Protozoal encephalitis associated with Sarcocystis calchasi and S. falcatula during an epizootic involving Brandt's cormorants (Phalacrocorax penicillatus) in coastal Southern California, USA

Between March and May 2019, wildlife rehabilitation centers along coastal southern California admitted increased numbers of Brandt's cormorants (Phalacrocorax penicillatus) with neurological disease including head tilt, nystagmus, torticollis, tremors, paresis, paralysis, and ataxia. Seven cormorants from Los Angeles County and one cormorant from Orange County were submitted for postmortem examination. Gross findings included thin to fair body condition, generalized congestion/hyperemia, nematode parasites in the ventriculus, and diarrhea in the seven birds from Los Angeles County while the one bird from Orange County had icterus. Histologic examination revealed sarcocysts in the adductor muscles and meningoencephalitis characterized by coalescing infiltrations of macrophages, lymphocytes and plasma cells with severe perivascular cuffing and gliosis in all eight cormorants. Rare to few numbers of schizonts were seen in the cerebrum of the seven cormorants from Los Angeles County whereas the cormorant from Orange County had numerous schizonts in various stages of development in the cerebrum, cerebellum, and brainstem. All eight birds were positive for the generic Sarcocystis spp. 28S PCR. The seven cormorants from Los Angeles County tested positive for the S. calchasi-specific ITS1 and confirmed by sequencing, while the analysis of the 28S sequence in the cormorant from Orange County showed a 100% homology to S. falcatula. This bird also was positive by immunohistochemistry for Sarcocystis spp. using a polyclonal antibody that detects S. falcatula and S. neurona. This report demonstrates for the first time that seabirds such as Brandt's cormorants may be intermediate or dead-end hosts for S. calchasi and/or S. falcatula, and that S. calchasi can cause epizootic infection in a seabird.