Microbiology-Viral Lower GI Infections

Question 1

What is the most common cause of acute gastroenteritis worldwide?

Answer 1

Viral

Question 2

What viruses are responsible for 95% of gastroenteritis cases?

Answer 2

Rotaviruses “infantile diarrhea”, norovirus and adenovirus “daycare diarrhea” (40 and 41) = 95% of cases. Astroviruses and coronaviruses are also common causes.

Question 3

What type of viruses are typically found in the GI tract?

Answer 3

Non-enveloped. Typically, viruses acquire their envelope from budding off of a cell. Once viruses get to the stomach, enveloped viruses are inactivated from acid and further inactivated by bile. This leaves only non-enveloped (naked capsids) to infect.

Question 4

How high of an infectious dose do you need for infection of a non-enveloped virus to cause gastrenteritis?

Answer 4

Very small, theres are highly contagious and can survive long periods of time as fomites.

Question 5

How are non-enveloped enteric viruses typically spread?

Answer 5

Fecal-oral route in places where people are in close proximity with one another (day care, cruises, schools).

Question 6

How do you clean an area that is a suspected reservoir of enteric viruses?

Answer 6

Bleach or 95% ethanol.

Question 7

What enteric viral infection are kids under 2 years old at high risk for? When are they at most risk?

Answer 7

Rotavirus, adult infections by rotavirus are rare. Peak transmission is in January, “winter diarrhea”, in the US due to being in closed quarters.

Question 8

What causes associated death in children infected with rotavirus?

Answer 8

Dehydration

Question 9

Shape, genome, site of replication and # of subtypes of rotavirus.

Answer 9

Shape: double shelled capsid. Genome: dsRNA, highly segmented. Site of replication: cytoplasmic. 4 major subtypes.

Question 10

What protein made by rotavirus is most important in its virulence?

Answer 10

VP4. After cleavage, t is responsible for binding of the virus to the surface of the enterocytes.

Question 11

Why is it so difficult to develop a vaccine for rotavirus?

Answer 11

Antigenic drift and antigenic shift due to segmentation of its genome. Immunity must be serotype specific in order to defend the body from this pathogen.

Question 12

How does rotavirus cause acute gastroenteritis?

Answer 12

VP4 is cleaved, the virus binds to surface epithelial cells. Virus replication occurs in the cytoplasm w/ its own viral polymerase. The virus assembles and is released. While they are replicating, they produce NFP4, which alters Na and glucose absorption, causing osmotic diarrhea. As enterocytes die, villi are lost, and kids will experience malabsorption.

Question 13

A mother brings in her 2 year old daughter complaining of vomiting, watery diarrhea, severe dehydration and loss of appetite. How do you diagnose this child if you suspect rotavirus? How do you treat?

Answer 13

Virus isolation from stool sample, ELISA or Rote test run a quick antigen-antibody assay, but do not distinguish the serotype. You must do PCR to figure out the serotype. Treatment is hydration and electrolyte replacement therapy.

Question 14

What is a laboratory clue in the fecal sample obtained in a child with suspected rotavirus.

Answer 14

Absence of fecal leukocytes

Question 15

What type of vaccine are Rotarix and Rotateq?

Answer 15

Rotarix = live attenuated human strain. Rotateq = live attenuated and reassorted human/bovine strain.

Question 16

What is the main calicivirus? Why is this so prominent?

Answer 16

Norovirus. 90% of cases of gastroenteritis are norovirus infections because it is very infectious even in small amounts.

Question 17

You are on a cruise. You love the seafood bar, but come down with vomiting, sudden abdominal crampy and loose watery diarrhea two days into your trip. Fecal leukocytes are absent when you get a stool culture. If norovirus is the culprit for ruining your trip, how did you get it?

Answer 17

Fecal-oral spread from food handlers or unwashed food. Note that fecal leukocytes are absent like they are in rotavirus also.

Question 18

Genome, replication site and virulence of norovirus.

Answer 18

Genome: +ssRNA. Replication: cytoplasmic. Virulence: heat & chlorine resistant.

Question 19

Why are there no good attempts at developing a vaccine for norovirus?

Answer 19

It cannot be grown in culture for study. The only way we know it is there is through PCR.

Question 20

How does norovirus cause disease?

Answer 20

It gets into the GI tract and causes broadening and blunting of small intestine villi. CD8 T cells and PMNs infiltrate.

Question 21

Why are people great sources for norovirus transmission?

Answer 21

Although symptoms resolve in about 3 days, you can shed the virus for weeks.

Question 22

You are on a cruise. You love the seafood bar, but come down with vomiting, sudden abdominal crampy and loose watery diarrhea two days into your trip. Fecal leukocytes are absent when you get a stool culture. If norovirus is the culprit for ruining your trip, how will you be treated?

Answer 22

Oral fluid and electrolyte replacement therapy. Also, make sure that contaminated areas are decontaminated.

Question 23

A mother brings in her 7 year old son. He has had acute onset diarrhea that has lasted about 1-2 weeks. Physical exam reveals swollen lymph nodes. He attends day care when school gets out. Why is this not rotavirus?

Answer 23

Rotavirus lasts 1-3 days. Adenovirus lasts 1-2 weeks and can become systemic, contacting mesenteric lymph nodes.

Question 24

What is the shape, genome and replication site of adenovirus?

Answer 24

Shape: Isocahedral capsid. Genome: ds linear DNA. Replication site: nucleus.

Question 25

How do you get infected with enteric adenovirus?

Answer 25

Protruding fibers bind the CAR (coxsackievirus and adenovirus receptor) -> infects mucoepithelial cells -> replicates in nucleus w/ its own DNA polymerase

Question 26

What is your differential in patients with gastroenteritis and no fecal leukocytes?

Answer 26

Rotavirus, norovirus, adenovirus, cholera, EHEC, ETEC, EPEC and Giardia.

Question 27

Characterize each category for rotavirus, norovirus and adenovirus.

Answer 27

*