Microbiology 241



BIO241 – MICROBIOLOGY

Viral Infections -- Chapters 21-26

Viral Infections

• Warts (verruca vulgaris)

o epidemiology: Human Papilloma viruses are transmitted via scratches

o pathogenesis: skin disfiguration from chronic benign tumors

o treatment: remove (excise) wart by surgery (incision, cryosurgery or lasersurgery) or by the use of chemicals such as nitric acid

o prevention: avoid contact with warts on other people

• Herpes

o epidemiology: Herpes Simplex Virus 1 (HSV-1) is transmitted by direct contact; immunocompromised people are especially vulnerable

o pathogenesis: recurrent chronic lesions (blisters) on face, fingers, hands ... becomes latent in local nerves and exhibits recurrence during periods of stress (physical or psychological); herpes means "to creep"

o treatment: acyclovir (zovirax) shortens episode, slows recurrence; valtrex is a second generation version of zovirax ... works better

o prevention: avoid contact with skin sores on other people

• Rubella (German measles)

o epidemiology: Rubella virus is transmitted via respiratory secretions before symptoms appear; ~10 cases normally reported each year in the US

o pathogenesis: upper respiratory infection leads to systemic infection resulting in a mild skin rash ("rubella" = "red, small" rash); complications - congenital rubella syndrome (retardation, deafness, cataracts, glaucoma, heart defects) from fetal infection in first trimester of pregnancy

o treatment: TLC

o prevention: MMR vaccine; avoid contact with respiratory secretions

• Rubeola (Measles)

o epidemiology: Rubeola virus is transmitted via respiratory secretions before symptoms appear; ~100 cases of measles reported in US each year

o pathogenesis: upper respiratory tract infection (10-14 days; "cold-like" symptoms) leads to systemic infection which results in Koplik spots, then skin rash (red and blotchy in people with light skin pigmentation; fine granular eruption in people with dark skin pigmentation) with high fever, delirium; complications - blindness (vitamin A deficiency), pneumonia (4-7%), encephalitis, seizures, death (~10%; kills ~1 million people (mostly children) per year worldwide); not teratogenic, but intrauterine rubeola infection can cause stillbirth, premature delivery, fatal congenital encephalitis; SSPE (subacute sclerosing panencephalitis)

o treatment: TLC

o prevention: MMR vaccine; avoid contact with respiratory secretions ... does MMR vaccine cause autism?

• Varicella (Chickenpox)

o epidemiology: Herpes Varicella-Zoster Virus is transmitted via respiratory secretions; most contagious human disease; ~50,000 cases per year in US (85% in 0-9 year-olds; 13% in 10-15 year-olds)

o pathogenesis: upper respiratory tract infection ("cold"-like symptoms) leads to systemic infection, which causes fever, vesicular eruptions (lesions) of skin; complications - secondary bacterial infections (pneumonia, encephalitis (coma)), death (20% of adults); Reye's syndrome; congenital defects if infected during first trimester of pregnancy; shingles or zoster, which results from stress-induced activation of latent virus, leading to painful lesions on the skin or eye ... 700,000-900,000 cases of shingles every year in the US; mostly in the over-50 crowd, peak incidence at 60-79 years of age

o treatment: TLC, symptomatic relief (for chickenpox - acetaminophen calamine lotion, acyclovir (zovirax), famvir or valtrex; for encephalitis, vidarabine (Vira-A) or famvir for shingles, Zostrix (OTC analgesic)

• Variola (Smallpox)

o epidemiology: Variola Virus - transmitted via respiratory secretions, vesicular fluid, or lesion crusts from infected persons; 0 cases per year in the whole world ... this disease is thought to have been eradicated in the 1970s (last "wild" case in Somalia in 1977)

o pathogenesis: upper respiratory tract infection leads to systemic infection (fever, chills, headache, backache) which leads to vesicular eruptions (lesions) of skin; complications - disfiguration due to massive scar formation; death in severe cases (up to 90%) ... bioterrorism information

o treatment: TLC

o prevention:

