No suitable cell culture system is currently available for the hepatitis B virus. Fortunately, the hepatitis B virus produces a DNA-dependent polymerase that is virus specific. Influenza A, influenza B, mumps virus, and parainfluenza virus may be cultured in primary monkey kidney cells. Influenza A, B, and C all may be cultured in eggs. Influenza A and B may be detected by hemadsorption, cytopathic effect, and hemagglutination; Influenza C may be detected by hemagglutination. Retroviridae may be cultured in T lymphocytes with methods of detection of transformation, reverse transcriptase, cytopathic effect, or immunofluorescence.

Human papillomavirus, herpes simplex virus, and hepatitis B virus are a sexually-transmitted viruses with double-stranded DNA genomes. While herpes simplex virus has a relatively large genome, the genome of both human papillomavirus and hepatitis B virus are both quite small.

The Tzanck smear stains for the presence of multinucleated giant cells that are formed as a result of fusion of cell membranes due to insertion of viral proteins into the membrane. Tzanck smear does not detect the presence of inclusion bodies, dead cells, herpes DNA, or cell envelope.

Herpes simplex type 1 and 2 (HSV-1, HSV-2) are both large-enveloped DNA viruses which cause latent and recurrent infections. However, HSV-1 is primarily associated with infections of the pharynx, skin, and central nervous system. On the other hand, HSV-2 is primarily associated with genital infections, representing approximately 70% of all such initial infections. HSV-2 infections recur more often as well. Human immunodeficiency virus type 1 and 2 (HIV-1 and HIV-2) are retroviruses with plus-strand RNA genomes. Both of these can be passed by sexual contact and result in long-term infection of multiple cells and tissues. Both can also give rise to acquired immune deficiency syndrome or AIDS, however HIV-1 is associated with a long-term infection which has been virtually 99% fatal after 10-15 years. Recent research has illustrated that a small number of individuals may be infected with somewhat less virulent strains and these individuals do not follow the normal time-course to AIDS. HIV-2 is associated with a far less virulent infection and may include a much larger percentage of "none-progressing" individuals as well. 

Hepatitis C is an enveloped icosahedral RNA virus with gene order characteristic of the family Flaviviridae. The genome of Hepatitis C is infectious and consists of a linear single stranded 9.5 kb molecule of RNA. The virus replicates in the cytoplasm. Hepatitis C is transmitted by paranteral and sexual routes. It is the most common cause of post-transfusion hepatitis. Hepatitis C is associated with acute infection, chronic liver disease, and cirrhosis. Hepatitis C viral infection may serve as a predisposing factor in primary hepatocellular carcinoma.

Hepatitis B virus is an enveloped DNA virus that is part of the Hepadnaviridae family. The genome of Hepadnaviridae family is characterized by the presence of a circular, partially double stranded DNA molecule. Hepatitis B virus consists of a icosahedral core within a closely adherent capsid that contains cellular lipid, glycoproteins, and a virus-specific surface antigen called Hepatitis B surface antigen (HBsAg). The virus encodes a reverse transcriptase and replicates through an RNA intermediate. Hepatitis B virus shows tropism to the liver and replicates in hepatocytes. Hepatitis B is also called serum hepatitis and is caused by a DNA virus known as hepatitis B virus. It is transmitted by parenteral or sexual routes. Hepatitis B has a longer incubation period, which is approximately 50-160 days. Onset of the disease is gradual and the infection can be acute or self-limiting or can lead to persistent viremia and chronic liver disease with immunologic complications.

The Hepatitis A virus is a naked icosahedron that is member of the Picornaviridae family. The genome of this virus is infectious and contains a single linear molecule of single stranded RNA. Hepatitis A is transmitted by feco-oral routes and was known as infectious hepatitis. The virus enters the body by ingestion and multiplies in intestinal epithelial cells. The virus then enters the circulation and invades parenchymal cells in the liver. Incubation period for Hepatitis A is 15-40 days.

Hepatitis D virus is a very small virus with tiny genome and is classified under genus Deltavirus. It is defective satellite virus and needs Hepatitis B virus as helper, i.e., it is infective only in the presence of Hepatitis B virus. The outer capsid of the virion contains Hepatitis B surface antigen, which is encoded by HBV co-infecting the same cell.

Hepatitis E virus is a naked virus, which has icosahedral capsid with surface depression. Hepatitis E virus is from the family Calciviridae and contains a single molecule of a single stranded RNA. Hepatitis A is transmitted by feco-oral routes and by contaminated food and water. Hepatitis E is associated with cholestasis and has a higher fatality rate in pregnant women.

Hepatitis A virus and Hepatitis E virus are not associated with:

• Parenteral transmission
• Chronic carrier state
• Chronic hepatitis
• Cirrhosis
• Hepatocellular carcinoma

Hepatitis B virus, Hepatitis C virus, and Hepatitis D virus are associated with:

• Parenteral transmission
• Chronic carrier state
• Chronic hepatitis
• Cirrhosis
• Hepatocellular carcinoma

The girl contracted rabies from the bat bite. Since she did not tell anybody about the incident, appropriate prophylactic measures were not taken. The neurologic symptoms she had are all consistent with rabies infections. Rabies is also referred to as hydrophobia because of the muscle spasms that occur when swallowing. The virus which causes rabies is a member of the family of Rhabdoviridae (rhabdovirus). The virus contains a single strand of RNA. Negri bodies are cytoplasmic inclusions seen with rabies. 

