INFECTIOUS DISEASES
MeVA Assay Aids Public Health Labs
in Fight Against Measles
by Alisa Bochnowski, senior specialist, Respiratory Diseases
Almost 20 years after measles was
declared eradicated, outbreaks of the
virus continue to plague the United
States. International travel to areas where
the virus remains endemic coupled
with communities with low vaccination
rates have led to hundreds of infections
over the last decade and, subsequently,
additional testing assistance from public
health laboratories. With the number of
confirmed cases currently surpassing
pre-eradication declaration levels—and
still rising—a new assay has given public
health laboratories a new tool in the fight
against the spread of the disease.
Rash or Reaction?
Measles vaccination of vaccine naïve
individuals is an important part of curbing
an outbreak; however, approximately 5%
of individuals vaccinated with a measles-
containing vaccine develop clinically
indistinguishable symptoms from measles
infection (e.g., fever, rash). The routinely
used measles virus reverse transcription
PCR (RT-qPCR) assay (MeV) cannot
distinguish between wild-type infection
and vaccine reaction, and sequencing,
which could delineate between wild-type
and vaccine associated rash, can take
up to 72 hours to yield results. To assist
in the rapid differentiation between the
two, CDC developed the Measles Virus
genotype A RT-qPCR (MeVA) based on the
detection of genotype A nucleoprotein
regions that are unique to the vaccine.
This assay was adopted by the Vaccine
Preventable Disease Reference Centers
in 2018 and used for testing during
outbreaks in New York, Washington and
Texas.
The reference center in Minnesota
recently employed the MeVA assay in
the case of a child from Minnesota that
received the MMR vaccine and then
traveled internationally. After returning
home to Minnesota, the child began
26
LAB MATTERS Spring 2019
exhibiting symptoms that raised the
suspicion of measles three weeks post-
vaccination. Because of the recent travel
and the vaccination history, the clinician
wanted to rule out wild-type measles
infection. At the Minnesota Department
of Health, they first ran the MeV assay,
which resulted in a late positive (Ct score
~38). Attempts to genotype this specimen
would likely have been indeterminate
since the sensitivity of the genotyping
assay decreases in specimens with Ct
scores higher than 34 and genotyping
would have pushed the result reporting
back 24-72 hours. Minnesota was able
to run the MeVA assay, which was
indeterminate, and combined with
early lab data and epidemiological case
investigation make a determination
to treat the rash as unrelated to either
measles or the vaccine.
Speeding Results for Treatment
Not only does the MeVA assay cut down
on time to diagnosis, it can also spare
patients from unnecessary medical
treatments and the public from panic.
During a 2017 outbreak of measles in
Washington, the delay in genotyping
confirmation resulted in two pregnant
women being given IVIG after exposure to
individuals who ended up having vaccine-
associated rashes, not wild-type cases.
Had MeVA been available, these pregnant
women would not have been treated with
IVIG. In another instance in Washington,
a person with a vaccine-associated rash
was reported to the media as a suspect
measles case due to concern about
multiple exposure sites. The public health
system had to mitigate public concern
and respond to this case for several days
before the rash was confirmed as vaccine
related. During the current outbreak of
measles in Washington and Oregon, the
MeVA assay is being used to differentiate
between wild-type and vaccine
associated rashes saving individuals from
Did you know?
You can request MeVA testing when
submitting specimens to the reference
centers for testing. By directly requesting
MeVA and supplying patient vaccination
history you can help identify the correct
diagnostic method and expedite testing.
Please contact [email protected]
for more information.
unnecessary medical treatments and the
public from unwarranted concern.
Sociopolitical trends coupled with a high
incidence of disease abroad indicate that
measles will continue to be an ongoing
public health issue in the United States.
Every measles outbreak affects the entire
public health infrastructure, but the
availability of the MeVA assay provides
a new tool to help public health officials
and clinicians make informed decisions
and to appropriately allocate resources
during outbreaks. n
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