TWiV #27: Leaving latency

twiv_aa_2001On episode #27 of the podcast “This Week in Virology”, Vincent, Dick, Alan, and Saul Silverstein revisit an ebolavirus needlestick accident, and discuss the role of TLR3 in formation of Negri bodies, a New England college closed by norovirus gastroenteritis, hand, foot, and mouth disease outbreak in China, and the exit of herpes simplex virus from latency by synthesis of VP16.

Click the arrow above to play, or right-click to download TWiV #27 or subscribe in iTunes or by email.

Hand, foot, and mouth disease outbreak in China

hand-foot-mouth-diseaseAn outbreak of hand, foot, and mouth disease in China has lead to 41,000 infections and 18 deaths this year. What is this disease and what causes it?

Hand, foot, and mouth disease (HFMD) is a rather common viral infection of children. There were 80,000 recorded cases of the disease just in China for 2007. The disease occurs globally, displaying seasonality (summer, early autumn) in temperate climates. It is caused by members of the genus enterovirus, Coxsackievirus A10 and A16 or enterovirus type 71, viruses that are related to poliovirus. The virions are composed of a positive-sense RNA surrounded by a capsid built with four different viral proteins. The predominant virus in the 2007 outbreak in China was enterovirus type 71. The identify of the virus causing the current outbreak is not known, but enterovirus 71 has already been identified in several patients.

HFMD is typically acquired through close contact with an infected individual. It begins with nonspecific symptoms such as fever and malaise, and is followed by the development of ulcerating sores on the tongue, gums, and insides of the cheeks. A skin rash then appears on the hands and soles of the feet. The infection is spread to others by the virus that is present in pharyngeal secretions, saliva, and fluid from the skin blisters.

Outbreaks of HFMD typically involve children because they are not immune to infection, and because children physically intereact in ways that promote transmission, especially in summer months when outdoor play is common. The disease is much less prevalent in adults because they are protected by immunity conferred by childhood infection.

HFMD is an acute viral infection which resolves within 1-2 weeks. When caused by Coxsackieviruses, the course of the disease is usually uneventful. However, enterovirus 71 can enter the central nervous system where it may cause encephalitis or a polio-like paralysis. How the virus reaches this site is not known. By analogy with poliovirus, we assume that the virus enters the bloodstream – possibly after replicating in the intestine – and then makes its way to the spinal cord. This virus has emerged as a significant neurological pathogen in Taiwan.

There are no vaccines or antiviral drugs available for treatment of HFMD, and little research is done on the viruses that cause the disease. This situation is likely to change with the emergence of enterovirus 71 as the most significant neurotropic enterovirus in some areas of the world.

Zhang, Y., Tan, X., Wang, H., Yan, D., Zhu, S., Wang, D., Ji, F., Wang, X., Gao, Y., & Chen, L. (2009). An outbreak of hand, foot, and mouth disease associated with subgenotype C4 of human enterovirus 71 in Shandong, China Journal of Clinical Virology, 44 (4), 262-267 DOI: 10.1016/j.jcv.2009.02.002

QIU, J. (2008). Enterovirus 71 infection: a new threat to global public health? The Lancet Neurology, 7 (10), 868-869 DOI: 10.1016/S1474-4422(08)70207-2

Arita, M., Wakita, T., & Shimizu, H. (2008). Characterization of pharmacologically active compounds that inhibit poliovirus and enterovirus 71 infectivity Journal of General Virology, 89 (10), 2518-2530 DOI: 10.1099/vir.0.2008/002915-0