Rabies. By Rosa Reynoso. Rabies; Etiological Agent: Rhabdoviridae family Lyssavirus genus type (4)

Transcription

1 Rabies By Rosa Reynoso Rabies; Etiological Agent: Rhabdoviridae family Lyssavirus genus type (4) Transmision: It is a zoonotic disease transmitted from infected animals to humans (4). Infected animals transmit the rabies virus through their saliva, which initially enters the body of an uninfected animal via a bite. It penetrates the first defenses, the skin and mucous membranes, proliferates in the peripheral nervous system, ultimately making its way to the brain, the central nervous system. The rabies will then travel to different organs of the body through the nerves (1, 2). Reservoirs: Wildlife animals, such as skunks, foxes, raccoons, and bats. Domestic animals, cats and dogs serve as reservoirs in human transmissions (1). General Characteristics: The rabies virus morphology is bullet shaped, characteristic of the Rhabdoviridae family. It is an enveloped RNA virus, made up of a single, negative strand. It includes an RNA polymerase component, which serves to produce a positive strand that will act as mrna. It will allow the production of more viral negative stranded RNA (3). The RNA virus is 60 x 180 nm in length, and contains spikes on its envelope for attachment, as an invasive virulence factor (2, 4). Key Tests for Identification: Before symptoms of a rabies infection occur in humans, a series of tests are needed to be able to identify the presence of rabies in humans. The most frequently used test is the direct fluorescent antibody tests, which tests for the antigens in samples of saliva, blood, skin, and cerebrospinal fluid in cases (2). Samples of serum and saliva can also be tested by reverse transcription and PCR (5). However, in cases where the infected person has died, samples are taken from the brain. In third world countries, a recently discovered test, named the rapid immunohistochemical test, only requires a light microscope to detect the formation of inclusion bodies in the nerve cell s cytoplasm (2). Signs and Symptoms of Rabies: Rabies is characterized as a latent virus, which on average takes about 2 months to develop the onset on illness, but the incubation period can last anywhere from 5 days to over a year. During the first stage of rabies, vague symptoms such as fever, loss of appetite, malaise, may appear that last from 2 to 10 days. It also includes pain and tingling sensations in the wounded area. This is where \\the virus is multiplying in skeletal muscle, before entering the central nervous system.

2 Because of the long incubation period and the nonspecific symptoms, it is difficult to diagnose a patient before it is too late (1). During the second stage of rabies, once the rabies virus enters the CNS, infected people may experience more severe symptoms. For example, hydrophobia is developed due to the reoccurring spasms when an infected person swallows liquids. At this stage, the patient switches between periods of agitation and relaxation (2). Other serious symptoms include paralysis, coma, and eventually death. In animals, evident symptoms of the rabies virus are periods of restlessness, followed by periods of excitement and irritability. Dogs exhibit snapping behavior, biting anything they come into contact with. Additionally, rabid animals can act unusually quiet, being unaware of their surroundings. They will bite if bothered, and it is usually common in cats (1, 2). Historical Information: Rabies is one of the oldest documented diseases in history, being recognized as a disease of humans and dogs in the beginning of the Bronze age in 3000 B.C (6). It is also mentioned in classical literal works, such as those of Aristotle in 300 B.C. Significantly, Louis Pasteur s invention of the rabies vaccine in 1886 introduced a method of preventing the spread of the rabies virus, but it wasn t widely used until the 1920 when vaccination in domestic animals began (4,7). Virulence Factors: The rabies virus is easily transmissible, once symptoms develop. Because it is a latent disease, it is able to survive in the body without recognition. It can use the spikes on its envelope for attachment, and after crossing the first lines of defense, the virus gains access into the peripheral nerves by mimicking the acetylcholine neurotransmitter. Then, it will penetrate the host s cell, causing body damage and cytopathic effects, such as the formation of inclusion bodies in nerve cells (1, 2). Treatment: Immediately treating the person after they have become bitten by a rabid animal, with the rabies vaccine can provide immunity against the virus. Also, human rabies immunoglobulins are administered to produce immediate antibodies, while the vaccine is put into effect in patients without any previous vaccinations. The vaccine is given in several timely doses on specific days after exposure, on or near the wounded area (1, 5). Unfortunately, there is not any effective treatment against the rabies virus, once it has entered the CNS, and began the onset of symptoms. Prevention

3 The rabies vaccine can be taken as a precaution if there is a possibility of coming into contact with infected wildlife animals, or when working in close proximity to the rabies virus, such as veterinarians. Other commonly used preventative steps are vaccinating domestic dogs and cats to prevent the transmission of rabies in humans. Also, sharing knowledge of the negative, dangerous effects of rabies to those living in high-risk areas of rabies, and avoiding contact with stray dogs and unfamiliar wildlife animals can prevent the spread of rabies (5). World Rabies Day, taken place on September 8 th annually, was implemented to raise awareness for rabies through mass pet vaccinations, and educating communities on the proper precautionary steps for remaining free of rabies (5). Local Cases or outbreaks: Since the 1940s, there has been a decrease in rabies transmitted to humans due to animal control programs and vaccines. Currently, there are only about one or two cases of deaths due to rabies reported in America. However, the rabies virus in those cases was acquired in countries where rabies was an endemic disease (8). Most of reported cases in America have been in wildlife animals, where they accounted for 92.4% of the cases in Raccoons were the primary reservoir, accounting for 40% of the wildlife cases, followed by skunks and bats, and ultimately coyotes (9). (11) Global Cases or outbreaks:

4 In less developed countries, with limited health resources, rabies is an endemic disease. It is responsible for thousands of human deaths due to rabies worldwide. Asia and Africa have the highest mortality rates caused by rabies. Latin America and the Caribbean have shown a decrease in human rabies cases (5, 10). Canine rabies has decreased from approximately 25,000 in 1980 to less than 300 in Human deaths due rabies transmitted from dogs have decreased from 350 in 1980 to less than 10 in 2010 (7). References: 1. Animal Bites and Rabies. Health Library. John Hopkins Medicine. 5 May Tortora, Gerard J., Berdell R. Funke, and Christine L. Case. Microbiology: An Introduction. 12th ed. San Francisco: Pearson Benjamin Cummings, Print. pg. 378; ; Rupprecht, Charles E., Rhabdoviruses: Rabies Virus. Medical Microbiology. 4th ed. The University of Texas Medical Branch at Galveston Smith, Yolanda. Rabies Virology. News Medical. 28 April Diagnosis in animals and humans. 20 September Center for Disease Control and Prevention.

5 6. Constantine, Dennis G. Sound and Fury: Non-Biological Sound for the Selective Capture of Rabies-Infected Bats. Wildlife Disease Association. October aspx 7. Taylor, LH. Global epidemiology of canine rabies: past, present, and future prospects. Dove Press. 8 July WHO expert Consultation on Rabies. World Health Organization Finnegan, Cristopher, Brookes, Sharon, et al., Rabies in North America and Europe. Journal of the Royal Society of Medicine. Jan Epidemiology and burden of disease. World Health Organization Cara, Ed., Wyoming's First-Ever Case Of Human Rabies Ends In Death Of 77-Year-Old Woman. Medical Daily. 7 Oct year-old-woman