Coalition For Animals
& Animal Research
CFAAR Arizona

Introduction

The development of vaccines is one of the most important breakthroughs in the history of medicine. Mere decades ago, diseases like smallpox, polio and diphtheria spread throughout the world with devastating results. People died, were paralyzed, crippled and disfigured by diseases that today, are preventable through vaccination. Several of these dreadful diseases are practically eradicated in the developed world and elsewhere, good progress is being made to reduce their spread. Indeed, successful vaccine development has played a vital role in preventing the huge burden of infectious diseases and their complications in developed countries and in raising the living standards and life expectancy of peoples in the developing world.

In the past, any number of infectious diseases could decimate a herd or flock of domesticated animals. Today, vaccines that protect animals are vital for raising livestock essential for world food production and our quality of life. Some of the first vaccines were developed to protect food-producing animals against disease. These veterinary vaccines also protect people from diseases because many animal diseases are transmissible to humans.

In the last ten years, new discoveries and ideas have led to breakthroughs in the way we approach vaccine sciences. Today, Americans are at the dawn of a new era in vaccine research. Genetic engineering has allowed scientists to create new vaccines with greater potential for protecting both humans and animals. Researchers are also hard at work developing vaccines to control certain existing and emerging infectious diseases, to protect populations against bio-terrorism, to treat cancers, and to attack other illnesses, such as Alzheimer's disease.

But what is a vaccine, really? What do vaccines do? What is the role of animals in vaccine development? And what does the future hold?

Historically, a vaccine is a pharmaceutical preparation, administered to stimulate active immunity to a specific disease. Most Americans are given their first vaccinations shortly after birth to protect them against such childhood illnesses as diphtheria, tetanus, pertussis (whooping cough), chickenpox, mumps, measles, German measles (rubella), and poliomyelitis. Each year, these early vaccinations help prevent the deaths of thousands of children. Although most people are immunized during childhood, adolescents and adults should keep vaccinations up-to-date by getting booster inoculations to maintain long-term protection against a number of serious illnesses.

The word vaccine is derived from the Latin word for cow, vacca, and the history of vaccines is, not surprisingly, linked to the cow, as we shall see. The ancient Greeks understood that people who survived plague epidemics were resistant when it struck again. And the ancient Chinese first inoculated people with a weakened strain of the smallpox (variola) virus to prevent further infection. The wife of a British ambassador, Lady Mary Wortley-Montague, introduced the practice of "variolation" to Britain in 1721 after observing the procedure performed in Turkey. But it was not until 1796 that the studies of English country doctor Edward Jenner finally set us on the path that led to what we now call a "vaccine." Aware of the variolation procedure, Jenner noticed that milkmaids who had contracted cowpox, a disease of cattle that causes little harm to humans, were immune to smallpox - a frequently fatal disease. He tested his theory regarding cowpox by scratching the skin of a young boy with fluids from the milkmaid's skin sores. A few weeks later he exposed the boy to smallpox, but the boy remained disease free. While such a procedure would be considered unethical today, Jenner was merely controlling the timing of the boy's exposure to smallpox - because in those days everyone was exposed eventually, usually during childhood.

News of Jenner's achievements spread quickly across Europe. However, it was almost 100 years before other vaccines were developed. And the next ones were developed primarily to prevent animal diseases. In 1879 the famous French scientist, Louis Pasteur, discovered that inoculating chickens with a weakened form of the cholera bacillus immunized them against more virulent forms of the disease. Pasteur then applied the same principle to anthrax, a disease that, in the 1870s, had decimated flocks of French sheep, goats, and other livestock. He also developed a vaccine to protect dogs against rabies. The vaccine was later used to save a child who had been bitten by a rabid dog. It was the first instance in which an animal served as model for the development of a vaccine for humans. Since Pasteur's experiments in the late 19th century, animal research has been critically important to the development of vaccines for both humans and animals and continues to be vital today.

What do vaccines do?

Vaccines are usually designed to prevent diseases commonly caused by microbes, such as bacteria, viruses, and fungi. Specific pieces (antigens) on these organisms stimulate the body's immune mechanisms in two ways: (a) by eliciting the production of antibodies, large protein molecules called globulins that circulate in the body and recognize, bond to foreign substances, and neutralize or help eliminate foreign substances (humoral immune response); and (b) by generating specialized types of immune cells that act to destroy cells infected by the organisms (cellular immune response). The antibodies are produced by B-Cells (B lymphocytes), which mature in the bone marrow, become plasma cells, and migrate to the spleen and lymph nodes. Highly specialized T Cells (T lymphocytes) mature in the thymus, and give rise to helper T cells and cytotoxic or killer T cells. Both responses act in concert to help control, if not completely rid, the body of the specific infection.

