Grey Horse Melanomas

Now What?

The good news: the swelling over Katie’s mammary glad has significantly decreased.

The bad news:  she now has lumps all over her underbelly.  The vet says it’s onchocerciasis.

So, one more disease I get to learn about first-hand.  And this one, though curable, is pretty disgusting.

Here’s what I found:

Onchocerciasis (Ventral Midline dermatitis) is a skin disease caused by a hair-like worm called Onchocerca cervicalis. The adult worm lives in connective tissue of the horse's neck. The majority of horses in the United States are infected, but a few develop a dermatitis. It is believed that the skin response is due to an allergic reactionn to the dying microfilaria (prelarvae stage of worms released by female worm into the bloodstream).

The filaria migrate under the skin and settle primarily on the midline of the abdomen from the chest to the groin, especially around the umbilicus. Other sites are the withers, face, eyelids, and legs. At these sites the parasites produce an itchy skin disorder with redness, moist shallow sores, crusting and scaling, and patchy hair loss. Spots up to 10 inches in diameter can develop. Scarring and loss of skin pigmentation may also develop.

These open sores attract Culicoides gnats and other flying insects. Gnats feeding on the open sores pick up filaria and introduce them to a new host. Biting flies and other insects aggravate the skin disorder and create pyoderma.

Treatment of Onchocerciasis

Ivermectin paste is completely effective in ridding the horse of filaria within 2 to 3 weeks. Minor reactions can occur with the use. Veterinary supervision is advised.

Adult worms are not affected by deworming agents and therefore serve as a reservoir for recurring infection. To keep the skin free of disease, ivermectin must be repeated at 4-month intervals. A deworming program incorporating ivermectin will effectively control the onchocerciasis.

NOTE:The filaria are capable of penetrating the eye and producing uveitis, a leading cause of blindness in horses.

I gave all the horses a dose of Ivermectin, and will repeat in two weeks, per my vet’s suggestion.  I also gave Katie some Banamine to help reduce the swelling and minimize any pain she might be feeling.  Now that the swelling has subsided over her mammary gland, I am a bit encouraged at the shrunken and stabilized size of the nodular melanoma (see photo).

Vet Visit

Yesterday, the vet came to immunize all the horses.  I had her check Katie’s melanoma, and she pointed out to me that, although the nodular growth on her udder has shrunk a bit, there is a swelling in the mammary itself that appears to be attached to the growth, and this seems to have grown.  It also is seeping a yellow liquid. 

Obviously, this melanoma is invasive and certainly explains Katie’s discomfort and stiff-legged gait.  The vet discussed de-bulking the mass, but she would do it ‘in the field’, which concerns me.  I have sent her an email to see if she will refer me to the UGA Veterinary Hospital. 

I am so very worried that I am going to lose Katie.  I have been praying for many more happy years together (riding or not), and hoping that all my efforts have bought her more time.  I fear that surgery will reveal more extensive growth, or that the growth will become more rapid as a result.

I may put her back on Cimetidine, as much as I hate to do it.  I just want to give her every possible opportunity for a pain-free, long life.  For now, I’m trying to process this information and develop a plan.