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.

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 parenteral 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 placed in a sole genus Hepevirus, within a new family Hepeviridae, 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 the following:

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

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

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

Among the respiratory viruses that can be isolated from throat secretions are influenza, parainfluenza, respiratory syncytial virus, and rhinovirus. These may also be present in nasal washes, nasopharyngeal swabs, lung biopsy, and aspirates of the lower respiratory tract. Additional respiratory viruses, which may be isolated from the stool in addition to the aforementioned locations, are the enterovirus and adenovirus. Certain viruses, which affect the central nervous system, may be isolated from throat swabs, including enterovirus. Cytomegalovirus and herpes simplex viruses are among the viruses, which also can cause CNS illness. These two also cause congenital or perinatal exanthem, in which case isolation may be made from throat swabs.

Prions are infectious particles composed solely of proteins. They are not composed of viral nucleic acids and do not need a helper virus to replicate. They do not contain host cell DNA instead of viral DNA within the capsid; they do not consist solely of a single molecule of circular RNA without a protein coat or envelope; and they are not protein particles that generate a strong immune response.

Hairy leukoplakia may be seen in people infected with HIV and AIDS. It is characterized by raised areas that are whitish-tan in color that have a feathery appearance. It is different from candidiasis of the tongue in that hairy leukoplakia cannot be scraped off. A 'hairy tongue' is not actually due to hair growth on the tongue; it consists of elongated papillae that have the appearance of grayish-black hair to the naked eye. This condition may be caused by antibiotic use, or there may not be any reason. Atrophic glossitis (or smooth tongue) presents as having a smooth surface due to papillae loss. The loss may indicate deficiency in riboflavin, niacin, folic acid, vitamin B12, pyridoxine, or iron. A geographic tongue is a benign condition with an unknown cause; it is characterized by a map-like pattern of smooth, red areas that do not have papillae as well as rough areas that still have papillae. Although candidiasis is also common with people with AIDS and the infection also causes the tongue to have a white coating, the coat can be scraped, and a sample can be analyzed for the presence of Candida.