Traditionally, active immunity has been achieved by administering classical vaccines composed of whole killed (inactivated) organisms or live, weakened (attenuated) organisms that have lost their disease-producing properties. Subunits of the organisms such as an outer coat protein or a toxin inactivated by formalin to become a toxoid are also used. Advances in genetic engineering are being used to improve traditional vaccines, create DNA vaccines, and develop more effective ways to deliver vaccines.

What is the contribution of animal research to vaccine production?

Animals have also been critical to determining how the immune system works. Scientists have been able to identify and describe the protective network of specialized organs (thymus, spleen, bone marrow lymph nodes) that produce different types of lymphocytic cells and a variety of antibodies and cytokines (small signal proteins that regulate immune activities) which are called into play when the body encounters a pathogen.

And finally, animals have played a vital role in detecting desirable and undesirable features of a newly developed vaccine. Patient ready vaccines may take years of testing to develop. Strict regulations prevent a vaccine from being used in humans until it passes tests for safety in preclinical evaluations in animals (e.g. rats, mice, nonhuman primates). Usually, it must also pass tests for efficacy in animals before evaluation in larger clinical studies to determine efficacy in humans. Scientists also rely on animals to learn how to enhance the immune response by determining the quality of the antigen, the route of injection, and the dosage required to elicit an optimal response

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.

 

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.

What does the future hold?

Many diseases for which researchers are attempting to develop vaccines are extremely complex. Some, like AIDS and malaria, are still not fully understood and present an enormous challenge. New technologies resulting from scientific advancements in the area of molecular biology are aiding the development of a new generation of vaccines. These preparations involve the introduction of engineered DNA into the body. Animal models are essential to their development because they continue to provide the best ways of identifying promising and safe vaccines before advancing to human trials.

New approaches to vaccines development - genetic immunization

Delivery Vehicles for Recombinant DNA Vaccines
By the early 1990s, scientists had begun to study new approaches to the production of vaccines that differ in structure from traditional ones. The strategy involves genetic engineering, or recombinant DNA technology, which permits scientists to combine a segment of DNA from one organism with the gene(s) of a second organism.

Plasmid Vaccines. Among the most frequently studied vaccines are recombinant plasmids, DNA strands originally derived from a bacterium, which have been altered to carry a gene(s) that directs the production of an immunizing protein (antigen) from another infectious agent. Without causing disease, the DNA is taken up by the body's cells where it directs the synthesis of proteins that elicit an immune response.

Live, Viral Vector Vaccines. A variety of live infectious but non-disease-causing RNA or DNA viruses or bacteria have been engineered to express the proteins of a disease producing organism. The vector enters the body's cells where the proteins are generated and then induce humoral and cellular immune responses.

Scientists have demonstrated that these recombinant vaccines activate the immune systems of rodents and nonhuman primates, eliciting both antibody-type immunity and killer cell-type immunity against a variety of disease-producing organisms. Researchers are currently conducting additional tests in animals to develop ways of enhancing the immune response before moving to the stage of clinical testing. DNA vaccines can be administered intranasally, injected intramuscularly, or delivered by gene gun, an instrument that propels tiny DNA-coated gold beads into the body's cells.

Recombinant vaccines raise hopes that one day they will be accepted for use in humans to prevent AIDS, malaria, hepatitis C, and other infectious agents for which currently available vaccines produce only limited protection or do not exist at all. Recombinant vaccines also extend some hope for the control of cancer. While cancer cells are not foreign, they carry proteins that are different from those of normal cells. Cancer vaccines are aimed at stimulating an immune response against these tumor proteins. At present, vaccines aimed at prolonging the lives of people whose tumors have been surgically removed are being tested in early trials.

The Search for New Vaccines for Old and Emerging Diseases

AIDS. The statistics regarding HIV/AIDS around the world are astonishing. First recognized in 1981, AIDS has since become a pandemic. At this writing, an estimated 20 million people have died of AIDS around the world, and an additional 40 million are infected. It is well accepted that this disease cannot be eliminated without a vaccine. Animal research plays an especially prominent role in evaluating the effectiveness of potential vaccines to prevent or control HIV/AIDS. Nonhuman primates, particularly rhesus monkeys, provide the best models because they can be naturally and experimentally infected with a virus related to HIV. This animal model system provides a counterpart for studying the disease and for exploring novel approaches, including the use of DNA vaccines to combat this deadly and widespread epidemic. Since the first vaccine trial in 1987, researchers have studied many different potential vaccines in human volunteers.

