EDUCATIONAL RESOURCES

Existing and emerging vaccines and the role of animal species in their development

Human diseases

Pasteur's early research opened the door to the development of vaccines that have defeated some of the deadliest diseases known to mankind. And animals have played a prominent role in the development of virtually all of these important vaccines discussed below.

Commonly administered vaccines
Live Attenuated	Measles, Mumps, Sabin-Polio, Varicella zoster
Whole Inactivated	Influenza, Salk-Polio
Toxoid	Tetanus, (lockjaw), Diphtheria
Subunit	Pertussis whooping cough), Hepatitis B

Some Commonly Administered Vaccines

Diphtheria is an acute toxin-mediated bacterial infection that primarily affects the nose and throat, producing serious complications, such as inflammation of the heart muscle and nerve damage. Successful immunization using formalin treated vaccine or toxoid has virtually eliminated the disease in North America, but it continues to occur in other parts of the world. Diphtheria toxoid is no longer administered alone because it is much more efficient to give it to children in combination with other vaccines.

Tetanus is a severely painful disease produced by a soil bacterium that enters the body through a deep and dirty puncture wound. The organism produces a powerful toxin causing muscles in the jaw (lockjaw), neck, and limbs to become rigid; it also produces painful seizure-like contractions. Formalin treated toxin or toxoid induces protection.

Pertussis or Whooping Cough is a highly contagious respiratory disease that affects more than 50 million people worldwide causing 350,000 deaths each year, primarily among infants. The use of a whole-cell bacterial vaccine has contributed to a dramatic decline in the incidence of this disease in America. For a time, the side effects resulting from the administration of the cellular vaccine discouraged parents from having their children immunized. However, scientists have since developed an acellular vaccine that is effective and well-tolerated.

Diphtheria toxoid, tetanus toxoid, and pertussis vaccine, (DPT) are usually administered as a combination to children beginning at two months of age, and periodic boosters are given to maintain long-term immunity. Hemophilus influenza type b (Hib) is a leading cause of bacterial meningitis threatening children under the age of five. A vaccine composed of bacterial capsular polysaccharide attached to a protein is often given together with DPT - the combination is known as DPT-Hib.

Measles is a highly contagious systemic infection caused by a virus. A typical case begins with fever and a rash on the head, neck, and face that spreads to the extremities. Complications from the disease are common in children. Prior to the availability of a vaccine, the actual number of cases was about three to four million annually and over 90% of the population had contracted measles by age 15. The number of cases has dropped precipitously following intensive efforts to immunize children with the live, attenuated virus vaccine developed in 1963.

Mumps is an acute viral disease that causes tenderness and swelling of one or more salivary gland in the cheeks and under the jaw (parotitis). Occasionally, adults encounter serious complications, such as orchitis or swelling of the testicles. In America, the administration of a live, attenuated vaccine licensed in 1967 resulted in a 90% decline in cases of mumps.

German Measles or Rubella is a relatively mild viral disease associated with a rash. However, rubella acquired during pregnancy can cause serious defects in the unborn fetus. A live vaccine developed in 1969 has markedly reduced the number of rubella cases.

Measles, mumps, and rubella viruses are all grown in tissue culture. For these vaccines, the viruses can still infect but have been so weakened that they no longer cause disease. They may be administered to infants at 12-15 months of age, either singly or in combination as an MMR vaccine. With high vaccination coverage in targeted areas, the incidence of these illnesses has dropped to record lows. In the future it may be possible to eradicate them altogether.

Hepatitis B is a serious global public problem. A staggering number of people are infected with this disease which is transmitted through the blood or bodily fluids of an infected person, commonly through the use of shared needles and high-risk sexual behavior. Globally, it is estimated that two billion people have been infected at some time in their lives, and another 350 million are carriers who can transmit the disease to others. Chronic infection causes increased risk for cirrhosis of the liver and liver cancer. A vaccine for hepatitis B was developed in the 1970s using a surface protein of the virus. The safety and efficacy of the vaccine were evaluated in chimpanzees, the only species, other than humans, susceptible to hepatitis B infection. It is effective in preventing but not curing chronic hepatitis. At present, a new vaccine is being developed using recombinant DNA technology.

Influenza is usually called "the flu." Epidemics of viral influenza occur mostly during the winter months. Most people are ill for only few days, but some, especially the elderly, may need hospitalization. In an average year in the U.S.A, influenza is associated with as many as 20,000 to 40,000 deaths and over 100,000 hospitalizations. The killed virus vaccine must be updated every year to respond to emerging new virus strains.

Poliomyelitis is commonly known as polio. Poliovirus infection can cause mild flu-like symptoms or serious damage of the nervous system, resulting in a decrease in muscle function (paralysis) in the arms, legs, and/or airways. At one time, polio was one of the most feared diseases in the world, and as recently as the 1950s, polio epidemics killed or paralyzed thousands of children in North America and Europe. The first polio vaccine, licensed in the U.S. in 1955, was developed through research with laboratory animals, particularly monkeys. The worldwide use of Salk inactivated polio vaccine and Sabin live, attenuated vaccine has led to a sharp decline in the number of world polio cases, virtually eliminating naturally occurring cases of the disease in the U.S. The developing world still suffers from polio epidemics, but the World Health Organization aims to eradicate the disease through vaccine use. Today the inactivated vaccine is recommended for childhood vaccination in the U.S. The oral attenuated vaccine is still used for worldwide vaccinations where outbreaks occur because it provides a rapid protective response.

Chickenpox (varicella) is an extremely contagious viral diseases characterized by a red, itchy rash. A highly effective vaccine composed of an attenuated strain of the virus (herpes zoster) can control dissemination of varicella. However, recovery from this mild infection does not always eliminate the virus, which can remain latent or dormant in the nervous system for many years. Reactivation of the virus, especially in older people results a bout of "shingles," characterized by a rash that ranges from a mild itch to intense pain.

Animal diseases

Vaccination has not only increased the life expectancy of people around the world, it has also had a significant impact on the health and welfare of animals.

Companion Animals. Vaccination is used to prevent life-threatening diseases in pets and their human families. It is estimated that there are 350 animal diseases that have a human equivalent. Many vaccines in common use have saved millions of dogs and cats from potentially serious and even fatal diseases. The vaccines that are commonly available for dogs and cats are listed in the table below. They are often administered in combination.

Healthy Livestock and Poultry. The raising of livestock is critical to world food production. The use of high quality vaccines in an established health program can help control many diseases of cattle, horses, pigs, sheep, goats, chickens, and other animals needed for food production. For example, some of the earliest vaccines were developed to prevent the spread of cholera in chickens, anthrax in sheep, and rabies in a number of different species. The vaccination of livestock reduces the economic impact that disease outbreaks can have on herds and preserves the safety of the food supply.

Endangered Species. The use of vaccines in wild animals can help prevent the further decline of threatened and endangered species and the spread of disease to other species, including humans.

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