Seasonal Disease Transmission.
Seasonal fluctuations are a common feature of acute infectious diseases. Diseases such as polio, measles, chickenpox, rotavirus, and influenza have distinct seasonal windows during which epidemics occur. Disease seasonality is a feature that is hidden in plain sight. Colloquial references to seasonality are common, including “the flu season” or the reference to rhinovirus infections as “the common cold” (due the occurrence of rhinovirus epidemics in Autumn as cold weather sets in). Although disease seasonality is pervasive, the seasonal structure of disease transmission is understudied and transmission seasonality has not been quantified for the majority of infections. One of my major contributions to science was showing that all human infectious diseases are seasonal. My single-author article The Calendar of Epidemics in PLoS Pathogens was in the Top 5 Most Viewed Press Released Articles of 2018 and has now been viewed over 24,000 times.
I have quantified the transmission seasonality for polio, measles, and chickenpox, and demonstrated how seasonality shapes spatial patterns of disease and informs interventions. During the Zika epidemic, I showed that risk of congenital Zika can be reduced by planning pregnancy such that the most sensitive period of gestation is aligned with the low transmission season. In addition, I have shown that, even in the absence of vaccination, poliovirus goes locally extinct in sink populations with greatly reduced transmission during the low-transmission season; however, the virus can persist because it is maintained over winter in sanctuary populations. The quantification of seasonal transmission is of practical importance because it can be used to identify windows of time when pathogens are vulnerable to being driven to extinction by vaccination and non-pharmaceutical interventions. I was featured this year in Science for my work on infectious disease seasonality and I have disseminated my findings widely, with coverage in The New York Times, The Atlantic, NPR’s Live Science, BBC News, The Weather Channel, The Smithsonian, among other media outlets.
Social Justice.
Since March 2020, my lab has expanded our research to focus racial health disparities and structural racism that was unmasked and magnified during the on COVID-19 pandemic. First. colleagues and I published a paper in the American Journal of Epidemiology outlining and defining social distancing inequity, an inequity in the ability to remain at home and socially distance during city lock-downs. We showed that the ability to stay home during the height of the pandemic was associated with race, income, and essential work. In addition, colleagues and I published an article in The Lancet to bring attention to the impact COVID-19 would have on women and girls, with emphasis on reproductive health justice. Most recently, I was appointed to New York City’s Mayoral Commission on Social Justice. I worked with a group of scholars, lawyers and activists to propose policy recommendations for the city to address justice issues across many aspects of society. Following this, I developed an undergraduate Biology course focused on social justice titled “Imagine a Just City” in which students will learn about structural racism in the US and explore policies and programs for creating Just Cities built on the principles of equity, fairness, and inclusivity. You can see my course advertisement here.
Biological Rhythms & Health.
Over the past 7 years I have establish myself as an internationally known researcher in chronobiology (the study of biological rhythms). My work on infectious disease seasonality has motivated me to work at the interface of chronobiology and epidemiology. I have collaborated with chronobiologists on several publications that set the foundation for wedding chronobiology with epidemiology.
As a disease ecologist, there is a great deal of potential for integrating experimental chronobiology data and epidemiology data to bridge scales for studying rhythms (i.e., bridging individual to population-level and circadian to seasonal-level). Since 2018-2020 I have led an international clinical investigation of seasonal and circadian rhythms in human physiology, we are now analyzing the data from this study and will soon start publishing our findings. Science Magazine created this video highlighting this work.
Sexual and Reproductive Health.
Since 2010 part of my research has focused on sexual and reproductive health. First, I have worked on human birth seasonality, confirming that populations across the world have seasonal birth pulses that display a latitudinal gradient in their peak timing. Second, colleagues and I have answered a 200-year old question by showing that birth seasonality is primarily driven by seasonal fertility, with peak fertility occurring in the months around the winter solstice. This work is now out in preprint form while our manuscript is in revision. Third, I have started collaborating with bioengineers to study breast milk composition. My contribution has been considering the components of the maternal immune system that are passed from mothers to infants via breastfeeding, and the implications for public health.
Climate Change in the Arctic.
Seasonal ecology of ice-associated seals. Accelerated climate change in the Arctic is leading to rapid restructuring of the Arctic’s physical environment, the most pronounced being the loss of seasonal sea ice, which is required as a platform for the seasonal breeding and rearing of pups by ice-associated seals. I studied the population genetics, seasonal migration, and daily behavior of ringed seals.
The goal of my work was to (1) determine how the loss of sea ice could disrupt ringed seal ecology and (2) evaluate the vulnerability of ringed seals to localized extinction. My genetic studies revealed that ringed seal populations throughout the Arctic interbreed, acting as a potential buffer against local extinction. This research has been cited over 100 times and helped inform the Endangered Species Act listing of Arctic Ringed seals as threatened due to climate change.
The Martinez Lab 