On episode #274 of the science show This Week in Virology, the TWiV team discusses recent cases of polio-like paralysis in California, and the virome of 14th century paleofeces.
You can find TWiV #274 at www.microbe.tv/twiv.
hepatitis a virus
Hepatitis A virus infections associated with berry and pomegranate mix
An outbreak of hepatitis A virus (HAV) infections in eight US states has been attributed to consumption of Townsend Farms Organic Anti-Oxidant Blend frozen berry and pomegranate mix purchased from Costco markets. Since March 2013, 118 individuals have acquired the infection and 80% report having eaten this fruit product. Townsend Farms has recalled some lots of this product because, according to the producer, one of the ingredients of the blend, “pomegranate seeds processed in Turkey, may be linked to an illness outbreak outside of the United States”. The Food and Drug Administration will soon begin testing for the presence of hepatitis A virus in the berry mix.
Hepatitis A virus is a member of the picornavirus family, which also contains poliovirus and rhinovirus. The virion is a naked, icosahedral particle containing a single strand of positive-sense RNA. Infection is typically acquired by ingestion of food contaminated by feces containing the virus. In one scenario, food is contaminated by an HAV-infected food handler who does not practice good hand hygiene. After ingestion, the virus enters the gastrointestinal tract and then passes to the blood. It then replicates in the liver leading to jaundice and elevated serum levels of liver enzymes. After replicating in the liver, HAV passes into the intestine via the bile canaliculi and is then shed in feces. The incubation period of the disease is on average 4 weeks, but infectious particles are present in feces about two weeks before the onset of clinical symptoms. The virus is most likely to be transmitted during this period as the infected individual does not display clinical symptoms.
There are six genotypes of HAV that circulate worldwide. According to the CDC, the virus strain causing this outbreak is HAV genotype 1B, which is often found in North Africa and the Middle East but is rarely isolated in the Americas. Genotype 1b caused a 2013 European outbreak linked to frozen berries, and a 2012 British Columbia outbreak in which a frozen berry blend was implicated. In the BC outbreak the berry blend contained pomegranate seeds from Egypt. This is likely why Townsend Farms recalled the berry mix when they found that it contained pomegranate seeds processed in Turkey.
A well-known outbreak of hepatitis A infection took place in November 2003 among the patrons of a single Pennsylvania restaurant. In this outbreak of 601 patients, 3 died and 124 were hospitalized. Infection was caused by consumption of salsa which had been prepared with green onions grown in northern Mexico that were contaminated with hepatitis A virus.
Transmission of HAV infection can be prevented by proper hand hygiene, avoiding hand contamination with fecal matter, or by using available vaccines.
PS if you buy whole pomegranates, don’t miss this video by the Produce Picker on how to cut them.
Happy as a clam? Maybe not.
This article was written for extra credit by a student in my recently concluded virology course.
by Adriana Lopez
The expression “Happy as a Clam†comes with new meaning as hepatitis A virus has been detected in clams, mussels, and oysters in markets for human consumption. As bivalve shellfish are excellent bio-accumulators of contaminants and chemicals, it is no surprise that they also harbor waterborne viruses such as hepatitis A in areas with poor sanitation. Since hepatitis A virus is spread via the fecal-oral route, food-borne outbreaks due to ingestion of shellfish harvested from polluted waters have not been uncommon.
Despite development of an effective vaccine against hepatitis A virus, it continues to be a serious disease worldwide. In developing countries, access to healthcare and vaccination may not be available and many remain susceptible to infection. Eating raw or undercooked shellfish may pose a serious food safety threat to those unvaccinated in the event the mollusks are infected. Though many people have inapparent infections at a young age and acquire immune memory to hepatitis A, infections in adults can be quite severe and have led to death in some instances. While hepatitis A vaccination has been routinely administered to children in developed countries, anti-vaccine sentiments and public complacency have led to decreased childhood vaccination of hepatitis A. Though herd immunity* will likely protect susceptible individuals in developed nations at present, potential for outbreaks in the future is greatly increased if people continue to refuse vaccination and shellfish suspect to contamination are imported/shipped to market. As such, the U.S. Department of Agriculture (USDA) is considering different approaches to ensure the safety of human health in shellfish consumption.
One of the most promising techniques being studied by the USDA in regard to hepatitis A contaminated shellfish is known as high pressure processing (HPP). This commercial technology is already used for processing of several products in the food industry and demonstrates potential for inactivation of hepatitis A virus in shellfish. In laboratory tests, HPP treatment of 60,000 pounds per square inch of pressure for five minutes exhibited inactivation of 99.9% of hepatitis A in oysters subjected to the pathogen. Since human hepatitis A virus strains are unable to replicate in the tissues of contaminated shellfish, virions damaged or inactivated by HPP processing are unable to replicate and repair themselves to restore infectivity. However, since shellfish osmoregulate – meaning the osmotic pressure of the organism’s body fluids are kept the same as the surrounding water – different pressures may need to be applied to inactivate virus for shellfish found at various depths as mutants may have been selected for pressure sensitivity. While there are some concerns for how this technique may affect the texture and taste of the shellfish, HPP is a promising technique for treatment of shellfish potentially infected with hepatitis A virus.
*herd immunity: the concept that if you immunize ‘enough people,’ (a complicated variable that differs according to the virus, social issues/beliefs, population, and environment) virus spread stops when the probability of infection drops below a critical threshold. Not everyone needs to be immunized to protect the population.
Kingsley, D. (2004). Inactivation of selected picornaviruses by high hydrostatic pressure Virus Research, 102 (2), 221-224 DOI: 10.1016/j.virusres.2004.01.030
Terio, V., Tantillo, G., Martella, V., Pinto, P., Buonavoglia, C., & Kingsley, D. (2010). High Pressure Inactivation of HAV Within Mussels Food and Environmental Virology, 2 (2), 83-88 DOI: 10.1007/s12560-010-9032-7
Kingsley, D., Calci, K., Holliman, S., Dancho, B., & Flick, G. (2009). High Pressure Inactivation of HAV Within Oysters: Comparison of Shucked Oysters with Whole-In-Shell Meats Food and Environmental Virology, 1 (3-4), 137-140 DOI: 10.1007/s12560-009-9018-5