The Spread of Infection by the Microsporidan, Nosema disstriae, in Insect Cell Lines

Nosema disstriae, a parasite of the forest tent caterpillar, Malacosoma disstria, was cultured with cell lines UMN‐MDH‐1 Malacosoma disstria, IPLB‐1075 Heliothis zea, and BTC‐32 Triatoma infestans. Infected cultured cells were used to infect the healthy cell lines. Electron micrographs of thin sections of 6‐day‐old cultures revealed infected cells that exocytosed vesicles containing vegetative and immature sporulating forms of the parasite. Some of these forms were believed to be responsible for intercellular transmission of the parasite. The spread of infection was augmented by culturing the cells at high densities; if the density was too low, there was little or no cross infection. Cross infection was inhibited, but not blocked completely, by high osmolality of the culture medium. The yield of spores from a confluent cell monolayer at the end of growth was generally 1–4 × 10⁷ per ml of culture medium.