HAD 381 - Quiz 8 - Intracellular Organisms & Viruses

RNA viruses: general characteristics:

• Can be ss (single-stranded) or dsRNA (double-stranded)

  • Most are ssRNA

• Include the medically important viruses

  • Hepatotropic viruses

  • Influenza viruses

  • Retrovirus

    • HIV

• Filoviruses

  • Ebola and Marberg

Hepatotropic Viruses: general characteristics:

• Causes hepatitis

• Inflammatory condition of the liver

Hepatotropic Viruses: signs & symptoms

• fatigue, fever, joint and abdominal pain, vomiting, anorexia, dark urine, hepatomegaly, elevated liver enzymes and jaundice

Hepatototrophic liver function tests for diagnosis:

• Six types identified:

• Hepatitis A virus (HAV), Hepatitis B virus (HBV), Hepatitis C virus (HCV), Hepatitis D virus (HDV), Hepatitis E virus (HEV), Hepatitis G virus (HGV)

• Other viruses such as EBV, CMV, and HSV can also cause hepatitis

• Specifically infect liver cells

Hepatitis A Virus (HAV): general characteristics:

• Enterovirus belonging to the family Picornaviridae

• Mode of transmission: fecal–oral route by ingestion of

  food/water contaminated with feces

• Occasionally parenteral transmission

• Called infectious hepatitis because can occur in outbreaks

• often affects large numbers of people

Hepatitis A Virus (HAV): Symptoms:

• Acute, chronic, or asymptomatic infections

  • Asymptomatic

• No clinical symptoms but liver enzymes are elevated

• Incubation period of 2-6 weeks

• Flu-like illness and pain in area of liver

• Viral shedding for up to 30 days after onset of symptoms

• Resolution in 6 months

HAV infection:

• Anti-HAV antibodies emerge at about 10 days

  • IgM antibodies peak at 30 days and are undetectable at about 6 months

  • IgG antibodies emerge after 14 days and peak at 30 days

• Can remain detectable for more than 10 years

HAV diagnosis & treatment:

• Diagnosed by demonstration of a significant rise in titers between acute and convalescent sera using RIA or EIA

• No specific treatment

  • rest is recommended during acute stage of illness

• Immunity conferred by the production of neutralizing antibodies directed against HAV

• HAV vaccine can be administered to prevent infection in uninfected individuals exposed to virus

• A serological profile of detectable antibodies to HAV infection. LFT, liver function tests.

Hepatitis C Virus (HCV): general characteristics:

• Belongs to the family Flaviviridae

• Formerly known as non-A, non-B hepatitis

• Mode of transmission is primarily parenteral

  • bloodborne

  • perinatal and sexual transmission is possible

• 20% of cases are acute and 80% can result in chronic infection

• Causes cirrhosis and liver cancer

• Leading cause of liver transplants

Parenteral transmission:

• The introduction of pathogens into the body through a route other than the gastrointestinal tract, such as through injections, cuts, or bites, bypassing the digestive system

HCV diagnosis & treatment:

• Diagnosis previously based on:

  • demonstration of elevated liver enzymes such as ALT

  • exclusion of known viral etiologic agents

• EIA procedure to screen donor blood for anti-HCV antibodies

• Treatment

  • Antiviral drugs such as ribaviron

  • Immunodulatory drugs such as interferon-alpha

Hepatitis D Virus (HDV): general characteristics:

• A defective virus because its genome lacks essential genes

  • Probably a subviral agent because it requires a helper virus, HBV

• HDV infection can only occur in individuals with HBV infection

  • must be transmitted simultaneously with HBV or as a superinfection of HBV infected individuals

• Transmission is parenteral like HBV

• Infection increases risk of cirrhosis and cancer

HDV: diagnosis:

• IgM antibodies appear first 6-7 weeks after infection then decline after the acute phase

• IgG antibodies appear during the acute phase and decline within a few months

• Both IgM and IgG are elevated in cases of chronic infection

• Diagnosis depends upon the detection of antibodies to the HDV (delta) antigen

Hepatitis E Virus (HEV): general characteristics:

