Hepatitis A

| MeshID = D006506

Hepatitis A, (formerly known as "infectious hepatitis"), is an acute infectious disease of the liver caused by Hepatitis A virus,cite book | author = Ryan KJ, Ray CG (editors) | title = Sherris Medical Microbiology | edition = 4th ed. | pages = 541–4 | publisher = McGraw Hill | year = 2004 | isbn = 0838585299 ] which is most commonly transmitted by the fecal-oral route via contaminated food or drinking water. Every year, approximately 10 million people worldwide are infected with the virus.cite journal
author=Thiel TK
title=Hepatitis A vaccination
journal=Am Fam Physician
volume=57
issue=7
pages=1500
year=1998
pmid=9556642
] The time between infection and the appearance of the symptoms, (the incubation period), is between two and six weeks and the average incubation period is 28 days.cite journal
author=Connor BA
title=Hepatitis A vaccine in the last-minute traveler
journal=Am. J. Med.
volume=118 Suppl 10A
issue=
pages=58S–62S
year=2005
pmid=16271543
doi=10.1016/j.amjmed.2005.07.018
url=http://linkinghub.elsevier.com/retrieve/pii/S0002-9343(05)00611-X
]

In developing countries, and in regions with poor hygiene standards, the incidence of infection with this virus approaches 100% and the illness is usually contracted in early childhood. Hepatitis A infection causes no clinical signs and symptoms in over 90% of these children and since the infection confers lifelong immunity, the disease is of no special significance to the indigenous population. In Europe, the United States and other industrialized countries, on the other hand, the infection is contracted primarily by susceptible young adults, most of whom are infected with the virus during trips to countries with a high incidence of the disease.cite journal
author=Connor BA
title=Hepatitis A vaccine in the last-minute traveler
journal=Am. J. Med.
volume=118 Suppl 10A
issue=
pages=58S–62S
year=2005
pmid=16271543
doi=10.1016/j.amjmed.2005.07.018
url=http://linkinghub.elsevier.com/retrieve/pii/S0002-9343(05)00611-X
]

Hepatitis A does not have a chronic stage and does not cause permanent liver damage. Following infection, the immune system makes antibodies against the hepatitis A virus that confer immunity against future infection. The disease can be prevented by vaccination and hepatitis A vaccine has been proved effective in controlling outbreaks worldwide.cite journal
author=Connor BA
title=Hepatitis A vaccine in the last-minute traveler
journal=Am. J. Med.
volume=118 Suppl 10A
issue=
pages=58S–62S
year=2005
pmid=16271543
doi=10.1016/j.amjmed.2005.07.018
url=http://linkinghub.elsevier.com/retrieve/pii/S0002-9343(05)00611-X
]

Virus

The Hepatitis virus (HAV) is a Picornavirus; it is non-enveloped and contains a single-stranded RNA packaged in a protein shell. There is only one type of the virus.

Pathogenesis

Following ingestion, HAV enters the bloodstream through the epithelium of the oropharynx or intestine. [Murray, P. r., Rosenthal, K. S., & Pfaller, M. A. (2005). "Medical Microbiology," 5th ed., Elsevier Mosby.] The blood carries the virus to its target, the liver, where it lives and multiplies within hepatocytes and Kupffer cells (i.e., liver macrophages). There is no apparent virus-mediated cytotoxicity, and liver pathology is likely immune-mediated. Virions are secreted into the bile and released in stool. HAV is excreted in large quantities approimately 11 days prior to appearance of symptoms or anti-HAV IgM antibodies in the blood. The incubation period is 15-50 days, and mortality is less than 0.5%.

