Monkeypox

Test code: S0025 - Qualitative detection of monkeypox virus (MPV) by polymerase chain reaction

Monkeypox virus (MPV) is an orthopoxvirus that is genetically distinct from other members of the Poxviridae family, including the variola, vaccinia, ectromelia, camelpox, and cowpox viruses. It was first identified as the cause of a pox-like illness in captive monkeys at the State Serum Institute in Copenhagen in 1958. Currently, MPV is regarded as the most important orthopoxvirus infection in human beings since the eradication of smallpox. By contrast with variola virus, however, MPV has a wide range of hosts, which has allowed it to maintain a reservoir in wild animals while sporadically causing human disease, and has precluded its global eradication by human vaccination.

Serological surveys suggest that many animals are infected with MPV under natural conditions, including squirrels, non-human primates, and rats. After 1997, human monkeypox attracted little attention worldwide until May, 2003, when the CDC received reports from the central USA of patients who developed fever and a rash after close contact with pet prairie dogs and other mammals. This outbreak, with a total of 81 identified cases (40% laboratory confirmed), was due to human monkeypox, a disease that had previously never been recorded in the western hemisphere. Traceback investigations identified an international shipment of about 800 small mammals from Ghana to Texas as the probable source for the introduction of MPV into the USA. Gambian giant rats from this shipment were transported from Texas via an Iowa animal vendor to a pet distributor in the Chicago area, where they were co-housed with prairie dogs (Cynomus spp). Infected prairie dogs were subsequently transported from the distributor to a vendor in Wisconsin, where they were sold to the index patient and others. Infected prairie dogs, which through a non-linear chain of distribution may have also been sold at "swap meets" in Illinois, Indiana, and Ohio, have been implicated as the source of primary infection for most of the US cases.

Although virus isolation can be used to diagnose monkeypox virus infection, a long incubation period is required to obtain results. Viral culture also increases the potential risk of laboratory personnel contacting this virus. Furthermore, viral culture is less sensitive, reliable and specific than polymerase chain reaction (PCR)-based techniques. Serological testing for MPVantigens is difficult because of the close antigenic relation between surface antigens among the orthopoxviruses. Various serological methods are available, including a virus-neutralising test with hyperimmune reference sera, a haemagglutination-inhibition assay with chicken erythrocytes, and detection of specific viral antibodies. The sensitivities of these tests vary (50–95%), however, and serological tests are not useful for the diagnosis of acute infection. Expert opinion is that no serological assay currently available can reliably diagnose orthopoxvirus infections with high sensitivity.

Monkeypox detection by PCR is the most rapid, sensitive and specific method for the diagnosis of this infection.

Utilities:

• Confirm the disease causing agent
• Ensure that animal groups and populations are free of MPV
• Early prevention of spread of this virus among a population
• Minimize human exposure to this virus

Specimen requirement: Lesion scab or vesicle fluid swab.

For specimen types other than those listed here, please call to confirm specimen acceptability and shipping instructions.

For all specimen types, if there will be a delay in shipping, or during very warm weather, refrigerate specimens until shipped and ship with a cold pack unless more stringent shipping requirements are specified. Frozen specimens should be shipped so as to remain frozen in transit. See shipping instructions for more information.

Turnaround time: 2 business days

Methodologies: Qualitative PCR

Normal range: Nondetected