A small, innocuous looking virus with just three genome segments, causes one of the most deadly infections in the United States. Hantaviruses circulate worldwide causing either hemorrhagic fever with renal syndrome (HFRS) or, in the case of the North and South American strains, Hantavirus pulmonary syndrome (HPS). Famously recognized in 1993 in the Four Corners region of the U.S., Sin Nombre Virus, a strain of hantavirus, still infects at least a few people in the U.S. every year.
Hantaviruses are thought of as a virus people only get directly from rodents, which cannot be transmitted person-to-person. Infections result from exposure to contaminated excretions/secretions of rodents infected with the virus, though the rodents themselves show no signs of disease. These rodents also transmit the virus to each other.
Coevolution with hosts
While many species may be drivers for the evolution of another, the term coevolution is applied when two species influence each other so much that they are evolving together, where one undergoes genetic change the other responds with genetic change. They are undergoing speciation together. It was thought for a while that rodents were unharmed by the virus due to long, ongoing rodent-hantavirus coevolution. Significant phylogenetic congruities have been shown, for example, the phylogeny shown:
New research might be indicating that’s not as true as we thought, phylogenetic analysis studies may be flawed, host range my be bigger, and rodent speciation doesn’t match up. While I’m not enough of a hantavirus or rodent expert to weigh in on this, certainly “whoa if true” to the coevolution theory.
In 1996, an outbreak of hantavirus in Argentina occurred, yet there was especially low rodent density and there was strong evidence for person-person transmission.
Then in 2011, a similarly unusually outbreak in Chile occurred. An Andes hantavirus, a close relative to the North American Sin Nombre virus (meaning “no name” as the native Americans), was shown to be transmitted person-to-person. In an outbreak of 5 human cases, symptoms developed in 2 household contacts and 2 healthcare workers after exposure to the first patient patient. Analysis of isolates from each patient supported person-person transmission for the all secondary-case patients.
Hantavirus found in human saliva
You might optimistically tell yourself that maybe this Andes hantavirus was a unique case. And maybe hantavirus was still really just a rodent disease that rarely spilled over to a person. But in Sweden in 2008, a Puumala hantavirus that causes hemorrhagic fever with renal syndrome (nephropathia epidemica) was found in human saliva of 10 patients. Whether or not this is actually a mode of transmission or not remains to be seen, but it does seem like hantaviruses are becoming more adept at infecting and transmitting between human hosts.
Climate change’s effect on hantavirus?
Hantaviruses frequently jump hosts and seem to circulate amongst bats, moles, shrews, and rodents, but climate change and human impact generally decreases rodent diversity. Intuitively you may assume hantaviruses would be less able to jump hosts as global warming/human impact goes on.
Perhaps colder areas will actually see a decrease in hantavirus outbreaks as a result of global warming, due to the expected decrease in vole/northern rodent species populations. Yet that doesn’t seem to be what’s happening. Hantavirus surveillance has indicated an INCREASE, not only in outbreaks, but in genetic diversity and abundance in rodent populations.
If climate change does end up resulting in low rodent densities, this may also present another hantavirus risk– providing selective pressure for the virus to change transmittance route.
- University of Utah. “Big, Old Mice Spread Deadly Hantavirus.” ScienceDaily. ScienceDaily, 9 January 2009.
2. Phylogeny and Origins of Hantaviruses Harbored by Bats, Insectivores, and Rodents. Wen-Ping Guo-Xian-Dan Lin-Wen Wang-Jun-Hua Tian-Mei-Li Cong-Hai-Lin Zhang-Miao-Ruo Wang-Run-Hong Zhou-Jian-Bo Wang-Ming-Hui Li-Jianguo Xu-Edward Holmes-Yong-Zhen Zhang – PLoS Pathogens – 2013
3. An Unusual Hantavirus Outbreak in Southern Argentina: Person-to-Person Transmission? Rachel Wells – Emerging Infectious Diseases – 1997
4. Hantavirus RNA in Saliva from Patients with Hemorrhagic Fever with Renal Syndrome. Lisa Pettersson-Jonas Klingström-Jonas Hardestam-Åke Lundkvist-Clas Ahlm-Magnus Evander – Emerging Infectious Diseases – 2008
5. Person-to-Person Household and Nosocomial Transmission of Andes Hantavirus, Southern Chile, 2011. Constanza Martinez-Valdebenito-Mario Calvo-Cecilia Vial-Rita Mansilla-Claudia Marco-R. Palma-Pablo Vial-Francisca Valdivieso-Gregory Mertz-Marcela Ferrés – Emerging Infectious Diseases – 2014