Organ Donor Data Point to a Potentially Hidden Burden of Human Rabies in the US

US scientists warn that fatal human rabies infections may be far more common than official records indicate, according to a new analysis of organ donor data. The study was prompted by a rare and tragic case in which a Michigan man died after receiving a kidney unknowingly infected with rabies.

The donor, a man from Idaho, had died weeks earlier and his organs were used to help others, with no suspicion of rabies at the time. Investigators later traced his infection to a seemingly minor scratch from a skunk on his rural property. Only after the transplant recipient died was the original donor’s rabies infection discovered.

This was just the fourth documented case in the US in which an organ transplant transmitted rabies from an undiagnosed donor to a recipient. Such events are exceptionally rare, but they raise troubling questions about how often rabies-related deaths may go unrecognized in the wider population.

Statistical model challenges assumptions

Researchers from the Pandemic Sciences Institute at the University of Oxford examined US rabies surveillance data from 2000 to 2024. During that 25-year period, the Centers for Disease Control and Prevention (CDC) recorded an average of 2.4 confirmed human rabies cases per year, totaling only 60 cases.

The researchers instead used the number of infected deceased organ donors as a statistical window into the broader population. Assuming these donors had an average national level of rabies exposure risk, their model suggests there should have been approximately 856 human rabies cases during the same period.

If the estimate is accurate, more than 90% of human rabies deaths in the US since 2000 may have gone undetected or been attributed to other causes. The authors estimate that only around 7% of cases are confirmed, with an optimistic upper bound of approximately 22% under the most favorable assumptions.

Why rabies often goes unrecognized

Rabies is almost always fatal once symptoms appear, but its early signs are nonspecific and can resemble many other neurological or infectious conditions. Symptoms may include fever, headache, difficulty swallowing, confusion, hallucinations or seizures, making diagnosis difficult without a clear history of exposure.

In the Idaho donor’s case, he developed difficulty walking and swallowing, experienced hallucinations and was later found unresponsive after an apparent cardiac arrest. In another donor case reported in 2005, the patient experienced nausea, vomiting, brain hemorrhaging and seizures before death, initially directing clinicians toward other possible diagnoses.

Only later did friends recall that the 2005 donor had mentioned a bat bite, a classic rabies risk. During his illness, however, the combination of symptoms did not strongly suggest rabies to the doctors treating him, illustrating how easily the disease can be missed without specific suspicion or testing.

Limits of current transplant screening

Routine laboratory screening of organ donors does not typically include testing for rabies. Transplant teams operate within a narrow window to keep organs viable and therefore focus on more common infections and conditions that can be detected quickly and reliably.

The CDC notes that rabies testing is rarely performed unless doctors already suspect the disease based on clinical findings. Confirming rabies can require specialized testing and additional time, which conflicts with the urgency of transplant decisions. As a result, rare infections such as rabies may occasionally go undetected.

The researchers argue that multiple documented rabies transmissions from undiagnosed donors imply the existence of a larger number of missed infections in the general population. Because only a small proportion of people who die in the US become organ or tissue donors, encountering infected donors should be particularly unusual if surveillance captures nearly all cases.

Uncertainties and public health implications

The authors acknowledge that their estimate depends on simplifying assumptions and does not fully account for geographic, occupational or socioeconomic differences in rabies exposure. Contact with wildlife such as bats, raccoons, skunks or foxes varies considerably across regions and communities.

To reconcile current official case numbers with perfect rabies surveillance, the researchers calculated that deceased organ donors would need to have a risk approximately 14 times higher than other people who die. The authors consider this unlikely without a clear behavioral explanation.

Experts emphasize that despite the findings, human rabies in the US remains rare compared with many low- and middle-income countries where the virus is more commonly transmitted by dogs. However, the analysis suggests that domestic cases may occur more often than previously recognized, particularly when deaths are attributed to unexplained neurological or cardiac events.

The study highlights the importance of obtaining detailed exposure histories, especially after contact with bats or other wild animals, and using post-exposure prophylaxis promptly when appropriate. It also raises questions about whether targeted changes to donor screening or greater public awareness could identify more infections before they result in fatal outcomes.

Public health agencies and clinicians may now need to consider whether current rabies surveillance strategies are sufficient and whether broader diagnostic testing could be useful in some unexplained severe neurological cases. Any changes would need to balance the extremely low overall incidence against laboratory capacity, costs and the practical realities of emergency medicine and organ transplantation.