<s>[INST] context: Reactivation of toxoplasmosis is most likely the answer, which is due to reactivation of bradyzoites in cysts from an earlier infection. In this case, encephalitis with focal lesions are present. High levels of IgG indicates chronic infection, the current infection is likely a reactivation of an earlier infection; therefore, recent exposures can be eliminated. So, Option 4 is ruled out. Exposure to pigeons suggests Cryptococcosis, which is often a reactivation infection. However, in cryptococcosis antibody levels are rarely monitored, and there is no mention of India ink stain or capsular polysaccharide in the cerebrospinal fluid, which are the major diagnostic methods. So, Option 1 is ruled out. In addition, based on the patient's symptoms, the infection is more likely to be encephalitis rather than meningitis or meningoencephalitis; also, retinochoroiditis is usually not present in cryptococcosis. The retinochoroiditis and lack of mucocutaneous lesions makes infection with Coccidioides less likely. Dese rheumatism (Coccidioides)is the disease caused by exposure to dese sand. So, option 2 is not the answer. [/INST] question: An untreated AIDS patient (CD4+ count of 180 cells/mm3) from southern California has developed progressively severe headache and mental confusion, along with ataxia and retinochoroiditis. Focal lesions are present on a computed tomography scan of his brain. No mucocutaneous lesions are found. He has been living under a bridge for the past 2 years. His level of immunoglobulin G (IgG) to the infectious agent is high. What is the most likely explanation for how this current infection staed? | options: A: Earlier exposure to pigeons B: Earlier exposure to dese sand C: Reactivation of bradyzoites in cysts from an earlier infection D: Recent exposure to cat feces | answer: C </s>