Wouldn't it be better to test the effect of a drug on humans right away?
Animal experiments are necessary to make sure they are safe for humans. But society generally agrees that they may only be conducted if the welfare of the animal is respected to the best possible extent. The Declaration of the World Medical Association, adopted in Helsinki in 1964, states that it is unethical to test new therapies directly on humans. The Helsinki is the foundation of many national laws on biomedical research.
The effects of new drugs, for example, are studied in human cell lines and then tested in animals for their effects and for their safety in the organism. If they show that the risk is low, the active substance can also be studied in clinical trials with human subjects.
Are processes in diseased humans and diseased animals comparable?
Yes, because even if a disease is artificially induced in a laboratory animal, the individual processes and mechanisms are the same if the disease breaks out naturally in humans. Therefore, experiments allow to draw conclusions about the situation in humans. Often, only part of the disease is triggered in the animal during an experiment. Even studying these partial processes may help understand the course and mechanisms of a disease. The advantage of this approach is that these experiments may cause less constraint in the animals. Genetically modified mice are playing an increasingly important role in this type of research.
Do animals react to drugs in the same way as humans?
Animals react the same way to some medicines and differently to others. Not every animal species reacts completely the same way, just as not all humans react exactly the same to all medicines and treatments. Still, there is enough comparability that general principles of action and side effects can be deducted.
There are many medicines that are used in the same way in both human and veterinary medicine. Many veterinary medicines contain the same active ingredient as the corresponding preparations for human medicine. Examples include various antibiotics, the painkiller buprenorphine, the anaesthetics propofol and isoflurane, insulin, the sedative Valium, the heart failure drug benazepril, carbimazole, which regulates the function of the thyroid gland, or levothyroxine for the treatment of hypothyroidism.
There are differences between different animal species or even breeds of the same species in how they react to certain active substances, especially regarding their tolerability. For example, the active ingredient permethrin, which is effective against parasites, should not be used in cats because it can be toxic to them. In dogs, on the other hand, it is a commonly used agent. Many Collies (and similar breeds) are hypersensitive to the anaesthetic gas isoflurane, whereas it can be used safely in other dog breeds.
Because of these differences, agents for use in humans must be tested in at least two animal species, rodents, and non-rodents, before clinical trials can be conducted in humans.
Does it make sense to study diseases due to lifestyle in animals?
Many diseases are multifactorial; several circumstances come together and trigger the disease. Because several factors play a role, one must consider each of these factors in treatment to arrive at a holistic treatment. The correct lifestyle cannot always prevent diseases. For example, people who have never smoked in their lives can get lung cancer; young, athletic people can get diabetes or die from a heart attack.
Often a certain gene or a component of the metabolism is partly responsible for a disease. Standardised experiments on animals are also necessary to understand the development of diseases. They help to perceive the subtle differences that may play a role in the development of a disease.
Don't humans and animals suffer from completely different diseases?
On the contrary, human, and veterinary medicine have a lot in common. Almost every disease that occurs in humans also exists in the same or a similar form in animals and is also treated in the same way. In addition, many surgical procedures are very similar in humans and animals, such as cruciate ligament operations in humans and dogs.
Diseases shared by humans and animals (a selection):
- Allergies, such as to dust mites and grasses: dogs, cats, rodents, rabbits.
- Cataracts: dogs, cats, rodents, rabbits
- Hearing loss, deafness: dog, cat
- Caries: dog, cat
- Asthma: cat
- Anaphylactic shock: all animal species
- Stomach ulcer: dog, cat
- Pancreatitis: dog, cat
- Breast cancer: dog, cat, other pets
- Uterine inflammation: Dog, cat, rodent, rabbit
- Cystitis: Dog, cat, rodent, rabbit
- Renal insufficiency: dog, cat, various rodents, rabbits,
- Immunodeficiency diseases caused by viruses: Cat, monkeys
- Cardiomyopathies and other heart diseases such as heart failure: dog, cat, rodents, rabbits
- Hypothyroidism and hyperthyroidism: dog, cat
- Kidney stones: dog, cat, rabbit
- Cancer of various organs: all species
- Inflammation of various organs: all species
- Epilepsy: dog, cat, gerbil
- Diabetes mellitus: dog, cat, various rodents, a large problem in chinchillas
- Senile dementia: dog, cat
- Various inflammations and infectious diseases such as toxoplasmosis, Lyme disease, salmonellosis, tuberculosis etc, many species