Horizontal Transmission of Cryptococcus neoformans in a Murine Model

Background- Cryptococcus neoformans is an opportunistic fungal pathogen which can cause a severe pulmonary infection known as cryptococcosis, which often progresses to fatal meningoencephalitis. Immunocompromised individuals, such as recipients of solid organ transplants and those who are HIV positive, are most susceptible. It is documented that Cryptococcus typically invades the body through inhalation of microscopic fungal spores from the environment, but less is known regarding whether cryptococcosis is a communicable disease. We wanted to test whether horizontal transmission would occur when an uninfected mouse inhaled or ingested fecal matter, from infected mice, in a caged environment. We hypothesize that as the infection disseminates throughout the gastrointestinal (GI) system we will see increasing amounts of Cryptococcus colony forming units (CFU) in the GI and in excreted feces. Methods-20 female BALB/c mice and 20 female C57BL/6 mice were obtained from Jackson Laboratory and housed in the animal care facility at the University of Massachusetts Medical School. The mice were divided into 10 cages with 4 mice per cage. Each group contained 2 mice infected with C. neoformans and 2 uninfected mice. Mice were placed in the same communal, closed environment under laboratory settings. The mice were given an orotracheal (OT) infection with a highly virulent strain of C. neoformans that stably expresses the mCherry fluorescent protein (KN99mCH). Fecal samples were collected every 3-4 days and at 50 days post infection (DPI) mice were sacrificed and lungs, brains, organs of the GI tract were harvested and plated. Results- From day 3-24 the number of fecal CFUs increases in OT infected mice until they died at approximately day 27. In the BALB/c population, 3 out of 10 uninfected mice acquired the infection. In the C57BL/6 population, 6 out of 10 uninfected mice acquired the infection. The mice were sacrificed at day 50 and their lungs, brains, and colon were harvested and plated. Quantitative culturing and fluorescence imaging demonstrate the capacity of C. neoformans to colonize various organs in the murine GI tract. Based on this data we can see that after Cryptococcus infection is established in the lungs it can disseminate to the GI before finally reaching the fecal matter. Conclusion- This study provides evidence that supports the hypothesis that uninfected animals housed in a communal environment with infected animals can acquire the infection through ingestion/ inhalation of fecal matter. It also shows that C. neoformans can be detected in the fecal matter of an infected host, which could serve as a diagnostic in resource-limited settings. Based on this data we can also see that after cryptococcal infection is established in the lungs it has the potential to disseminate to the GI tract and be excreted in the fecal matter