Döhle bodies are seen in white blood cells with burns, infections, trauma, and some other conditions. Russell bodies are intracellular accumulations of protein. Foam cells are lipid-laden macrophages. Howell-Jolly bodies are nuclear remnants seen in red blood cells, particularly after splenectomy.

The morphologic changes in the liver are often similar for the various categories of viral agents. The liver can appear normal in size and color but is sometimes slightly edematous, enlarged, and bile-stained. On the cellular level, liver cell injury and necrosis and periportal inflammation can be seen.

Hepatitis A virus (HAV) is a small RNA virus 27 nm in diameter that can be detected in the feces during the late incubation and preicteric phase of the illness. With the onset of jaundice, antibody to HAAV (anti-HAV) becomes measurable in the serum. Initially, the level of anti-HAV antibody of the IgM class rises sharply, making it an accurate and simple diagnostic measure of HAV infections. Hepatitis A does not demonstrate a carrier state. Hepatitis B does have a carrier state.

HAV is primarily transmitted through oral ingestion of fecal contaminated material. Transmission by blood transfusion is possible, but is uncommon. HAV is commonly spread among children, or food or water contaminated by fecal matter. Undercooked shellfish may also harbor the virus.

HBV is primarily transmitted parenteral and across mucous membranes, especially by sexual intercourse. The average length of the incubation period is 120 days. HBsAg has been found in almost every body fluid from infected persons - blood, semen, saliva, tears, ascites, breast milk, urine, and even in feces.

Non-A, non-B hepatitis has been known since 1975. Non-A and Non-B viral hepatitis is now known as hepatitis C (HCV) and hepatitis E (HEV). HCV, like HBV, is transmitted primarily by the parenteral route and possibly through sexual contact. It can affect any age group, but mainly adults. Clinical features are malaise, lassitude, anorexia, headache, low-grade fever, and the loss of desire to smoke. Patients experience arthralgias, arthritis, urticaria, and transient skin rashes (the prodromal phase). In addition there may be discomfort in the right upper quadrant, usually attributed to stretching of the liver capsule.

The prodromal phase is followed by the icteric phase and the onset of jaundice. The icteric phase lasts 4 to 6 weeks. A feeling of improvement is noted. Appetite returns and the fever subsides. The icteric phase is associated with hyperbilirubinemia (both conjugated and unconjugated fractions). Recovery begins 1 to 2 weeks from the onset of jaundice and lasts from 2 to 6 weeks. Easy fatiguability is a common complaint.

Treatment including bed rest during the acute phase and a diet that is both acceptable and nutritious are the usual general measures. Prevention requires immunization for HAV as well as passive and active immunization for HBV.

Most viruses enter the cell using endocytosis, the invagination of the plasma membrane into smaller virus-sized depressions coated on the cytoplasmic side with a cellular protein known as clathrin. These detach from the plasma membrane and become vesicles free in the cell's cytoplasm. These vesicles fuse with acidic compartments called endosomes. Endosomes then fuse with lysosomes containing degradative enzymes to reduce the ingested molecules to small breakdown products.

Macrophages and other phagocytic cells have receptors for the Fc portion of the antibody molecule. These receptors provide a "handle" for phagocytes to bind coated particles. The coating of pathogens and foreign particles by antibodies is opsonization.

The simplest and most direct way in which antibodies can protect from pathogens or their toxic products is by binding to them, thereby blocking their access to cells that they may infect or destroy. This is known as neutralization and is important for protection against bacterial toxins and against pathogens such as viruses, which can thus be prevented from entering cells and replicating.

Phagocytosis is the ingestion of these coated pathogens or particles by macrophages or other phagocytes, followed by internalization and destruction by intracellular digestion.

Pinocytosis is the simple cellular uptake of fluid and solutes. It is a much simpler process than phagocytosis.

Both the enterovirus group (which includes the poliovirus, coxsackieviruses, and echoviruses), and the Reoviridae, (which includes the reovirus, orbivirus, and rotavirus), have an RNA genome. The genomes of the enterovirus group are linear and single-stranded, whereas those of the Reoviridae are double-stranded and may be either linear or segmented.

The Picornaviridae family of viruses contains the enterovirus and the rhinoviruses, which have numerous properties in common with each other. Viruses of this family lack an envelope, and are icosahedral, with a diameter of 20nm. The genome is a single-strand RNA. The enteroviruses are stable to acid, while the rhinoviruses are acid-sensitive.

Most of the families of RNA viruses infecting human consists of single strand of RNA, except the family Reoviridae. The virions in Reoviridae family consists of double stranded RNA, made up of 10-12 segments that separates them from other RNA viruses. Reoviruses are naked with icosahedral symmetry. Reoviruses replicate in the cytoplasm and are released by cell lysis. Reoviridae family is composed of eight genera including the following:

• Orthoreovirus
• Orbivirus
• Rotavirus

Orthoreovirus is associated with mild upper respiratory disease, gastrointestinal infection, and biliary atresia. Orbivirus causes febrile illness accompanied by headache and myalgia. Orbivirus is the etiological agent of Colorado tick fever that is transmitted by the wood tick. Rotaviruses are implicated in epidemic diarrhea in young children.