Cuterebra

July 9, 2010

In last week’s column we discussed reasons you might want to keep your cat strictly indoors.  Well, here is another one: the Cuterebra botfly.

Cuterebra is a type of botfly that lays its eggs around entrances to rodent or rabbit burrows.  The larvae (maggots) hatch out of that egg when they feel the body heat of the animal entering or exiting its burrow.  Normally the larvae would climb onto the rodent or rabbit.  But if your dog or cat is out hunting in the area of the burrows, the larvae might mistake your pet as a suitable host.  This can be bad news both the botfly and the pet.

After hopping on an animal, the larvae enter the body through the nose, mouth or skin wound.  Totally gross, I know, but it does happen.  What happens next is even nastier.  The larvae begin to migrate through the deeper tissues toward the skin.  Once beneath the skin, they create a breathing hole through the animal’s skin.  The ensuing bump eventually gets to the size of your thumb.  Pets may scratch or lick at the bump.  If the pet has an allergic reaction to the larvae then the area may be quite red and irritated.  If you look closely at these bumps you can make out the two little black nostrils of the larvae peeking out of the hole.  They will retract if you try to mess with them.  The hole is quite tiny compared to the size of the larvae that is maturing underneath.

Normally the larvae would eventually pop through the skin and fall to the ground where it would turn into a pupae before emerging as an adult botfly.   Fortunately, we can surgically remove these guys before they reach maturity, but you never want to try to pop one out of the tiny breathing hole.  First of all the hole is too small, so it would hurt your pet if you tried to extricate the large larvae.  Also if you burst the larvae, you could cause a dangerous allergic reaction in your pet.  We numb the area and then make the hole bigger and very carefully extract these big, white, gross larvae. (It actually is a quite rewarding little surgery).

Unfortunately more problems than just skin lesions can arise.  This is because the dog and cat are what we call aberrant hosts for the Cuterebra.  The Cuterebra is genetically programmed to be doing this in a rodent or rabbit.  In a dog or cat the larvae sometimes get confused and don’t make it to the surface of the skin.  They can even end up in the pet’s brain where they cause serious stroke-like symptoms and sometimes death.   In fact, this whole life cycle was worked out at Cornell University College of Veterinary Medicine when scientists there began to note a correlation between stroke symptoms in cats and the spring hatching of the botfly.

It is warm enough here that there is no specific season for the botfly, so symptoms can be seen year-around in South Carolina.  Fortunately, it is still fairly rare, but you can prevent an infection by keeping your dogs away from known rodent and rabbit holes and by keeping your cat indoors.

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