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They concluded that ideal treatment would be early surgical removal of the lesion,
followed by daily intravenous and topical administration of Amphotericin B, with
periodical extirpation of small necrotic tracts as necessary. Cost and a fairly high risk
of nephrotoxicity due to Amphotericin B may be a deterring factor and more
recently some strains of Pythium have shown resistance to amphotericin B (Eaton
1993).More recent information has cast serious doubt on the efficacy of parentral
Amphoteracin B and parentral treatment is now questionable
Local treatment:
After surgical removal of the tumour, Amphotericin B (50g Amphotericin B in 10ml
sterile water) + 10ml DMSO in gauze was applied and bandaged in place. Treatment
is continued daily for at least 1 week.
More recently a severe case involving bone lesions in a mare was treated by surgery
followed by daily packing with Ketaconazole, Rifampin, DMSO and 2N HCI applied
to the wound cavity under bandages pre-coated with 10% Povidone-iodine ointment
to stop leaking of the initial dressing. Immunotherapy was used as an adjunct to
treatment in this case (Eaton 1993).
Originally the production of a phenolised vaccine manufactured by the
department of Tropical Veterinary Science, Townsville, showed indications of
success in the treatment of early lesions. Results of vaccination compare favourably
with surgery and when used in conjunction with surgery, has given very good results.
This is given in 2ml doses weekly for 2-6 weeks. Lesions show some regressions in
7-10 days after the first injection, but reaction at the injection site can be moderate to
severe. Indications of successful treatment are reduction of pruritus, drying of
exudate, expulsion of 'kunkers', fibrosis of granuloma and eventually, complete
epithelialization (Miller 1981).
Recently two types of vaccines were produced (Newton & Ross 1993), one being
that originally developed in 1981 by Miller who produced a vaccine prepared with
killed sonicated whole-cell hypha antigen of P. insidiosum.
A second vaccine prepared by precipitation of soluble antigen from Pythium growth
medium showed a similar cure rate with less side effects at the injection site and
reportedly has a longer shelf life (Mendoza et al 1992). Successful treatment depends
on a number of factors such as the age of the horse, general physical condition,
previous treatment, age/size/site of the lesion and whether there is bony
involvement. Young fresh lesions of 2 weeks duration responded very well to
immunotherapy alone, but if present for more than 2 months, there was a poor
response to this treatment (Mendoza et al 1992).
Horses with infection in the bone have mostly died, even though they have some
clinical improvement with surgery and post-operative medical treatment (Alfaro &
Mendoza 1990).
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ACVSC Proceedings Dermatology Chapter Science Week 2005