Rhabdoviruses represent a diverse family of RNA viruses recognized by their distinctive bullet or rod-like shape. While many species exist within this family, certain rhabdoviruses are responsible for significant diseases in both humans and animals globally. Understanding these viruses involves examining their structure, the specific illnesses they cause, how they spread, and the measures available for prevention.
What Are Rhabdoviruses?
Rhabdoviruses are a group of viruses belonging to the Rhabdoviridae family, characterized by their unique bullet-shaped or bacilliform appearance. These viral particles typically measure about 75 nanometers in width and around 180 nanometers in length. Their genetic material consists of a single strand of negative-sense RNA, ranging from approximately 10.8 to 16.1 kilobases in length.
Each rhabdovirus virion is enveloped and contains a helical nucleocapsid. The genome encodes five structural proteins: the nucleoprotein (N), phosphoprotein (P), matrix protein (M), glycoprotein (G), and large protein (L), which functions as an RNA-dependent RNA polymerase. The Rhabdoviridae family is diverse and can infect a broad spectrum of hosts, including mammals, birds, fish, insects, and plants.
Diseases Caused by Rhabdoviruses
Rhabdoviruses are responsible for a range of diseases, with varying degrees of severity across different hosts. The rabies virus (RABV), a member of the Lyssavirus genus, is the most significant rhabdovirus in human health. Rabies is a fatal neurological disease that causes acute encephalomyelitis in warm-blooded animals and humans.
In humans, symptoms progress through three stages: prodromal (fever, headache), excitative (agitation, aggression, hydrophobia), and paralytic (paralysis, death). The incubation period for rabies can be long, with symptoms often appearing 4 to 8 weeks after exposure. Without prompt medical intervention, rabies is almost always fatal.
The Vesicular Stomatitis Virus (VSV), which belongs to the Vesiculovirus genus, primarily affects livestock such as cattle, horses, and swine, causing vesicular lesions on the mouth, tongue, and hooves. In humans, VSV infections are less severe than rabies, presenting with flu-like symptoms, including chills, fever, and muscle pain, and resolve within 7 to 10 days without complications.
How Rhabdoviruses Spread
Rhabdoviruses employ various transmission pathways depending on the specific virus and host. For the rabies virus, transmission to humans most commonly occurs through the bite or scratch of an infected mammal. The virus is present in the saliva of rabid animals and is introduced into the muscle tissues at the wound site. From there, the virus slowly travels along peripheral nerves to the central nervous system, where it replicates.
While dog bites account for the majority of human rabies cases globally, other wild mammals such as bats, raccoons, skunks, foxes, and coyotes are significant reservoirs and vectors. Less common transmission routes for rabies include aerosol exposure or corneal transplants.
Vesicular Stomatitis Virus (VSV) often spreads through direct contact with infected animals, their saliva, or other body fluids. Insect vectors also play a role in transmitting various rhabdoviruses, especially those affecting plants and some animal species.
Preventing Rhabdovirus Infections
Preventing rhabdovirus infections involves a combination of public health measures and individual actions. For rabies, vaccination is a primary prevention strategy for both humans and animals. Pre-exposure prophylaxis involves a series of vaccine doses, which provides some protection and simplifies post-exposure treatment.
For individuals potentially exposed to rabies, immediate post-exposure prophylaxis (PEP) is crucial and effective in preventing disease onset. PEP consists of thorough wound cleaning with soap and water, followed by the administration of human rabies immune globulin (HRIG) around the wound, and a series of rabies vaccine doses. HRIG provides immediate, passive immunity until the body can develop its own active immune response from the vaccine.
Controlling rabies in animal populations has significantly reduced human cases in many parts of the world. Public health advisories also emphasize avoiding contact with wild animals, especially those exhibiting unusual behavior, and reporting suspicious animal encounters to animal control. For other rhabdoviruses like VSV, biosecurity measures in livestock and vector control strategies can help limit spread.