Hepatitis C. This virus is transmitted through exposure to blood and other bodily fluids, often by contact with intraveneous drug users and persons who engage in high risk sexual behavior. Hepatitis C virus (HCV) infections have a high rate of chronicity, causing cirrhosis and liver cancer in the U.S. Almost 4 million Americans are chronically infected with HCV, resulting in up to 10,000 deaths annually. The isolation of the HCV- DNA in 1987 enabled scientists to begin the quest for a vaccine that protects against the long-term complications of the virus. To date, immunization studies using DNA vaccines that encode for HCV envelope proteins have been shown to be effective in the chimpanzee, the only known animal model susceptible to infection.

Malaria. One of the largest public health problems in the world, malaria affects between 300 million and 500 million people claiming two to three million lives annually. Spread by mosquitoes, malaria parasites invade liver cells and red blood cells. Vaccine development has been extremely difficult because the parasite is extremely complex and undergoes various cyclical changes in the mosquito vector and the human host. New candidate vaccine antigens are being discovered as scientists sequence the genome of the parasites at the various stages of its life cycle. At the present time, only certain monkey species can be infected by human malarial parasites. Potential vaccine candidates that have successfully protected these monkeys are now being tested in clinical trials in malaria endemic areas of the world.

Tuberculosis. The current vaccine, called BCG vaccine (Bacillus Calmette-Guerin), is a weakened strain of bovine tuberculosis (TB); however, it is not highly effective. Despite having a vaccine and antibacterial treatment modalities, three million people die from this disease each year. Although significant challenges remain, researchers have successfully protected mice against TB using a newly developed DNA vaccine that encodes for a protein of the organism. The availability of small animal models with pulmonary TB has enabled scientists to screen large numbers of potential vaccine candidates.

Periodontal Disease. Periodontitis or gum disease, which caused by certain oral bacteria affects 80 percent of the world's adults. Symptoms of this disease include pain, swelling, and bleeding of the gums that can lead to tooth loss. Some scientists believe that periodontitis may be an important risk factor for atherosclerosis and heart disease. Attempts to develop a vaccine to prevent or halt the progression of this disease are underway at this time.

Respiratory Disease. Respiratory Syncytial Virus (RSV) causes lower respiratory tract infections that can be life-threatening for infants and the elderly. At present, there is no licensed vaccine and so-called traditional vaccines have proven ineffective. Scientists are attempting to develop a recombinant RSV vaccine that is suitable for intranasal instillation. Tests for determining the safety and level of resistance that can be achieved by the vaccine are being conducted in the chimpanzee, the only animal that develops a respiratory illness similar to humans.

Leprosy. Also known as Hansen's disease, leprosy has been a public health threat for thousands of years. It affects the skin, nerve endings, upper respiratory system, and eyes, causing severe disfigurement. There is a very low incidence of the disease in the United States, but, tragically, it is endemic in 91 countries around the world. Development of a vaccine for leprosy has been slow due to the lack of animal models for the disease. The only established model is the nine-banded armadillo. Many experts believe that the eradication of this disease will be impossible without a vaccine, but only a few laboratories are working on one.

Hookworm Disease. Causing mild diarrhea or cramps in most people, this intestinal parasite can lead to serious health problems, including mental and physical retardation in newborns and children. Infection occurs in tropical and sub-tropical areas and is estimated to infect up to 1/5 of the world's population. The overwhelming scope of this disease continues despite attempts to control the disease through improvements in living conditions. A hookworm vaccine is currently under development using recombinant technology.

The tragic events of September 11, 2001, have fundamentally changed how the United States views the threat of biological attacks. Biological weapons, composed of either bacteria, viruses, or microbial toxins, can be used against civilian and farm animal populations to terrorize and harm our way of life. Medical experts estimate that these agents, some of which are stockpiled at various sites around the world, pose a very real threat. Consequently, the U.S. and other countries continue to carry out research on a variety of dangerous microbes in order to develop vaccines (and other biologicals) to counteract terrorism and combat natural outbreaks of highly contagious diseases.

Indeed, actions to address the threat of deliberately introducing a disease causing agent into a population have taken on a new urgency. This topic is the current focus of national planning efforts by agencies of the federal government responsible for protecting the public, e.g., the Department of Health and Human Services, including the National Institutes of Health, the Food and Drug Administration, and the Centers for Disease Control and Prevention; the Department of Defense; and the National Academy of Sciences. The common goal is to prepare for and respond to acts of bioterrorism.

