Wednesday, December 7, 2016

Detection of the Hepatitis A Virus

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.
            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.
            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.
Purpose of TaqMan Probe Photo Credit: Manit Arya
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.