Virusphere by Frank Ryan

Author:Frank Ryan [Frank Ryan]
Language: eng
Format: epub
Publisher: HarperCollins Publishers
Published: 2019-02-13T16:00:00+00:00

14

A Taste for the Liver

Viral hepatitis is one of the most serious contemporary plagues of humanity. The problem is a global one, involving a handful of different viruses. The historical identification of the causative viruses was one of the most fascinating scientific investigations of the second half of the twentieth century, and one that has revolutionised certain aspects of epidemiological medicine and public health. It has also introduced new ways of preparing protective vaccines, including the first application of genetic engineering in their preparation. But what of the viruses themselves and their behaviour once they find the target organ: the liver? This organ is the main biological factory of our bodies. It is extensively involved in the digestion of food, in a comprehensive variety of protein manufacture, for example, the blood-clotting factors, and in the detoxification and removal of potential poisons that enter the bloodstream. It is also heavily involved in the fightback against the blood-borne stages of many of the previously described viral fevers, becoming a site of massive viral replication, but fortunately for us all, paradoxically escaping serious damage. This saving grace is down to the fact that these viruses target the Kupffer cells of the liver, which are an intrinsic part of the reticuloendothelial system, which deals with the immune reaction to foreign invaders. The true ‘hepatitis’ viruses preferentially target the glandular cells of the liver, called the ‘hepatocytes’.

To understand this key observation, we need to understand how the liver works as the largest glandular organ in the body.

Architecturally, the liver works through its unique microscopic structure, which is known as the lobular anatomical architecture. And given the many different functions it serves, it means that the liver is a vital organ, as necessary for life as the heart or the lungs. We are familiar with the term ‘cirrhosis of the liver’, which implies a process of severe damage to the lobular architecture of the liver through repeated or persisting damage to the hepatocytes. One of the commonest causes of cirrhosis is long-term excessive consumption of alcohol. Contiguous hunks of the lobules are destroyed, followed by extensive scarring, which destroys the fine lobular architecture. This inevitably reduces the efficiency of the many different functions the liver provides. A similar process of cirrhosis can also be caused by persisting viral infection of the liver.

We have already come across viruses capable of infecting the hepatocytes, such as herpesviruses, cytomegalovirus, Epstein-Barr virus and the yellow fever virus. Our modern world is also subject to prevailing endemics of five different groups of viruses, known as hepatitis A, B, C, D and E, all of which target the hepatocytes. These viruses have no kinship with one another and they give rise to differing patterns of disease, making it essential that medical authorities approach each virus in its own light, examining its particular idiosyncrasies of taxonomic classification, structural anatomy, modes of transmission and, most important of all, making use of such knowledge to address specific prevention and therapy.

Hepatitis A, like the poliomyelitis virus, is a picornavirus.

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