Throughout history, our world has been plagued by viruses. A handful of these remain aggressive killers to this day. There are many viruses that affect humans, and they all behave in different ways. Viruses can have two different genomes—RNA or DNA. They can also have very different replication strategies. One thing all viruses have in common is they must replicate inside of a host cell, as they do not have the ribosomes that are needed for a cell to make proteins from messenger RNA. Because of viruses’ inability to perform metabolic processes or replicate on their own, they are readily referred to as obligate intracellular parasites.
The question of “where did viruses come from?” seems only to lead to more questions. It is widely believed that that the truth lies somewhere within three hypotheses:
The Progressive Hypothesis
This hypothesis suggests that viruses began with one mobile genetic piece that could move within the genome and then begin to leave one cell and enter another. A double strand of DNA is converted from a single stand of RNA using transcriptase after the RNA enters the host cell. The DNA then travels to the cell nucleus where it uses integrase to insert the viral DNA into the host cell’s genome. At this point, with the help of RNA polymerase, the host cell transcribes and translates the viral genes and then produces a new single-stranded RNA genome called a progeny virus. The progeny virus leaves the cell and the cycle begins again.
The Regressive Hypothesis
This hypothesis suggests that viruses evolving from free living ancestors lost their genetic material over time causing them to use other live cells in order replicate. It is possible that viruses and the live cell developed a symbiotic relationship that eventually turned parasitic, causing the virus to lose genes that were previously essential for replication. Without the genes the virus was no longer able to replicate independently, rendering it an obligate intracellular parasite.
The Virus First Hypothesis
This hypothesis, unlike the progressive and regressive hypotheses, assumes that viruses existed before cells. This century has seen several investigators proposing the virus was the very first replicating entity, possibly even before bacteria existed. This is further supported by the fact that some RNA have enzymatic properties allowing them to catalyze chemical reactions. This may have allowed replicating RNA to develop the capability to infect the very first cells, making today’s single strand RNA the decedents of the pre-cellular molecule.
No matter how viruses developed, it appears they are here to stay. Humans have to find ways to live with viruses, whether that is just letting them run their course, as with the common cold; developing a vaccine, as with smallpox; or extreme social distancing and wearing of masks, as with the novel Sars-CoV-2. Here are some the most common and some of the deadliest:
This virus typically causes symptoms of the upper respiratory tract such as sneezing, coughing, sore throat, fever, headache, runny nose and congestion. There are over 200 different virus strains that cause the common cold. The incubation period of a cold can be less than 48 hours. To avoid catching a cold you should wash your hands frequently, stay away from people who are sick, get plenty of rest, reduce your stress and wear a mask when in close quarters.
Rotavirus is common among infants and children (up to age 5). Symptoms include watery stools and vomiting lasting from three to eight days, causing dehydration and even death. The primary route of transmission tends to be fecal-oral or through the ingestion of contaminated food or water. Treatment consists of hydration and symptom management. In most cases the virus will only last a few days and further intervention is not necessary. There are now two types of rotavirus vaccines that are very effective.
This novel coronavirus was identified in Wuhan China in late 2019. Coronavirus is a generic term used for viruses that have crown-like protrusions on them (corona is the Latin word for crown). COVID-19 is related to other viruses we have seen in the past; Middle Eastern Respiratory Syndrome (MERS) and Sudden Acute Respiratory Syndrome (SARS). According to the CDC, Sars-CoV-2 can have a large variety of symptoms and can include: cough, loss of smell, fever or chills, fatigue, loss of appetite, loss of taste, body aches, shortness of breath, nausea or vomiting, diarrhea, pneumonia, new onset confusion, cyanosis of the lips or face and decreased oxygen saturation. Physicians across the world are also reporting some unusual findings. In middle-aged adults they are seeing vascular changes leading to strokes in otherwise healthy adults. In children they are seeing vascular changes as well, symptomatically similar to Kawasaki’s disease. We still have a lot to learn about this novel virus over the coming months and years.
Marburg Virus was first identified in 1967 in Marburg and Frankfurt, Germany and Belgrade, Yugoslavia simultaneously. Thirty-one people became ill with hemorrhagic fever including medical professionals and people that cared for them. There were seven deaths from the initial outbreak. Studies determined that the infection resulted from exposure to imported green monkeys during research. Marburg Virus is carried by African fruit bats (that can be asymptomatic). Primates, including humans, can be infected with Marburg Virus. The virus has an incubation period of five-ten days and many of the symptoms are similar to other infectious diseases making clinical diagnosis difficult. The ELISA test should be used to confirm infection and performed only in a high containment lab.
