(-)Strand RNA Viruses

Question 1

all (-)strand RNA viruses are [nonenveloped/enveloped]

Answer 1

all (-)strand RNA viruses are enveloped (from host membranes) with glycoprotein spikes

Question 2

what is the function of the M1 and M2 proteins of influenza (-)ssRNA viruses?

Answer 2

M1: interacts with glycoproteins
M2: forms ion channel, which lowers pH to allow for viral uncoating

Question 3

what must (-)ssRNA viruses carry with them in order to replicate?

Answer 3

must carry RNA-dependent RNA polymerase in the virion, which can create mRNA transcripts from (-)RNA genome

[in contrast to +ssRNA viruses which do not contain any enzymes, use host instead]

Question 4

what is the shape of influenza (-)ssRNA viral nucleocapsids?

Answer 4

helical !

Question 5

contrast the function of hemagglutinin and neuraminidase of influenza (-)ssRNA viruses and the effectiveness of antibodies against each of them, respectively

Answer 5

HA (hemagglutinin): binds sialic acid on human cells for receptor-mediated endocytosis - antibodies against HA are neutralizing

NA (neuraminidase): cleaves sialic acid so that newly formed viruses exiting the cell do not reattach - antibodies against NA stop spread but do not eliminate infection

Question 6

how is viral protein production regulated in +strand vs -strand RNA viruses?

Answer 6

(+)ssRNA viruses regulate protein at translational level (transcribe long polypeptides which are cleaved into multiple proteins)

(-)ssRNA viruses regulate protein at transcriptional level (segmented transcripts, each will be made into a separate protein)

Question 7

what is different about viral transcription in Influenza Virus as compared to other RNA viruses?

Answer 7

Influenza (-ssRNA virus) replicates viral genome in the nucleus, while most RNA viruses replicate in the cytoplasm

*note that envelope comes from plasma membrane upon exit from cell though

(DNA viruses replicate in the nucleus)

Question 8

what 2 viral infections is Reye’s Syndrome linked to?

Answer 8

Varicella (chickenpox) and Influenza

accumulation of fat in liver, brain swelling and acute brain damage

occurs in children, highly fatal, cause unknown

*Tylenol now given to children instead of aspirin (and other drugs containing salicylic acid)

Question 9

what class of antibody is most effective against Influenza (-ssRNA virus)?

Answer 9

IgA in nasal secretions

also high IgG in serum, but not as protective

*recall that anti-HA (hemagglutinin) Abs are neutralizing, while anti-N (neuraminidase) Abs only stop the spread

Question 10

which human influenza strain (-ssRNA virus) is associated with endemics?

Answer 10

Influenza A, which is then subdivided by HA and N subtypes

(there is also Influenza B and C)

Question 11

antigenic drift vs shift

Answer 11

antigenic drift: point mutations in virus cause annual epidemics

antigenic shift: recombination of different HA and N cause creation of a new subtype of virus, cause pandemics - Influenza A only
(when 2 Influenza A viruses from different animals co-infect one cell and genetic exchange occurs)

*note that segmented transcripts of influenza allow for genetic recombination that facilitates antigenic shift

Question 12

what kind of Influenza (-ssRNA virus) has potential to cause serious illness in humans and pandemics (because it easily mutates), but rarely spreads human-human?

Answer 12

Asian Avian Influenza: rare human-human spread, but can cause serious illness (respiratory, death)

Question 13

Paramyxoviridae are (-)ssRNA viruses which include Parainfluenza, Mumps, Measles, RSV, Nipah, and Hendra. How do Paramyxoviridae affect infected cell morphology?

Answer 13

Paramyxoviridae cause syncytia (cell fusion), via glycoprotein spikes on their envelope —> multi-nucleated giant cells with inclusion bodies

Question 14

Which Paramyxoviridae infects the lower respiratory tract of infants and children and presents with a croup, or “barking cough”?

Answer 14

Parainfluenza (1-4): (-)ssRNA virus, infects infants and children, causes lower respiratory tract infection with croup

Question 15

where does Mumps (Paramyxoviridae, -ssRNA virus) infection originate, and how does it progress?

