Category Archives: biosecurity

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.

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.

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.


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.

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.

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.

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.

War as a Driver in Tuberculosis Evolution

by Michelle Ziegler

Russia has been all over the news lately. Beyond our recent election, increased Russian activity on the world stage has public health consequences for Europe and farther afield. It has been known for a long time that post-Soviet Russia had and continues to have serious public health problems. One of their particular problems that they have shared with the world is their alarmingly high rate of antibiotic resistant tuberculosis. There is no mystery over the root cause of their antibiotic resistance woes — poor antibiotic stewardship (Garrett, 2000; Bernard et al 2013).

A study by Vegard Eldholm and colleagues that came out this fall sheds light on the origins of particularly virulent tuberculosis strains with high rates of antibiotic resistance that recently entered Europe.  A large outbreak among Afghan refugees and Norwegians in Oslo, Norway, provided a core set of 26 specimens for this study that could be compared with results generated elsewhere in Europe (Eldholm et al, 2010). The Oslo outbreak clearly fits within the Russian clade A group that is concentrated to the east of the Volga River in countries of the former Soviet Union. They name this cluster the Central Asian Clade, noting that it co-localizes with region of origin of migrants carrying the MDR strains of tuberculosis reported in Europe.

Figure 5. Phylogeny of the Afghan Strain Family (ASF). Colored boxes represent the country of origin: Afghanistan is orange; other countries are gray. (Eldholm et al, 2016)

When the Oslo samples are added to the family tree, phylogeny, of recent tuberculosis isolates from elsewhere in Europe a distinctive pattern emerges. The branches on the family tree are short and dense, suggesting that this is recent diversity, that they calculate to have occurred within approximately the last twenty years (Eldholm et al, 2016).

The Central Asian Clade spread into Afghanistan before drug resistance began to develop, probably during the Soviet-Afghan war (1979-1989) producing the Afghan Strain Diversity clade. Slightly later, the Central Asian Clade still in the former Soviet states begins to accumulate antibiotic resistance as the public health infrastructure crumbles in the wake of the dissolution of the USSR. The invasion of Afghanistan by the US and its allies in 2002 toppled the Afghan state, crippling infrastructure and spurring refugee movements within and out of Afghanistan. The lack of modern public health standards in Afghanistan since their war with the introduction of these strains by the Soviets in the 1980s provided fertile ground for the establishment and diversity of tuberculosis in the country. Instability has been pervasive throughout the entire region sending refugees and economic migrants from both Afghanistan and the former Soviet states into Europe.

Movements of the Central Asian Clade (CAC) since c. 1960 and the subsequent Afghan Strain Family (ASF). (Eldholm et al, 2016)

Their dating of the last common ancestor for the Central Asian Clade to c. 1961 is significantly younger than the previous dating of 4,415 years before present for the Russian clade A (CC1) of the Beijing lineage of Mycobacteria tuberculosis. They account for this difference by noting differences in their methods of assessing sequence differences and note that their method is in line with other recent evolutionary rates for other tuberculosis clades.  The diagnosis dates and length of the arms on their reconstructed phylogeny suggests that there were multiple, independent introductions of the cases from Afghanistan and the former Soviet republics. This is consistent with a repeated periods of refugee movements from central Asia into Europe.

The rapid proliferation and diversification of the Afghan Strain Family may be explained by a known syndemic between tuberculosis and war (Ostrach & Singer, 2013). Conditions of war everywhere disrupt food systems, destroy critical infrastructures such as electricity and water systems, interrupts medical supplies, and the human public health infrastructure of the country. Malnutrition and stress are known contributors to immune suppression. Many pathogens flourish simultaneously in these conditions increasing the infectious challenges the population must fend off. Diarrheal diseases are the most acute and demanding of rapid attention, allowing longer-term diseases like tuberculosis to slip through the overburdened healthcare system. Afghanistan has experienced nearly forty years of war, political instability, and repeated infrastructure destruction. Thus, they were primed for both the establishment of new tuberculosis strains during the Afghan-Soviet war in the 1980s along with the proliferation and diversification of tuberculosis during the Afghan-American war of the last sixteen years.

Established syndemics between tuberculosis and war have been made retrospectively following the Vietnam war and the Persian Gulf war of 1991 (Ostrach & Singer, 2013). In Vietnam, prolonged malnutrition caused an eruption of tuberculosis along with malaria, leprosy, typhoid, cholera, plague, and parasitic diseases.  A WHO survey in 1976 found that Vietnam had twice the incidence of tuberculosis over all of its neighboring countries (Ostrach & Singer, 2013). When the military intentionally targets water infrastructure as it did in Vietnam and Iraq, the production of civilian infectious disease is a tactic of war. In both Vietnam and post-Gulf war Iraq, more civilians died of malnutrition and infectious disease than enemy soldiers died of all causes (Ostrach & Singler, 2013).

It seems likely that this is just one of the first studies to establish a link between serious infectious disease developments and the Afghan wars. The current war zones throughout central Asia and the Middle East already have ramifications for the public health of the entire world that walls along borders will not be able to stop. Most of the cases in the Oslo outbreak were Norwegians, not Afghan immigrants. Diseases will spread beyond the migrants so country of origin screening will be of little use before long.


Eldholm, V., Pettersson, J. H. O., Brynildsrud, O. B., Kitchen, A., Rasmussen, E. M., Lillebaek, T., et al. (2016). Armed conflict and population displacement as drivers of the evolution and dispersal of Mycobacterium tuberculosis. Proceedings of the National Academy of Sciences of the United States of America, 201611283–16.

