Relationship of two arthropod-borne rhabdoviruses (kotonkan and Obodhiang) to the rabies serogroup.

Indirect immunofluorescence confirmed the antigenic relationship between kotankan and Obodhiang viruses and Mokola virus that had originally been shown by complement fixation test. This relationship suggests inclusion of these two arthropod isolates in the rabies subgroup of the Rhabdoviridae family. Cross-reactivity with Mokola virus was also demonstrated by direct immunofluorescence but was easily eliminated when conjugates were diluted. No crossreactivities were found by neutralization tests or by surface immunofluorescence. Other than these immunological ties to the rabies serogroup, other biological characteristics of kotonkan and Obodhiang viruses were distinct. Maximum yield of infectivity of kotonkan and Obodhiang in cell culture was at 30 C, antigen usually filled the cytoplasm of infected cells diffusely, and syncytia were formed before severe cytonecrosis. By electron microscopy, virus particles and their nucleocapsids appeared cone shaped (mean lengths: kotonkan, 182 nm; Obodhiang, 170 nm). Viral morphogenesis took place on plasma membranes of cells in culture, mouse brain neurons, and inflammatory cells (macrophages) in brain lesions. All of these characteristics of the two viruses, and the known association of kotonkan virus with an acute, febrile illness of cattle in Nigeria, suggest a biological relationship with bovine ephemeral fever virus. The latter is known to exist in the same geographic area but exhibits no serological cross-reaction with either kotonkan or Obodhiang virus. The question of whether these two viruses deserve placement in an expanded rabies subgroup (at the cost of a less precise definition of the subgroup) or in a separate subgroup (which would include bovine ephemeral fever virus) of the Rhabdoviridae family will only be answered by further physicochemical characterization and comparison.