This is caused by a coagulase-positive Staphylococcus aureus and is a distinct clinical entity from greasy pig disease. It can be diagnosed by culture of swabs taken before treatment. It is a disease of growing pigs kept in very dirty conditions. The pigs will show pustules all over their bodies. The condition is self-limiting if the dirty conditions are removed. Antibiotics should not be given as they are unnecessary and will lead to resistant strains of Staphylococcus spp.

Streptococcal pustular dermatitis

β-Haemolytic Streptococcus spp. can be isolated in pure culture from pustules on the growing pig’s skin. It is assumed that they are the cause of the dermatitis. The condition is not self-limiting but does respond very well to single injections of long-acting penicillin.

Ulcerative necrotic granuloma

The cause of these granulomata found on the skin of growing pigs is obscure. Fusobacterium necrophorum is often isolated but this is unlikely to be the underlying cause. Treatment with antibiotics needs to be prolonged.

Skin Diseases Caused by Fungi

Ringworm

This is very rare in pigs. It is usually caught from rats or mice and is caused by Trichophyton mentagrophytes. Pigs can be infected with Trichophyton verrucosum if they are run with cattle. Treatment in pigs is rarely necessary, as the disease is self-limiting. It should not be confused with pityriasis rosea, which is not caused by a fungus. Ringworm can be diagnosed by seeing fungal hyphae on skin scrapings. Pityriasis rosea will get better in 2 weeks and affect only one or two litters. Ringworm will affect large numbers of pigs and take 4 months to recover. There is no licensed treatment available for pigs in the UK. Griseofulvin should not be used as pigs are a food-producing animal. Enilconazole, licensed for cattle, could be used as a wash under the cascade system. This might be attractive to owners of pet pigs on account of the zoonotic implications with ringworm infections.

Skin Diseases Caused by Parasites

Demodectic mange

This is caused by Demodex phylloides. These mites will be found in normal hair follicles. If they occur in very large numbers they will cause small pustular lesions on the body. Normally only when pustules are seen on the face, which when incised will reveal a thick caseous pus containing thousands of mites, is a diagnosis of demodectic mange made. These mites are easily seen without staining under the high power on a microscope. In the author’s experience demodectic mange occurs only in animals with a depressed immunity, e.g. animals on prolonged corticosteroid medication or prolonged NSAIDs treatment. Treatment is not easy. Corticosteroid medication and NSAIDs treatment should cease. Antibiotics are helpful. The pigs should be washed at weekly intervals with amitraz solution.

Fleas

Pigs living in close association with humans will be bitten by the human flea Pulex irritans. They may also be infested with the cat flea Ctenocephalides felis, as well as the sticktight poultry mite Echidnophaga gallinacea which is actually a flea. In equatorial Africa they will be infested by the human burrowing flea Tunga penetrans. Treatment is by dipping or spraying with diazinon.

This is caused by Sarcoptes scabiei var. suis. It is the most important and common parasitic disease of pigs (Fig. 12.3). It is a zoonotic disease but human cases resulting from contact with pigs are extremely rare. Crusting particularly on and around the ears and eyes (Fig. 12.4), with pruritis, are the main signs. The mites are readily seen from skin scrapings provided these are not really deep scrapings, as the mites tend to dwell fairly superficially and so a scalpel blade is not required. The author favours the use of a spoon. The preferred site to sample is the ear margins and inside the pinnae towards the canal. Often the mites can be seen without any preparation just spread on a microscope slide and examined under low power. However many authorities suggest dissolving the crusts in warm 10% w/v potassium hydroxide. This is a fairly lengthy process. The prepatent period can be as short as 10 days but it is normally 2 weeks. The normal picture of an infection is for lesions to be seen a month after new infected pigs are brought on to the premises. If the condition occurs in the ears the self-trauma will result in aural haematomata. Spread of infection occurs via pig-to-pig contact, particularly from the sow to her piglets. Treatment of mange is accomplished with injections of ivermectin or doramectin. Normally a single injection of doramectin will be effective but ivermectin injection should be repeated after 7 days. Control should be carried out by 6-monthly oral medication of ivermectins in the food.

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