The pathogenesis of both acute and viral hepatitis is slowly being unravelled. Thus far, most data show that members of the hepadnaviridae family are not highly cytotoxic per se. It appears that the intense levels of cellular death are primarily due to host defence mechanisms against the HBV infection.
The virus is most efficiently transmitted through percutaneous introduction. Sexual transmission and perinatal transmission are less efficient, typically requiring high titres of virus. HBV is most concentrated in the liver and blood, with lesser amounts found in saliva and semen.
On average, the liver weighs about four pounds and is the only organ able to regenerate itself even when up to 25% of it is removed.
The liver has many functions involved in digestion and metabolite conversion. Some of its key functions are:
fluid is stored in the gallbladder for release when needed in digestion.
Bile is necessary for the digestion of fats as it dissolves fat down into
small globules. Bile works in the same way as detergent lifts oil off
greasy plates. Bile also assists in the absorption of fat soluble vitamins
(i.e. vitamin A, D, F, and K) In addition, bile converts beta-carotene
to vitamin A.
The primary site of HBV replication is, without surprise, the liver. However, various extrahepatic sites have been proposed. Hemapoetic stem cells have been postulated to support viral replication. This could account for various hematological abnormalities sometimes found in patients with acute hepatitis.
HBV replicative intermediates and/or viral transcripts have also been found in extrahepatic sites. These include mononuclear cells, bile duct epithelial, endothelial, pancreatic acinar cells, and smooth muscle tissue. They have also been found in adrenal glands, gonads, cultured bone marrow, kidneys, lymph nodes, spleen, and thyroid glands of acute hepatitis B infected patients.
Elfassi, E., Romet-Lemmone, J.L., Essex, M., Frances-McLane, M. and Haseltine, W.A. 1984. Evidence of Extrachromosomal Forms of Hepatitis B Viral DNA in Bone Marrow Culture Obtained from a Patient Recently Infected with Hepatitis B Virus. Proc Natl Acad Sci USA; 81: 3526-3528.
Hadchouel M., Pasquinelli, C., Fournier, J.G., et al. 1988. Detection of Mononuclear Cells Expressing Hepatitis B Virus in Peripheral Blood from HBsAg Positive and Negative Patients by in situ Hybridization. J. Med. Virol.; 24: 27-32.
Laure, F., Zagury, D., Saimot, A.G., Gallo, R.C., Hahn, B.H. and Brechot, C. 1985. Hepatitis B Virus DNA Sequences in Lymphoid Cells from Patients with AIDS and AIDS-related Complex. Science; 229: 561-563.
Lie-Injo, L.E., Balasegaram, M., Lopez, C.G. and Herrera, A.R. 1983. Hepatitis B Virus DNA in Liver and White Blood Cells of Patients with Hepatoma. DNA; 2: 301-308.
Noonan, C.A., Yoffe, B., Mansell, P.W.A., Melnick, J.L. and Hollinger, F.B. 1986. Extrachromosomal Sequences of Hepatitis B Virus DNA in Peripheral Blood Mononuclear Cells of Acquired Immune Deficiency Syndrome Patients. Proc Natl Acad Sci USA; 83: 5698-5702.
Romet-Lemonne, J.L., McLane, M.F., Elfassi, E., Haseltine, W.A., Azocar, J. and Essex, M. 1983. Hepatitis B Virus Infection in Cultured Human Lymphoblastoid Cells. Science; 221: 667-669.
Shen, H.D., Choo, K.B., Lee, S.D., Tsai, Y.T. and Han, S.H. 1986. Hepatitis B Virus DNA in Leukocytes of Patients with Hepatitis B Virus-Associated Liver Disease. J Med Virol; 18: 201-211.
Yoffe, B., Noonan, C.A., Melnick, J.L. and Hollinger, F.B. 1986. Hepatitis B Virus DNA in Mononuclear Cells and Analysis of Cell Subsets for the Presence of Replicative Intermediates of Viral DNA. J Infect Dis; 153: 471-477.
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