Even if you take the best possible care of your guinea pig, he may become an unhappy host to a varied collection of parasites, either internal, external or both. By knowing what to look for, you can help to eradicate most of these pests before they have the opportunity to harm your pet. External Parasites
Routinely check your guinea pig's skin for signs of parasites, flea dropping (specks of hard, black "dirt") and dandruff. Also check his coat for lice eggs glued to the hair. Frequent or persistent scratching is a good indication that your guinea pig has a parasite problem. Telltale Signs
Cheyletiella mites look like a very bad case of dandruff across the back, and severe infestations can result in scaling skin.
Fleas can be tracked down by the "dirt" they leave behind, even if you can't spot the fleas themselves. If you see hard, shiny drops of "dirt" on your guinea pig's skin, scrape some off and place it on a damp paper towel or tissue. If the dirt shows red or pinkish spots on the paper towel, your guinea pig has fleas.
Sarcoptes mange mites are too small to be seen, but leave behind scabs and crusts as they burrow into their host. They are most commonly found on the face, ears and genitalia, and they cause intense itching and irritation.
Ticks are easily diagnosed as they swell with blood and turn brownish white. If an engorged tick releases and drops to the floor, it can look almost like a rotting grape. To remove a tick, firmly pinch the skin around the tick and pull hard to extract the entire tick, including the head. Make sure the tick's head is removed. If left behind, the head can cause an infection. Put the extracted tick in a jar full of vinegar to kill it. Flushing a tick down the toilet will not kill it.
Flies can be very dangerous to your guinea pig, laying eggs on the guinea pig's soiled rectal area. Maggots grow and burrow into the animal's flesh, feeding off it. Internal Parasites
Internal parasites can pose a health risk to you as well as to your pet, and they are often difficult, if not impossible, to detect except through blood tests and screenings performed by your veterinarian.
If your guinea pig has persistent diarrhea, loses weight, licks anal region repeatedly or you see signs of maggots, larvae or eggs in the hair around the anus, you should visit your exotic animal veterinarian immediately to determine if there is a parasite infestation.