Q: We took Jake, our 10-week-old pit bull, to the veterinarian because he has very little hair and scratches almost constantly, even though we see no fleas.

The vet said Jake has Demodex mites and prescribed a monthly chewable pill that kills them as well as fleas and ticks.

Where could Jake have caught the mites? Can he pass them to us or our other dog?

A: Demodex mites are normally present in small numbers on dogs’ skin, so you don’t need to worry about Jake passing them to other dogs.

And since these mites are species-specific, they won’t spread to humans, cats or other pets.

In some puppies, an inherited immune system abnormality causes the mites to proliferate. Fortunately, treatment is effective, and the condition rarely returns.

The disease also can develop in an adult dog whose immune system is suppressed.

Demodex mites are microscopic, cigar-shaped creatures that live in hair follicles. If they proliferate, they cause demodectic mange, also called demodicosis (pronounced “de mo di CO sis”), that can be localized or generalized.

Clinical signs include hair loss, crusting, redness, scabs and thickened skin. Scratching occurs in dogs with secondary skin infections.

The diagnosis is confirmed by seeing Demodex mites with the microscope.

Affected dogs should be sterilized so they don’t pass on the genetic predisposition to demodicosis and because recurrences are common during a female’s heat cycles.

Treatment options include medication to kill the mites, a shampoo or gel that flushes the mites from the hair follicles, and an antibiotic if the skin is infected.

•        •        •

Q: Mr. Mistoffelees, our 9-month-old cat, had little energy and a poor appetite, so we took him to the veterinarian.

The vet noted that he had lost weight and his abdomen was full of fluid. She did some tests and said he has FIP, which is always fatal.

We were so overwhelmed that we didn’t hear what she said about FIP. What can you tell us about this horrible disease?

A: FIP, or feline infectious peritonitis, develops when a common, harmless virus, the feline coronavirus, mutates within a cat’s body.

Feline coronavirus is easily transmitted from cat to cat, infecting half the cats in single-cat homes and up to 90% of cats in multicat households and catteries. The virus does not infect dogs, humans or other species.

Coronavirus may cause mild diarrhea that resolves on its own or produce no clinical signs at all.

However, in a small percentage of infected cats, the usually innocuous feline coronavirus mutates into the deadly FIP virus.

While the coronavirus is contagious, the mutated FIP virus is not. Though FIP can occur at any age, half of affected cats are under 2 years old.

FIP occurs in two forms: wet and dry. Both are characterized by decreased energy, appetite and weight.

Cats with the wet form, like Mr. Mistoffelees, also have fluid in the abdomen (known as the peritoneal cavity, which gives the disease its name) or sometimes the chest.

Cats with the dry form don’t accumulate fluid in their body cavities, but they often have abnormalities of the eyes or nervous system. Other clinical signs depend on which organs are affected.

The wet form usually appears one to two months after a stressful event, such as rehoming, surgery or illness. The wet form is more rapidly progressive than the dry form, which develops over months to years.

Sadly, there is no cure for FIP. After diagnosis, the typical survival time is days to weeks for the wet form and weeks to months for the dry form.

My heart is with you and Mr. Mistoffelees.

Lee Pickett DVM practices companion animal medicine in North Carolina. Click here to ask her questions for her weekly column. The opinions expressed are her own.