Laboratory animal numbers 2025

How infectious diseases are studied using animals in research

April 22, 2026

April 24 is World Day for Laboratory Animals. We are taking this opportunity to publish the laboratory animal figures for the Max Planck Institute for Infection Biology. Here you will find the number of laboratory animals used by species and the severity levels of the experiments compared to previous years through 2020. In 2025, the majority of animal experiments at the Institute were conducted on zebrafish and the fish species Danionella cerebrum to study the infectious disease tuberculosis.

A white mouse is sitting on a gnawed piece of wood in a plastic cage filled with bedding. — Mice were used less frequently in experiments compared to the previous year.

© Max Planck Institute for Infection Biology

Mice were used less frequently in experiments compared to the previous year.

© Max Planck Institute for Infection Biology

In 2025, 1,883 animals were used at the Max Planck Institute for Infection Biology in scientific experiments and for training. This means that the number of laboratory animals remained constant compared to the previous year (1,875 animals). The most frequently used animals were zebrafish (861 animals). On a larger scale, the fish species Danionella cerebrum was used in 2025 (535 animals), while the number of mice used declined compared to the previous year (900 animals in 2024; 482 animals in 2025). Three rats were used for training our animal care trainees. In addition, two experiments with clawed frogs were completed. A brief introduction to the clawed frog Xenopus can be found on our experimental animals page.

Tuberculosis Research with Zebrafish and Danionella cerebrum

Every year, over ten million people contract tuberculosis, and more than one million of those affected die. At the Max Planck Institute for Infection Biology, the Cronan Lab is researching the central structure of tuberculosis infection: the granuloma, an accumulation of immune cells that forms around tuberculosis bacteria.

Granulomas prevent immune cells and antibiotics from reaching the tuberculosis bacteria. Mark Cronan’s research group is looking for ways to dissolve granulomas and make them accessible to antibiotics. The interaction between pathogens and immune cells is complex. For this reason, granulomas can currently only be studied in living organisms.

Overview of the number of laboratory animals

In 2025, 482 mice, 861 zebrafish, 535 Danionella cerebrum fish, 3 rats, and 2 clawed frogs were used in animal experiments.

A suitable model for tuberculosis granulomas

In humans, granulomas usually form in the lungs. Although zebrafish have gills instead of lungs, they form structures very similar to human granulomas when infected with tuberculosis. For this reason, many findings from experiments with zebrafish can be extrapolated to human granulomas. This also applies to the fish species Danionella cerebrum, which is similar to the zebrafish. Although mice are more commonly used as laboratory animals, they do not develop comparable granulomas.

Animal experiments in tuberculosis research

To study tuberculosis granulomas, researchers at the Institute infect zebrafish and Danionella cerebrum with the bacterium Mycobacterium marinum, a close relative of the human tuberculosis pathogen. The fish become ill and form granulomas, which is why the experiment is classified as moderate in severity under the legal framework. In addition, researchers breed genetically modified fish, for example, to specifically stain immune system cells. These breeding procedures are considered animal experiments and are classified as low severity. Further information on the severity levels of animal experiments can be found on our website.

Number of mice used reduced by half

Compared to the previous year, the number of mice used has nearly halved, from 900 to 482. As in previous years, the animals were used for research on immune cells and the infectious disease malaria. The majority of the experiments on mice involved genotyping. The genotype refers to the entire genetic makeup of a living organism. During genotyping, researchers examine the mice’s genetic material to determine whether a genetic modification was successful. To obtain genetic material for the study, a small piece of tissue—usually taken from the ear—is sufficient. These studies are classified as low-impact experiments under current regulations. Currently, these breeding efforts are being conducted in preparation for future experiments.

Animal experiments by severity level

In 2025, 39.8% of animal experiments involved mild stress, 51% involved moderate stress, and 3.7% involved severe stress. In 5.5% of the experiments, vital functions were not restored. — Animal experiments at the Max Planck Institute for Infection Biology, broken down by severity level. In 2024, a large series of experiments was completed to investigate an immune mechanism known as neutrophil extracellular traps. To conduct the experiments, mice had to be killed (“no restoration of vital functions”). By 2025, these experiments were being conducted only to a limited extent.

Animal experiments at the Max Planck Institute for Infection Biology, broken down by severity level. In 2024, a large series of experiments was completed to investigate an immune mechanism known as neutrophil extracellular traps. To conduct the experiments, mice had to be killed (“no restoration of vital functions”). By 2025, these experiments were being conducted only to a limited extent.

Animal testing in malaria research

Every year, nearly 250 million people contract malaria. The two malaria vaccines approved in recent years represent a major advance in the fight against the disease, but they must still be administered multiple times during infancy and have an efficacy of less than 70 percent. For this reason, researchers continue to search for vaccines.

In the Vector Biology research group, mice were used to test a potential vaccine against malaria. To identify the vaccine candidate, the experiments were preceded by extensive testing in cell cultures, which made it possible to avoid a large number of animal experiments. However, whether a vaccine provides the desired protection must be tested on a living organism.

Use of Rats in Animal Care Training

At the Max Planck Institute for Infection Biology, we also train animal care technicians. An important part of the training is handling animals. Since no rats were used in experiments at the institute last year, these training components were conducted outside of scientific animal experiments. Trainees learn, among other things, how to safely transfer animals between cages, how to draw blood, and how to euthanize rats.

Animal experiments remain a vital component of infection research
Animal experiments remain indispensable in biomedical research—including at the Max Planck Institute for Infection Biology. According to the current state of research, they are an important part of the experimental toolkit, particularly for investigating the complex mechanisms of our immune system.
The research groups at the Max Planck Institute for Infection Biology use a variety of animal-free methods. These include, for example, computer models as well as experiments with cell cultures, bacteria, invertebrates, and human donor tissue. Before researchers resort to animal testing, they always assess whether an animal-free method is sufficient to answer the scientific question.
Even though the development of alternative methods is steadily advancing and some animal experiments have now been replaced, allowing for a reduction in the number of animals used, a complete replacement of animal experiments is not currently foreseeable. These experiments will continue to be necessary in the future for gaining new insights and developing new therapeutic approaches and methods.