Plague’s Blast from the Past Carries a Major Lesson: One Health Matters

Epidemics and pandemics can rewrite history. The Great Plague of the medieval ages, or “The Black Death,” which killed 75-200 million and wiped away 60% of the European population, is one of history’s most catastrophic examples. The last plague pandemic occurred in the 19th century, killing 10 million in the Indian sub-continent alone.

Of course, scientific advances have achieved significant progress in fighting diseases such as plague. We no longer believe in the obsolete theory of miasma (that plague is caused by bad air), and we understand better the pathogen (Yersinia pestis bacteria), the vector (fleas), and the reservoir (small rodents) that play a central role in the plague transmission cycle. We have rapid diagnostic tests to screen for the disease and multiple antibiotics to treat it. Plague should have been a scourge of a bygone era. Yet, Madagascar has been battling a plague outbreak, with cases that rapidly doubled from 500 in mid-October to over 1,554 cases and a death toll of 113 as of October 27, according to WHO-Africa.

Plague is also a prime example of a disease requiring a blended response, drawing on animal, human, and environmental health disciplines—in short, a One Health approach. As we approach One Health Day on November 3rd, the plague epidemic underscores the need for collective action from experts in these fields to prevent, detect, respond to, and recover from current and future infectious disease threats.

Why are we seeing a re-emergence of plague—an age-old nemesis?
There are likely multiple factors responsible for the current epidemic, but in truth, plague never vanished. It simply hid in plain sight as a neglected disease. Like Ebola not too long ago, Plague has reared its head in countries with weak health systems, exacerbated in regions with inflated structural inequalities and extreme poverty. Characteristic determinants of plague include poor housing and sanitation and uncollected garbage—but they aren’t the only factors.

While recent evidence suggests that the plague bacillus still causes several thousand cases each year, Anthropocene-era developments are increasing the risk of plague, along with other zoonotic and vector-borne diseases for vulnerable communities. Madagascar alone is home to roughly half of the world’s plague cases annually. Plague was introduced on the island via steamboats from India in the late 19th century, but was controlled in the 1950s with improved hygiene, antibiotics, and insecticides. While some blame the recent rise in incidence on the country’s worsening political architecture, there may be another major force at play: environmental forces including climate change. Recent research hints that plague’s occurrence in Madagascar is affected by local climate factors—which are influenced by large-scale climate phenomena such as El Nino and a lesser known Indian Ocean Dipole (IOD)—possibly intensifying and interacting as drivers of the disease.

In recent years, Madagascar has also seen strong cyclones, including Cyclone Enawo in March 2017—the strongest cyclone to hit the country in 13 years. Storms contribute to plague’s revival by damaging crops, displacing people, and bringing rodents out of hiding. When flooding kills rodents, fleas are forced to move to alternative hosts or humans. Local variations in temperature and rainfall—often dictated by phenomena such as El Nino and IOD—can also influence several other factors that affect the plague’s incidence, including flea survival, rodent burrow preference, human mobility, and post-storm housing conditions. It’s too early to directly link climate change as a major cause of the current epidemic, but it could be a piece of the puzzle. Anthropogenic drivers such as rapid urbanization, and socio-economic factors also compounded the outbreak by increasing the contact between plague reservoirs and people.

Isn’t Plague endemic in Madagascar? How is this outbreak worse?
While plague is endemic in Madagascar, most cases have typically been bubonic plague, transmitted by fleas. What’s unprecedented about Madagascar’s recent outbreak is that majority of cases are of the pneumonic variety—and pneumonic plague is both lethal if untreated (within 24 hours) and highly contagious, since it is transmitted from human to human. 

While plague incidence previously was limited to remote areas in Madagascar, this is the first time the outbreak is concentrated in two of the largest cities of the country, Antananarivo and Toamasina, increasing the risk of a full-fledged epidemic. While antibiotics can cure the disease, the rapid infectivity and quick onset of pneumonic plague along with weak health service delivery in the country present major challenges to control the disease. The stigma associated with plague as a disease of poverty, makes the situation tougher in the country. Even as the disease has spread to 14 of 22 regions in the country, the country is currently facing major challenges in financing, service delivery (despite provision of 1.2 million antibiotic doses by the World Health Organization), and disease surveillance (less than 30% of contacts have been traced).

How can the One Health approach help?
Despite plague’s reputation as an ‘ancient scourge,’ very little is known about the disease’s dynamics in animal reservoirs and about the changing vulnerabilities for humans. As Madagascar, with support from international institutions, donors, and NGOs, responds to the outbreak, leveraging a One Health approach—emphasizing multi-sectoral collaboration between animal, human, and environmental health experts—could optimize preparedness across disease prevention, surveillance, response, and recovery efforts.

Multi-sectoral collaboration and communication can be beneficial in many aspects of disease control, with engagement, for example of community leaders and ministries of health, agriculture, disaster response, and environment to help rapidly curb ongoing transmission of the outbreak. Similarly, collaborating with environmental specialists and national and international meteorological services can help enable prevention and early warning systems based on weather, climate and ecological forecasting. Working with veterinarians, public health experts, anthropologists, entomologists, and environment specialists will improve understanding of early outbreak control options, enhance disease risk reduction, and develop early warning systems based on climate forecasting. Additionally, a One Health approach will enable us to make preemptive decisions to manage and prevent plague outbreaks in a sustainable manner—reducing the need for the more expensive “fire hose” approach.

Antimicrobial resistance (AMR) and insecticide resistance (IR) also pose major threats to controlling diseases such as plague. In 1995, 2 multi-drug resistant strains of Yersinia pestis were isolated in Madagascar—making the One Health approach even more imperative.

Sulzhan Bali (@sulzhan) is an international development consultant specializing in health security, and a Bosch Global Governance Futures Fellow in global health. **

Catherine Machalaba (@cmachalaba) serves as Policy Advisor at EcoHealth Alliance, and is a doctoral student in environmental health. **

Richard Seifman is an active member of the Global Fund to Fight AIDS, TB and Malaria Technical Review Panel and a board member of the National Physicians Alliance.**

**The views in this article are authors’ alone and do not represent the views of the organizations with whom they work.

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