Lyme disease during pregnancy remains one of the least explored aspects of infectious disease epidemiology, even though its potential consequences may extend across generations.
A growing number of researchers argue that millions of people around the world could be living with a Borrelia infection acquired before birth, yet this possibility is rarely acknowledged in mainstream medical discussions. The lack of attention is striking, especially considering the scale of Lyme disease and the complexity of its clinical presentation.
This article presents a comprehensive re‑examination of global projections for congenital Lyme disease, using mathematical modeling based on incidence, prevalence, and seroprevalence data. By combining worldwide birth statistics with estimated probabilities of transplacental transmission and the known gaps in diagnosis, the analysis attempts to understand how many individuals might have been infected in utero over the past several decades. Although the exact numbers depend on the assumptions used, the models consistently suggest that congenital transmission could represent a far more significant pathway than currently recognized.
Read the full article here: Lyme Disease and Pregnancy: Global Projections of Undiagnosed Congenital Infection. Understanding the risks associated with Lyme disease in pregnancy is important not only for clinicians but also for public health planning. If congenital infection is more common than assumed, then the global burden of Lyme disease may be substantially underestimated. This would have implications for diagnosis, treatment strategies, and long‑term health monitoring.
Global Estimates and Why They Matter
Estimating the number of people who may have acquired Borrelia before birth requires combining several types of epidemiological data. The models draw on global incidence estimates, worldwide seroprevalence studies, and reported prevalence figures. When these are applied to the annual number of births—approximately 140 million worldwide—even small probabilities of vertical transmission can translate into large numbers of affected individuals.
The central idea is simple: if a certain percentage of pregnant women are infected or have been exposed to Borrelia, and if even a small fraction of those infections can cross the placenta, then the cumulative number of congenital infections over decades becomes substantial. This is especially true in regions where seroprevalence reaches 20 percent or more, meaning that a significant portion of the population has been exposed to Borrelia at some point.
How the Models Were Constructed
The analysis uses three independent approaches. The first is based on annual incidence, using an example estimate of 12.3 million new infections per year. The second relies on global seroprevalence, which has been estimated at around 14.5 percent. The third uses a reported global prevalence of 62.1 million people living with Lyme disease in 2018. Each approach reflects a different way of estimating how many pregnant individuals might be infected at any given time.
To estimate congenital transmission, the models incorporate several additional factors. These include the number of live births per year, the proportion of the year during which pregnancy occurs, the probability of vertical transmission, and the percentage of infections that remain undiagnosed. A 50‑year time window is used to estimate how many individuals born during that period might still be alive today, with a survival factor applied to account for mortality.
Although the original calculations rely on formulas, the underlying logic is straightforward. For each model, the number of potentially infected mothers is estimated first. This number is then multiplied by the assumed probability of transmission to the fetus. The resulting annual estimates are projected over 50 years and adjusted for survival and diagnostic gaps. The final numbers vary widely depending on the assumptions, but they consistently show that congenital infection is plausible on a large scale.
What the Numbers Suggest
The results of the models span a broad range. Under the most conservative assumptions—very low transmission probabilities and lower estimates of maternal infection—the cumulative number of congenital infections over 50 years reaches only into the tens of thousands. However, when higher seroprevalence values and more substantial transmission probabilities are used, the estimates rise into the millions.
For example, using the seroprevalence‑based model with a vertical transmission probability of one percent, the cumulative number of congenital infections over 50 years exceeds nine million. If three‑quarters of these cases remain undiagnosed, the number of people living today with an unrecognized congenital Borrelia infection could be more than seven million. Under higher transmission assumptions, the numbers become even larger, reaching tens or even hundreds of millions in the most expansive scenarios.
The prevalence‑based model produces more moderate results, while the incidence‑based model yields lower estimates unless higher transmission probabilities are used. The wide range of outcomes reflects the uncertainty surrounding key parameters, especially the true rate of vertical transmission and the proportion of infections that go undiagnosed.
Understanding the Limitations
The models are only as accurate as the data they rely on. Global Lyme disease reporting is inconsistent, and incidence estimates vary widely between countries. Seroprevalence studies measure exposure rather than active infection, which complicates the interpretation of risk during pregnancy. The true probability of vertical transmission is also uncertain, with published estimates ranging from extremely low to relatively high depending on the study.
Another limitation is the assumption that all infected or previously exposed mothers have the same likelihood of transmitting the infection. In reality, factors such as the timing of infection, immune response, treatment history, and co‑infections may influence transmission risk. The models also treat global populations as homogeneous, even though Lyme disease risk varies dramatically by region.
Despite these limitations, the models serve an important purpose: they illustrate how even conservative assumptions can lead to significant cumulative numbers when applied to global populations over long periods.
A Broader Scientific and Philosophical Perspective
The possibility of widespread congenital Borrelia infection raises deeper questions about how societies understand and respond to chronic infectious diseases. Lyme disease is already known for its complex and sometimes controversial clinical presentation. Adding the dimension of congenital transmission challenges traditional assumptions about when and how infection occurs.
One of the most striking issues is the disconnect between emerging evidence and the level of attention the topic receives. Despite decades of case reports and biological plausibility, vertical transmission remains under‑recognized in many medical guidelines. This may reflect broader social and institutional tendencies to overlook conditions that are difficult to diagnose, chronic in nature, or lacking in clear economic incentives for research.
From a philosophical standpoint, congenital infection introduces the idea of “inherited disease burden,” where an infection becomes part of a person’s biological starting point. This challenges conventional ideas about individual responsibility for health and highlights the long‑term consequences of environmental and infectious exposures.
The scientific implications are equally significant. If seroprevalence reaches 28 percent in some regions, what does this mean for children born in those populations? Could certain chronic, unexplained, or “idiopathic” conditions have roots in early, unnoticed infection? These questions open new avenues for research and call for more comprehensive diagnostic strategies.
Conclusion
Estimating the global number of people infected with Borrelia before birth is not simply an academic exercise. It reflects a broader gap in our understanding of Lyme disease and its long‑term effects on human health. The models presented here, despite their limitations, suggest that congenital transmission may contribute far more to the global burden of Lyme disease than previously assumed.
Recognizing this possibility is the first step toward improving research, diagnostics, and public health strategies. The sooner the medical community acknowledges the potential scale of congenital infection, the better equipped society will be to address its consequences for current and future generations.
