What's The Deadliest Viral Disease?

By Krista Conrad on April 16 2020 in Did You Know

3D medical animation still showing rabies virus with length of about 180nm. Image credit: www.scientificanimations.com/Wikimedia.org
3D medical animation still showing rabies virus with length of about 180nm. Image credit: www.scientificanimations.com/Wikimedia.org
  • More than 59,000 people die from rabies each year.
  • In 2013, there were 5,865 cases of laboratory-confirmed rabies cases in animals in the U.S.
  • More than 15 million people receive rabies vaccination each year.

Contagious diseases caused by viruses have caused great distress over the years, threatening human lives with outbreaks that take the world by storm. Widepsread events include the 2014 outbreak of ebola in West Africa, H1N1 in 2009 and, most recently, the 2020 COVID-19 pandemic.

These outbreaks have been cause for concern with high mortality and rapid infection rates, but it may be surprising to note none of the well-known viral infections are noted as the most deadly. That title has been set aside for a common, but often overlooked, disease with a 100% mortality rate according to the Centers for Disease Control and Prevention (CDC): rabies.

The rabies virus is carried in the saliva of infected animals and transmitted to healthy animals or human beings, usually through a bite, and there is no known cure once symptoms appear. In the United States, between one and three people contract the disease each year, but it remains an issue globally with tens of thousands of deaths occurring from rabies each year, mainly in southeast Asia and Africa.

What Is A Virus?

 Diagram of the structure of tobacco mosaic virus (TMV). Image credit: Thomas Splettstoesser (www.scistyle.com)/Wikimedia.org

A virus is generally smaller than bacteria and as a parasite, does not have the capacity to thrive without a host body. Though not all bad - some viruses actually protect their host from other infections - they are the most common cause of contagions resulting in widespread disease ranging from serious pandemics like the novel coronavirus to influenza and the common cold.

Incapable of reproducing on their own, viruses rely on invading healthy living cells and using the host's metabolic processes, inserting genetic material into the host's DNA, or bursting host cells.

Viruses are contagious, meaning they possess the ability to be transmitted from one person to another, for varying periods of time depending on the type. There is also an incubation period for viruses to take root in a new host, which is known as a latent period between the time of exposure and the time symptoms show.

What Are Viral Infections?

There are several types of viral infections.

Respiratory infections affect the lungs, nose and throat and are most commonly spread by inhaling droplets from cough, sneeze or saliva tht contain virus particles. These range from the common cold (usually rhinovirus, though there are more than 200 viruses that cause colds) to seasonal influenza and respiratory syncytial virus (which causes colds and infections like pneumonia and bronchiolitis). The best means of avoiding respiratory infections is to practice hand-washing, cover noses and mouths when coughing or sneezing and avoid contact with infected individuals.

Viral skin infections can range from mild to severe, usually resulting in some sort of rash. The most common include molluscum contagiosum, which typically found in children and produces small flesh-coloured bumps that disappear in six to 12 months; herpes simplex virus-1, which causes cold sores and is trasmitted through saliva; and varicella-zoster (chickenpox) virus, which is known for its itchy, oozing blisters, fatigue, and high fever. Avoiding these diseases is achieved by avoiding skin-to-skin contact with infected individuals, though varicella may also be airborne.

Foodborne viral infections are the most common causes of food poisoning. Examples are hepatitis A, norovirus, and rotavirus, all of which cause mild to severe gastrointestinal symptoms. These viruses can be quelled by practicing proper hand-washing protocol, as the illnesses are transmitted via fecal-to-oral routes.

Scanning electron microscope of HIV-1 (in green) budding from cultured lymphocyte. Multiple round bumps on cell surface represent sites of assembly and budding of virions. Image credit: Photo Credit: C. GoldsmithContent Providers/Public Domain

Sexually-transmitted viral infections spread through contact of bodily fluids and include human papillomavirus, hepatitis B, genital herpes, and HIV. The best way to avoid contracting an STD is to practice safe sex or abstain.

Other serious viral infections are Epstein-Barr virus, which causes mononucleosis, West Nile virus, and viral meningitis.