▪ vaccine

▪ the US stopped routine universal vaccination against smallpox in the 1970s because there is a bigger chance of harming those who are immunodeficient than there is of saving others (since the disease was eradicated worldwide during that decade)

▪ smallpox vaccine is, however, made available to healthcare workers in the US

▪ perhaps as few as 20% of those vaccinated a generation ago are still immune

▪ countries other than the US still vaccinate (or at least did so as recently as 20 years ago)

▪ avoid contact with respiratory secretions, vesicular fluid, or lesion crusts from infected persons

• Rabies

o epidemiology: Rabies Virus is transmitted via bites of infected animals (bats, raccoons, skunks, dogs, etc.) ... some think that this disease inspired the vampire legend

o pathogenesis: CNS damage leads to death in 2-8 weeks

o treatment: TLC

o prevention: vaccine (only disease known for which the vaccine can sometimes prevent onset of disease, even after infection has occurred)

• Poliomyelitis

o epidemiology: Polio Virus is transmitted via water (summer); fewer than 10 cases per year in the US now, but ~50,000 or more during the first half of the 20th century; ~25 cases per year, worldwide

o pathogenesis: intestinal infection leads to infection of motor neurons, damage causes paralysis; complications include muscle atrophy, paralysis, death (postpolio syndrome, which only affects those who had polio earlier in their lives, and for which there is some help)

o treatment: TLC, supportive measures ... such as braces, wheelchairs or iron lungs

o prevention:

▪ sanitation ... adequate treatment of drinking water and prevention of its contamination with sewage

▪ vaccines ... more on vaccines

▪ injectable polio vaccine (IPV)

▪ inactivated viruses - doesn't cause disease, but induces production of neutralizing antibodies (only)

▪ Jonas Salk developed this vaccine

▪ IPV administration via injection

▪ oral polio vaccine (OPV)

▪ attenuated, infectious viruses - can cause disease in immunocompromised children, but induces CTLs as well as neutralizing antibodies

▪ Albert Sabin developed this vaccine

▪ OPV administration via mouth

▪ CDC recently decreed that only IPV should be used for vaccinating infants in the US

▪ World Health Organization (WHO) is spearheading a move to eradicate polio, and good progress is being made in this effort, even though it means difficult treks into remote areas; more on polio vaccine strategies

• Mad Cow Disease (Bovine Spongiform Encephalopathy)

o epidemiology: as established by Prusiner, prions are ingested by people eating beef from cattle stricken with Bovine Spongioform Encephalopathy (BSE); this disease was discovered in Great Britain in the 1980s, and ~100 Brittons have died of it so far, but BSE has yet to emerge in the US (Official Mad Cow Home Page)

o pathogenesis: prions are taken up from the digestive tract and somehow get into the brain, where they interact with cell receptors, changing their conformation, which causes accumulation of prion molecules as the cells replace the altered receptor molecules; this causes accumulation of fibrils of insoluble prion complexes and results in slow degeneration of the central nervous system with obvious dysfunction, progressive dementia, and vacuolar degeneration of the brain known as new variant Creutzfeldt-Jakob disease (nvCJD) disease

o treatment: TLC

o prevention: avoid eating beef that may contain prions ... how to tell if your cow has mad cow disease (alt: mad cow disease ... sound with animation ... mad cow dance)

• Infectious Mononucleosis

o epidemiology: Epstein-Barr Virus (EBV) and Cytomegalovirus ( CMV) are transmitted by close oral contact (kissing); prevalent among teens in US; ~90% of adults in the US have antibodies against EBV

o pathogenesis: First, sore throat (pharyngitis) with swollen glands (cervical lymphadenitis) and fever develops; then mononucleosis (monocytosis), muscle aches and fatigue develop; acute illness usually lasts 7-14 days, but it is important not to overexert for up to 6 weeks; complications include hepatitis, meningitis, myocarditis, paralysis, ruptured spleen, facial paralysis, chronic fatigue syndrome ("yuppie flu"), and death (rare)