• Family Hepeviridae

• Mode of transmission is fecal–oral route

• Causes an acute self-limiting illness with no chronic phase

• Symptoms similar to those of HAV except in pregnant women where mortality rate is high

• No vaccine available

• Diagnosis through demonstration of IgM antibodies during acute phase

Hepatitis G Virus (HGV): general characteristics:

• Family Flaviviridae

• Discovered in 1995

• Associated with acute and chronic cases of hepatitis

• Transmitted by parenteral route

  • Blood transfusions and intravenous drug use

• Diagnosis through use of EIA, PCR, and Western blot techniques

Picornaviridae: general characteritics:

• Includes the following medically important genera:

  • Enteroviruses, which includes the coxsackie and polio viruses

  • Rhinoviruses which are a major cause of the common cold

  • Heptovirus including hepatitis A virus

• Are very hardy and resistant to many disinfectants

• Members of this family cause a variety of diseases from asymptomatic to symptomatic

• Aseptic meningitis, a disease seen in infants less than a year old, may be fatal

Enteroviruses: Includes 5 groups

• Polioviruses types 1-3

• Coxsackie A viruses types 1-24

• Coxsackie B viruses types 1-6

• Echoviruses types 1-34

• Enteroviruses serotypes 68-71

Enteroviruses: general characteristics:

• Second most common viral infectious agents in humans

• Cause febrile illnesses, respiratory illnesses, rashes, aseptic meningitis, and paralysis

• Children tend to be affected during summer, fall and winter months

• Resistant to most commonly used disinfectants

  • Detergents

  • 70% alcohol

  • Phenolic compounds

• Halides (iodine and chlorine solutions) can inactivate enteroviruses and are effective

• CSF is specimen of choice in cases of aseptic meningitis

• Nucleic acid assays faster than cell culture

Enteroviruses: transmission:

• primarily fecal–oral route but also respiratory aerosols

Poliomyelitis viruses: general characteristics:

• ssRNA

• Etiologic agents of polio especially in children

• Transmitted thru oral-fecal route via ingestion of contaminated food and water

• Multiplies in gastrointestinal tract then invades blood and finally CNS causing irreversible paralysis

• 95% of cases are asymptomatic

• Vaccine has eradicated it in developed countries but still significant threat in 3rd world countries

Two types of polio vaccines:

• Salk inctivated poliovirus vaccine (IPV) 1955

• Sabin oral live poliovirus vaccine (OPV) weakened poliovirus 1961

  • Vaccine-associated parlytic poliomyelitis 3/million

  • Cost in the developing world is about US $0.25 per dose

Coxsackie viruses: general characteristics;

• Human pathogens include coxsackie A and B

• They are both implicated in aseptic meningitis

Coxsackie viruses: Coxsackie A 16

• Cause of hand, foot, and mouth disease in children

• Fever, mouth blisters, and rash

• Aseptic meningitis

  • Human foot and mouth disease (HFMD) (Cattle)-Plum Island

Coxsackie viruses: Coxsackie A 24:

• hemorrhagic conjunctivitis

Coxsackie viruses: Coxsackie B:

• infectious pericarditis, myocarditis, Bornholm disease

  (pleurodynia)

Coxsackie viruses: Coxsackie B 24:

• Type 1 diabetes

Rhinoviruses: general characteristics:

• Major cause of common cold primarily during fall and spring

• Rare cause of bronchitis and pneumonia

• Very hardy, heat stable and resistant to effects of desiccation

Rhinoviruses: factors associated with transmission:

• Close proximity of individuals in cold weather

• Viral shedding in nasal secretions before symptoms

• Shedding persists for several days after recovery

• 1/2 of cases are asymptomatic but still shed virus

• Hands of infected individuals transfer nasal secretions to inanimate objects

• Self inoculation of uninfected persons by rubbing eyes or nose

Rhinoviruses: diagnosis & prevention:

• Laboratory diagnosis rarely attempted because of mild nature of infection

• Control thru hand washing and avoiding contact between eyes, nose, and hands

• Vaccine not likely due to number of serotypes

Coronaviruses: general characteristics

• Enveloped, ssRNA

• Cause of pharyngitis and most colds occurring during the winter months

• Transmission via respiratory secretions

• Word “Coronavirus” is derived from Latin corona, meaning crown or halo.

