Unit 4 Chapter 20

What are herpesviruses?

• are enveloped DNA viruses

• over 100 members in this group

  • many causes illness in humans

• common illnesses caused by herpesviruses are:

  • herpes simplex 1

  • herpes simplex 2

  • varicella zoster

  • Epstein Barr

  • human cytomegalovirus infection

What is Herpes simplex 1 and 2?

• generally referred to as herpes

  • HS1 causes oral herpes

  • HS2 causes genital herpes

• tend to cause latent infections

  • after the initial infection, they stay dormant in neurons until some environmental factor causes their reactivation

    • resulting in the host experiencing another outbreak of symptoms

What is varicella zoster?

• is responsible for both chickenpox (varicella) and shingles (herpes zoster)

  • bc of variations, chicken pox and shingles are becoming increasingly rare

• prior to vaccines, the course of disease was:

  • initial infection occurred sometime in childhood

  • followed by an uncomfortable, mid/moderate illness that lasts 1 to 2 weeks

  • once the initial illness is resolved, the virus stays dormant for years/decades

  • once a person reaches their 50s or 60s, the virus is often reactivated and causes a second course of infection called shingles

What is Epstein Barr virus?

• is very common

• most adults show evidence of having been infected atleast once, even unknowingly

  • in some people, the virus causes a mild illness that doesn’t require any medical intervention

  • in others it leads to a case of mononucleosis that warrants treatment

• most fully recover from the associated illness but have lingering effects

  • some may even develop cancer as a result of persistent or repeated infection

What is human cytomegalovirus?

• another common virus

• generally doesn’t cause serious problems for people

  • however, those who are immunocompromised or pregnant can experience more serious consequences from infection

    • people w/ weakened immune systems may experience problems with vision, digestion, pneumonia, or encephalitis bc of the virus

    • infants that become infected before birth may experience liver problems, microencephaly, jaundice, seizures and a variety of other health issues

What is the papilloma virus?

• are a very large group of non-enveloped DNA viruses

  • more than 100 species and capable of infecting animals

• most are relatively harmless

  • cause different types of warts

    • they can be uncomfortable sometimes, but generally do not cause serious health effects

• some strains of papilloma can lead to cancer

  • particular strains are associated with cancers of the cervix, oral cavity, and genital regions

• a vaccine has been developed that helps prevent some of these infections

  • has led to a lowered incidence of these types of cancers

What are influenza viruses?

• enveloped RNA viruses

• can infect a variety of species

• prone to a relatively high rate of mutation

• divided into 4 main categories, A-D

  • types A and B are most likely to cause widespread human infections

    • type A leads to pandemics because it can spread human to animals as well as human to human

    • type B can also cause serious infections but can only spread from human to human and hasn’t been associated with any pandemics

    • type C can infect humans and causes mild illness

    • type D doesn’t infect humans

• has 2 surface antigens :hemagglutinin (H) and neuraminidase (N)

  • are important virulence factors

    • play a role in entry and exit of the target, causes red blood cells to clump together

  • have several varieties and the combinations are always changing

    • meaning the antibodies from a previous infection might not be protective for a new infection

What is Human Immunodeficiency Virus (HIV)?

• found on every continent except antarctica

• killed atleast 32.7 mil people

• no cure and no vaccine for this viral infection

  • the only medications can only keep viral levels in the body low but not eliminate them

• belongs to retroviruses group

  • enveloped RNA viruses that synthesize DNA from RNA once they enter a host cell

  • is then “pasted” into a host cell chromosome (the viral DNA becomes part of the host DNA, and when the host DNA is copied, it passes on the viral DNA too

    • is one of the reasons HIV cannot yet be eliminated from the body

• basically this virus becomes part of the person it has infected

• the main cells that become infected are: T-helper cells (CD4 cells)

  • normally assist in immune activities (activating B cells, that create antibodies and create long-term immunologic memory)

  • once these cells are infected, the body’s immune system weakens over time

    • if HIV isn’t treated with anti-retrovirals, the person’s immune system will soon not even be able to fight off mild infections

      • in which case their condition turns into AIDS (acquired immunodeficiency syndrome)

        • while HIV can be treated, AIDS cannot and that person will die

What is polio?

• causing disease since Egyptian times

• was common and widely spread due to industrialization

• is transmitted through the fecal-oral route, even indirectly like food or water

  • when the virus is excreted from the body of one person and ingested by another

    • the virus multiplies mainly in the intestines of the recipient

    • then travels through the blood to the central nervous system

    • once it reaches the CNS, it starts to destroy motor neurons, especially those responsible

      for the extremities and breathing

• some people may be asymptomatic while they’re infected, others may develop a mild flu-like illness, and others may die

• is no longer common in the US and other developed regions

  • however, Africa, India, and the Middle East where the disease breaks out periodically

    • despite word-wide eradication efforts via vaccines

What is Rotaviruses?

• non-enveloped RNA viruses

• cause 200,000 deaths (almost all children) every year

• several subtypes:

  • type A: causes most of the diseases in humans

• when someone’s infected, typical symptoms include:

  • large amounts of watery diarrhea

    • leading to dehydration and death

• for children who survive this illness but become chronically infected, permanent damage to the intestinal lining may happen and lead to malnutrition

  • most kids recover from rotavirus infections realtively quickly and easily (in US/developed countires)

  • cases may become fatal (in undeveloped countries)

• there is a vaccine that prevents most serious cases of disease in children who receive it

• features ALL rotaviruses have:

  • a double capsid (extra difficult to destroy w/ standard disinfection

What are measles, mumps, and rubella?