▪ EBV pathogenesis overview

▪ CMV pathogenesis overview

o treatment: TLC (much bed rest, little strenuous exercise, no alcohol)

o prevention: avoid contact with respiratory secretions of infected persons

• Dengue Fever

o epidemiology: caused by Dengue Fever Virus, which is transmitted by Aedes aegypti or Aedes albopictus mosquitoes; endemic in Africa, the Caribbean, Central and South America, Southeast Asia and Australia ... 1/3 of people worldwide live where they can get this disease; 50-100 million cases worldwide each year; ~100 cases per year imported into the US by travelers; ~100 cases per year imported into the US by travelers

o pathogenesis: mosquito "injects" virus into bloodstream; this rarely fatal disease is characterized by sudden onset of high fever and rash together with severe headache, and severe muscle, joint and eye pain (sometimes called "breakbone" fever); complications include hemorrhagic fever, with bleeding from gastrointestinal and other mucosal membrane orifices of the body, which can lead to shock and death in up to 20% of cases (mortality is ~1% with appropriate treatment)

o treatment: TLC, fluid replacement in hemorrhagic fever cases

o prevention: vaccines (under development); mosquito repellent use; mosquito control

• Hepatitis A and E

o epidemiology: Hepatitis A or Hepatitis E virus; ~3500 cases per year in US; transmitted via raw shellfish, produce, other fecally-contaminated foods, especially in institutions

o pathogenesis: intestinal infection with Hepatitis A or E virus leads to anorexia, nausea, vomiting, low-grade fever; systemic distribution leads to liver damage, which causes jaundice; some people are asymptomatic, however; complications - chronic disease, relapses are common; ~100 deaths per year in US

o treatment: TLC (prolonged rest)

o prevention: Hepatitis A Vaccine, sanitation (good food handling techniques, adequate sewage treatment and drinking water purification), gamma globulin injection

• Hepatitis B, C and D

o epidemiology

▪ Hepatitis B Virus - hepatitis B is transmitted by sexual (especially in men who have sex with men) contact (55% of infections) and IV drug injection, transfusion, tatoos, and can be transmitted from mother to infant during the process of birth; ~5,000 cases reported each year in US, but CDC estimates actual infections may be as high as 20,000 per year with as many as 1.25 million chronic cases in the US and 200-300 million cases worldwide

▪ Hepatitis C virus - hepatitis C is transmitted in the same ways as hepatitis B (injection of illegal drugs, transfusion, tatoos or engaging in unprotected sex); ~800 new reported cases of hepatitis C per year in US, but CDC estimates actual infections may be as high as 20,000 per year with ~3.2 million chronic cases in US and ~100 million cases worldwide

▪ Hepatitis virus D - defective virus (may be a viroid) that only infects hepatitis B victims; hepatitis D is primarily transmitted via infected blood; CDC estimates there may be ~70,000 carriers in US

o pathogenesis:

▪ hepatitis B - 50% asymptomatic, but in the other 50%, liver infection leads to fatigue, anorexia, taste changes, vomiting and jaundice (indicating liver damage); complications include damage to intestines (clay-colored stools), and kidney (dark urine); chronic disease, carriers (6-10%); cirrhosis; hepatitis D virus co-infection; death (~5,000 per year in US)

▪ hepatitis C - 70% asymptomatic, 30% have mild symptoms; complications include chronic liver infection, carrier state (~40%); cirrhosis; risk factor for hepatocarcinoma; death (~10,000 per year)

▪ hepatitis D - only infects those who are already infected with hepatitis B virus, but makes these cases more severe because it causes progressive liver damage; death (20-30%, ~1000 per year)

o treatment: α-interferon for hepatitis B and C; TLC (prolonged bed rest); liver transplant

o prevention: avoid high-risk behavior; use condoms; get hepatitis B vaccine; hepatitis B immune globulin for those who have been exposed, but have not yet exhibited signs or symptoms of disease

