In dogs, the most common form of meningitis is known as "steroid responsive" meningitis. The name is derived from the fact that the inflammation can be treated by using corticosteroids and because the reason it occurs is not known. This form of meningitis may seem more common than it is due to the infrequency of complete necropsy (autopsy) examinations in veterinary medicine, but even when pretty intensive effort is made to determine an underlying cause for meningitis it is impossible to find one in many cases. In one study published in 1995 (the Journal of Veterinary Internal Medicine, Tipold), the author could not find a specific cause for meningitis in about 33% of the cases. This problem normally occurs in young dogs but they are usually older than four months of age.
There are a bunch of other causes of meningitis, including viral infections, bacterial infections, fungal infections and parasites. There are several meningitis syndromes that are not clearly understood, other than steroid responsive meningitis. Granulometous meningoenephalitis of older dogs is an example of one of these conditions.
The two viral diseases in dogs that are known to cause meningitis are distemper and parvovirus, with distemper being much more likely to be the culprit in viral meningitis. The findings on the necropsy exam that you have mentioned do not rule out distemper, which can sometimes be hard to definitively identify. Most of the pathologists we have dealt with will at least mention it as a strong possibility unless they think something else is going on.
Bacterial infections that can lead to meningitis include staphylococcal infections, pasteurellosis and sometimes other bacteria. The biggest problem with bacterial meningitis is that it is hard for antibiotics to penetrate the blood/brain barrier so it is sometimes necessary to use antibiotics for a really long time in order to control these infections.
Most (possibly all) of the systemic fungal infections such as histoplasmosis and blastomycosis can cause meningitis.
Congenital liver diseases often lead to encephalitis. This is different than meningitis but close enough that it seems reasonable to include the congenital liver diseases in the differential diagnosis for your puppy, since there is evidence of liver disease.
Fortunately, in dogs, there does not seem to be a highly contagious meningitis (other than distemper virus, which doesn't survive well in the environment). It still seems very likely that there is very little risk to a new puppy you might adopt after even this much time.
I found this information written by:
Mike Richards, DVM 4/27/99
After much research I also found that animal illnesses such as colds, distemper, flu, ect.., are not transmissable to humans via dogs.