Ultrastructural aspects of replication of the New Jersey serotype of vesicular stomatitis virus in a suspected sand fly vector, Lutzomyia shannoni (Diptera: Psychodidae)

Transmission electron microscopy was used to examine replication of the New Jersey serotype of vesicular stomatitis virus (VSNJ) (Rhabdoviridae: Vesiculovirus) in Lutzomyia shannoni (Diptera: Psychodidae), a recently implicated sand fly vector. Following ingestion of an infectious blood meal, female sand flies were fixed and examined at approximately 12-hr intervals for six days. The New Jersey serotype of vesicular stomatitis virus was first detected in the abdominal midgut after 34 hr of incubation. Virus next appeared in fat body and the thoracic midgut at 48 hr, while salivary glands first contained visible virus in apical cavities 5-6 days after infection. Flight muscles and nervous tissue occasionally contained small numbers of VSNJ virions, while virus was never detected in the ovaries or malphigian tubules. The midgut and fat body appeared to be major sites of VSNJ virus replication. In all tissues examined, virus matured primarily by budding from the plasma membrane. Virions were occasionally observed within vacuoles, along with nucleocapsids. In the midgut, budding occurred exclusively from the basolateral plasma membrane, while maturation in salivary gland cells involved apical budding. Accumulation of virions adjacent to basal laminae surrounding several tissues suggested that this structure physically impedes virus dissemination within the sandfly. The paucity of virus budding 120-144 hr after infection suggested that the VSNJ virus infection was modulated in Lu. shannoni.