How Mange, a Terminal Disease, Afflicts Red Fox

How Mange, a Terminal Disease, Afflicts Red Fox

Illustration by Adelaide Tyrol

The strangest animal I had ever seen crossed in front of my car, near the Thetford–Norwich line on the Connecticut River in Vermont last summer. It had a pointed snout, a tubular body and a long skinny tail. Riding high on gangly legs, it looked like a weasel on stilts.  The creature lingered beside the road, and I managed a better look.  It was a fox, and it was hairless except for a tuft of fur on its head and another on the tip of it tail.  The emaciated animal showed no reaction to my passing car; instead it just gazed blankly.  Had I swerved, I might have mercifully ended its misery.

What I had seen was the terminal stage of sarcoptic mange.  The cause of the disease is a tiny, eyeless mite, Sarcoptes scabei, practically invisible to the human eye.  Mites are eight-legged, roundish creatures that are close cousins to ticks. More than 30,000 species exist in the world, and most—such as the ubiquitous house dust mite that eats flakes of dead skin—are benign and aid in the decomposition of plant and animal material. Some are agricultural pests or parasites,
such as the mites that decimate honeybee colonies or
those that can raise havoc with poultry.

So how did Sarcoptes scabei bring such misery to that unfortunate fox? Mites are passed from animal to animal by close contact or in bedding.  Male and female mites meet on the animal’s skin and mate. The male mites soon die, while the females burrow into the outermost layer of skin, creating a maze of tunnels and feeding on the body fluids oozing from the minute wounds. As they burrow, they lay eggs. After two or three weeks the female dies at the end of her tunnel. The eggs soon release larvae that work their way to the skin’s surface. There, they migrate to new sites and make other burrows, where they go through a series of molts before adulthood. Males find females, impregnate them, and the cycle starts anew.

During the process, mites deposit excrement that invokes an intense immune response, an inflammation that is terribly itchy. The animal scratches and bites at the irritation, often breaking the skin, allowing in various types of bacterial infections. The scratching also pulls out fur, which worsens the situation because mites prefer skin without hair. The animal is constantly on the move, sleepless and exhausted, and eventually dies from multiple stresses, such as hypothermia, infection and starvation. Shooting a mangy fox is an act of kindness.

Encountering an infected fox does not suggest an epidemic, however. Mange seems largely confined to individuals or certain fox families. The animals pick up mites in a den used by an infested fox – which is possible because an adult mite that drops off its host can survive for up to three weeks without feeding.

The disease is held in check among the greater fox population because usually each fox den is used only about one out of every three years. In areas of high fox populations, however, a single den may get continuous use, and this increases the likelihood that mange will spread. Awful as the disease is, it can help keep a fox population at a healthy level.

In certain urban and suburban areas across the world, where enormous overpopulation can occur, the drop in numbers of red fox due to the disease can be staggering. The city of Bristol, UK, once recorded almost 40 adult foxes per square kilometer, a number that plunged 95 percent once mange arrived.   

Anyone in New Hampshire or Vermont who sees a mangy fox, after becoming concerned about the animal’s suffering, is likely to wonder if the disease could travel to pets or livestock or other wild animals.  In fact, different animals are cursed with their own variety of Sarcoptes scabei.  For instance, there is S. scabiei var. canis for dogs, var. bovis for cattle, var. suisfor pigs, and, yes, var. hominis for us humans. In humans, mites cause the itchy but highly treatable disease known as scabies. 

Interestingly, grey fox, the deep forest relative of the red fox, seldom gets mange, possibly because the fox mite does not survive on them very well. There are rare reports of mange transmission from foxes to dogs, but that usually only occurs in places with exceptionally high fox populations.  Fortunately, when the pet dog gets mange the condition is easy to treat, either with a chemical dip or with pills.

Li Shen is an adjunct professor at Dartmouth Medical School and a member of the Thetford Conservation Commission.

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Discussion
  1. Mary Huntington → in Boothbay Harbor, Maine
    Oct 05, 2010

    If a fox with mange visits my property daily is there something I can feed it, such as Natural Way dog food, lamb&rice;? Chicken raw or cooked? How would I trap it so as to get it to The Lincoln County Animal shelter?

  2. Li Shen → in Thetford Center, Vermont
    Oct 06, 2010

    I’m not an expert on what sick foxes like to eat, but a fox with mange might eat any of the foods you mention. So will skunks, raccoons, stray dogs and assorted rodents, so be aware that you can’t control what animal helps itself to this food.  You could attempt to trap the fox using a large Havahart trap, with the same caveat.  Good luck.

  3. Greg Moore → in Ketchum, Idaho
    Dec 13, 2012

    Do you know of any studies done to determine whether recreational/commercial trapping reduces the incidence of mange in wild furbearers?

  4. Carol → in United States
    Sep 12, 2014

    I know this is pretty late to comment, but we had a mange fox in our residential neighborhood.  This is great information.  We were told that the mange kills the hunger of the animal which is why they are not aggressive.  So attempting to feed and catch would probably not work.  Also the fox was probably dead within a day or two of that sighting.  This is probably better to happen in the wild as their is apparently no cure.

  5. Liz van Caloen → in Mianus River, Stamford CT
    Jul 07, 2017

    Just saw bony, reddish fox with long, straight and not bushy tail. It was scratching and scratching itself, also dragging its butt like a dog with worms. Right in my yard, next to wooded area by Mianus River. We have occasionally seen foxes in the yards but they usually run from wooded area to wooded area and do not linger. This guy was in plain sight for about 10 minutes. Very different behavior.

  6. Carson → in Chesterfield, Va.
    Aug 08, 2017

    Just saw a red fox that looked like it had just come from a sheep shearing. I was about fifty feet away and didn’t see any bare skin but it definately had short hair from head to tip of tail.

  7. Maxine → in Dickinson Center, N.Y.
    Aug 10, 2017

    I just killed a skunk that had the mange this afternoon. The only small amount of hair it had was on its tail. I didn’t realize that skunks could get mange.

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