Generation of a Lineage II Powassan Virus (Deer Tick Virus) cDNA Clone: Assessment of Flaviviral Genetic Determinants of Tick and Mosquito Vector Competence

Kenney Joan L. , Anishchenko Michael , Hermance Meghan , Romo Hannah , Chen Ching-I , Thangamani Saravanan , and Brault Aaron C.
Published Online:1 Jul 2018


The Flavivirus genus comprises a diverse group of viruses that utilize a wide range of vertebrate hosts and arthropod vectors. The genus includes viruses that are transmitted solely by mosquitoes or vertebrate hosts as well as viruses that alternate transmission between mosquitoes or ticks and vertebrates. Nevertheless, the viral genetic determinants that dictate these unique flaviviral host and vector specificities have been poorly characterized. In this report, a cDNA clone of a flavivirus that is transmitted between ticks and vertebrates (Powassan lineage II, deer tick virus [DTV]) was generated and chimeric viruses between the mosquito/vertebrate flavivirus, West Nile virus (WNV), were constructed. These chimeric viruses expressed the prM and E genes of either WNV or DTV in the heterologous (from one species to another) nonstructural (NS) backbone. Recombinant chimeric viruses rescued from cDNAs were characterized for their capacity to grow in vertebrate and arthropod (mosquito and tick) cells as well as for in vivo vector competence in mosquitoes and ticks.

Results demonstrated that the NS elements were insufficient to impart the complete mosquito or tick growth phenotypes of parental viruses; however, these NS genetic elements did contribute to a 100- and 100,000-fold increase in viral growth in vitro in tick and mosquito cells, respectively. Mosquito competence was observed only with parental WNV, while infection and transmission potential by ticks were observed with both DTV and WNV-prME/DTV chimeric viruses. These data indicate that NS genetic elements play a significant, but not exclusive, role for vector usage of mosquito- and tick-borne flaviviruses.



I’m no microbiologist and without the full article and better understanding of what this NS backbone is, 

The study shows 4 things:

  1.  The NS elements gave a 100 fold “test tube” increase in viral growth in tick cells.  These organisms are extremely fastidious and difficult to study in a lab.  It’s even tougher to figure out how this plays out in the human body.
  2. INFECTION & TRANSMISSION potential by ticks was observed with both DTV and WNV.  Read that sentence again.
  3. Why didn’t this make the news?
  4. Mosquitoes are nasty but ticks are a whole other monster.  Mosquito research gets all the money.  Why?  This pdf by Lyme Advocate Jill Auerbach shows that while there were only 5,700 cases of WNV in 2012, research dollars were $29 million, whereas, Lyme cases in 2012 were 312,000 but received only $25 million.  While the number of the infected continue to soar the research dollars for Lyme are radically reduced in successive years:

Disease New Cases (annual) NIH Funding

Hepatitis C 2012




$112 million

West Nile Virus 2012


$29 million



$3 billion (11% total NIH budget)

Influenza 2012


$251 million

Lyme disease 2012


$25 million

Lyme disease 2013


$20 million

*Lyme disease 2004             198,040                                  $34.4 million


      New Cases 2015

CDC funding 2016

Lyme Disease

           380,690  (10 x 38,069)
2016 numbers not yet available

 $10 million

This does NOT include other Tick-borne diseases

Houston, we have a problem.