Category Archives: Zika

El Niño and Possibly New World Primates Contributed to Zika Explosion

by Michelle Ziegler

The explosion of Zika-related birth defects this past year came out of the blue. Zika has been known since the 1940s but was seen as a mild dengue-like illness (Fauci & Morens, 2016). Leaving aside how and why microcephaly has appeared so dramatically, it is undeniable that Zika’s emergence and transmission in the Americas have been unusually rapid and extensive.

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Aedes aegypti from Tanzania (Source: Muhammad Mahdi Karim, 2009, GNU Free Documentation License)

Two papers published in December focusing on the Aedes mosquito vectors begin to shed light on how Zika was able to be established so quickly and pervasively. Zika utilizes the same tropical mosquito Aedes aegypti as dengue; it was once known as the yellow fever mosquito. It is also the vector of the chikungunya virus.

As first observed in West Africa many years ago, Zika epidemics followed a chikungunya epidemic by a couple years. Chikungunya was the emerging infectious disease of 2013, the year that Zika is believed to have arrived in South America (Fauci & Morens, 2016). Unrecognized by public health workers at the time, a Chikungunya epidemic was simultaneously chugging along under the radar in at least Salvador, the capital of the Bahai state of Brazil, during the peak of Zika epidemic of 2015 (Cardoso et al, 2017).

El Niño 2015-2016

In the first study by Cyril Caminade and colleagues at the University of Liverpool modeled Zika transmission in the two critical vector species in the Americas, the tropical Aedes aegypti found primarily in South America and the temperate Aedes albopictus found in the southern United States. It is thought that Zika transmits better from A. aegytpi but more research is needed to fully understand the differences. They developed a two vector, one host model where the climate is a variable to compare the effect of climate patterns on Zika transmission. They ran these simulations for each vector individually and together against historic climate data sets.

When they compared the worldwide distribution of the vectors and climate, they were able to show that all of the countries where Zika has been reported were predicted in their model. Ominously, South America was the most friendly region in the world for Zika (Caminade et al, 2016). The model for Zika produced a map that correlates extremely well with the global distribution of dengue. Due to the overlap of A. aegypti and A. albopictus territory, they found a high probability that Zika would transmit well in most of the southern United States.

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Risk of Zika transmission based on their models A. winter of 2015-2016 B. Risk over the last 50 years. (Caminade et al, 2016)

The global climate anomaly known as El Niño is known to impact mosquito-transmitted diseases, so they had a particular interest in comparing the 2015-2016 El Niño to historic data sets. The map shows the predicted Ro (reproduction number) for Zika around the world in 2015-2016  and in the bar graph compared to the last 50 years. The conditions for Zika were the best for the last 50 years. Other hot spots that did not experience a Zika epidemic, like India, did have a record year for dengue. They also note that the African hot spot for ideal transmission conditions corresponds and to Angola where there was a Yellow Fever outbreak. In short, it was a very good year for Andes aegypti! And now, as of January 2017, Yellow Fever had added to their misery in a Brazil.

A Sylvatic Reservoir? 

Understanding if Zika will establish a sylvatic reservoir in South America is of vital importance for projections and mitigation of future Zika epidemics in Brazil and elsewhere in South America. Zika was initially detected in a sentinel monkey in Uganda and has since been detected in a wide variety of smaller primates in Africa and Asia. Using a model originally proposed for dengue they were able to show that primates with rapid birth rates and short lifespans are ideal for establishing sylvatic Zika. In primates with short life span, five years or less, and rapid birth rates, the establishment of a sylvatic reservoir is “nearly assured” (Althouse et al, 2016). They predict that a primate population as small as 6,000 members with 10,000 mosquitoes could support a sylvatic reservoir (Althouse et al, 2016). Ironically, since infection rate is dependent upon bites per primate, a small primate population with a large mosquito population is better at maintaining the reservoir than a large primate population. Old World monkeys like the African Green Monkey, a known African host of Zika, are already established in free-living troops in South American forests.  While A. aegypti favors human environments, A. albopictus prefers forested environments and has been spreading in Brazil.  It could be a prime candidate for a bridging vector between a sylvatic and domestic Zika cycle. Studies on Zika vulnerability and incidence in all South American primates has to be a priority. Our ability to manage Zika in the future depends on it.


