Coccidioides posadasii and SARS-CoV-2 Co-infection in the K18-hACE2 Transgenic Mouse Model

Abstract

Early reports showed that patients with COVID-19 who had a previous diagnosis of Coccidioidomycosis (Valley fever, VF) who had cleared VF months and years prior had re-emergence of VF after COVID-19. However, total numbers of annual cases reported to CDC did not appear to rise dramatically. We therefore investigated serial infection of Coccidioides posadasii (C.p.) and variants of SARS-CoV2 in an K18-hACE2 transgenic mouse to assess the impact on disease outcomes. We intranasally challenged mice sequentially with sub-lethal doses of 100 plaque forming units (PFUs) per mouse of SARS-CoV-2 (variants WA-1, Delta, Omicron BA1) and 24 hours later with 100 arthroconidia per mouse of a low virulence Coccidioides posadasii strain 1038 and vice versa. Lungs, brain, and spleen were extracted and cultured to assess fungal burden and half of the lung was saved for histopathology. To assess pathogenesis, we repeated experiment but sacrificed a subset of mice on days 1, 3, 5, and 6 post-infections in order to assess viral/fungal burden in the lungs. Serum was collected at each time point to measure differences in systemic cytokine/chemokine responses. Experiments were conducted under IACUC protocol # 21-025 at Northern Arizona University. We examined differences in disease outcome between the co-infected groups and groups that only received a primary infection. Co-infected groups had a more severe disease progression as well as decreased survival. Interestingly, results differed depending on SARS-CoV-2 variant (WA-1, Delta, Omicron), infection timing (CoV2 first, C.p. second or vice versa). The groups that were infected with the virus first had decreased survival, increased morbidity (significant weight loss), and increased fungal and viral burdens. There were also differences in immune responses and number/size of spherules, the virus first groups had an increase in circulating pro-inflammatory cytokines and larger more abundant spherules. This is the first in vivo investigation of a co-infection of SARS-CoV-2 and Coccidioides to date. Because of the increased severity of disease, we contemplate the serious implications to the populations that live in areas of high fungal burden and how the SARS-CoV-2 virus can complicate disease progression.