Editing Hepatitis (section)

=== Viral hepatitis ===

==== Hepatitis A ====
Hepatitis A is found throughout the world and manifests as large [[outbreak]]s and [[epidemic]]s associated with fecal contamination of water and food sources.<ref name="Carroll chapter 35">{{Cite book|title=Medical Microbiology|last=Carroll|first=Karen|publisher=McGraw-Hill|year=2015|isbn=978-0071824989|location=New York|chapter=Chapter 35: Hepatitis Viruses}}</ref> Hepatitis A viral infection is predominant in children ages 5–14 with rare infection of infants.<ref name="Carroll chapter 35" /> Infected children have little to no apparent clinical illness, in contrast to adults in whom greater than 80% are symptomatic if infected.<ref>{{Cite web|url=https://www.cdc.gov/hepatitis/hav/|title=Hepatitis A Information {{!}} Division of Viral Hepatitis {{!}} CDC|website=www.cdc.gov|access-date=2016-03-08|url-status=live|archive-url=https://web.archive.org/web/20160304081005/http://www.cdc.gov/hepatitis/hav/|archive-date=2016-03-04}}</ref> Infection rates are highest in low resource countries with inadequate public sanitation and large concentrated populations.<ref name="Harrison's Principles, chapter 360 (Acute Viral)" /><ref name="Aggarwal 488–496">{{Cite journal|last1=Aggarwal|first1=Rakesh|last2=Goel|first2=Amit|title=Hepatitis A|journal=Current Opinion in Infectious Diseases|volume=28|issue=5|pages=488–496|doi=10.1097/qco.0000000000000188|pmid=26203853|year=2015|s2cid=22340290}}</ref>  In such regions, as much as 90% of children younger than 10 years old have been infected and are immune, corresponding both to lower rates of clinically symptomatic disease and outbreaks.<ref name="Carroll chapter 35" /><ref name="Aggarwal 488–496"/><ref>{{Cite web|url=https://www.who.int/mediacentre/factsheets/fs328/en/|title=WHO {{!}} Hepatitis A|website=www.who.int|access-date=2016-03-08|url-status=live|archive-url=https://web.archive.org/web/20140221042107/http://www.who.int/mediacentre/factsheets/fs328/en/|archive-date=2014-02-21}}</ref> The availability of a childhood [[vaccine]] has significantly reduced infections in the United States, with incidence declining by more than 95% as of 2013.<ref>{{Cite web|url=https://www.cdc.gov/hepatitis/hav/havfaq.htm#general|title=Hepatitis A Questions and Answers for Health Professionals {{!}} Division of Viral Hepatitis {{!}} CDC|website=www.cdc.gov|access-date=2016-03-08|url-status=live|archive-url=https://web.archive.org/web/20160306221037/http://www.cdc.gov/hepatitis/hav/havfaq.htm#general|archive-date=2016-03-06}}</ref> Paradoxically, the highest rates of new infection now occur in young adults and adults who present with worse clinical illness.<ref name="Harrison's Principles, chapter 360 (Acute Viral)" /> Specific populations at greatest risk include: travelers to endemic regions, men who have sex with men, those with occupational exposure to non-human primates, people with [[clotting disorder]]s who have received [[clotting factors]], people with history of [[chronic liver disease]] in whom co-infection with hepatitis A can lead to fulminant hepatitis, and intravenous drug users (rare).<ref name="Carroll chapter 35" />

==== Hepatitis B ====
{{main|Hepatitis B}}
[[File:HBV replication.png|thumb|HBV replication]]
[[Hepatitis B]] is the most common cause of viral hepatitis in the world with more than 240 million chronic carriers of the virus, 1 million of whom are in the United States.<ref name="WHO Hepatitis B">{{Cite web|url=https://www.who.int/mediacentre/factsheets/fs204/en/|title=Hepatitis B|website=World Health Organization|language=en-GB|access-date=2016-03-09|url-status=live|archive-url=https://web.archive.org/web/20141109161444/http://www.who.int/mediacentre/factsheets/fs204/en/|archive-date=2014-11-09}}</ref><ref name="Carroll chapter 35" /> In approximately two-thirds of patients who develop acute hepatitis B infection, no identifiable exposure is evident.<ref name="Harrison's Principles, chapter 360 (Acute Viral)" />  Of those acutely infected, 25% become lifetime carriers of the virus.<ref name="Carroll chapter 35" /> Risk of infection is highest among intravenous drug users, people with high-risk sexual behaviors, healthcare workers, people who had multiple transfusions, organ transplant patients, dialysis patients and newborns infected during the birthing process.<ref name="Carroll chapter 35" /> Close to 780,000 deaths in the world are attributed to hepatitis B.<ref name="WHO Hepatitis B" /> The most endemic regions are in sub-Saharan Africa and East Asia, where as many as 10% of adults are chronic carriers.<ref name="WHO Hepatitis B" /> Carrier rates in developed nations are significantly lower, encompassing less than 1% of the population.<ref name="WHO Hepatitis B" /> In endemic regions, transmission is thought to be associated with exposure during birth and close contact between young infants.<ref name="Harrison's Principles, chapter 360 (Acute Viral)" /><ref name="WHO Hepatitis B" />

