Vaccination programs have controlled measles infection in many parts of the world, and the interruption of measles virus (MV) transmission has been demonstrated in some countries including the United States (1
) and Australia (4
). Despite these achievements, measles continues to be a major childhood disease, causing nearly 800,000 fatalities annually (22
), and this has prompted the World Health Organization to undertake a phased approach to its elimination in other geographical locations.
Laboratory diagnosis of measles infection is achieved primarily through the demonstration of MV-specific antibodies. The introduction of PCR into diagnostic laboratories has provided an alternative method to virus isolation for detecting MV strains and has facilitated their characterization. In the MV genome, genetic variability exists in the nucleoprotein (N) and hemagglutinin (H) genes, with the greatest degree occurring in the carboxy-terminal end of the expressed N gene (1
). This variability can be utilized in molecular typing of wild-type MV strains. A standard genotyping system and nomenclature for characterization of MVs have been established by the World Health Organization and are updated annually (24
). Currently, eight clades, designated A to H, have been identified and incorporate 22 genotypes (24
When coupled with epidemiologic techniques, molecular characterization has proven to be a powerful adjunct to measles control by providing the means to identify the infected source and subsequent transmission pathways of the virus. In addition, it facilitates assessment of the effectiveness of measles vaccination programs by detecting temporal changes in MV genotypes within a particular geographical region and distinguishing indigenous from imported transmission.
As nucleic acid techniques are used by more virology laboratories worldwide, the number of newly identified genotypes and the rate at which they have been found have increased (24
). This suggests that our understanding of the extent of MV genetic heterogeneity is incomplete. To obtain a better understanding of the global picture of MV genotypes, the expansion of measles surveillance to remote areas of the world that lack the infrastructure for appropriate collection, processing, storage, and shipment of specimens for virologic testing is important.
MV initially infects and replicates in the respiratory epithelium. The virus extends to local lymph nodes where it is amplified, resulting in viremia. A few days before the onset of rash, virus can be cultured from the mucous membranes of the nasopharynx, conjunctivae, and mouth of an infected individual, suggesting that the respiratory tract is the site of virus release and that oral fluid is a rich source of the virus (19
). Accordingly, oral fluid (saliva) has been used successfully for the detection of MV-specific antibodies (2
) and also for the detection of MVs by reverse transcriptase (RT)-PCR and their subsequent genetic characterization (12
). A major advantage of oral fluid dried onto filter paper is that it provides a format for specimen transport that is simple, convenient, and inexpensive. In addition, it offers the potential for use as a single specimen for measles serological confirmation and MV genotyping.
The utility of dried blood spots on filter paper has also been established for the detection of MV-specific antibodies (5
) and the detection of MV RNA by RT-PCR (6
). However, we have shown that blood for the detection of MV RNA by RT-PCR is a less optimal specimen type than samples collected from the respiratory tract, where MV RNA remains detectable for a period of up to 2 weeks after rash onset (21
). Consequently, we compared the suitability of oral fluid samples dried onto filter paper with that of nose/throat swabs (NTS) for simultaneous detection and genetic characterization of MV strains in laboratory-confirmed measles cases, including an assessment of the effects of heat, humidity, and transport time.