Astrovirus

Jump to: navigation, search

An astrovirus is a type of virus that infects humans. They have been poorly studied due to the fact that they do not grow in culture. Astroviruses belong to the family Astroviridae along with a virus known as mamastrovirus. They were first described in the year 1975 using electron microscopes during an outbreak of diarrhoea. Astrovirus has a non-segmented, single stranded, positive sense RNA genome within a non-enveloped icosahedral capsid.

Effects

Members of a relatively new virus family, the astroviridae, astroviruses are now recognised as a major cause of gastroenteritis in children and adults. They are non-enveloped viruses displaying cubic symmetry, approximately 28-30nm in diameter. The genome consists of a positive sense single strand of RNA encoding a varying array of structural proteins.

A study of intestinal disease in the UK, published in 1999 determined incidence as 3.8/1000 patient years in the community (95%CI, range2.3-6.4), the fourth most common known cause of viral gastroenteritis. Studies in the USA have detected astroviruses in the stools of 2-9% of children presenting symptoms; illness is most frequent in children of less than two years, although outbreaks among adults and the elderly have been reported. Early studies carried out in Glasgow demonstrated that a significant proportion of babies excreting virus particles, 12%, did not exhibit gastrointestinal symptoms, and seroprevalence studies carried out in the US have shown that 90% of children have antibody to HastV-1 by age 9, suggesting that (largely asymptomatic) infection is common. There is, as with most viral causes of gastroenteritis, a peak of incidence in the winter.

Symptoms include diarrhoea, headache, malaise and nausea, vomiting being a less common complaint, and are usually milder than those experienced with rotavirus infection, and as a result dehydration is less severe. Incubation takes 3-4 days, and symptoms persist for less than 5 days in uncomplicated cases.

Diagnosis is achieved using electron microscopy; immune amplification is not necessarily required due to large numbers of virus particles in the stools. ELISAs, immunofluorescence, and nucleic acid based techniques have all been used.

Treatment may not be required, rehydration using oral rehydration therapy helps maintain electrolyte balance. There is potential for development of vaccination as it appears infection proffers some short-term protection against viruses of the same serotype.

Differential diagnosis

Astrovirus infection must be differentiated from other causes of viral, bacterial, and parasitic gastroentritis.

Organism Age predilection Travel History Incubation Size (cell) Incubation Time History and Symptoms Diarrhea type8 Food source Specific consideration
Fever N/V Cramping Abd Pain Small Bowel Large Bowel Inflammatory Non-inflammatory
Viral Rotavirus <2 y - <102 <48 h + + - + + - Mostly in day cares, most common in winter.
Norovirus Any age - 10 -103 24-48 h + + + + + - Most common cause of gastroenteritis, abdominal tenderness,
Adenovirus <2 y - 105 -106 8-10 d + + + + + - No seasonality
Astrovirus <5 y - 72-96 h + + + + + Seafood Mostly during winter
Bacterial Escherichia coli ETEC Any age + 108 -1010 24 h - + + + + - Causes travelers diarrhea, contains heat-labile toxins (LT) and heat-stable toxins (ST)
EPEC <1 y - 10 6-12 h - + + + + Raw beef and chicken -
EIEC Any ages - 10 24 h + + + + + Hamburger meat and unpasteurized milk Similar to shigellosis, can cause bloody diarrhea
EHEC Any ages - 10 3-4 d - + + + + Undercooked or raw hamburger (ground beef)  Known as E. coli O157:H7, can cause HUS/TTP.
EAEC Any ages + 1010 8-18 h - - + + + - May cause prolonged or persistent diarrhea in children
Salmonella sp. Any ages + 1 6 to 72 h + + + + + Meats, poultry, eggs, milk and dairy products, fish, shrimp, spices, yeast, coconut, sauces, freshly prepared salad. Can cause salmonellosis or typhoid fever.
Shigella sp. Any ages - 10 - 200 8-48 h + + + + + Raw foods, for example, lettuce, salads (potato, tuna, shrimp, macaroni, and chicken) Some strains produce enterotoxin and Shiga toxin similar to those produced by E. coli O157:H7
Campylobacter sp. <5 y, 15-29 y - 104 2-5 d + + + + + Undercooked poultry products, unpasteurized milk and cheeses made from unpasteurized milk, vegetables, seafood and contaminated water. May cause bacteremia, Guillain-Barré syndrome (GBS), hemolytic uremic syndrome (HUS) and recurrent colitis
Yersinia enterocolitica <10 y - 104 -106 1-11 d + + + + + Meats (pork, beef, lamb, etc.), oysters, fish, crabs, and raw milk. May cause reactive arthritis; glomerulonephritis; endocarditis; erythema nodosum.

can mimic appendicitis and mesenteric lymphadenitis.

