Rabies

Diagnosis

An overview of laboratory techniques in the diagnosis and prevention of rabies and in rabies research

Laboratory techniques in rabies, 4th edition, 1996

The laboratory occupies a central place in efforts to meet the threat of rabies. Laboratory results influence both the decision whether or not to proceed with a course of treatment, and the decision on the need to institute elaborate measures for controlling an epizootic in ac ommunity. The laboratory must also provide the necessary assurance that the biological products used for treatment and prevention in humans and animals are efficient and safe.

The documents mentioned below [in pdf] describe selected methods for arriving at a diagnosis in the laboratory, for determining the acceptability of biological products in rabies prophylaxis, and for conducting rabies research. Most laboratory workers can decide for themselves whether one or other of the techniques given here is within their competence, but often they are not aware of certain pitfalls and limitations of particular methods. In addition, a choice of procedures can ease the work and provide a decisive answer more quickly. These considerations are partially covered in the relevant sections of this manual; here the various techniques can be used by laboratories with limited resources.

The institution of treatment measures in exposed individuals, as recommended in the eighth report of the WHO Expert Committee on Rabies, should never await the results of laboratory diagnosis. A laboratory diagnosis may be delayed for a variety of reasons and early treatment, both local and systemic, can be a critical factor in saving the life of the patient.

A laboratory report should be as clear and unequivocal as possible, and should stipulate exactly the procedures used. A positive test by any one of several recognized procedures overrides negative reactions in the others. Where a doubtful result is obtained in any single test, recourse to the other tests available is essential in order to arrive at a definitive conclusion. Until this conclusion is reached, treatment should be continued. Even with a negative laboratory report, circumstances may occasionally justify the initiation or continuation of treatment by the physician, e.g. suspicious clinical signs in the animal, or an attack in an area where rabies is enzootic by an animal that could not be caught or killed. Considerable experience has demonstrated, however, that a complete set of negative results obtained in a reliable diagnostic laboratory can usually be accepted with confidence, and that the treatment can be terminated or modified at that point.

More information on laboratory techniques in the diagnosis of rabies