• these viruses are not closely related, but they are prevented by a combined vaccine (MMR)

• Measles

  • one of the most contagious diseases

  • spread via respiratory droplets

    • after an incubation period of 1-2wks, people usually develop a characteristic rash and symptoms of respiratory illness

      • includes cough, runny nose, and watery eyes, high fever as well

  • most people recover and maintain life-long immunity

    • some people may be left with permanent disability or die

• Mumps

  • characterized by swelling of the salivary glands near cheek and jawline

    • someone may experience swelling on 1 or both sides of their face

    • usually goes away w/in 2 wks and person makes a full recovery during that time period

  • some people may also experience a fever, a headache, muscle soreness, and other general symptoms of tiredness and body aches

  • this infection may also possibly cause inflammation of the testicles, ovaries, pancreas, or even brain all have long-lasting consequences

• Rubella

  • German measles

  • another generally mild illness

    • can cause serious complications for developing fetuses

      • if a pregnant woman is exposed to and infected with this virus, once born the baby may experience problems like:

        • heart defects

        • hearing difficulties

        • eye problems

        • cognitive difficulties

        • growth problems

• although immunization prevents most cases of congenital rubella symptoms

  • with declining rate of vaccination, its possible we’ll see more cases in the next few decades

What is Hepatitis? What types are there?

• an inflammation of the liver

• caused by a variety of factors, including viral infections

• 3 main viruses that cause viral hepatitis

  • though they aren’t closely related from a genetic perspective

  • the ALL infect the liver and cause inflammation

    • Hepatitis A

    • Hepatitis B

    • Hepatitis C

What is Hepatitis A?

• a Picornavirus transmitted through the fecal-oral route, typically via food and water

  • once entering the GI tract, the virus moves into the blood stream and enters the liver

    • then it multiplies and causes an inflammatory response

• typical signs and symptoms:

  • nausea, vomiting, diarrhea, abdominal pain, general fatigue, and fever

• many people have no symptoms, those that do generally recover on their own quickly

• its uncommon but IS possible for this virus to cause severe damage to the liver and/or induce liver failure

• there is a vaccine for this type of hepatitis

  • in unvaccinated communities, this disease can be prevented via handwashing and other sanitation techniques

What is Hepatitis B?

• an enveloped DNA virus

• spread via body fluids

  • blood, semen, and vaginal secretions can all spread the virus

• the illness is mild and self-limiting

  • may experience abdominal pain, nausea, fatigue, and jaundice that eventually goes away as the body fights the infection

  • these people are usually treated with supportive care that helps ease symptoms and makes their pain level decrease

• for some people, this infection can become chronic and lead to liver cirrhosis/liver cancer

  • they are treated with antiviral medications and monitored for indications of cirrhosis and cancer

• there is a vaccine that can prevent infection

• standard precautions preventing/limiting the exchange of bodily fluids help decrease transmission too

What is Hepatitis C?

• an enveloped RNA virus that causes typically the most serious form of viral hepatitis

• this virus is passed from person to person via blood

  • most cases of transmission happen via equipment used to inject drugs (needles are common, straws too)

• for years, hepatitis C wasn’t able to be cured and the infection often lead to cirrhosis and liver cancer

  • people w/ this virus could manage symptoms w/ various medications, but nor cure and was fatal often

• recent developments in pharmacology have led to the development of a medication that can cure the disease in most people

  • however still no vaccine

  • however the new medication have a chance at clearing the virus from their body and not suffering permanent damage to their livers

What are prions?

• infectious pieces of proteins

• unique among microbes because:

  • they have no lipids, carbs, nucleic acids

• they’re very similar in structure to proteins found w/in the membranes of cells in the CNS

  • is similar enough that the immune system does not appear to recognize them as foreign invaders

  • different enough that when the prions insert themselves into the cell membrane, it causes them to lose their shape and fall apart

    • this is when the immune system tries to clear the damaged cells

      • resulting in holes, which get larger as the disease progresses

• general symptoms of prion infections include:

  • confusion, fatigue, difficulty with coordination (walking/talking), hallucinations, and others depending on the prion

• as of right now, prion diseases are always fatal

• we don’t always know how prion infections are transmitted

  • sometimes from contaminated food products, genetic component, some may be transmitted during organ/tissue transplants, other times it’s a mystery

What are different prion infections?

• Creutzfeldt–Jakob Disease

  • 15% of cases are hereditary in nature

  • other people, those who have undergone medical procedures and received certain tissue types (nervous tissue)

  • other people acquire this via unknown reasons

  • symptoms include:

    • depression, agitation, difficulty walking, and disorientation

• Kuru

  • the prion that causes this disease was the first prion discovered

  • remains one of the most sensational infectious agents

    • in some cultures, it was common to consume certain body parts, especially the brain of deceased relatives

  • has a long incubation period, once it manifests, the person usually starts to have trouble walking/standing, coord. problems, headaches, tremors, and may sometimes have incontrollable fits of laughter

• Fatal familial insomnia

  • cases always seem to be hereditary

    • the gene that causes it is found in ~40 families worldwide

  • this specific prion damages the thalamus, partly responsible for sleep

  • once this disease starts, ~40yrs, there is a progressive loss in the ability to sleep

    • though insomnia is often the most noticeable symptom at first

    • symptoms can also include conditions like difficult walking and thinking clearly

  • eventually, the brain damage this prion causes becomes so complete and the lack of sleep so pervasive, the person dies

• bovine spongiform encephalopathy

  • aka mad cow disease

  • the source of this prion is infected beef

    • if a person consumed infected beef w/ this prion, they will develop BSE

  • this prion has an incubation period of ~12yrs (can be more/less)

  • once symptoms start, the progression is usually quick and people often experience difficulty with:

    • vision, abnormal muscle movements, problems with balance and coord., and personality changes