Ausschuss für Hygiene / Working Group on Hygiene

Risks of infection from biological materials

In order to keep the laboratory animal colonies and units, especially of rodents, free from unwanted microorganisms, all potential sources of infection should be identified. There is no doubt that infected animals represent the highest risk. All biological material originating from such animals e.g. serum, ascitic fluid, tumours, organ explants or cells may be contaminated. Such materials must, therefore, be considered as possible sources of infection. Some murine viruses, like Minute virus of mice (MVM), K virus, Mouse encephalomyelitis virus (MEV) and Mouse adenovirus, were first isolated from contaminated virus-pools. Polyoma virus, Kilham rat virus (KRV) and Toolan's H-l virus were found originally in contaminated tumours.

Storage of contaminated biological material at low temperatures (deep freezing) does not reduce infectiousness. Therefore, long-stored samples can be dangerous and may represent a serious health risk for animals or even for humans. For instance, in tumours originating from rodents, Lymphocytic choriomeningitis virus (LCMV) and Hanta viruses have been found. Both agents have been reported to cause infection in humans, which could be traced to contaminated biological material. Other agents, despite the lack of clinical symptoms in animals or humans, can still influence the results of animal experiments, leading to misinterpretations and to the need to repeat experiments. Examples of this are parvoviruses like Minute virus of mice (MVM), Kilham rat virus (KRV), and, not to be forgotten, Lactate dehydrogenase virus (LDV). LDV, especially is often a contaminant of biological material originating from mice. Recently published data offer evidence that LDV can be present in a high percentage (up to 70%) of transplantation tumours. As this virus causes a lifelong viraemia, inevitably all material originating from LDV infected mice is contaminated with the virus.

In general, it may be possible to decontaminate biological material contaminated with viruses. Choice of procedure depends strongly upon the material itself and upon the virus involved. In the case of cell-free samples, i.e. serum or ascitic fluid, physical or biochemical procedures are often suitable to make the material virus- or agent-free. Cellular material like tumours for passaging may be suitable for decontamination in a host species which is refractory to the contaminating virus. In the case of LDV, in vitro cultivation of contaminated cells is the most reliable method for elimination of this virus. In many cases, however, the elimination of an agent will not be possible, or only with considerable effort and costs.

Prevention and screening methods for early diagnosis of contamination are thus of high priority and importance. It is strongly advised that, prior to the use of materials of animal origin, which bear a potential risk of infection, virus contamination should be monitored. Only biological material which has been proven to be free of infectious agents should be allowed to be used. The method recommended for the monitoring of virus contamination is the so-called Mouse/Rat antibody production test (MAP/RAP-test): the material to be tested is injected into agent- and antibody-free animals, and 3 to 4 weeks later blood samples from these animals are examined for antibodies against likely agents.
Besides the MAP-test other methods can be considered for the detection of virus contamination, e.g. cell culture techniques or molecular-biological methods, especially Polymerase chain reaction (PCR).

Author: Werner Nicklas, DKFZ Heidelberg, Germany
Published in Lab. Anim. 29:471-472 (1995)