Suckling mouse cataract agent is a helical wall-free prokaryote (spiroplasma) pathogenic for vertebrates

Abstract

THE suckling mouse cataract agent (SMCA) is a filterable organism originally isolated from a pooled extract of rabbit ticks (Haemaphysalis leporis-palustris) collected near Atlanta, Georgia in April 1961 (ref. 1). The agent grows to high titre in the eyes and brains when inoculated intracerebrally into newborn mice in which it induces cataract, uveitis and chronic brain infection^1–3. SMCA has also been grown to high titre in embryonated hen's eggs, in which it produces a lethal infection in 4–9 d (ref. 1). The agent has not been grown in tissue culture or in artificial media, but growth in a rabbit lens organ culture has been reported⁴. Stained SMCA-infected tissues failed to show the presence of rickettsiae and, as a result of such negative inferences and other characteristics of the agent^3–5, it was considered to be a candidate slow virus⁶. Within the past few years however, ultrastructural and biological studies showed that a wall-free prokaryote was consistently associated with the acute and chronic disease in mice and with lethality in chick embryos^7,8. Although the agent resembled mycoplasmas morphologically, it differed from them in its apparent non-cultivability on conventional mycoplasma medium. We now report that the organism associated with the suckling mouse cataract syndrome is a prokaryote similar to the spiroplasmas—a group of mycoplasmas known previously only from plants and insects.