References

Caminade, C., Turner, J., Metelmann, S., Hesson, J. C., Blagrove, M. S. C., Solomon, T., et al. (2016). Global risk model for vector-borne transmission of Zika virus reveals the role of El Niño 2015. Proceedings of the National Academy of Sciences of the United States of America, 201614303–28. http://doi.org/10.1073/pnas.1614303114

Cardoso, C. W., Kikuti, M., Prates, A. P. P. B., Paploski, I. A. D., Tauro, L. B., Silva, M. M. O., et al. (2017). Unrecognized Emergence of Chikungunya Virus during a Zika Virus Outbreak in Salvador, Brazil. PLoS Neglected Tropical Diseases, 11(1), e0005334–8. http://doi.org/10.1371/journal.pntd.0005334

Althouse, B. M., Vasilakis, N., Sall, A. A., Diallo, M., Weaver, S. C., & Hanley, K. A. (2016). Potential for Zika Virus to Establish a Sylvatic Transmission Cycle in the Americas. PLoS Neglected Tropical Diseases, 10(12), e0005055–11. http://doi.org/10.1371/journal.pntd.0005055

Fauci, A. S., & Morens, D. M. (2016). Zika virus in the Americas—yet another arbovirus threat. New England Journal of Medicine, 374(7), 601–604. http://doi.org/10.1056/nejmp1600297

The Pathogen Buzz of 2016

by Michelle Ziegler

Altmetrics recently released the Top 100 scholarly articles list for the year (captured on 15 Nov 2016). Their ranking captures the public discussion on academic articles judged by shares of the online edition, news articles, blog posts and tweets that include the digital object identifier code (doi). (So if you want to improve the Altmetrics number of your papers make sure that all blog posts/tweets/news articles have the doi somewhere.) Note that generating discussion is not the same as being the best papers produced. At least one one this list, on ‘Patient 0’ HIV-1,  seemed to generate a fair amount of complaints.

Overall, the list was dominated by medical and health science (49) and biological science (14), altogether being 63% of the top 100 articles. Some of the other categories are a little vague, such as physical science (6) vs. earth and environmental science (6) vs. material science (1). History and archaeology combined to produce only six of the top 100 and one of them, on the ‘Tully monster’, really should be paleontology (or biology?). We also have to keep in mind that Altmetrics misses most of the humanities journals. The Altmetric scores in the top hundred have also approximately doubled between 2014 and 2016. The lowest score in 2016 is 1605 and the lowest score in 2014 was only 746.

One highlight this year is that 47% of the top 100 were either freely available or open access. I noticed about midway through this past year that papers expected to get a lot of attention were often freely available or open access. The difference between freely available vs open access may be whether or not the authors had to pay for the open availability (?). I wonder if the freely available remain free forever, or only until the news dies down?

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Zika vector Aedes aegypti (Courtesy of CDC/Public Health Image Library #9261)

When it comes to pathogens, this year’s list comes with the distinctive buzz of a mosquito, Aedes aegypti, carrying this year’s emerging infectious disease, the Zika virus. Of the twelve papers directly related to infection, six are on Zika. Looking at the 2015 list, it’s clear that Zika put pathogens in the news this year. There are hardly no pathogen related papers in the 2015 list and in 2014, there were only five  – four on ebola and one on ancient Yersinia pestis. So clearly Zika has made a far bigger splash than even the much more lethal ebola.