While many of these viruses may be fought with proper treatment once discovered, there is one that is renowned for its high mortality rate and resistance to treatment: rabies.

    What Is Rabies?

    Bites by infected rabid dogs is a common mode of transmission to humans. However, some other species can also transmit the disease to humans like infected foxes, bats, cats, etc.

    Rabies is a viral infection transmitted through direct contact with saliva or brain tissue of an infected animal. Most often, this occurs through broken skin from animal bites although it is possible, though rare, for infection to occur from exposure through scratches, abrasions, or open wounds. There has not been proof that petting rabid animals or contact with their blood, urine, or feces is a source of infection. The virus becomes non-infectious when it dries out and is exposed to sunlight.

    It can affect the body in two ways: entering the peripheral nervous system directly and migrating to the brain, or replicating within muscle tissue where it is hidden from the host's immune system and can enter the nervous system.

    Once the rabies virus enters the nervous system, it causes acute inflammation of the brain, ultimately leading to coma and death of the host.

    There are two types of rabies: furious or encephalitic, which occurs in 80% of cases and is most likely to produce hyperactivity and hydrophobia (fear of water and drinking fluids), or paralytic or "dumb," of which the dominant symptom is paralysis.

    The incubation period of rabies can be anywhere from three to 12 weeks before symptoms appear, though it has also been documented to take as little as five days in some cases and more than two years in others. Symptoms tend to appear sooner if the bite is closer in proximity to the brain.

    What Are The Symptoms Of Rabies?

    Rabies typically begins with flu-like symptoms lasting for a few days, including fever, headache, nausea, and vomiting, but over time the range of symptoms broadens to include agitation and anxiety, confusion, hyperactivity, difficulty swallowing and fear of drinking fluids due to that difficulty, excessive salivation, hallucinations, insomnia, and partial paralysis.

    Which Animals Are Carriers Of Rabies?

    All mammals can contract rabies, but certain species are better known as common carriers of the disease. In the U.S., rabies has been identified in bats, coyotes, raccoons, skunks, foxes, and mongooses. Rabies is still prevalent in dogs in some countries worldwide, like Africa and southeast Asia, but in the U.S. vaccination of canines has reduced instances of the virus in the beloved family pets.

    Rabies may also be found in farm animals like cows, goats, and horses.

    Can You Survive Rabies?

    Throughout history there have been only a handful of cases where people survived contracting the rabies virus. For this reason, anyone in a position where they could potentially come into contact with rabid animals is encouraged to be vaccinated against the disease.

    However, if treated immediately - before symptoms present - the likelihood of surviving is much higher. Left untreated, a person who contracts rabies will live only about seven days after showing symptoms.

    When Should Someone See A Doctor?

    Medical attention should be sought immediately after any animal bite, especially if the type of animal could possibly be infected. Before visiting a physician, the wound should be washed with soap and water.

    A doctor will assess the bites and decide whether treatment for rabies is necessary. The treatment is called postexposure prophylaxis. In the U.S., this consists of one dose of immune globulin and four doses of rabies vaccine over a 14-day period, with the first being administered by the physician. The vaccines are given in the arm, similar to influenza and tetanus.

    Preventing Rabies Infection

    Christine Wilde from Salt Lake City administers a rabies vaccination to a local kitten in El Salvador. Image credit: 807th Medical Command (Deployment Support) from Salt Lake City (Fort Douglas), UT, United States of America /Wikimedia.org

    There are a few ways to reduce the risk of contracting the rabies virus. The easiest means of prevention is to vaccinate all pets and keep pets inside or well-supervised when outdoors to prevent them from coming into contact with wild life. Rabbits and other small pets should be kept away from potential predators.

    Stray animals should always be reported to local authorities, and people should avoid approaching wild animals. Infected wild animals may appear not to be fearful of humans, which is a symptom of the disease and should raise red flags.

    When travelling, jetsetters should get the rabies vaccine prior to a vacation, especially if the destination is a country where rabies or stray animals are more prevalent.

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