Answer 15

via respiratory secretions, replicates in parotid gland, causes primary infection in upper respiratory tract

can spread to any organ - CNS, gonads, deafness (sequelae), fetal complications

infection confers immunity for life, prevent with MMR live attenuated vaccine

Question 16

which Paramyxoviridae (-ssRNA) does this describe?
- one of the most infectious childhood diseases
- viable for hours in respiratory droplets on fomites
- major cause of mortality of children in developing countries
- causes formation of multinucleated giant cells
- presents with Kolik’s spots

Answer 16

Measles: extremely infectious childhood disease (winter/spring epidemics), causes multinucleated giant cells

primary infection in respiratory tract, then dissemination in blood —> Koplik’s spots, maculopapular rash (spreads down body)

complications: punctuate keratitis, Subacute Sclerosing Panencephalitis, Giant Cell Pneumonia

Question 17

what are the key clinical findings of Measles infection? (Paramyxoviridae, -ssRNA)

Answer 17

Measles: one of the most infectious childhood diseases

multinucleated giant cells, Koplik’s spots, maculopapular rash

Question 18

Pt is a 3yo F presenting with a respiratory tract infection her mother said has been spreading throughout the kindergarten class during February. PE is significant for Koplik spots and a full-body rash the mother states began on the upper torso.

What is going on?

Answer 18

Measles (Paramyxoviridae, -ssRNA): one of the most infectious childhood diseases, viable for hours in respiratory droplets on fomites (spreads easily), causes winter and spring epidemics

major cause of child mortality in developing countries, MMR vaccine in USA

Question 19

Which Paramyxoviridae (-ssRNA) has the potential for serious complications including Punctuate Keratitis, Subacute Sclerosing Panencephalitis, and Giant Cell Pneumonia?

Answer 19

Measles: one of the most infectious childhood diseases, viable for hours in respiratory droplets on fomites (spreads easily), causes winter and spring epidemics, Koplik spots

Punctuate Keratitis: inflammation of cornea, synergistic with Vit A deficiency (problem in developing countries were vaccination against Measles is not common)

Subacute Sclerosing Panencephalitis: degenerative CNS disease, hits about 10 years later

Question 20

what is the single most important cause of viral lower respiratory tract disease in infants and children?

Answer 20

Respiratory Syncytial Virus: Paramyxoviridae (-ssRNA), greater exposure = greater immunity

hand washing! for prevention

Question 21

what shape is Rhabdoviridae (Rabies) under a microscope, and what would indicate that a cell has been infected with Rabies?

Answer 21

Rhabdoviridae: bullet shaped, helical nucleocapsid

infected cells contain Negri bodies (inclusion bodies - site of viral replication)

Question 22

what are the clinical phases of rabies infection? (3)

Answer 22

Prodromal (nonspecific)

Acute neurological (neuro dysfunction)

Coma (death due to respiratory arrest)

Question 23

T/F: Rabies inactivated vaccine can be effectively given after a person is bitten

Answer 23

TRUE: Rabies is a slow developing disease, so the vaccine can be given after being bitten and an immune response can develop in time

multiple doses (4) needed for Rabies vaccine

Question 24

During rounds, you encounter a farmer from the midwest presenting with hemorrhagic fever. It has been determined to be of -ssRNA viral origin. The patient says there are many field mice on the farm, but there is a lack of rodent control.

What is the causative agent?

Answer 24

Arenaviridae: -ssRNA, rodent host that enter homes in winter or on farms

causes either CNS disease or hemorrhagic fever:
- Lymphocytic Choriomeningitis
- Lassa fever
- Hemorrhagic fever

*rodent control is only reliable way to prevent

you catch Arenavirus from entering an ARENA full of mice

Question 25

what -ssRNA virus family does this describe?
- mostly arthropod borne with rodent hosts
- can cause meningitis (La Crosse virus), hemorrhagic fevers, cardiac/pulmonary disease (Sin Nombre Virus), Heartland Virus (via Lone Star tick)

Answer 25

Bunyaviridae: -ssRNA viruses, wide range of diseases

Bunyaviridae give ya a BUNYA different diseases

Question 26

which -ssRNA virus is pleomorphic and has just one molecule of RNA?

Answer 26

Filoviridae - Embola/Marburg viruses

cause severe hemorrhagic fevers, death from shock

Question 27

what kind of virus is Rotavirus? (features of the virus)

Answer 27

Rotavirus: dsRNA genome, no envelope, 2 icosahedral capsids made of protein spikes (Ab against these are neutralizing)

Question 28

what is the purpose of the 2 icosahedral capsids of Rotavirus?

Answer 28

Rotavirus: dsRNA virus, no envelope (exits via cell lysis)

dsRNA must remain in capsid because it is a red flag to immune system - outer capsid degrades upon endocytosis but inner capsid hides dsRNA

mRNA leaves inner capsid via small pores

Question 29

what kind of disease is Rotavirus significant for?

Answer 29

Rotavirus: dsRNA virus, most common diarrheal pathogen in infants/children worldwide

transmitted via fecal-oral, respiratory secretions, fomites

natural immunity increases with exposure (age)

*vaccines are live attenuated