• Under EM each virion appears corona or halo. This is due to the presence of viral spikes peplomers emanating from each proteinaeous envelope.

• Common human corona viruses

  • Alphacoronaviruses: HcoV-229E, HCoV-NL63

  • Beta coronaviruses: HCoV-oc43, HCoV-HKU1

• Effects upper respiratory and gastrointestinal tract of mammals and bird.

  • SARS-CoV-1

  • Mers-Cov

  • SARS-CoV-2

Severe acute respiratory syndrome (SARS):

• China earliest case in healthcare worker.

• 8422 cases reported in August 2003 from 30 countries

• Cause of severe acute respiratory syndrome (SARS) that emerged in 2003

• Bat natural reservoir

• Chills, fever, myalgia, headache, pharyngitis, rhinorrhea and diarrhea

  • Cough, shortness of breath and difficulty breathing, Acute respiratory distress syndrome (ARDS)

SARS diagnosis:

• History of travel to Far East (China, Taiwan, Hong Kong, etc.)

• Exposure to known cases of SARS

• Symptomology

• Radiographic evidence

• Specimens: nasopharyngeal, oropharyngeal, bronchial aveolar lavage and lung tissue

• Tests: immunofluorescence, nucleic acid assays, serology

  • Difficult to grow in culture

SARS diagnostic tests:

• Conventional reverse transcriptase PCR (RT- PCR) and real time reverse transcriptase PCR( real-time RT-PCR) assay detecting RNA virus:

• 2 type of specimens- nasopharyngeal and stool specimen

  OR

• The same specimen collected on 2 or more occasions during the course of the illness.

SARS prevention:

• Early recognition of infected patients

• Hospitalization when necessary

• Contact and airborne infection isolation precautions

• Cough etiquette

SARS treatment:

• None available at this time

• Possible vaccine being investigated

Middle East Respiratory Syndrome (MERS): general characteristics:

• April 2012, new virus that has not been seen in humans before. After that 26 countries reported the cases.

• Middle East Respiratory Syndrome Corona Virus (MERS- CoV).

• 3-4 out of every 10 died with MERS (36% case fatality rate), can affect anyone.

• Fever, cough, and shortness of breath, and can also include diarrhea, nausea, or vomiting

• Complications- pneumonia, respiratory failure, septic shock

• Zoonotic virus

• Originated in bats and was transmitted to dromedary camels.

• Most of the human cases do not have a history of direct contact with camels. Then the transmission may be indirect.

MERS clinical manifestation:

• Acute respiratory illness, cough shortness of breath.

• Gastrointestinal symptoms

• More sever complications such as pneumonia and kidney failure.

• Pre-existing conditions like diabetes, cancer, heart and lung disease or weakened immune system had severe cases.

• Life cycle of MERS

• Criteria serving as guidance for who should be tested for MERS-CoV infection in the United States

MERS treatment:

• Currently no medicine is available to cure.Treatment for is done to help support your body while it fights the disease. This is known as supportive care. Supportive care may include:

• Pain medicines. These include acetaminophen and ibuprofen. They are used to help ease pain and reduce fever.

• Bed rest. This helps your body fight the illness. Care during severe illness may include:

• IV fluids. These are given through a vein to help keep your body hydrated.

• Oxygen. Supplemental oxygen or assisted ventilation may be given. This is done to keep enough oxygen in your body.

• Vasopressor medicine. These help to raise blood pressure that is too low from shock.

• No antiviral drug

• Care and support of vital organ.