Category A: Among the 20 or so potential bioweapons, smallpox, anthrax, and plague have generated the highest level of worry. These are followed by botulism, tularemia, and hemorrhagic fevers. A committee of experts has judged that these agents pose a high risk to national security because they have the potential for major public health impact, the greatest number of deaths and economic losses, and psychological damage. Other agents considered to be of somewhat lesser importance have been placed in Category B and Category C. They will not be discussed in this brochure. (See article -November 2000, New Frontiers: Biowarfare, Bioterrorism: Are We Prepared?)

Vaccines to Combat Bioterrorism - Category A Agents.

Smallpox (Variola major). This virus is considered one the most dangerous potential weapons. It causes fever and a rash on the face, neck and arms progressing to pustular lesions and scabs. Death results in 30 percent of cases. This disease was effectively eradicated in the late 1970s, and vaccination has not been required since 1972. The smallpox virus is contained in a few research laboratories. Since 1983, the U.S. has about 200 million doses of the Dryvax vaccine. Fortunately, the vaccine has retained its potency and recent tests indicate that it can be diluted ten-fold and still confer protection.

Until now, vaccination has been recommended only for persons who are at high risk for infection because the vaccine can cause serious complications such as fever and severe local reactions, some of which can be life threatening to some groups, such as persons with immune deficiencies. Whether the federal government should make smallpox vaccine widely available in the current situation is still under debate, but a panel of medical experts has concluded that nationwide vaccination for Americans is too risky. Advance smallpox vaccination would reduce the number of people ultimately infected in an attack by bioterrorists, but itself would cause some serious side effects and a small number of deaths, raising a question about the ethical consequences of wholesale immunization.

While a newer vaccine is under development, it is not ready for use at this time. The virus must be produced in cell culture using FDA approved reagents and tested for safety and efficacy in appropriate animal models, a process that may take at least two years.

Anthrax (Bacillus anthracis). The bacterium causing anthrax produces stable spores that remain viable and infective in the soil for years. The spores are easily aerosolized increasing their ability to be inhaled by people. Anthrax occurs naturally in hoofed animals and uncommonly infects humans who have contact with contaminated animal products. Its potential as a biological weapon has been recognized for many years. Inhaled spores germinate and release toxins that cause pulmonary disease. Unless the victim gets early antibiotic treatment, the disease is almost always fatal. Experts estimate that spores sprayed into the air could be dispersed over long distances infecting and killing thousands of people. Research on monkey models advanced to the development of anthrax vaccines in 1970. The currently available vaccine has been used to vaccinate some U.S. military personnel; however; it is not available for civilian use. Anthrax assaults delivered in mailed letters in 2001 have led to significant interest in the development of new vaccines as counter-measures for combating this problem. Scientists are seeking new knowledge of how the anthrax organism causes disease in order to develop strategies for new vaccine candidates that require fewer doses.

Plague (Yersinia pestis). As early as 541 AD, bubonic plague swept Egypt and the rest of the world, killing between 50 and 60 percent of the population. In 1346, a second plague, known as the "Black Death" killed millions. The bubonic form of the plague is spread to humans by fleas found on infected rats. It is so named because it causes the swelling of lymph glands in the armpits and groin called "buboes." The pneumonic form of plague is easily readily transmitted from person-to-person through face-to-face contact and is therefore considered a dangerous biological weapon. Early antibiotic administration is essential for successful treatment. There are ongoing research efforts to find and develop a vaccine to protect against this highly dangerous disease. Vaccination with the killed vaccine reduces the severity of the disease but does not prevent the pneumonic form.

Botulism (Clostridium botulinum). This bacterium produces a highly lethal toxin that binds to nerve endings and paralyzes muscle. Ordinarily, people are exposed to the toxin after eating contaminated food. Treatment consists of the administration of antitoxins produced in horses. Botulinum toxoid is available in limited quantities and is only used to protect laboratory workers.

Tularemia (Francisella tularensis). This bacterial agent causes fever, headache, chills, aches, and sore throat, symptoms that worsen and lead to incapacitation and ultimately, death. Airborne tularemia has been recognized for some time as a potential biological weapon because it is highly infectious and easy to disseminate. During the cold war, both the East and West created strains that are resistant to antibiotics. The U.S. has a live, attenuated vaccine, which until recently has only been used to immunize laboratory workers who might be exposed to the disease; however, the vaccine is not effective after exposure.

Hemorrhagic Fever Viruses (Filoviruses-Ebola and Marburg). Ebola hemorrhagic fever is one of the most virulent viral diseases known, killing its victims 50-90% of the time. The natural reservoir of the Ebola virus is the rain forests of Africa and Asia, but scientists have not yet learned how outbreaks occur. Up to now, most human infections have resulted from contact with nonhuman primates who are infected from the natural reservoir. No vaccine or specific treatment exists; however, researchers are attempting to develop a DNA vaccine using selected genes of the virus.