"Helper T-Cell": A subtype of T-lymphocytes which cooperate with B-lymphocytes for the synthesis of antibody to many antigens; they play an integral role in immunoregulation.
Hemophiliac: An individual inflicted with hemophilia which is an inherited hemorrhagic disease characterized by excessive or sometimes spontaneous bleeding.
Hepatitis: A disease characterized by inflammation of the liver, usually producing swelling and in some cases, permanent or even life-threatening damage to the liver. Viral hepatitis (hepatitis caused by a virus) is one type of hepatitis. Hepatitis can also be caused by a number of other factors, including chemicals and drugs or alcohol.
Hepatitis A: Hepatitis A is a food-borne type of viral hepatitis, which can be transmitted by contaminated food or water (the virus is present in fecal matter of infected individuals). Not usually life threatening, hepatitis A infection is normally self-limiting. The disease is quite common worldwide, particularly in the non-industrialized nations.
Hepatitis B: Hepatitis B is a potentially life-threatening blood-borne disease of the liver, which is transmitted primarily by sexual activity or exposure to blood. About 20 percent of those infected progress to chronic liver disease. A form of viral hepatitis, hepatitis B is quite
Hepatitis C: Hepatitis C is a life-threatening, blood borne disease of the liver, which is transmitted by exposure to blood. A particularly dangerous form of viral hepatitis, it is caused by an RNA virus. Hepatitis C can lead to serious, permanent liver damage, and in many cases, death. More than 80 percent of those who are infected will progress to chronic liver disease. It is suspected that there are, at present, more than 4.5 million people in the United States that are infected with hepatitis C, and more than 200 million around the world.
Hepatitis D: Infection with hepatitis D (HDV) occurs only in patients already infected with hepatitis B. Hepatitis D is spread mainly by contaminated needles and blood. I.V. drug users have a high incidence. The simultaneous infection with HBV and HDV produces more severe illness, and higher rates of long term liver failure, than HBV alone. The disease is usually self-limited, and due to its co-dependence on HBV, hepatitis is effectively prevented via the HBV vaccine.
Hepatitis E: Hepatitis E, whose symptoms and methods of transmission resemble hepatitis A, is caused by a virus commonly found in the Indian Ocean region, Africa, and in underdeveloped countries. The symptoms of hepatitis E are like those of hepatitis A, although the period of illness may be as long as
several months. Hepatitis E is rarely, if ever, responsible for cases of chronic hepatitis.
Hepatitis G: A newly identified strain of hepatitis, hepatitis G is currently under study. The first major study of virus has reported that those infected by means other than blood transfusions did not develop chronic liver disease, although for most the virus remained in their blood for several years. It is not clear at this time how widespread hepatitis G is, what the means of transmission are, or what its precise effects are on infected patients.
Herpes: An inflammatory disease of the skin or mucous membrane marked by eruption of a cluster of vesicles.
HIV: Human Immunodeficiency Virus, the virus which causes AIDS. HIV is a retro- virus that attacks the human immune system.
Host cell: A cell which has been infected with a virus. Viruses use host cells as a part of their life cycles, using the processes of the host cell to reproduce themselves.
Hypoglycemia: A condition marked by lower than normal level of sugar (glucose) in the blood; characterized clinically by sweating, trembling, palpitation, hunger, and weakness; may result from excessive production of insulin by the pancreas or excessive administration of insulin to a diabetic.