Rabies virus

Rabies or “Hydrophobia” is a zoonotic viral infectious disease because it is transmitted from animals (dogs, bats, foxes, skunks, and raccoons) to humans (Figure 1). Rabies is a disease present in more than 150 countries, and is the cause of the death of almost 55,000 people every year.

The rabies virus attacks on the central nervous system (brain and spinal cord) of the animal and is excreted in its saliva by which can be transmitted to other animals. There are others ways beside bite by which a person can become infected by rabies such as non-bite exposure and human to human transmission. The initial symptoms of rabies are: flu, fever, headache, and infection that can progress quickly to hallucinations, paralysis, and eventually death.

Figure 1. Cycle of transmission of the virus. Notice that the virus is transmitted from an animal to humans and the virus affect the brain cells. Source: http://www.medindia.net/patients/patientinfo/rabies.htm

Characteristics of Rabies virus

Rabies virus (Figure) is a specie of the Lyssavirus genus of Rhabdoviridae family, which is grouped in the order Mononegavirales together with the Filoviridae (e.g., Ebola virus).

Figure 2. The virus structure. Notice the presence of the 5 proteins and the spikes that surround the virus. Source: http://www.infectionlandscapes.org/2013/05/rabies.html

Rabies virus is a rod- or bullet-shaped, enveloped virus that has a single stranded negative-sense RNA genome. The negative sense RNA means that the genome is complementary to mRNA and thus must be converted to positive-sense RNA, which is similar to mRNA and thus can be immediately translated by the host cell, by an RNA polymerase before translation. All rabies viruses have a rigid bullet shape with a flat base and a round tip. Their genomes are responsible to encode five genes that code for: nucleoprotein (N), phosphoprotein (P), matrix protein (M), glycoprotein (G), and a viral RNA polymerase (L). Another two major structural components complete the structural of the virus: helical ribonucleoprotein core (RNP) and surrounding envelops. Approximately 400 trimeric spikes, which are found on the surface of the virus, are formed by glycoprotein (G). Finally, the processes of replication and transcription are critically related to nucleoprotein (N).

An interesting characteristic of Rhabdoviruses is that they have the most diverse hosts. For example, they are widespread among a great diversity of organisms such as plants, insects, fishes, mammals, reptiles and crustaceans. The reasons for why they have these diverse host is because they have a large number of possible molecule receptors. For example, despite the fact that rabies virus can only infect cell lines of neural origin, RABV viruses have acquired the ability to use ubiquitous receptors of non-neural cell types. Many studies have shown different molecules as the ubiquitous receptors for RABV such as phospholipids, gangliosides, and three proteins: the nicotinic acetylcholine receptor (nAChR), the neural cell adhesion molecule (NCAM), and the low-affinity nerve-growth factor receptor, p75NTR.

Epidemiology

According to the WHO the number of people who die every year around the world due to rabies in developing countries is a large number. For example, in Asia 30,000 people die every year, and in Africa 24,000. In Europe, due the policy of animal vaccination, the human rabies has disappeared from many European countries, but the virus is still present and some cases of canine rabies (Figure 3) have been found.

Figure 3. Dog infected by rabies virus. Source: http://dermnetnz.org

http://www.affordableanimalremoval.com/rabies/

References

Albertini, A. V., Baquero, E., Ferlin, A., & Gaudin, Y. (2012). Molecular and Cellular Aspects of Rhabdovirus Entry. Viruses (1999-4915), 4(1), 117-139.

Yousaf, M. Z., Qasim, M., Zia, S., Khan, M. R., Ashfaq, U. A., & Khan, S. (2012). Rabies molecular virology, diagnosis, prevention and treatment. Virology Journal, 950.