Encephalitozoon cuniculi (ECUN) is a microsporidium that can infect most mammals. Frequently diagnosed in rabbits where this is a spectrum of different clinical presentations, ECUN infection in guinea pigs has been less studied. The purpose of the present study is to evaluate whole antigen and PTP2 antigen ELISA (previously validated in rabbits) in clinically normal, ECUN suspect, and clinically abnormal (but not ECUN suspect) guinea pigs. Both IgM and IgG levels will be determined. In addition, a newly validated assay for the quantitation of serum amyloid A in guinea pigs will be evaluated for utility both as a single measure and for prognostic value during treatment. A minimum of n=40 guinea pigs of various breeds will be assessed. Testing will include complete blood count, basic biochemistry panel, ECUN serological testing, serological testing for other common guinea pig infectious agents, blood PCR for ECUN, and serum amyloid A testing. Reference intervals will be generated from normal individuals for all testing.