Clostridium perfringens Any ages > 106 16 h - - + + + Meats (especially beef and poultry), meat-containing products (e.g., gravies and stews), and Mexican foods. Can survive high heat,
Vibrio cholerae Any ages - 106-1010 24-48 h - + + + + Seafoods, including molluscan shellfish (oysters, mussels, and clams), crab, lobster, shrimp, squid, and finfish. Hypotension, tachycardia, decreased skin turgor. Rice-water stools
Parasites Protozoa Giardia lamblia 2-5 y + 1 cyst 1-2 we - - + + + Contaminated water May cause malabsorption syndrome and severe weight loss
Entamoeba histolytica 4-11 y + <10 cysts 2-4 we - + + + + Contaminated water and raw foods May cause intestinal amebiasis and amebic liver abscess
Cryptosporidium parvum Any ages - 10-100 oocysts 7-10 d + + + + + Juices and milk May cause copious diarrhea and dehydration in patients with AIDS especially with 180 > CD4
Cyclospora cayetanensis Any ages + 10-100 oocysts 7-10 d - + + + + Fresh produce, such as raspberries, basil, and several varieties of lettuce. More common in rainy areas
Helminths Trichinella spp Any ages - Two viable larvae (male and female) 1-4 we - + + + + Undercooked meats More common in hunters or people who eat traditionally uncooked meats
Taenia spp Any ages - 1 larva or egg 2-4 m - + + + + Undercooked beef and pork Neurocysticercosis: Cysts located in the brain may be asymptomatic or seizures, increased intracranial pressure, headache.
Diphyllobothrium latum Any ages - 1 larva 15 d - - - + + Raw or undercooked fish. May cause vitamin B12 deficiency



8Small bowel diarrhea: watery, voluminous with less than 5 WBC/high power field

Large bowel diarrhea: Mucousy and/or bloody with less volume and more than 10 WBC/high power field
† It could be as high as 1000 based on patient's immunity system.

The table below summarizes the findings that differentiate inflammatory causes of chronic diarrhea[1][2][3][4][4]

Cause History Laboratory findings Diagnosis Treatment
Diverticulitis Abdominal CT scan with oral and intravenous (IV) contrast bowel rest, IV fluid resuscitation, and broad-spectrum antimicrobial therapy which covers anaerobic bacteria and gram-negative rods
Ulcerative colitis Endoscopy Induction of remission with mesalamine and corticosteroids followed by the administration of sulfasalazine and 6-Mercaptopurine depending on the severity of the disease.
Entamoeba histolytica cysts shed with the stool detects ameba DNA in feces Amebic dysentery

Luminal amebicides for E. histolytica in the colon:

For amebic liver abscess:

References

Caul, E. O. 1996. Viral gastroenteritis: small round structured viruses, caliciviruses and astroviruses. Part II. The epidemiological perspective. J. Clin. Pathol. 49:959-964

Caul, E. O. 1996. Viral gastroenteritis: small round structured viruses, caliciviruses and astroviruses. Part I. The clinical and diagnostic perspective. J. Clin. Pathol. 49:874-880

Treanor, J. J., R. Dolin. 2005. Astroviruses and picobirnaviruses. 2201-2203, in: Mandell, Douglas and Bennett’s Principles and practice of infectious diseases (6th Ed.). Mandell G. L., Bennett J. E., Dolin R. (Editors). Elsevier Churchill Livingstone.

Viral Gastroenteritis. 67-72, in: Notes on Medical Virology (11th Ed.) M. C. Timbury. 1997. Churchilll Livingstone.

Kapikan A. Z., R. M. Chanock. 1989. Viral Gastroenteritis. 293-340, in: Viral infections of humans (3rd Ed.) Evans A. S. (Ed.) Plenum Medical Book company

Wheeler J. G., D. Sethi, J. M. Cowden, P. G. Wall, L. C. Rodrigues, D. S. Tompkins, M. J. Hudson, P. J. Roederick. 1999. Study of infectious intestinal disease in England: rates in the community, presenting to general practice, and reported to national surveillance. Br. Med. J. 318:1046-1050

  1. Konvolinka CW (1994). "Acute diverticulitis under age forty". Am J Surg. 167 (6): 562–5. PMID 8209928.
  2. Silverberg MS, Satsangi J, Ahmad T, Arnott ID, Bernstein CN, Brant SR; et al. (2005). "Toward an integrated clinical, molecular and serological classification of inflammatory bowel disease: report of a Working Party of the 2005 Montreal World Congress of Gastroenterology". Can J Gastroenterol. 19 Suppl A: 5A–36A. PMID 16151544.
  3. Satsangi J, Silverberg MS, Vermeire S, Colombel JF (2006). "The Montreal classification of inflammatory bowel disease: controversies, consensus, and implications". Gut. 55 (6): 749–53. doi:10.1136/gut.2005.082909. PMC 1856208. PMID 16698746.
  4. 4.0 4.1 Haque R, Huston CD, Hughes M, Houpt E, Petri WA (2003). "Amebiasis". N Engl J Med. 348 (16): 1565–73. doi:10.1056/NEJMra022710. PMID 12700377.

Linked-in.jpg