Immunity (the ability to resist infection based on mobilization of the immune system) to many diseases can result from a prior infection of the same agent. Getting the measles, for example, protects the host from being infected again later. Thus, a person can contract many diseases only once. Colds and influenza, on the other hand, stem from viruses that continue to produce new strains that avoid the body's predeveloped defenses, so that they may be contracted repeatedly. Prior exposure also does not protect against many microbial toxins, such as those involved in botulism food poisoning or against some parasitic infections, such as schistosomiasis, tapeworm, and athlete's foot.
Infection by a similar agent can in some cases provide protection from a disease. Contracting cowpox, for example, protected people from later getting the much more serious disease, smallpox. Similarly, it appears that having yaws (a disease caused by the spirochete bacterium Treponema pertenue and spread by direct contact) offers protection from syphilis (caused by T. pallidum).
Acquiring immunity through vaccination has played a major role in the control of a variety of diseases, particularly viral infections that are otherwise untreatable. This involves exposing a person to a material that will stimulate immunity to a particular agent. The material used may be a killed, inactivated, or weakened strain of the agent, a portion of its surface, one of its products, or a closely related agent.
One of the greatest successes of vaccination has been with smallpox. This once devastating disease killed millions in the Old World and scarred countless others. It was then brought to the New World, where it killed millions of Native Americans, in some cases wiping out entire cultures. In fact, the infection was spread intentionally to some tribes by European invaders who distributed infected blankets (an early example of biological warfare). Vaccination with material from the pustules (pox) of victims was practiced in Asia for at least several centuries, but sometimes lead to serious infection. In 1798, Edward Jenner reported on his experiments and observations in England involving cowpox, a related but mild disease of cows and milkmaids. He developed a vaccine based on this virus that provided immunity to smallpox. Vaccination was so successful that by 1966, the World Health Organization undertook a program to eradicate smallpox worldwide. In part because humans are the only known reservoir, the aggressive surveillance (tracking) and vaccination programs succeeded—the last "natural" case of smallpox occurred in 1977 (a small outbreak occurred among laboratory workers in England the following year). Since the disease no longer exists (the virus has been stored in two laboratories, in Atlanta and Moscow), vaccination has now been discontinued.
Another great success of vaccination has been with polio. This viral disease has now been eliminated in the Americas, the western Pacific, and Europe, and was scheduled for worldwide eradication by the end of 2002. (This target was missed, with 12 countries in Asia and Africa still not virus free as of early 2005; see www.who.org for updates.)
Table 12.8 shows the vaccinations approved for use in the United States, with those recommended for children and the general population indicated by footnote a. Some, such as DTP (diphtheria, tetanus, pertussis), are typically given as combined vaccinations, although individual inoculations or other combinations are possible (marked as footnote b). The others are designed for special populations that are at higher risk of a particular
TABLE 12.8 Licensed Vaccines and Toxoids Available in the United States
Route of Administration
Bacillus of Calmette and
Guerin (BCG) Cholera
Diphtheria-tetanus-acellular pertussis (DTaP) Diphtheria-tetanus-pertussis (DTP)a
DTP-Haemophilus influenzae type b conjugate (DTP-Hib)
Haemophilus influenzae type b conjugate (Hib)a Hepatitis Ba Influenza
Japanese encephalitis Measles6
Mumps6 Pertussis Plague
Poliovirus vaccine, inactivated (IPV) Poliovirus vaccine, oral (OPV)a Rabies
Rubella (German measles) Tetanus6
(Td or DT)6 Typhoid (parenteral)/
(Ty21a oral) Varicella (chickenpox)a Yellow fever
Live virus Inactivated bacteria Live bacteria
Toxoids and inactivated bacterial components Toxoids and inactivated whole bacteria
Toxoids, inactivated whole bacteria, and bacterial polysaccharide conjugated to protein Bacterial polysaccharide conjugated to protein Inactive viral antigen Inactivated virus or viral components Inactivated virus Live virus Live virus
Bacterial polysaccharides of serotypes A/C/Y/W-135 Live virus
Inactivated whole bacteria Inactivated bacteria Bacterial polysaccharides of 23
pneumococcal types Inactivated viruses of all three serotypes Live viruses of all three serotypes
Inactivated virus Live virus
Inactivated toxin (toxoid) Inactivated toxins (toxoids)
Inactivated bacteria/live bacteria
Live virus Live virus
percutaneous Subcutaneous or intradermal Intramuscular
Subcutaneous Subcutaneous Subcutaneous
Subcutaneous Intramuscular Intramuscular Intramuscular or subcutaneous Subcutaneous
Intramuscular or intradermal Subcutaneous Intramuscular Intramuscular
"Part of standard recommended vaccination program for children. b Alternative form of recommended vaccination for children.
disease based on occupation (including the military), travel to areas where the disease is endemic, or other factors. Most vaccinations are given as an injection, but a few are taken orally.
In some cases, the immune system can be "helped" by injection of an immune globulin, or antibody. Approved immune globulins are listed in Table 12.9.
TABLE 12.9 Immune Globulins and Antitoxins Available in the United States
Botulinum antitoxin Cytomegalovirus immune globulin, intravenous (CMV-IGIV) Diphtheria antitoxin Immune globulin (IG)
Immune globulin, intravenous (IGIV)
Hepatitis B immune globulin (HBIG) Rabies immune globulin (HRIG)
Tetanus immune globulin (TIG)
Vaccinia immune globulin (VIG)
Varicella-zoster immune globulin (VZIG)
Prophylaxis for bone marrow and kidney transplant recipients Treatment of respiratory diphtheria Hepatitis A pre- and postexposure prophylaxis; measles postexposure prophylaxis Replacement therapy for antibody deficiency disorders; immune thrombocytopenic purpura (ITP); hypogammaglobulinemia in chronic lymphocytic leukemia; Kawasaki disease Hepatitis B postexposure prophylaxis Rabies postexposure management of persons not previously immunized with rabies vaccine Tetanus treatment; postexposure prophylaxis of persons not adequately immunized with tetanus toxoid Treatment of eczema vaccinatum, vaccinia necrosum, and ocular vaccinia Postexposure prophylaxis of susceptible immunocompromized persons, certain susceptible pregnant women, and perinatally exposed newborn infants
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