If you have flu symptoms, it is a good time to remember that ferrets are susceptible to influenza too. Ferrets can catch influenza from people, and conversely can pass influenza to people (it appears that ferrets catch the flu more readily from people than people do from ferrets).
Disclaimer: if you suspect that your ferret is ill, do not try to make a diagnosis yourself. Check with your veterinarian! The information provided here is for informational purposes only and is not intended to replace consultation with a veterinarian knowledgeable about ferrets.
Ferrets are susceptible to most strains of influenza that infect humans, including both types A and B. It causes similar symptoms and runs a similar course. Symptoms include thick clear discharge from the nose and eyes, sneezing, conjunctivitis (swollen red membranes around the eye), decreased appetite, lethargy, and high fever. It will usually run it's course over 5 or more days, just like the human disease. However, in some ferrets it can be fatal, particularly the old and young, and those with depressed immune systems. Complications such as bacterial infections like pneumonia are a threat.
As with people, treatment is supportive, which means treating the symptoms and letting the virus run it's course. Once a diagnosis is made, your veterinarian may be able to suggest medications to make the ferret more comfortable. You must also ensure that your ferret remains hydrated. If your ferret is very lethargic or off feed and water (monitor closely), treatment with fluids and/or force feeding may be necessary. Also, if the discharge from the nose or eyes becomes discolored (yellow or green), or if a ferret is coughing a lot, contact your vet.
Prevention included limiting contact with your ferrets if you have flu symptoms, and limiting contact with a ferret that has influenza. Frequent hand washing is one of the most effective ways to prevent the spread of infections (either to or from ferrets). Owners should also isolate sick ferrets from other ferrets in the house.