Ebola Virus Disease (EVD)
EVD was first identified in 1976 in the Democratic Republic of the Congo near the Ebola River. It is believed that Ebola is an animal-borne virus that originated in non-human primates and bats, although this has not been confirmed by scientists. There is an entire subgroup of viruses within the genus Ebolavirus including; Zaire ebolavirus, Sudan ebolavirus, Tai Forest ebolavirus, Bundibugyo ebolavirus, Reston ebolavirus and Bombali ebolavirus. Only the first four are known to infect humans. EVD is spread through direct contact with blood or bodily fluids of an infected or deceased person, indirect contact through bedding or equipment, contact with infected primates or fruit bats, or through the semen of a man even if they are recovered from EVD. Symptoms of EVD include fever, muscle aches, fatigue, vomiting, diarrhea, abdominal pain and unexplained hemorrhaging. At the end of 2019 the Food and Drug Administration (FDA) approved the first vaccine, rVSV-ZEBOV (tradename “Ervebo”).
The first recorded case of rabies in a dog dates back to circa 1930 BC, and yet the first human treatment was not available until 1885 when Louis Pasteur treated a child with the rabies virus. The boy endured 13 injections over eleven days and would end up making a full recovery. This became the only post-exposure treatment available. It is now common practice in the U.S. to vaccinate dogs, cats and ferrets. The U.S. now only reports between two and nine cases of rabies per year. There is a preexposure vaccine for rabies which is typically given to people who are at high risk such as research lab employees, spelunkers, veterinarians and animal control officers. The incubation period can be weeks to months and the first symptoms can be very similar to the flu, including weakness, muscle aches, fever and headache. Later symptoms include hallucinations, fear of water delirium, insomnia and abnormal behavior. Once symptoms appear, rabies is almost always fatal There have only been 20 reported cases of human survival of rabies without treatment.
Human Immunodeficiency Virus (HIV)
Around 1920 in the Democratic Republic of the Congo it is believed that HIV crossed from chimpanzees to humans. From 1920 to the 1980s it is not known how many people were infected as it did not have notable symptoms. The current epidemic is believed to have started in the mid to late 1970s. Acquired Immunodeficiency Syndrome (AIDS) is caused by HIV. There is currently no cure for HIV; however, there have been great advances in the treatment and control of the virus. HIV decreases the number of T cells which are responsible for helping one’s immune system to fight infections. HIV is mainly spread through sexual contact or sharing of needles with an infected person. HIV is not spread by mosquitoes, saliva, tears or hugging. Abstinence and no sharing of needles are the best forms of HIV prevention, but there are also some new medications for preexposure prophylaxis (PrEP) and post-exposure prophylaxis (PEP). There are currently three types of HIV tests: the NAT looks for the virus in the blood; the antigen/antibody test; and the HIV antibody test.
A, B, C and D are the four known types of Influenza. Influenza D does not currently affect people but has the potential to do so in the future. Influenza is a contagious respiratory illness that causes fever, cough, sore throat, runny nose, body aches, headaches, fatigue and occasionally vomiting or diarrhea. These symptoms can range from mild to severe and even cause death. Each year between 3 and 11 percent of the population have influenza with symptoms. The only vaccine that was available for the 2019-2020 flu season was the quadrivalent influenza vaccine. This season’s vaccine included the following: A/Brisbane/02/2018 (H1N1) pdm09-like virus, A/Kansas/14/2017 (H3N2)-like virus, B/Victoria, and B/Yamagata virus components. It is recommended that individuals are vaccinated each year by the end of October for maximum protection. There are multiple FDA approved antiviral prescription medication treatments available for the treatment of influenza including Tamiflu®, Relenza®, Rapivab®, and Xofluza®.
Do you have questions about infection prevention? The skilled nursing facility consultants at Richter are always available to answer your questions and provide additional training to your staff on infection prevention practices, CMS and CDC infection control regulatory compliance, viruses (including COVID-19) and multi-drug-resistant bacteria. For these and other LTPAC clinical challenges, 866-806-0799 to schedule a free consultation.
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Jennifer Leatherbarrow RN, BSN, RAC-CT, IPCO, QCP, CIC, is Manager of Clinical Consulting for Richter.