A new study published in PLOS Neglected Tropical Diseases sheds light on the 1857 yellow fever epidemic in Lisbon, providing new insights into how environmental and social factors shaped the spread and impact of the disease in an urban, pre-vaccination context.
The research includes the contribution of Ana B. Abecasis, researcher from THOP-GHTM Research Group, at Instituto de Higiene e Medicina Tropical, Universidade NOVA de Lisboa (IHMT NOVA), who participated in the scientific review and interpretation of the findings.
Reconstructing a 19th-century epidemic
The study set out to reconstruct the dynamics of one of Lisbon’s most devastating epidemics, analysing how spatial, environmental and sociodemographic factors influenced transmission and mortality patterns.
Using a combination of historical and modern epidemiological approaches, the research team digitised archival records of cases and deaths and mapped them across Lisbon’s 34 parishes. These data were analysed through spatial modelling and epidemiological methods to estimate transmission dynamics, including the basic reproduction number (R₀), and to assess the role of environmental and sociodemographic factors.
High transmission and unequal impact
The findings reveal the scale and intensity of the epidemic. An estimated 18,000 people were infected, resulting in 5,652 deaths—around 4.2% of Lisbon’s population at the time. Transmission was particularly intense, with an estimated basic reproduction number of about 5 and infection attack rates ranging between 10.3% and 13.5%.
The study also uncovered significant spatial inequalities. Fifteen of the city’s 34 parishes were identified as high-risk hotspots, mainly located in coastal and low-elevation areas where environmental conditions likely favoured mosquito breeding. The epidemic peaked in October 1857 and subsided by January 1858.
Patterns of mortality further highlighted social disparities. Most deaths occurred at home rather than in hospitals. While working-age men accounted for a large share of fatalities, women working at home were found to have a higher probability of dying, pointing to differences in exposure and access to care.
Relevance for today
The authors conclude that the interaction between environmental conditions and social structure played a decisive role in shaping the epidemic’s trajectory. These historical findings remain highly relevant today, particularly in the context of climate change, urbanisation and the potential re-emergence of mosquito-borne diseases in Europe.
By revisiting past epidemics with modern tools, the study provides valuable insights for anticipating and managing future public health threats.
“Yellow fever is not a disease of the past. Lisbon remains vulnerable”
In an interview with Healthnews, Ana B. Abecasis, the facilitator of Genomic Surveillance and Population Mobility-CCI at GHTM,warns that “yellow fever should not be considered a disease of the past”, emphasizing that “global mobility, climate change, pressure from tourism, and persistent inequalities in access to healthcare could make Lisbon and other parts of Portugal potentially vulnerable to the introduction of the virus”. She further highlights the need to strengthen epidemiological and entomological surveillance, as well as health system preparedness, stressing that “vaccination remains the most effective preventive measure”.
The full interview can be read here: Ana Abecasis: “A Febre Amarela não é uma doença do passado. Lisboa continua vulnerável”
The role of GHTM | IHMT NOVA historical epidemiological archives
Complementary insights from an interview with Diário de Notícias further contextualize the study’s implications for current public health risk assessment. From the standpoint of GHTM | IHMT NOVA, Ana B. Abecasis emphasized the foundational role of historical epidemiological records in enabling the present analysis. She noted that “the reconstruction of the 1857 epidemic was made possible through the systematic access to and examination of archival outbreak data preserved within the institution’s documentary collections”, maintained by the Library and Museum Management Office of IHMT NOVA, coordinated by Salima Rehemtula. “Such materials”, she argued, “constitute a critical resource for elucidating transmission dynamics, identifying underlying social determinants of health, and informing the anticipation of epidemiological risks in contemporary settings”. Read the entire interview here: Febre amarela pode regressar à Europa? Investigador português diz que há esse risco
The article is available in full on the journal website of PLOS Neglected Tropical Diseases:
Spatial and social determinants of the 1857 yellow fever epidemic in Lisbon
