Emerging Disease: Severe Fever with Thrombocytopenia Syndrome (SFTS)
The appearance of new and deadly disease in central China has been linked to a previously unknown virus. The disease, descriptively named Severe Fever with Thrombocytopenia Syndrome (SFTS), is marked by fever, gastrointestinal distress, and in some cases, a mortality approaching 30%. Heightened surveillance of the disease began in 2009, though reports of the disease began filtering out of China as many as five years ago.
Originally thought to be associated with infection by Anaplasma phagocytophilum, failure to isolate this pathogen in most clinical cases, and isolation of novel virus seem to suggest that this disease is in fact, the result of this previously unknown virus, though researcher’s do note that they have not properly determined this via Koch’s postulates.
There’s a reason that many diseases, including the flu generally come from Southeast Asia every year, and often times are believed to have come from China. The social, cultural, and agricultural conditions in China lead to humans living in close proximity with domesticated swine and fowl. This is a perfect environment in which viruses can swap genetic material and jump between species.
Consider for a moment the geographic occurrence of SFTS in China (image taken from Yu et al. 2011)
Geographic Distribution of SFTS in China from Yu et al. 2011
Compare this with a map showing the distribution of agriculture in China:
Further compare these two with a map showing the population densities in China:
Though certainly not a scientific analysis, these maps suggest that the areas more affected by this particular disease are not only the highest with respect to population density, but are also areas of high agricultural density. Again, this results in humans and domestic animals, specifically swine and fowl, which are known reservoirs of influenza at the very least, living in extremely close proximity, creating an environment conducive to viruses acquiring the ability to infect a new host species.
Indeed there is further evidence from sequence analysis and phylogenetic tree construction that implies this new virus originally infected animals, and has acquired the ability to infect humans.
Firstly, this virus is a member of the Bunyaviridae family of viruses; this particular family of viruses are vector-borne viruses, usually transmitted by mosquitoes, ticks, sandflies, etc, but are sometimes found in rodents, as is the case with hantavirus. More specifically, the SFTS virus is classified in the genus Phlebovirus, which are transmitted by the Phlebotominae sandfly, a blood-feeding fly known to transmit a number of diseases between warm-blooded animals.
Whether or not this virus will become a concern globally remains to be seen, but in my opinion, this is not very likely. Again, the virus is transmitted via arthropod vectors, and thus far is not transmitted from human to human as was the case with SARS. SARS is noteworthy not only as an emerging disease, but as a genuine scientific hysteria… similar to the swine flu hysteria of a couple of years ago. Recall that initial reports regarding the mortality of SFTS claimed mortality rates as high as 30%, though later reports suggest a mortality of about 12%, which is still extremely lethal. That said, trends in viral evolution tend towards decreased pathogenicity over time; it’s more beneficial to the virus to keep the host alive, as more viral particles will be produced.
That said, irrespective of the mortality of this particular virus, dealing with this particular virus and the disease that it causes are going to primarily issue of sanitation as opposed to actual medical intervention. Certainly bubonic plague, which is still around, can be killed by antibiotics, though the disease can be primarily dealt with by simply keeping the environment cleaner. Eliminating rodents, removing fleas, and keeping houses clean and free of arthropod vectors does wonders for preventing plague. The living conditions in particular in China are what resulted in the appearance of this disease, and what resulted in its spread among the dense population of China’s unique urban agricultural environment.
As a final note, this represents another example of viruses being agents of evolution and genetic diversity, and not disease. Indeed viruses do in fact cause disease, though I personally believe this to be an unfortunate side effect of their true role in the global biome, as I’ve previously discussed here and here.