Transmission

The virus spreads by the fecal-oral route and infections often occur in conditions of poor sanitation and overcrowding. Hepatitis A can be transmitted by the parenteral route but very rarely by blood and blood products. Food-borne outbreaks are not uncommon,cite journal
author=Brundage SC, Fitzpatrick AN
title=Hepatitis A
journal=Am Fam Physician
volume=73
issue=12
pages=2162–8
year=2006
pmid=16848078
] and ingestion of shellfish cultivated in polluted water is associated with a high risk of infection.cite journal
author=Lees D
title=Viruses and bivalve shellfish
journal=Int. J. Food Microbiol.
volume=59
issue=1-2
pages=81–116
year=2000
pmid=10946842
url=http://linkinghub.elsevier.com/retrieve/pii/S0168-1605(00)00248-8

doi=10.1016/S0168-1605(00)00248-8] Approximately 40% of all acute viral hepatitis is caused by HAV. [Insert footnote text Murray, P. r., Rosenthal, K. S., & Pfaller, M. A. (2005). "Medical Microbiology," 5th ed., Elsevier Mosby.] Infected individuals are infectious prior to onset of symptoms, roughly 10 days following infection. The virus is resistant to detergent, acid (pH 1), solvents (e.g., ether, chloroform), drying, and temperatures up to 60oC. It can survive for months in fresh and salt water. Common-source (e.g., water, restaurant) outbreaks are typical. Infection is common in children in developing countries, reaching 100% incidence, but following infection there is life-long immunity. HAV can be inactivated by: chlorine treatment (drinking water), formalin (0.35%, 37oC, 72 hours), peracetic acid (2%, 4 hours), beta-propiolactone (0.25%, 1 hour), and UV radiation (2 μW/cm2/min).

ymptoms

Early symptoms of hepatitis A infection can be mistaken for influenza, but some sufferers, especially children, exhibit no symptoms at all. Symptoms typically appear 2 to 6 weeks, (the incubation period ), after the initial infection. [cite web | title = Hepatitis A Symptoms | publisher = eMedicineHealth | url = http://www.emedicinehealth.com/hepatitis_a/page3_em.htm#Hepatitis%20A%20Symptoms | date = 2007-05-17 | accessdate = 2007-05-18]

Symptoms can return over the following 6-9 months which include: [cite web | title = Hepatitis A : Fact Sheet | publisher = Center for Disease Control | url = http://www.cdc.gov/Ncidod/diseases/hepatitis/a/fact.htm | date = 2007-08-09 | accessdate = 2007-12-07]


*Fatigue
*Fever
*Abdominal pain
*Nausea
*Diarrhea
*Appetite loss
*Depression
*Jaundice, a yellowing of the skin or whites of the eyes
*Sharp pains in the right-upper quadrant of the abdomen
*Weight loss
*Itching

Diagnosis

Although the virus is excreted in the feces towards the end of the incubation period, specific diagnosis is made by the detection of Hepatitis A virus specific IgM antibodies in the blood.cite journal
author=Stapleton JT
title=Host immune response to hepatitis A virus
journal=J. Infect. Dis.
volume=171 Suppl 1
issue=
pages=S9–14
year=1995
pmid=7876654
] IgM antibody is only present in the blood following an acute hepatitis A infection. It is detectable from one to two weeks after the initial infection and persists for up to 14 weeks. The presence of IgG antibody in the blood means that the acute stage of the illness is past and the person is immune to further infection. IgG antibody to HAV is also found in the blood following vaccination and tests for immunity to the virus are based on the detection of this antibody.cite journal
author=Stapleton JT
title=Host immune response to hepatitis A virus
journal=J. Infect. Dis.
volume=171 Suppl 1
issue=
pages=S9–14
year=1995
pmid=7876654
]

During the acute stage of the infection, the liver enzyme alanine transferase (ALT) is present in the blood at levels much higher than is normal. The enzyme comes from the liver cells that have been damaged by the virus.cite journal
author=Musana KA, Yale SH, Abdulkarim AS
title=Tests of liver injury
journal=Clin Med Res
volume=2
issue=2
pages=129–31
year=2004
pmid=15931347
url=http://www.clinmedres.org/cgi/pmidlookup?view=long&pmid=15931347
]

