|Aedes Mosquito Ranges In the United States|
. . . yesterday's widely reported `1st case' (in Harris County, Texas) is far from the first Zika infected traveler to arrive in the United States. Yet somehow that narrative has made it all the way from local media reports to appearing in the prestigious BMJ (British Medical Journal) News this morning:
BMJ 2016; 352 doi: http://dx.doi.org/10.1136/bmj.i212 (Published 13 January 2016) Cite this as: BMJ 2016;352:i212
A traveler who had recently returned from Latin America to Texas has had Zika virus infection diagnosed, the first case to be recorded in the United States, local health officials report. The case was identified in Harris County, Texas, which includes the city of Houston.Umair A Shah, executive director of Harris County Public Health and Environmental Services, warned travelers that Zika virus can now be found in much of the world. “We encourage individuals traveling to areas where the virus has been identified …
In fairness, the BMJ isn't the only publication to have regurgitated this `news' (see Medscape Medical News First Zika Virus Case in Continental United States Confirmed in Texas).
Those who have been following Zika for more than a few weeks are fully aware that the virus has been imported into the United States a number of times, going back more than five years.
Scientific American got the story right yesterday:
A patient in Texas is the most recent of the 20+ U.S. travelers that have acquired the disease outside America
As did the always reliable Maggie Fox of NBC News.
Zika virus, suspected of causing severe birth defects in Brazil, has been diagnosed in a traveler in Houston.
Officials in Harris County confirmed the case Monday. It's not the first time a tourist has carried Zika to the U.S., the Centers for Disease Control and Prevention says. And Zika is not poised to spread across the country just yet, but some experts are worried.
(Continue . . .)
In fact, five years ago the EID Journal carried a remarkable Dispatch on the first Probable Non–Vector-borne Transmission of Zika Virus, Colorado, USA, involving two researchers infected in Africa, one of whom returned to the United States and passed the virus (presumably via sexual contact) to his wife.
This was the first instance where sexual transmission of an Arbovirus was suspected, the author’s writing:
Results also support ZIKV transmission from patient 1 to patient 3. Patient 3 had never traveled to Africa or Asia and had not left the United States since 2007. ZIKV has never been reported in the Western Hemisphere. Circumstantial evidence suggests direct person-to-person, possibly sexual, transmission of the virus.
Since then there have been at least twenty imported cases of Zika reported in the United States. Given that most people infected experience mild or subclinical symptoms, the real number is undoubtedly much higher.
What we haven't seen (outside of Puerto Rico) is locally acquired Zika via infected mosquitoes.
Last month in The International Exchange Rate Of Infectious Diseases we looked at the process by which international travelers - infected with Zika, Dengue, or Chikungunya - could `seed' the virus into the local mosquito population.
It generally takes multiple introductions by viremic travelers, but as we saw with the introduction of Chikungunya to the Caribbean in late 2013, and Zika to Brazil in 2014, when the conditions are right, the virus can get a foothold and spread rapidly.
Mosquito borne viruses are viewed as a big enough emerging threat to the United States that last year, the CDC’s Grand Rounds, featured a presentation (now archived) called:
We see hundreds of imported cases of mosquito borne diseases in the United States each year – each with at least the potential to seed local mosquito populations with the virus – but so far locally acquired cases have remained rare.
In 2003, a CDC EID study found that economics and lifestyle may have a lot to do to with our lack of locally transmitted Dengue (see Texas Lifestyle Limits Transmission of Dengue Virus).But given the availability of two competent mosquito vectors (Aedes Aegypti & Aedes Albopictus), and repeated introductions of the virus from travelers coming from regions where the virus is endemic, our luck in this matter probably won't last forever.