Detection
of the Hepatitis A Virus
By Samantha Lin
Hepatitis A
is one of the five
hepatitis viruses that infect the liver. These viruses are a major health
problem since it can affect millions of people around the world. Although there
is a vaccine that prevents the virus, transmission is still possible especially
in countries without access to the vaccine. Out of the five hepatitis viruses,
Hepatitis A accounts for half the total number of human hepatitis infections
diagnosed worldwide. Although there is no specific treatment after contracting
the virus, there are ways of detection to help prevent it. Each year, there are
approximately 30,000
to 50,000 cases of Hepatitis A in the United States. So what are the main
sources and how do we prevent this virus?
Contaminated Produce
Hepatitis A virus is transmitted
through the ingestion of contaminated food as well as through the fecal-oral
route. Common foods associated with the virus are contaminated drinking water,
raw or undercooked shellfish from contaminated water, and raw produce. Green
vegetables are the most common produce (spinach, green onions, and lettuce) that
are contaminated with Hepatitis A virus. These produce are exported and grown
in large volumes and are commonly eaten raw in ready-to-eat salads. The virus
can enter the produce in a variety
of locations including the roots from the soil, as well as the leaves. Since
the virus is commonly found in contaminated water, washing these vegetables can
be a source of contamination. Since the produce is grown in such large numbers,
further contamination could occur during processing. Contamination could occur
in the soil where they grow, in the handling process, and when washing the vegetables.
These vegetables are often consumed raw, which makes consumers susceptible to
the Hepatitis A virus.
Prevention
Washing your hands seems like a
simple mundane task, but it is an effective method to prevent the spread of the
virus. Since the virus can often be spread through food handlers, sanitation of
hands, as well as the food plant is important. Hepatitis A has no specific
treatment and recovery can take several months. There are both mild and severe
symptoms which includes fever, diarrhea, and jaundice. To prevent exposure
to the virus, sanitation is very important. Especially when traveling to areas where
hepatitis A is common, avoid food from street vendors. Foods that are eaten
raw should be avoided since they may have been washed in contaminated water.
Food can also be cooked properly on your own to ensure proper sanitation
method.
Detection
In terms of detection, the Nested Real-Time
Polymerase Chain Reaction (NRT-PCR) can be used to find presence of the virus.
Since Hepatitis A can cause outbreaks, a rapid detection is necessary. NRT-PCR is a highly
sensitive and specific method that combines multiple PCR methods. It uses a TaqMan
probe for detection that allows for good specificity and reproducibility in
the detection. The probe is basically a fluorescent light that looks
specifically for a gene during Polymerase Chain
Reaction (PCR). As the name suggests, the Polymerase Chain Reaction
consists of multiple cycles.
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TaqMan Probe
The photo shows how the TaqMan probe is used to detect the target
Hepatitis A virus. The probe contains a reporter dye on one end, and a quencher
on the other. The reporter and quencher which are shown as the star and circle
are used together in order to emit a fluorescence when the virus is detected.
The reporter is a fluorescent molecule that monitors the PCR. As the virus is
detected, the PCR accumulates and the fluorescence increases. When the quencher
is close to the reporter (TaqMan probe is intact), it suppresses the
fluorescence. However, when the virus is detected and the probe is broke apart
and separates the reporter and quencher. This then gives of a fluorescent
light. The data can be seen with a computer and can show positive or negative
for the detection of the virus.
With the
help of this detection method, the number of Hepatitis A
cases is gradually declining. Along with the vaccine, detection methods
like this have allowed us to find the Hepatitis A virus in the vegetables
before distribution. This helps in surveillance and reduces the number of
outbreaks. The use of nested real-time PCR is a rapid method that has proven to
work with the Hepatitis A virus. Using this new technology, it can be applied
to other pathogens in order to minimize other diseases. This method can detect the
virus and therefore be able to help prevent outbreaks. I can’t wait to see what
impact this method has.