Hepatitis A virus is present in the blood, (viremia), and feces of infected people up to two weeks before clinical illness develops.pmid15931347]

Treatment

There is no specific treatment for hepatitis A. Sufferers are advised to rest, avoid fatty foods and alcohol (these may be poorly tolerated for some additional months during the recovery phase and cause minor relapses), eat a well-balanced diet, and stay hydrated. Approximately 15% of people diagnosed with hepatitis A may experience one or more symptomatic relapse(s) for up to 24 months after contracting this disease.Fact|date=February 2008

Prognosis

The United States Centers for Disease Control and Prevention (CDC) in 1991 reported a low mortality rate for hepatitis A of 4 deaths per 1000 cases for the general population but a higher rate of 17.5 per 1000, in those aged 50 and over. Death usually occurs when the patient contracts Hepatitis A while already suffering from another form of Hepatitis, such as Hepatitis B or Hepatitis C or AIDS.Fact|date=February 2008

Young children who are infected with hepatitis A typically have a milder form of the disease, usually lasting from 1-3 weeks, whereas adults tend to experience a much more severe form of the disease.Fact|date=February 2008

Prevention

Hepatitis A can be prevented by vaccination, good hygiene and sanitation.Fact|date=February 2008

Vaccine

Hepatitis A vaccines protect against the virus. Vaccines contain inactivated Hepatitis A virus providing active immunity against a future infection.cite web | title = Avaxim | work = NetDoctor.co.uk | url = http://www.netdoctor.co.uk/medicines/100003051.html | accessdate = 2007-03-12]

Epidemiology

HAV is found in the feces of infected persons and those who are at higher risk include travelers to developing countries where there is a higher incidence rate, [ [http://wwwn.cdc.gov/travel/yellowBookCh4-HepA.aspx#362 Chapter 4 - Hepatitis, Viral, Type A - Yellow Book | CDC Travelers' Health ] ] and those having sexual contact or drug use with infected persons. [ [http://www.cdc.gov/Ncidod/diseases/hepatitis/a/fact.htm Hepatitis A: Fact Sheet | CDC Viral Hepatitis ] ] There were 30,000 cases of Hepatitis A reported to the CDC in the U.S. in 1997. The agency estimates that there were as many as 270,000 cases each year from 1980 through 2000. [ [http://www.cdc.gov/Ncidod/diseases/hepatitis/a/global_hepA_epi.pdf Index | CDC Viral Hepatitis ] ]

HAV outbreaks still occur in and caused by poor hand hygiene among infected, sometimes symptomatic restaurant employees failing to wash their hands after toilet breaks.

Epidemics

The most widespread hepatitis A outbreak in the United States afflicted at least 640 people (killing four) in north-eastern Ohio and south-western Pennsylvania in late 2003. The outbreak was blamed on tainted green onions at a restaurant in Monaca, Pennsylvania. [ [http://www.cdc.gov/mmwR/preview/mmwrhtml/mm5247a5.htm Hepatitis A Outbreak Associated with Green Onions at a Restaurant - Monaca, Pennsylvania, 2003 ] ] In 1988, 300,000 people in Shanghai, China were infected with HAV after eating clams from a contaminated river. [ Murray, P. r., Rosenthal, K. S., & Pfaller, M. A. (2005). "Medical Microbiology," 5th ed., Elsevier Mosby. ]

ee also

* Hepatitis
* Hepatitis B
* Hepatitis B in China
* Hepatitis C
* Hepatitis D
* Hepatitis E
* Hepatitis F
* Hepatitis G
*Maurice Hilleman

References

External links

* [http://www3.niaid.nih.gov/ NIAID] Bioinformatics Resource Center)
* [http://www.cdc.gov/ncidod/diseases/hepatitis/a/index.htm CDC's hepatitis A links]
* [http://www.cdc.gov/ncidod/diseases/hepatitis/a/fact.htm CDC's hepatitis A Fact Sheet]
*
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