• Acute Common Coryza (Common Cold)

o epidemiology: transmitted via respiratory secretions (both directly and indirectly), ~120 Rhinovirus strains, ~30 Adenovirus strains, Respiratory Syncytial Viruses (more about RSV), and others (coronaviruses, Coxsackie viruses, echoviruses, reoviruses) cause millions of colds each year in US ... especially in children; Severe Acute Respiratory Syndrome (SARS) emerged in China in 2003; this disease is casued by a novel coronavirus (SARS-CoV) ... WHO reported that 8,098 people worldwide developed SARS during the 2003 outbreak, and 774 of them died; the most recent cases of SARS were laboratory-acquired infections in China in April 2004

o pathogenesis: nasal epithelial infection causes pharyngitis (cell damage, inflammation) which causes nasal congestion and secretions, sneezing, sore throat, and coughing (how to distinguish between colds and flu); complications - croup (persistent, hoarse cough in infants)

o treatment: TLC - symptomatic relief; antibiotics not useful (treatment advice from a pharmacist or from a student health center)

o prevention: avoid contact with respiratory secretions of infected persons

• Influenza

o epidemiology: Influenza Viruses cause 100-150 million cases per year in the US ... leading to 10,000-40,000 deaths each year (incidence this year); named from the Italian phrase influenza de freddo (influence of the cold); virus continually changes its surface structures by antigenic drift and antigenic shift (check out this animation to see how Influenza Virus does this), thus generating "new" strains which are able to infect people who had previously been infected with the "old" strains; this disease is the world's record-holder for the most people killed in the shortest time ... it spread throughout the world and killed more than 20 million people in 18 months, beginning in March 1918 ... Want to know where/when the flu is likely to be worst in the US? Check out this site! ... newest influenza threat is avian influenza

o pathogenesis: after 1-4 days (average of 2 days), nasal epithelial infection leads to abrupt onset of rhinitis (inflammation causes nasal secretions, sneezing), then pharyngitis (inflammation causes sore throat, coughing), then bronchitis (due to ciliated epithelial cell loss) which leads to malaise, chills, fever, headache, nonproductive cough, muscle aches, joint soreness, weariness; the disease itself usually lasts for several (5-7) days, but the cough and malaise can last for 2 or more weeks (how to distinguish between colds and flu); complications include primary influenza viral pneumonia or secondary bacterial pneumonia ... together, influenza and pneumonia together constitute the number 8 killer in the US ... 61,472 people died of this combination in 2004; Guillain-Barre syndrome; Reye's Syndrome (aspirin induces Reye's Syndrome in children?)

o treatment: TLC - symptomatic relief (but don't treat children with aspirin); amantadine prevents influenza A; neuraminidase inhibitors (Relenza, Tamiflu) shorten length of illness by one day (if taken at onset of signs and symptoms) ... more treatment info

o prevention: vaccine (who should get it? ... elderly, diabetics, anemics; cardiac, pulmonary, renal patients ... what about kids?) avoid contact with respiratory secretions of infected persons

▪ description of the 2006-2008 vaccine

▪ Pandemic Flu: We Are Not Prepared

• Mumps

• epidemiology: Mumps virus is transmitted via respiratory secretions or saliva before symptoms appear; ~400 cases of mumps reported in the US each year (most age 5-10); ~one-third asymptomatic; down from 152,000 cases in 1968; the name comes from the English word "mump" (to sulk, to be sullen)

• pathogenesis: parotid salivary gland infection causes fever, accumulation of saliva (parotid swelling, tenderness) after 16-18 days; complications - infection of ovaries, testes, thyroid, pancreas, CNS (meningitis, encephalitis, deafness)

• treatment: TLC

• prevention: MMR vaccine, avoid contact with respiratory secretions or saliva of infected persons ... does MMR vaccine cause autism?

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