Ostrach, B., & Singer, M. C. (2013). Syndemics of War: Malnutrition-Infectious Disease Interactions and the Unintended Health Consequences of Intentional War Policies. Annals of Anthropological Practice, 36(2), 257–273.

Bernard, C., Brossier, F., Sougakoff, W., Veziris, N., Frechet-Jachym, M., Metivier, N., et al. (2013). A surge of MDR and XDR tuberculosis in France among patients born in the Former Soviet Union. Euro Surveillance: Bulletin Européen Sur Les Maladies Transmissibles = European Communicable Disease Bulletin, 18(33), 20555.

An Anniversary year for Natural Disasters: 1815, 1665, and 1315

There are major natural disasters every year. In the last year alone we have had the major earthquake in Nepal just in the last couple days and a historic epidemic of Ebola. It’s too soon to tell how these latest disasters will seen by history and effect historical interpretations. This year there are three natural disaster anniversaries that stand out from the rest not just due to their mortality but also because of their impact on how we interpret the past.

Tambora, 1815

Mount Tambora Volcano, Sumbawa Island, Indonesia
Mount Tambora Volcano, NASA image (public domain)
Just a few weeks ago there was a minor splash in the news to mark the 200th anniversary of the eruption of Tambora on April 5, 1815. The photo to the right is the caldera of Tambora taken from space. As tragic as the thousands of deaths directly related to the eruption are, 1815 is best known as the ‘year without a summer’, a volcanic winter. It is impossible to know how many deaths resulted from crop failures and unseasonable weather. As the most recent volcanic winter, 1815 is an important because we have the most reliable scientific data, economic data, and descriptions of the effects on health and culture from people in all walks of life all over the globe. I don’t know as much about Tambora and its after effects as I would like, so I’m planning on reading The Year Without a Summer by historian William Klingman and meteorologist Nicholas Klingman (2013). If I like it, maybe you will hear more about it later this year.

Great Plague of London, 1665

This year is also the 350th anniversary of the Great London Plague that was followed closely by the Great London fire. Despite its reputation, the great plague of London was not the last major plague of Europe by a long shot.

17th century London
17th century London

The 1665 plague of London claimed up to 100,000 lives, about as many as died in the Marseille plague of 1720-3. Fifty years later, a similar size plague struck Moscow under Empress Catherine the Great. Yet, the London Plague is the one that gets the most attention.

A great deal of the notoriety of the Great Plague of London comes from the amount and quality of resources available in English.  Daniel Dafoe immortalized the plague in his novel, Journal of a Plague Year written in 1722. A savvy author, Dafoe timed it to take advantage of plague fears in southern Europe, concurrent with the plague in Marseille. It is testament to the Dafoe’s skill as a writer than his novel is often taken as historical evidence. I think I’ll mark the anniversary by reading Defoe’s classic.

The London plague has also been magnified by it linkage with the great fire of London in 1666. The relationship between the fire and the plague has been controversial. It has been sometimes assumed that the fire ended the plague, but the plague was winding down before the fire began. However, it is likely that the fire removed the environment that had supported the plague preventing its return; over 80% of the citizens of London were left homeless. Restoration of the capital city after the great fire also immortalized 1665-6 in the history of London.

Great European Famine, 1315

A less combustible but perhaps equally deadly anniversary this year is that of the Great Famine of 1315 that effected most of continental Europe. Seven hundred years ago the famine began and, while its hard to estimate famine mortality over three to seven years, perhaps up to 15% of Northern Europeans died. It began with soaking and then flooding rains that destroyed winter crops for two years with yields of wheat and rye in England and Wales 60% below normal in 1316, and again in 1321 with similar drops in yield. Also beginning in 1315 the great bovine pestilence, possibly rinderpest,  begins in Central Europe and spread across the continent: France and Germany, the Low Countries,  Denmark and England by 1319. In just one year, England and Wales lost approximately 62% of all bovines (Slavin 2012). The loss of dairy and beef was compounded by the fact that oxen provided the vast majority of traction and fertilizer. With similar losses across Europe, it took nearly 25 years to return cattle numbers to the pre-epizootic levels.

There was no respite for the 14th century. The childhood survivors of the famine and food shortage were the adults who were cut down by the Black Death in the 1340s. What effect malnutrition had on their developing immune system is a line of inquiry being explored by anthropologists Sharon DeWitte and historian Philip Slavin (2013). Let us not forget, it still got worse, between the crop failures and panzootic of 1315 and the Black Death in 1346 , the Hundred Years’ War begins in 1337.


Devaux, C. A. (2013). Small Oversights That Led to the Great Plague of Marseille (1720-1723) Lessons From the Past. Infection, Genetics and Evolution, 14(C), 169–185. doi:10.1016/j.meegid.2012.11.016 (for comparisons to other epidemics)

Slavin, P. (2010). The Crisis of the Fourteenth Century Reassessed: Between Ecology and Institutions — Evidence from England (1310-1350). EHA Paper, 1–14.

Slavin, P. (2012). The Great Bovine Pestilence and its economic and environmental consequences in England and Wales, 1318–501. The Economic History Review, 1–28.

Dewitte, S., & Slavin, P. (2013). Between Famine and Death: England on the Eve of the Black Death—Evidence from Paleoepidemiology and Manorial Accounts. Journal of Interdisciplinary History, 1–25.