• Corticosteroids

• Interferon

• Convalescent serum

• Intravenous immunoglobulin

• Nitazoxanide

• Ribavirin

• Interferon plus ribavirin

MERS prevention:

• Distancing, washing hand, cover your mouth, clean and disinfect frequently.

Coronavirus Disease (COVID-19) pandemic: general characteristics:

• an infectious disease caused by the SARS-CoV-2 virus.

• Nucleocapsid surrounded by envelope.

• Envelope is lipoprotein in which proteins are embedded

  • Spike protein (S)

  • Membrane glycoprotein (M)

  • Envelope protein (E)

• Non structural protein

• Include enzyme which help in replication such as RNA dependent RNA polymerase, helicase, etc.

• Life cycle of COVID-19

COVID-19 diagnostic tests:

• Nucleic Acid Amplification Tests (NAATs).

  • Nucleic acid amplification tests (NAATs), including PCR tests, are more likely to detect the virus than antigen tests. NAATs tests are the “gold standard”

• Antigen Tests: Antigen tests* are rapid tests that usually produce results in 15-30 minutes. Positive results are accurate and reliable. However, in general, antigen tests are less likely to detect the virus than NAAT tests, especially when symptoms are not present. Therefore, a single negative antigen test cannot rule out infection.

Flow chart of different viral families

Cycle threshold (Ct) value:

• The number of reaction cycles it takes to reach that threshold

• CORONAVIRUS

COVID-19 treatment options:

• FDA has authorized or approved several antiviral medications used to treat mild to moderate disease in people who are more likely to get very sick.

  • Paxlovid- Orally

  • Remdesivir – IV – for 3 days

  • Lagevrio- Orally

• SARS-CoV-2 shares approximately 79.5% genomic homology with SARS-CoV while only about 50% similarity with MERS-CoV, indicating that SARS-CoV is closer to SARS-CoV2.

Orthomyxoviridae, orthos, “straight”; myxa “mucus”: Influenza Viruses:

• Enveloped, single-stranded negative-sense RNA

  • a positive-sense RNA must be produced by an RNA- dependent RNA polymerase (RdRp) prior to translation

Influenza Viruses: general characteristics:

• Enveloped, single-stranded, segmented, negative-sense RNA

• Projections resembling spikes embedded in lipoprotein viral envelope

  • Hemagglutinin A (H)

    • Major glycoprotein of influenza virus

    • Responsible for attachment to host cells

  • Neuraminidase (N)

    • Glycoprotein enzyme on surface of virus

    • Responsible for release of viral progeny from cell

• Combinations of 19 hemagglutinins and 9 neuramidases determine subtype such as H1N1, H5,N1, etc.

  • Influenza strains can show species specificity due to variation in hemagglutinin genes

• Mutations enable the viral proteins to bind to receptors on host cells

  • passing from animals to humans can lead to a pandemic

• Lack polymerases with proofreading activity (cannot find and fix errors during replication)

  • a characteristic of many RNA viruses

  • Lead to a high mutation rate

• Mutations in hemagglutinin genes can allow the virus to easily pass from animals to humans leading to a pandemic

• Have a high mutation rate they lack DNA polymerases which find and fix DNA

  • a characteristic of many RNA viruses

• Are able to escape host defenses through antigenic variation

• Influenza A most implicated in pandemics

  • Spanish flu (1918-1919, H1N1), Asian flu (1957-1958, H2N2), Hong Kong flu (1968-1969, H3N2), Avian flu (2003, H5N1), Novel swine flu (2009-????, H1N1)

• Types A and B cause life-threatening infections in humans

  • Most cases of the flu are self-limiting

  • Complications, such as bronchitis and pneumonia, can be very serious in infants, elderly, and chronically ill patients

• Appear in November to December and linger through March or April

• Transmission is through respiratory aerosols

Antigenic Drift:

• refers to the gradual accumulation of point mutations in the genes encoding the surface proteins hemagglutinin (HA) and neuraminidase (NA) due to the virus’s error-prone RNA polymerase.

