Neuroviruses. Structure and biological properties of poliovirus, lyssavirus, encephalitis viruses

The family Picornaviridae Two groups of picornaviruses are of medical importance: the enteroviruses – viruses of enteric tract the rhinoviruses – viruses of respiratory tract

Polioviruses is the causative agent of poliomyelitis Morphology 1.Size: nm in diameter 2.Genome: single-stranded (ss) (+) RNA 3.Capsid: Composed of 60 capsomers arranged in icosahedral symmetry. Each capsomer is made of one molecule each of the four virion proteins VP1, VP2,VP3 and VP4.

Antigenic types  Type 1 is the most common and causes epidemic  Type 2 usually causes endemic infections  Type 3 strains have caused epidemic.

Cultivation 1.Primary monkey kidney tissue cultures 2.Vero, HeLa and Hep-2

CPE

Epidemiology and pathogenesis The virus is transmitted by fecal-oral route through ingestion There are four types of poliovirus infection: 1.Inapparent infection (90-95%). 2.Minor illness (4-8%) 3.Non-paralitic poliomyelitis (1-2%). 4.Paralitic poliomyelitis (0,1-2%).

Laboratory diagnosis Direct demonstration of viruses Isolation of virus Serology

Prophylaxis Two types of vaccines are available. 1.Salk´s killed polio vaccine (Inactivated polio vaccine, IPV) 2.Live attenuated polio vaccine (Sabin´s vaccine, OPV – oral polio vaccine).

Rhabdoviruses 1.Vesiculovirus. 2.Lyssavirus.

Rabies virus

Cultivation Animals. Chick embryos. Tissue culture. Different types: 1. Street virus. 2. Fixed virus

Laboratory diagnosis Immunofluorescence test Demonstration of Negri bodies. Antibody detection Isolation of the virus PCR

Negri bodies

Prophylaxis 1.Pre-exposure prophylaxis 2.Post-exposure prophylaxis. It includes: Local treatment Hyper immune serum Vaccination

Flavivirus

Antigenic structure haemagglutitin complement fixing antigen neutralizing antigen

Pathogenesis The virus enters the body through the bite of the insect vector. It multiplies in the reticuloendothelial system and leads to viraemia. In some cases, the virus is transported to the target organs, such as the central nervous system in encephalitis, the capillary endothelium in haemorrhagic fevers and the liver in yellow fever

Flaviviruses Japanese B encephalitis virus. Human infection occurs from these reservoir birds by several species of Culicine mosquitoes Russian spring-summer encephalitis (RSSE). Infection is transmitted by the bite of Ixodid ticks. Wild rodents and birds are other reservoirs. The virus is excreted in milk of infected goats.

Laboratory diagnosis 1.Virus isolation 2.Serology Prevention : specific