Wednesday, August 10, 2016

Beasts Aplenty

The world is on fire about arthropod-borne viruses, or "arboviruses". The simple mosquito bite can transmit a battery of diseases, including the currently popular West Nile virus, dengue virus, and zika virus. While these viruses are not new, the emergent nature has taken our media by storm, and is illuminating the universe of zoonotic diseases.

There's one virus, though, that for me, was the original. This virus has infected history and popular culture alike, but still hasn't achieved the level of fear that we see with some of these other, more emergent viruses. The fact that more people aren't absolutely terrified of this virus is beyond me, considering that it is the most deadly virus in the world, whereas dengue and zika have relatively low mortality rates.

Image from 7 Bloodcurdling Werewolf Tales That Will Keep You Up at Night
The rabies virus is a unique, non-segmented, negative stranded RNA virus of the Rhabdoviridae family. Unlike most diseases that hijack the circulatory system for dispersal through the body, rabies attacks the nearest nerve. The virus actually replicates in the nerve cell, slowly moving up to the brain.

The rabies virus is quite literally shaped like a bullet. The lipid envelope is lined with glycoproteins that help with viral attachment.
The slow progression is part of the issue, because most people don't know they've been exposed to the virus until much later, when the symptoms start to set in. By the time symptoms occur, the virus has replicated and multiplied significantly, so a large amount of virus hits the brain.

The first symptoms are nonspecific and mild, with fever, weakness, headaches, and malaise. Some patients report a tingling and itching sensation at the site of the bite. After the nonspecific symptoms, confusion, anxiety, and agitation set in. Cerebral dysfunction leads to fits, and the body starts to lose the ability to sense temperature, pain, and pressure. These fits lead to erratic behavior.

It is common for patients to experience a phobia of water, too. As the virus is most commonly transmitted by bite, the fear of water is an evolutionary advantage for the virus. Without water, the virus is concentrated in saliva, without being diluted by water, making it more likely to be transmitted.

It is also possible for patients to experience "dumb rabies", with lethargic and comatose-like symptoms prior to death.

Once these symptoms start, recovery and survival is extremely rare. Disease progression usually lasts between 1 and 3 weeks, from start to finish. There have been only a small number of people who have survived a rabies infection, some from experimental treatments, and others for unknown reasons. Post-exposure prophylaxis of human anti-rabies antibodies needs to be administered before the onset of these symptoms, otherwise death is guaranteed.

Given its intense lethality, rabies has inspired a significant amount of medical development. Louis Pasteur developed the first rabies vaccine in 1885. Pasteur achieved successful development of the vaccine by serial attenuating, or weakening the virus in rabbits.

Rabies kills approximately 60,000 people a year, worldwide. We don't typically worry about it here in North America, due to pet vaccination and local animal control, so most of the deaths occur in poor, rural, and developing regions of the world. In the last two weeks, though, Sheffield, MA has been experiencing the worst rabies outbreak in decades. Residents of Sheffield have reported rabid foxes, skunks, and even a RABID WOODCHUCK.

Rabies has played an integral part in the development of some of the most horrific monsters. The concept of man morphing into a wild beast evolved from human exposures to animal diseases. The best examples of this are the werewolf and Dracula (or, vampires in general).

It all starts with a bite.

1 comment:

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