Family Rhabdoviridae, genus Lyssavirus; bullet-shaped, enveloped virus; approximately 75nm in diameter by 180 nm in length; single-stranded, negative-sense RNA genome.
Recombinant rabies virus vectors: Replication-deficient rabies vectors can be useful tools for investigation into neuronal trafficking or targeted expression in neurons. SADdG-mCherry/EnvASADdG is an example of a modified rabies virus. This modified version of the rabies virus forces neurons it infects to produce a red fluorescent protein called mCherry. mCherry makes the infected cells glow red so they are visible under a microscope. The benefit is the ability to trace a neural circuit on the cellular level as only connected/attached neurons are affected.
Initial deletion: This modification deletes a gene which encodes the rabies virus envelope B19- glycoprotein (RG) and which is required for the production of competent or infectious viral particles from the virus genome in transduced cells. As a result, the mutant virus cannot spread to any other surrounding cells from the originally infected cells.
If the B19-glycoprotein is (intentionally) over-expressed as a transgene in a defined group of infected cells, the virus can trans-synaptically transport to adjacent cells only (single-step) and never go beyond.
Second modification: This alters the tropism of the virus so that it cannot infect any mammalian cells except those that express a genetically-specified neuronal population transgene which encodes the envelope receptor (TVA) of this pseudotyped virus. Since mammalian neurons do not express TVA, the injected virus cannot infect wild-type human neurons.
If the virus is able to infect a TVA-positive neuron, it can replicate and strongly label the first-order (initially infected) neurons, but since its genome lacks the B19 glycoprotein, it cannot infect other neurons by itself.
In short, the risk for infection is specified by transgene expression and retrograde transport is limited to a single synapse. Thus the resultant virus becomes a “mono-synaptic” transneuronal tracer and significantly reduces the biohazardous risk because the virus has no potential to infect or trans-synaptically transport to any mammalian cells, including human and mice.
In general, as the rabies virus is a negative-strand RNA virus, it does not integrate into the cell genome and has no chance to produce a G protein RNA template. Therefore, there is essentially no risk to generate replication competent rabies virus.
Pseudotyped rabies virus: Rabies virus in which the rabies envelope gene is deleted can be pseudotypes with a number of different envelope genes, including EnvA, VSV-g, avian sarcoma leucosis virus glycoprotein, or HIV env. This pseudotyping alters the cell tropism of the virus and can be useful for specific experimental purposes.
PLEASE NOTE: The following are Stanford Biosafety definitions for the following terms, and may not be the consistent elsewhere.
|Rabies virus||Wild-type rabies virus|
|Mutant rabies virus||Rabies virus that has been mutated from the original wild-type sequence|
|Pseudotyped rabies virus||Rabies virus in which the envelope gene has been replaced with the envelope gene from another virus|
|Pseudorabies virus||NOT A RABIES VIRUS; A herpesvirus that predominantly infects swine, but can also infect a range of other mammals, including rodents|
What are the hazards?
Initial symptoms of rabies include fever, headache, malaise, and upper respiratory and gastrointestinal tract disorders, which can last 4-10 days. Specific symptoms develop as either encephalitis or paralysis.
The risk for rabies transmission varies in part with the species of biting animal, the anatomic site of the bite, and the severity of the wound. Although risk for transmission might increase with wound severity, rabies transmission also occurs from bites by some animals (e.g., bats) that inflict rather minor injury compared with larger-bodied carnivores, resulting in lesions that are difficult to detect under certain circumstances. Any penetration of the skin by teeth constitutes a bite exposure. All bites, regardless of body site or evidence of gross trauma, represent a potential risk. For the past several decades, the majority of naturally acquired, indigenous human rabies cases in the United States have resulted from variants of rabies viruses associated with insectivorous bats. The contamination of open wounds or abrasions (including scratches) or mucous membranes with saliva or other potentially infectious material (e.g., neural tissue) from a rabid animal also constitutes a non-bite exposure. Two cases of rabies have been attributed to probable aerosol exposures in laboratories, and two cases of rabies have been attributed to possible airborne exposures in caves containing millions of free-tailed bats (Tadarida brasiliensis) in the Southwest. However, alternative infection routes cannot be discounted.
Parenteral injection, droplet or aerosol exposure of mucous membranes or broken skin with infectious fluids or tissues.
|Exposure of mucus membrane (eyes, nose, mouth)||Use of safety goggles or full face shields. Use of appropriate face mask|
|Injection||Use of safety needles; NEVER re-cap needle or remove needle from syringe|
|Aerosol inhalation||Use of appropriate respiratory protection|
|Direct contact with skin||Gloves, lab coat, closed shoes|
The above PPE are often required IN ADDITION to working in a certified Biosafety Cabinet.
Susceptibility to disinfectants: Susceptible to 70% ethanol, phenol, formalin, ether, trypsin, β- propiolactone and some other detergents.
Use in Lab: BSL-2
Use with Animals: ABSL-2 housing
How can I protect myself?
Consultation is available to determine if vaccination with the Rabies vaccine is appropriate for personnel using rabies.
Wash the wound with a soap solution, followed by 70% ethanol or an iodine containing solution. Following wound care, a clinician must decide whether to begin passive and/or active immunization. There is no established treatment for rabies once symptoms have begun, but supportive therapy may include intubation, sedation, mechanical ventilation, fluid and electrolyte management, nutrition, and management of intercurrent illnesses and complications. Incubation period of 1-3 months is typical, although incubation more than 1 year has been reported in humans. Administration of rabies POST-exposure prophylaxis is a medical urgency, not a medical emergency, but decisions must not be delayed. Prophylaxis is occasionally complicated by adverse reactions, but these reactions are rarely severe. Therefore, when a documented or likely exposure has occurred, POST-exposure prophylaxis should be administered regardless of the length of the delay, provided that compatible clinical signs of rabies are not present in the exposed person. Rabies virus is inactivated by desiccation, ultraviolet irradiation, and other factors and does not persist in the environment. In general, if the suspect material is dry, the virus can be considered noninfectious. Non-bite exposures other than organ or tissue transplants have almost never been proven to cause rabies, and post-exposure prophylaxis is not indicated unless the non-bite exposure met the definition of saliva or other potentially infectious material being introduced into fresh, open cuts in skin or onto mucous membranes.