Animal models of infection

The use of various animals as models for microbiological infections has been a fundamental part of infectious disease research for more than a century. Now, techniques of genetic alteration and manipulation have made possible the design of animals so as to be specifically applicable to the study of a myriad of diseases.

The intent for the use of animals as models of disease is to establish an infection that mimics that seen in the species of concern, usually humans. By duplicating the infection, the reasons for the establishment of the infection can be researched. Ultimately, the goal is to seek means by which the infection can be thwarted. Development of a vaccine to the particular infection is an example of the successful use of animals in infectious disease research.

The development of the idea that maladies could be caused by bacterial infection grow from animals studies by Louis Pasteur in the mid-nineteenth century. The use of animals as models of cholera and anthrax enabled Pasteur to develop vaccines against these diseases. Such work would not have been possible without the use of animals.

Subsequent to Pasteur, the use of animal models for a myriad of bacterial and viral diseases has led to the production of vaccines to diseases such as diphtheria , rabies , tuberculosis , poliomyelitis , measles , and rubella.

Animal models are also used to screen candidate drugs for their performance in eliminating the infection of concern and also to evaluate adverse effects of the drugs. While some of this work may be amenable to study using cells grown on in the laboratory, and by the use of sophisticated computer models that can make predictions about the effect of a treatment, most scientists argue that the bulk of drug evaluation still requires a living subject.

A key to developing an animal model is the selection of an animal whose physiology, reaction to an infection, and the nature of the infection itself all mirror as closely as possible the situation in humans. The study of an infection that bears no resemblance to that found in a human would be fruitless, in terms of developing treatment strategies for the human condition.

The need to mirror the human situation has led to the development of animal models that are specifically tailored for certain diseases. One example is the so-called nude mouse, which derives its name from the fact that it has no hair. Nude mice lack a thymus, and so are immunodeficient in a number of ways. Use of nude mice has been very useful in the study of immunodeficiency diseases in humans, such as acquired immunodeficiency syndrome. As well, this animal model lends itself to the study of opportunistic bacterial infections, which typically occur in humans whose immune systems are compromised.

Depending on the infection and the focus of study, other animals have proven to be useful in infectious disease research. These animals include the rabbit, rat, guinea pig, pig, dog, and monkey. The latter in particular has been utilized in the study of AIDS , as primates are the genetically closest relatives to humans.

The advent of molecular techniques of genetic alteration has made the development of genetically tailored animal models possible. Thus, for example, mouse models exist in which the activity of certain genes has been curtailed. These are known as transgenic animals. The involvement of the gene product in the infectious process is possible on a scale not possible without the use of the animal.

The data from animal models provides a means of indicating the potential of a treatment. Furthermore, if a disease in an animal does not exactly mimic the human's condition, for example cystic fibrosis in mice, the use of the animal model provides a guide towards establishing the optimal treatment in humans. In other words, the animal model can help screen and eliminate the undesirable treatments, narrowing the successful candidates for use in human studies. Further study, involving humans, is always necessary before something such as a vaccine can be introduced for general use. Such human studies are subject to rigorous control.

The use of animals in research has long been a contentious issue, mainly due to questions of ethical treatment. This climate has spawned much legislation concerning the treatment of research animals. As well, in most institutions, an evaluation committee must approve the use of animals. If the research can be accomplished in some other way than through the use of living animals, then approval for the animal study is typically denied.

See also AIDS, recent advances in research and treatment; Giardia and giardiasis; Immunodeficiency