• If a mutation alters the structure of HA or NA in a way that helps the virus escape pre-existing immune recognition, it can give the virus a selective advantage.

Effects of antigenic drift:

• Causes seasonal flu epidemics, requiring frequent updates to flu vaccines.

• Results in milder but recurrent outbreaks since population immunity is only partially effective.

Antigenic shift:

• a rapid and dramatic genetic change that occurs when two

  different influenza A viruses infect the same host and undergo reassortment, leading to a new viral strain with a completely different HA or NA subtype.

• This reassortment can generate a completely new influenza A virus with a novel HA and/or NA protein, against which humans have little to no immunity.

Antigenic effects:

• Causes pandemics because the new strain can spread rapidly in a population with no pre-existing immunity.

Influenza type A infections:

• Found to infect swine, horses, birds, and other animals

• Asian flu and Hong Kong flu caused by strains resulting from reassortment of human and avian viruses

• Wild birds are the only animals having all subtypes of influenza A

• H5N1 is the etiologic agent of the avian or bird flu

  • 2003 strain of H5N1 responsible for outbreak in southeast Asia

  • H5N1 strains able to merge genes with strains found in hosts such as humans and birds

  • Outbreak continues to this day and is a major cause of concern because of increased virulence in humans

  • Infection acquired by close contact with fowls

  • No cases of human-to-human transfer documented at this point

Influenza type A clinical manifestations:

• Often asymptomatic or mild

• Symptoms: fever, chills, myalgia, sore throat, and cough

• Fatalities associated with viral pneumonia or secondary bacterial infection

Influenza type A preventation:

• Vaccination is most effective method

  • Live attenuated vaccine (weakened virus)

• Individuals with allergies to chicken eggs should not be vaccinated because the virus is propagated in chicken eggs

Influenza type A specimens of choice:

• Nasal washings or aspirates are best

• Throat swabs can be used but contain less virus

Influenza type A screening:

• Rapid immunoassay

• Monoclonal antibody assay detects either influenza A or B or both

• sensitivity about 80% depending on specimen quality

Influenza type A more sensitive assays:

• direct immunofluorescence

• cell culture

  • Primary monkey kidney and A-549 (human lung carcinoma)

  • Cytopathic effect (CPE) in 3-5 days

  • Cell rounding

  • Vacuoles in cell lawn

• Hemabsorption

  • Influenza virus-infected cells absorb guinea pig RBCs

  • Hemagglutinin binds to sialic receptor on blood cells

RT-PCR:

• Detect viral RNA

Influenza type B: general characteristics

• Causes a milder upper respiratory disease in younger children

• Complications such as pneumonia are rare

• Reye’s syndrome with use of salicylates (aspirin) to reduce fever in children

Influenza type C: general characterisitcs:

• Associated with a common mild illness in early childhood

Influenza Vaccination:

• Those at risk for complications and healthcare workers should be vaccinated

• New vaccine reformulated each year because each epidemic is antigenically different.

• Vaccine confers immunity to specific strains or subtypes

• 2 types

• Killed: TIV trivalent (3 strains; usually A/H1N1, A/H3N2, and B) inactivated vaccine

• Live: LAIV nasal spray (mist) of live attenuated influenza vaccine.

• Individuals with allergies to chicken eggs should not be vaccinated because the virus is propagated in chicken eggs

• Changes in virus (surface antigens) occur so immunity to one strain does not prevent susceptibility to another strain

Orthomyxoviridae: Treatment:

• Oseltamivir (Tamiflu) effective in children and pregnant women

• Zanamivir, a neuraminidase inhibitor, used in prophylaxis and treatment of influenza A and B- inhaled medication not recommended for patients with respiratory illness.

• Baloxavir Marboxil (Xofluza)- effective in older- single dose.

• Amantadine and rimantadine effective against influenza A but not influenza B

  • Differentiation is very important

• Peramivir (Rapivab)- Intravenous antiviral for hospitalized patients or those unable to take oral medication.

