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I recently read a somewhat alarmist notice by the state board of health in NH who claimed that some man had tested positive for Jamestown Canyon virus, a rare disease even in its natural environment of Colorado. Supposedly the man has not travelled out of state.

So, I am wondering how it is possible for such a virus to be transmitted. My understanding is that a mosquito only bites twice then it breeds, so basically what has to happen is the first bite has to be on an infected human (or animal) and then the second bite on the victim. So, if this guy got Jamestown Canyon virus, then he must have been in mosquito range of some other infected creature of which we have no knowledge.

Now, unless there is some type of animal that is endemically infected with Jamestown Canyon virus which is transferable to humans, it would seem unlikely to me that there would be any source from which the man could have gotten the virus.

So, I am wondering what kind of plausible scenario would have made this disease transmission possible, assuming it really occurred?

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Via Wikipedia:

The virus is transmitted in saliva to a vertebrate host when an infected mosquito takes a blood meal. It thus cycles between mosquito and vertebrate amplifier hosts, mainly white-tailed deer. In a study from Newfoundland, JCV was significantly associated with large mammals such as sheep, cattle and horses. In Michigan and Ontario moose and bison are believed to be the primary reservoir.[3]

The virus winters in mosquito eggs, which it reaches by transovarial transmission. The female mosquito lays eggs that carry the virus, and the offspring can transmit the virus to deer or ruminants and humans. Infected mosquitoes were found equally distributed throughout the state of Connecticut, irrespective of land use.[4]

So, the virus has a reservoir in (primarily) deer, an infected deer gets bitten by a female mosquito, the mosquito lays eggs with the virus, the resulting mosquitoes can spread the disease by biting another large animal or human.

The reservoir needs to be large enough to ensure the virus survives year over year, but there doesn't need to be any special mechanism for it to travel outside the predominant range; there have been cases in several states in the northeast, though rare.


References [3] and [4] are:

[3] Goff G, Whitney H, Drebot MA (2012). "Roles of host species, geographic separation, and isolation in the seroprevalence of Jamestown Canyon and snowshoe hare viruses in Newfoundland". Appl. Environ. Microbiol. 78 (18): 6734–40. doi:10.1128/AEM.01351-12. PMC 3426688. PMID 22798366.

[4] Andreadis TG, Anderson JF, Armstrong PM, Main AJ (2008). "Isolations of Jamestown Canyon virus (Bunyaviridae: Orthobunyavirus) from field-collected mosquitoes (Diptera: Culicidae) in Connecticut, USA: a ten-year analysis, 1997–2006". Vector Borne Zoonotic Dis. 8 (2): 175–88. doi:10.1089/vbz.2007.0169. PMID 18386967.

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