Applied Veterinary Virology: The isolation and identification of viruses using cell cultures

Applied Veterinary Virology:

The isolation and identification of viruses using cell cultures

Authors: Prof Estelle Venter
Licensed under a Creative Commons Attribution license.

SAFETY IN THE LABORATORY

Micro-organisms may enter a laboratory in diagnostic specimens. Excretions, secretions, blood, serum, tissues and cell cultures may be infectious, particularly, but not only when they are derived from sick animals. In order to infect a laboratory worker, an agent must gain access to the body by inhalation or ingestion, or through broken skin, the conjunctiva or other mucous membranes.

Aerosols:Infectious agents may become aerosolized by spillage or breakage of containers and centrifuge tubes or through the use of high speed blenders. Aerosols may occur on opening evacuated blood collection tubes, specimen containers, and culture tubes or when a needle is withdrawn e.g. from a stoppered vaccine bottle. Aerosols may also occur when using pipettes, by applying a hot inoculating loop to a culture, and by expelling air bubbles from syringes containing infectious agents. In tissue cultures some cell types do generate gas during their normal metabolism which can cause aerosols of infectious agents to develop when tubes or other containers are opened. Larger droplets fall and may contaminate the underlying surfaces. Small particles may remain suspended in the air for considerable periods and inhaled.

Eyes:May be infected by aerosols, splashing or rubbing with an infected finger resulting in conjunctival and/or corneal infections.

Oral infection can result from the dangerous technique of mouth-pipetting, from smoking, eating or drinking in the laboratory, or from unwashed contaminated hands.

Skin:Injuries from needles, broken glassware and scratches or bites of laboratory animals may serve as portals of infection for viruses such as hepatitisvirus, rabies virus and arboviruses. The skin can directly be infected by dermotropic viruses, e.g. vaccinia.

Vectors:Mosquitoes, ticks, fleas, mites, and other ectoparasites are potential sources of laboratory-acquired infection unless properly controlled or contained, whether they are being used in experimental work or just happen to be present on animals or in material brought into the laboratory.

High risk pathogens:Any diagnostic virology laboratory must maintain sufficiently high safety standards to avoid danger in the event that a specimen, probably unrecognized, happens to contain one of the pathogens of high risk. For practical purposes the following may be regarded as the ‘Category A Pathogens’ primarily dangerous to man: the haemorrhagic fever viruses (Lassa fever virus, Marburg virus, Ebola fever virus and Crimean-Congo fever virus), rabies virus, simian herpes B virus and smallpox virus. Routine diagnostic laboratories are unlikely to have the techniques and equipment required to safely handle and identify these viruses, and when one or more of them is suspected the investigation should immediately be transferred to an approved reference laboratory for testing. Nevertheless, if the diagnostic laboratory is liable to receive specimens containing dangerous pathogens, it is useful to have a small room away from the main laboratory activities in which they can be managed. This room must have facilities for controlled access and entry through an airlock with changing and washing facilities, and be provided with an exhaust protective cabinet, filtered exhaust ventilation and minimal essential equipment for work with potentially high-risk materials, e.g. preparation of electron microscope grids and the setting up of other tests.

Dangerous chemicals:Dangerous chemicals fall into several categories. Special care must be taken in handling or storing large quantities of these materials, and all containers must be clearly and properly labelled.

  • Caustic or corrosive compounds

Included in this category are acids or bases, which may burn or otherwise damage the skin or other human tissue. Such compounds may also cause corrosion of equipment.

  • Poisons

This category includes substances that are sufficiently poisonous that the inhalation or ingestion of relatively small amounts of them may induce serious deleterious effects or death. Poisons may be solid, liquid, or gaseous in nature.

  • Flammables

These include materials that easily ignite or burn, and serve as fuel for a fire.

  • Explosives

Although many explosive materials are also flammable, these compounds may explode under special conditions. They must, therefore, be handled in such a way as to eliminate exposure to, or attainment of, these conditions.

  • Radioactive materials

Only government approved laboratories may work with radioactive material. These laboratories are required to follow certain prerequisites, e.g. laboratory benches and floors must be covered with a specific type of material, storage space for radioactive material must be appropriate, and notices informing workers and others of the danger of radioactive material must be prominently displayed.

Disposal of infected materials:No infected material should leave the laboratory except as properly packaged samples sent to other laboratories. It is the responsibility of the laboratory staff to ensure that no infected items reach the washing section of the department.

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