==== Hepatitis C ====
{{main|Hepatitis C}}
[[File:HepC replication.png|thumb|HepC replication]]
Chronic [[hepatitis C]] is a major cause of liver cirrhosis and hepatocellular carcinoma.<ref name="Rosen - Clinical Practice">{{Cite journal|last=Rosen|first=Hugo R.|date=2011-06-23|title=Clinical practice. Chronic hepatitis C infection| journal=The New England Journal of Medicine| volume=364| issue=25| pages=2429–2438| doi=10.1056/NEJMcp1006613|issn=1533-4406|pmid=21696309}}</ref> It is a common medical reason for liver transplantation due to its severe complications.<ref name="Rosen - Clinical Practice" /> It is estimated that 130–180 million people in the world are affected by this disease representing a little more than 3% of the world population.<ref name="Final Recommendation Statement: Hepatitis C: Screening">{{Cite web|url=https://www.who.int/mediacentre/factsheets/fs164/en/|title=Hepatitis C|website=World Health Organization|language=en-GB|access-date=2016-03-08|url-status=live|archive-url=https://web.archive.org/web/20160131041006/http://www.who.int/mediacentre/factsheets/fs164/en/|archive-date=2016-01-31}}</ref><ref name="Carroll chapter 35" /><ref name="Rosen - Clinical Practice" /> In the developing regions of Africa, Asia and South America, prevalence can be as high as 10% of the population.<ref name="Carroll chapter 35" /> In Egypt, rates of hepatitis C infection as high as 20%  have been documented and are associated with [[Iatrogenesis|iatrogenic]] contamination related to [[schistosomiasis]] treatment in the 1950s–1980s.<ref name="Harrison's Principles, chapter 360 (Acute Viral)" /><ref name="Carroll chapter 35" /> Currently in the United States, approximately 3.5 million adults are estimated to be infected.<ref>{{Cite journal|last1=Edlin|first1=Brian R.|last2=Eckhardt|first2=Benjamin J.|last3=Shu|first3=Marla A.|last4=Holmberg|first4=Scott D.|last5=Swan|first5=Tracy|date=2015-11-01|title=Toward a more accurate estimate of the prevalence of hepatitis C in the United States|journal=Hepatology|language=en|volume=62|issue=5|pages=1353–1363|doi=10.1002/hep.27978|issn=1527-3350|pmc=4751870|pmid=26171595}}</ref> Hepatitis C is particularly prevalent among people born between 1945 and 1965, a group of about 800,000 people, with prevalence as high as 3.2% versus 1.6% in the general U.S. population.<ref name="Harrison's Principles, chapter 360 (Acute Viral)" /> Most chronic carriers of hepatitis C are unaware of their infection status.<ref name="Harrison's Principles, chapter 360 (Acute Viral)" /> The most common mode of transmission of hepatitis C virus is exposure to blood products via blood transfusions (prior to 1992) and intravenous drug injection.<ref name="Harrison's Principles, chapter 360 (Acute Viral)" /><ref name="Carroll chapter 35" /> A history of intravenous drug injection is the most important risk factor for chronic hepatitis C.<ref name="Rosen - Clinical Practice" /> Other susceptible populations include those engaged in high-risk sexual behavior, infants of infected mothers, and healthcare workers.<ref name="Carroll chapter 35" />

==== Hepatitis D ====
{{main|Hepatitis D}}
The [[hepatitis D]] virus causes chronic and fulminant hepatitis in the context of co-infection with the hepatitis B virus.<ref name="Carroll chapter 35" /> It is primarily transmitted via non-sexual contact and via needles.<ref name="Harrison's Principles, chapter 360 (Acute Viral)" /><ref name="Carroll chapter 35" /> Susceptibility to hepatitis D differs by geographic region.<ref name="Harrison's Principles, chapter 360 (Acute Viral)" /><ref name="Carroll chapter 35" /> In the United States and Northern Europe, populations at risk are intravenous drug users and people who receive multiple transfusions.<ref name="Harrison's Principles, chapter 360 (Acute Viral)" /><ref name="Carroll chapter 35" /> In the Mediterranean, hepatitis D is predominant among hepatitis B virus co-infected people.<ref name="Harrison's Principles, chapter 360 (Acute Viral)" /><ref name="Carroll chapter 35" />

==== Hepatitis E ====
{{main|Hepatitis E}}
Similar to Hepatitis A, [[hepatitis E]] manifests as large outbreaks and epidemics associated with fecal contamination of water sources.<ref name="Harrison's Principles, chapter 360 (Acute Viral)" /> It accounts for more than 55,000 deaths annually with approximately 20 million people worldwide thought to be infected with the virus.<ref name="WHO - Hepatitis E"/> It affects predominantly young adults, causing acute hepatitis.<ref name="Harrison's Principles, chapter 360 (Acute Viral)" /><ref name="HEV FAQs for Health Professionals">{{Cite web|url=https://www.cdc.gov/hepatitis/hev/hevfaq.htm#section1|title=HEV FAQs for Health Professionals {{!}} Division of Viral Hepatitis {{!}} CDC|website=www.cdc.gov|access-date=2016-03-09|url-status=live|archive-url=https://web.archive.org/web/20160308031004/http://www.cdc.gov/hepatitis/hev/hevfaq.htm#section1|archive-date=2016-03-08}}</ref> In infected pregnant women, Hepatitis E infection can lead to fulminant hepatitis with third trimester mortality rates as high as 30%.<ref name="Carroll chapter 35" /><ref name="HEV FAQs for Health Professionals" /> Those with weakened immune systems, such as organ transplant recipients, are also susceptible.<ref name="HEV FAQs for Health Professionals" /> Infection is rare in the United States but rates are high in the developing world (Africa, Asia, Central America, Middle East).<ref name="Harrison's Principles, chapter 360 (Acute Viral)" /><ref name="HEV FAQs for Health Professionals" /> Many genotypes exist and are differentially distributed around the world.<ref name="WHO - Hepatitis E" /> There is some evidence of hepatitis E infection of animals, serving as a reservoir for human infection.<ref name="Carroll chapter 35" />