Earlier today I posted on a conference announcement by Dr Nikos Vasilakis of a 5th human dengue virus (DENV) discovery, "the first new dengue virus type in 50 years"
Weeeell. There is more to understanding that headline than I initially thought.
Turns out, and please excuse the complete ignorance of dengue literature in my earlier post, dengue coming to humans from the jungle (mosquito to non-human primate, occasionally spilling over to humans; the so-called sylvatic cycle) is not an entirely new thing. Jungle? What am I on about? DENV-5 is a new sylvatic serotype, and it must be a pretty genetically and antigenically distinct one at that, in order to get a new number.
Dr Vasilakis has written about sylvatic spillovers previously and in great detail - see this article in Nature Reviews|Microbiology from 2011. One comment was particularity interesting...
Whether this holds true for DENV-5 remains to be defined but we know this new serotype (it elicted a very distinct antibody response in infected monkeys from that due to DENV1-4) was isolated from a human in Malaysia during 2007.
Sylvatic dengue viruses have infected humans before but there have been no sustained epidemics and they seem to have been related to 1 of the 4 serotypes currently endemic in humans.
One example, published in PLoS Neglected Tropical Diseases, sequenced the complete genome of a distinct sylvatic DENV-2 serotype isolate that caused dengue haemorrhagic fever (DHF) in a male in Malaysia in 2008. This was the first report of a sylvatic DENV causing DHF in a human. This ancestor of the human lineage DENV-2 was genetically related to a 1970 isolate (P8-1407) also obtained from Malaysia (where Gulden is endemic), after it infected a "sentinel" monkey. Such animals are kept in an area and sampled to see if they have become infected - a way of measuring mosquito and haemorrhagic virus activity in this case.
Another example includes a sylvatic DENV-1 from 2005 isolated in Malaysia and similar to a 1972 sylvatic DENV-1 isolate (P72_1244).
I hope that adds some value to my earlier post.
Also see Crawford Killian's post on this topic from 2011.