Academic journal article Bulletin of the World Health Organization

Laboratory Diagnosis of Measles Infection and Monitoring of Measles Immunization: Memorandum from a WHO Meeting

Academic journal article Bulletin of the World Health Organization

Laboratory Diagnosis of Measles Infection and Monitoring of Measles Immunization: Memorandum from a WHO Meeting

Article excerpt

Introduction

Measles continues to be a major health problem in developing countries, and results in the deaths of approximately 1.13 million infants and children, with 45 million cases worldwide per annum. Also, some industrialized countries have reported an increase in the number of measles cases over the last 3-5 years. The disease is characterized by a prodromal stage with fever and respiratory symptoms, and 4-5 days after the onset of the respiratory symptoms a maculopapular rash usually occurs. The WHO case definition calls for the presence of fever and rash with one or more of the following symptoms: cough, coryza, or conjunctivitis. Owing to its highly infectious nature, measles affects virtually all children who are not immunized, and in some countries the disease causes over 20% of all infant deaths.

In many countries, measles infection is frequently diagnosed on clinical grounds alone, although the signs and symptoms of the disease are easily confused with those of other conditions that are associated with a rash. Furthermore, several recent studies have indicated that measles virus may circulate in vaccinated populations, causing mild symptoms or even asymptomatic infections. Laboratory diagnosis of measles infection is therefore recommended, both to detect it and to differentiate it from other conditions, including many other infectious diseases (dengue and other arboviral infections, roseola infantum, rubella, varicella, tick-borne rickettsioses, meningococcaemia, and scarlet fever) as well as noninfectious conditions.

The lack of measles diagnostic laboratories in many countries and absence of techniques suitable for use at the primary health care level often result in misdiagnosis of the disease.

In many developing countries measles surveillance is incomplete and does not reflect the incidence or the age distribution of cases. For effective control and the eventual eradication of the disease, a sensitive surveillance system is indispensable, and the ability to diagnose measles unequivocally is therefore essential. The development of measles diagnostic methods that are sensitive, specific, affordable and practicable for screening under field conditions has been recently identified as a high priority by the WHO Expanded Programme on Immunization (EPI). Also, in view of the efforts to develop new generations of vaccines that should facilitate the eradication of measles, diagnostic tools to determine antibody levels and protective immunity are required.

Most of the current laboratory techniques for the diagnosis and surveillance of measles are based on classic biological assay systems, which are both labour-intensive and time-consuming. The advent of molecular biology and the better understanding of immunological principles of protection have created the opportunity to develop more appropriate diagnostic tools for measles.

Under the auspices of WHO, a network of regional and national laboratories for the diagnosis of viral diseases has been established for the laboratory confirmation, epidemiological surveillance, and reporting of diseases caused by human immunodeficiency virus (HIV), enteroviruses, arboviruses, and respiratory viruses. It is now proposed to use this network or establish a similar network for measles. The present article describes the proposed laboratory network, reviews available laboratory tests, and recommends at what level the tests should be implemented.

The laboratory network

The capability to confirm the clinical diagnosis of measles is required, especially with increased immunization coverage and the diverse clinical presentation. As global control of measles is approached, the contribution of the diagnostic capabilities at all levels will become increasingly important. Experience has shown that a tiered system of referral laboratories is required, with essential capabilities available at the local level, supported by more sophisticated capacities in regional laboratories and international reference centres. …

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