Virus–Host Interactions of Hepatitis Virus Infections in Humans
المؤلف:
Stefan Riedel, Jeffery A. Hobden, Steve Miller, Stephen A. Morse, Timothy A. Mietzner, Barbara Detrick, Thomas G. Mitchell, Judy A. Sakanari, Peter Hotez, Rojelio Mejia
المصدر:
Jawetz, Melnick, & Adelberg’s Medical Microbiology
الجزء والصفحة:
28e , p522
2025-12-03
13
Currently, there is evidence for five hepatitis viruses—types A, B, C, D, and E. A single infection with any is believed to confer homologous but not heterologous protection against reinfection. A possible exception may be HCV; reinfection with HCV may occur.
Most cases of hepatitis type A presumably occur without jaundice during childhood, and by late adulthood there is a widespread resistance to reinfection. However, serologic studies in the United States and several Asian countries indicate that the incidence of infection may be declining as a result of improvements in sanitation commensurate with a rise in the standard of living coupled with expanded use of the vaccine in some countries. It has been estimated that as many as 60–90% of young middle- to upper-income adults in the United States may be susceptible to type A hepatitis.
Infection with HBV of a specific subtype (eg, HBsAg/adw) appears to confer immunity to other HBsAg subtypes, probably because of their common group a specificity. The immunopathogenetic mechanisms that result in viral persistence and hepatocellular injury in type B hepatitis remain to be elucidated. As the virus is not cytopathic, it is believed that hepatocellular injury during acute disease represents a host immune attack against HBV-infected hepatocytes.
Host responses, both immunologic and genetic, have been proposed to account for the frequency of HBV chronicity in those infected as infants. About 95% of newborns infected at birth become chronic carriers of the virus, often for life. This risk decreases steadily with time so that the risk of infected adults becoming carriers decreases to 10%. Hepatocellular carcinoma is most likely to occur in adults who experienced HBV infection at a very early age and became carriers. Therefore, for vaccination to be maximally effective against the carrier state, cirrhosis, and hepatoma, it must be carried out during the first week of life.
HCV genotypes 1–4 are the predominant types circulating in Western countries and display some differential characteristics. Genotype 1 is predominant in North America, Japan, and Western Europe. It shows the poorest response to interferon (IFN) therapy and may have a more deleterious effect on the progression of human immunodeficiency virus (HIV) type 1 disease than other HCV genotypes. In contrast, HCV genotype 2 responds the best to IFN-based therapies. Genotype 3 shows the highest rate of spontaneous clearance, and genotype 4 seems to have the highest frequency leading to chronic infection after acute infection.
Less is known about host immune responses to HCV. The majority of acute infections are asymptomatic or mild, and chronic infections usually progress slowly and insidiously. It appears that the immune response is slow to develop and relatively weak, reflecting the fact that HCV has particularly effective immune evasion mechanisms.
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