The surgical removal of excess granulated tissue together with a single dose of a drug combination has proven to be an effective treatment for horses suffering from pythiosis, or swamp cancer, in a limb.
Pythiosis is a distressing and troublesome condition caused by infection with the organism, Pythium insidiosum.
Pythiosis has worldwide distribution in horses and has been known by different names according to geographical location – “bursatte” in India, “leeches” and “swamp cancer” in Australia and the United States, and “ferida da moda” in Brazil.
In horses, the pathogen causes ulcerative, granulomatous lesions mainly in skin tissue or just beneath it. P. insidiosum can also cause gastrointestinal, ocular, and disseminated forms of the disease in other animals.
Horses tend to get infected by standing in water carrying the organisim. In horses, skin lesions are more frequent in the limbs, chest and abdomen – parts which are in direct contact with water containing zoospores – the infective stage – of P. insidiosum.
It is hypothesized that the zoospores are not able to penetrate the intact skin, but a small lesion such as a mosquito bite is enough to allow entry. P. insidiosum tends to survive best in regions where water does not reach freezing temperatures in the cooler months.
Treatment of horses with pythiosis in a limb is challenging, Renata Dória and her colleagues reported in the journal, BMC Veterinary Research.
The study team set about evaluating the effectivness of administering amphotericin B in a 10 percent solution of dimethylsulfoxide. The combination was delivered intravenously into the region of the pythiosis, ensuring it spread through the fine blood vessels – the capillaries – in a process known as intravenous regional limb perfusion.
All 15 horses treated in the study had complete resolutions of their lesion from six to nine weeks after the single treatment, the researchers reported.
No complications were observed at the site of the intravenous delivery.
They noted that, before the start of treatment, there was anemia and marked leucocytosis which resolved following treatment. Serum biochemistry showed no significant changes.
They said that giving the solution was easy, relatively inexpensive, and it proved to be an effective way to treat horses with pythiosis in a limb. The cases in the study resolved with no noticeable local or systemic complications.
The researchers noted that traditional treatment methods involved a range of drugs that are considered hazardous, and are expensive when administered systemically to horses.
“And because Pythium insidiosum is not a true fungus, this protistal organism has increased resistance to most available antifungal agents,” they added.
The study team noted earlier research pointing to 92 percent resolution of limb-related cases of pythiosis when horses were treated with amphotericin B alone, with some cases requiring two treatments.
“We hypothesized that better results with fewer complications might be achieved if dimethylsulfoxide is added.”
They felt it would achieve a higher concentration of amphotericin B within the infected tissues. Dimethylsulfoxide has also been shown to be an effective anti-inflammatory agent, they noted.
They theorized that it may also inhibit fungi growth as a result of its effect on the immune response and as a result of reducing endotoxin-induced tissue damage. These factors, and its ability to penetrate biological membranes, provided the rationale for its use in conjunction with an antifungal drug for regional limb perfusion, they said.
Their hypothesis proved correct, with all cases resolving.
The researchers administered 50mg of amphotericin B in 6mL of dimethylsulfoxide (10 percent of the total volume) to compose the final solution.
Doria was joined in the research by Mariana Carvalho, Silvio Freitas, Luciane Laskoski, Edson Colodel, Fábio Mendonça, Marco Silva, Renan Grigoletto and Paulo Fantinato Neto, from a range of Brazilian universities.
Evaluation of intravenous regional perfusion with amphotericin B and dimethylsulfoxide to treat horses for pythiosis of a limb.
Renata GS Dória, Mariana B Carvalho, Silvio H Freitas, Luciane M Laskoski, Edson M Colodel, Fábio S Mendonça, Marco AG Silva, Renan Grigoletto and Paulo Fantinato Neto.
BMC Veterinary Research 2015, 11:152 doi:10.1186/s12917-015-0472-z
The full study can be read here.