Paramyxovirus family: categorization:

• Enveloped, helical RNA

• Respirovirus genus

  • Parainfluenza virus

• Pneumovirus genus

  • Respiratory syncytial virus (RSV)

  • Metapneumonia virus

• Morbillivirus genus

  • Measles virus

  • Canine distemper virus

• Rubulavirus genus

  • Mumps virus

Parainfluenza viruses: general characteristics:

• Acute respiratory illnesses in children

• Croup, an upper respiratory infection, causing laryngitis and associated with characteristic hoarse cough like the bark of a seal

• Pneumonia and bronchitis in infants

• Transmission via inhalation of droplets or person to person contact

Parainfluenza viruses: diagnosis & prevention:

• Specimen

• throat swabs or nasopharyngeal washings

• Direct fluorescent antibody to demonstrate virus in respiratory secretions

• Cell culture: primary monkey kidney, human neonatal kidney, or human lung cancer

  • CPE can take up to 14 days

    • Round, granular cells and syncytia

• Immunofluorescence or hemadsorption on cells exhibiting CPE

Parainfluenza viruses: treatment:

• No vaccine or effective treatment; hand hygiene is best prevention

• PCR is more popular test

Respiratory Syncytial Virus (RSV): general characteristics:

• Named for characteristic CPE

  • Syncytia are created when cells merge to form large, multinucleated cells

• Major cause of upper respiratory diseases in infants

  • Range from mild disease, to bronchiolitis and pneumonia, to severe respiratory distress and death

  • Increased risk of RSV pneumonia in premature infants or those with congenital heart defects or chronic lung disease

  • Pneumonia increases risk of asthma later in life

• Most infections in late winter and early spring

  • Peak in February and March

  • Nursery outbreaks associated with high infection rates and some fatalities

• Transmission via direct contact with respiratory secretions

Respiratory Syncytial Virus: infection in adults:

• Acute, febrile, upper respiratory infection

• may be chronic and severe in elderly

• Can lead to bronchiolitis and pneumonia

RSV diagnosis:

• Specimen: nasal washing or aspirates

• Procedure: direct fluorescent antibody technique

• Rapid antigen tests or more sensitive molecular tests like RT-PCR (real-time reverse transcription-polymerase chain reaction) to detect the virus

• Direct immunoassays

  • enzyme immunoassays (EIA) used in most labs

    • sensitivity & specificity > 80%

• Direct fluorescent antibody or viral cultures should be used to confirm negative direct immunoassay tests

  • Cell culture: HEp-2 (human larynx cancer) and H292 and A-549 (human lung cancers) for demonstration of syncytia in 3-5 days

RSV prevention & treatment:

• No vaccine is available

  • hand washing is important control measure

• Ribavirin is an effective antiviral drug

Measles virus: general characteristics:

• Enveloped, ssRNA

• Also known as rubeola virus

• Highly infectious disease spread by respiratory

  aerosols

Measles clinical manifestation:

• Incubation period of 10 days

• Symptoms: fever, cough, coryza (runny nose), conjunctivitis, and generalized erythematous rash

• Koplik’s spots: bright red spots with white centers on the oral mucosa are diagnostic and, if apparent, no laboratory diagnosis required

• Skin rash and Koplik’s spots are diagnostic and laboratory diagnosis is not needed

Measles diagnosis:

• Laboratory diagnosis when required

• Specimen: NP swab or urine

• Cell culture: human kidney cells showing distinctive multinucleated cells

• Serologic tests to demonstrate IgM antibodies

  • acute phase of infection

• EIA or serum neutralization assays used to obtain antibody titers

Measles vaccination:

• Best means of protection

• Prior to vaccine, as much as 95% of population infected at sometime during life

• Vaccine given at the age of 18 months as a part of the measles, mumps, rubella (MMR) vaccine

• Booster administered before 5th birthday

• In 2019 there were 1282 cases reported in 31 states in unvaccinated children

Mumps virus: general characteristics:

• Enveloped, ssRNA

• Cause of mumps or epidemic parotitis, a self- limiting systemic viral disease

• Transmission via droplets of infected saliva

• Symptoms: painful swelling of parotid glands, fever, headache, and sore throat

• Pancreas, ovaries and testes can be infected

• Orchitis can lead to infertility

• Photo shows mumps due to infection of the parotid or salivary glands by the virus. The resulting neck swelling is easily recognized.