Pathogens in the 2016 Top 100:

6. Rasmussen, S. A., Jamieson, D. J., Honein, M. A., & Petersen, L. R. (2016). Zika virus and birth defects—reviewing the evidence for causality. New England Journal of Medicine, 374(20), 1981-1987. DOI: 10.1056/nejmsr1604338

17. Zipperer, A., Konnerth, M. C., Laux, C., Berscheid, A., Janek, D., Weidenmaier, C., … & Willmann, M. (2016). Human commensals producing a novel antibiotic impair pathogen colonization. Nature, 535(7613), 511-516. DOI: 10.1001/jama.2016.0287

19. Singer, M., Deutschman, C. S., Seymour, C. W., Shankar-Hari, M., Annane, D., Bauer, M., … & Hotchkiss, R. S. (2016). The third international consensus definitions for sepsis and septic shock (sepsis-3). Jama, 315(8), 801-810.17. DOI: 10.1001/jama.2016.0287

20. Mlakar, J., Korva, M., Tul, N., Popović, M., Poljšak-Prijatelj, M., Mraz, J., … & Vizjak, A. (2016). Zika virus associated with microcephaly. New England Journal of Medicine, 374(10), 951-958. DOI: doi/10.1056/NEJMoa1600651

 
25. Miranda, R. C., & Schaffner, D. W. (2016). Longer contact times increase cross-contamination of Enterobacter aerogenes from surfaces to food. Applied and Environmental Microbiology, 82(21), 6490-6496. DOI:10.1128/aem.01838-1620.

31. McGann, P., Snesrud, E., Maybank, R., Corey, B., Ong, A. C., Clifford, R., … & Schaecher, K. E. (2016). Escherichia coli Harboring mcr-1 and blaCTX-M on a Novel IncF Plasmid: First report of mcr-1 in the USA. Antimicrobial agents and chemotherapy. DOI: 10.1128/aac.01103-16

 
37. Cao-Lormeau, V. M., Blake, A., Mons, S., Lastère, S., Roche, C., Vanhomwegen, J., … & Vial, A. L. (2016). Guillain-Barré Syndrome outbreak associated with Zika virus infection in French Polynesia: a case-control study. The Lancet, 387(10027), 1531-1539. DOI: 10.1016/s0140-6736(16)00562-6

46. Worobey, M., Watts, T. D., McKay, R. A., Suchard, M. A., Granade, T., Teuwen, D. E., … & Jaffe, H. W. (2016). 1970s and ‘Patient 0’HIV-1 genomes illuminate early HIV/AIDS history in North America. Nature, 539(7627), 98-101. DOI: 10.1038/nature19827

49. Fauci, A. S., & Morens, D. M. (2016). Zika virus in the Americas—yet another arbovirus threat. New England Journal of Medicine, 374(7), 601-604. DOI: 10.1056/nejmp1600297

54. Tang, H., Hammack, C., Ogden, S. C., Wen, Z., Qian, X., Li, Y., … & Christian, K. M. (2016). Zika virus infects human cortical neural progenitors and attenuates their growth. Cell stem cell, 18(5), 587-590. DOI: 10.1016/j.stem.2016.02.016

86. Liu, Y. Y., Wang, Y., Walsh, T. R., Yi, L. X., Zhang, R., Spencer, J., … & Yu, L. F. (2016). Emergence of plasmid-mediated colistin resistance mechanism MCR-1 in animals and human beings in China: a microbiological and molecular biological study. The Lancet Infectious Diseases, 16(2), 161-168.54. DOI: 10.1016/S1473-3099(15)00424-7

92. Brasil, P., Pereira, Jr, J. P., Raja Gabaglia, C., Damasceno, L., Wakimoto, M., Ribeiro Nogueira, R. M., … & Calvet, G. A. (2016). Zika virus infection in pregnant women in Rio de Janeiro—preliminary report. New England Journal of Medicine. DOI: 10.1056/NEJMoa1602412

Before we leave the buzz of 2016, we have to mention this year also saw the passing of Dr. Donald Henderson (1928-2016) who led the effort to eradicate smallpox. Henderson died in August; his obituary from the New York Times can be found here.

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Henderson administering a smallpox vaccine in about 1972 (WHO).