Mumps virus: laboratory diagnosis:

• Specimen: saliva or urine

• Direct detection through immunofluorescence

• Diagnosis most commonly made through serologic testing using EIA to measure IgG and IgM

  • 4-fold rise in titer is diagnostic

• Other serologic tests include hemagglutination inhibition and complement fixation

Mumps virus prevention:

• Immunization with MMR vaccine

Togaviridae: Rubella virus: general characteristics:

• Enveloped, ssRNA

• Causative agent of rubella or German measles

  • also called 3-day measles or epidemic roseola

• Transmission via inhalation of respiratory droplets

• In young children, rubella is mild and in most cases,

  asymptomatic

• In adults, infection is more severe

• Symptomatic infection: fever, rash on face, trunk, or limbs, red papules on the soft palate, conjunctivitis, and lymphadenopathy

Rubella: Congenital infection:

• Transmission from infected mother to fetus

• With primary infection, there is no protective antibody to cross placenta and protect fetus

• Infection during 1st trimester can result in severe developmental defects

  • cataracts, glaucoma, deafness, congenital heart disease, mental retardation, spontaneous abortion, premature birth, and fetal death

Rubella virus: Postnatal infection:

• transmission through breast milk but usually a mild disease

Rubella diagnosis:

• Specimens: saliva, nasopharyngeal secretions, and urine

• Can be cultured on African green monkey kidney cells but does not produce CPE

  • Rarely used

  • PCR or immunofluorescence to confirm presence of virus

• Serologic tests

• Passive hemagglutination

  • red cells or latex particles coated with viral antigen

• EIA for IgM or IgG antibodies

  • IgM indicates acute illness and used to diagnose congenital infection in newborn

  • IgG indicates current immune status

Rubella prevention:

• Attenuated vaccine for children around 1 year old

• Part of MMR vaccine

• Booster given again before child starts school

Arbovirus infections: general characteristics:

• Name derived from arthropod-born viruses

• Often cause severe or fatal infections

  • Humans are not native hosts and have no inherent resistance

• Insect vector is most often the female mosquito

  • Monkeys, horses, birds, reptiles, and amphibians serve as sources of infection

  • Infections most prevalent during late spring, summer, and early fall when mosquitoes and ticks are most active

• Encephalitis viruses symptoms

  • fever, nausea, headaches, stiff neck and back, photosensitivity and confusion

  • in severe cases, coma and death

• Even in nonfatal cases neurological sequelae include mental deficiencies, deafness, blindness, and paralysis

Arboviruses: Alphaviruses: general characteristics:

• Eastern equine encephalitis virus (EEE) (2019- 29 cases in US)

• Western equine encephalitis virus (WEE)

• Venezuelan equine encephalitis virus (VEE) of North, Central and South America

Arboviruses: Flaviviruses:

• St. Louis encephalitis virus (SLE)

• West Nile virus

• Originated in Africa

• Appeared in U.S. in 1999

• LI- elderly

• Yellow fever virus

• Africa and South America

• Causes degeneration of liver

• causing jaundice, so the name yellow fever, kidneys, and heart

• Dengue fever virus

• Worldwide

• Associated with internal bleeding, loss of plasma, and shock

Zika virus:

• Started in Brazil in 2015. Spread by mosquitos. Can cause mild disease also Guillain-Barre (transient paralysis)

• Virus can be passed to fetus. Causes birth defect (microcephaly)

Gastroenteritis Viruses: general characteristics:

• Noroviruses, rotaviruses, and adenoviruses (already discussed)

• Cause illnesses associated with vomiting, diarrhea or both

• Often referred to as “stomach flu”

• Spread via fecal-oral route

Noroviruses: general characteristics:

• Nonenveloped, ssRNA

• Very hardy and not inactivated by pH or heat

• Symptoms: low-grade fever, abdominal pain, vomiting, and diarrhea

• Complete recovery after 1-5 days

• Nearly 50% of all foodborne outbreaks of gastroenteritis caused by noroviruses

• Can be serious or fatal in older adults

• Can be one of the causative agents of traveler’s diarrhea

• Isolated during outbreak in Norwalk, Ohio in 1968 (Norwalk virus)

• Symptoms: “Winter vomiting bug”

• Complete recovery after 1-5 days

• Outbreaks occur in closed or semiclosed communities, such as long- term care facilities, dormitories, and cruise ships

Noroviruses; diagnosis:

• Specimen of choice is feces but vomitus acceptable

• Molecular techniques such as real-time PCR

• Electron microscopy can identify the small round virus but is not practical for most laboratories

Rotoviruses: general characteristics:

• Small, nonenveloped, dsRNA

• “Rota” is Latin word for “wheel” and describes morphology of the virus

• Double capsid seen with electron microscope resembles wheel with wide hub and short spokes radiating from hub to rim of the wheel

• Transmission via fecal-oral route

  • Transmission is often via contaminated water and foods such as oysters, clams, and raw shellfish

• Infection may be asymptomatic, mild, or severe dehydrating diarrheal illness

  • Symptoms: fever, vomiting, diarrhea, and dehydration due to water loss

• Most cases in infants 16-24 months of age

  • Most common cause of severe diarrhea

  • Leading cause of mortality

  • In developing countries, many children succumb to complications of infection

Rabies Virus: general characteristics:

• Family Rhabdoviridae; ssRNA

• Transmission via bite of infected animals

• possibly transplant surgery

• Virus shed in saliva of infected animals

  • dogs, cats, foxes, raccoons, and bats

• Rabies always fatal once symptoms appear

• Virus enters peripheral nerves and travels to central nervous

  system

  • Causes encephalitis and myelitis

• Symptoms

  • May take months to show

  • Pain at the bite site

  • Flu-like symptoms

  • CNS invasion associated with:

    • Insomnia, anxiety, confusion, hallucinations, and hydrophobia

    • Eventually host succumbs to coma and death

Rabies Virus: diagnosis & prevention:

• Biopsy of brain demonstrating presence of Negri bodies

• Seen in 70-80% of cases

• Negri bodies are eosinophilic inclusions in cytoplasm of neurons

• EIA testing to detect antibodies

• Rapid fluorescent-focus inhibition test (RFFIT) for antibodies

• Flow cytometry could be used to detect rabies virus antigen in infected cells

• Prevention: vaccination in humans and animals

Rabies treatment:

• Virus must travel from bite site to brain and spinal cord to cause serious damage but is extremely slow

• Postexposure treatment consists of vigorous cleansing of wound site

• Administration of vaccine and immunoglobulin is extremely effective in providing protection from lethal effects

• Negri bodies, as seen in the neural cell in the center, is characterisitc for rabies

Emerging Viruses: Hantavirus: general characteristics:

• RNA virus in the family Bunyaviridae

• Produces 2 distinct diseases

• Hemorrhagic fever with renal syndrome (HFRS)

• Hanta virus pulmonary syndrome (HPS)

  • Pulmonary syndrome fills the lungs with fluid so patient literally drowns

• Transmission: aerosolized urine and feces of rodents

• Appeared in 1993 in four corners area of the U.S. (Arizona, Colorado, Utah, and New Mexico)

• Has the potential a bioterrorism agent

• Humans may become infected when they inhale airborne virus or come into direct contact with infected rodents or their urine, feces, or pests

Emerging viruses: Rift valley fever virus: general characteristics:

• Family Bunyaviridae

• Primarily found in cattle in Africa

• Transmission via mosquitoes or contact with animals

• Causes ocular infections, meningoencephalitis, or hemorrhagic fever

• Primarily found in cattle