As H5N1 bird flu spreads across mammals and has now reached rats, we are reminded of Chapter 7 in our new book, The Fed and the Flu: Parsing Pandemic Economic Shocks. That chapter focuses on the Plague of Justinian in the Eastern Roman Empire, where plague (caused by the Yersinia pestis bacterium) spread with the range of infected oriental rat fleas. These fleas hitchhiked across the empire, carried by small mammals such as rats and, new research suggests, gerbils. We will excerpt from the chapter at the end of this commentary.
For now, we want to inventory the bird flu virus’s spread in the United States as it continues to develop as a pathogen-based economic shock and a growing epidemic risk. As this is written, we have not seen a cluster of human-to-human transmission. We have seen human sickness that was likely to have originated from human contact with a sick bird or mammal. Human death is not prevalent, so far. The cases are idiosyncratic, not epidemic spread. That could change with a single mutation, or it may never change. Anyone who says that they know is not cognizant of history.
This disease spread isn’t just birds anymore, since evidence now includes cattle and, worse, the disease vector of the rat. History tells us much about the danger of rats and disease. We are seeing changes in the virus as it better adapts to infect mammals. The D1.1 variant’s appearance in cows is especially concerning since that variant has caused more severe disease in the humans who have caught it.
We will leave it to our readers to connect the dots between the bird flu epidemic risk and economic damage and the disruptive activities that we witness every day in public health policy with Trump 2.0. Readers are advised to carefully watch the Musk operation shutting down federal information sources. If we don’t have data, we give the pathogen a better chance to work against all of us. Pathogens like bird flu don’t check your political voter ID.
Here’s the list. An excerpt from Chapter 7 follows the list.
“Bird flu confirmed in rats for first time, USDA reports,” https://www.cbsnews.com/news/bird-flu-in-rats/
“Detections of Highly Pathogenic Avian Influenza in Mammals,” https://www.aphis.usda.gov/livestock-poultry-disease/avian/avian-influenza/hpai-detections/mammals
“We’re Running Out of Chances to Stop Bird Flu,”
“H5 Bird Flu: Current Situation,” https://www.cdc.gov/bird-flu/situation-summary/index.html
“USDA Reported H5N1 Bird Flu Detections in Wild Birds,” https://www.cdc.gov/bird-flu/situation-summary/data-map-wild-birds.html
“The bird flu outlook has only gotten worse,” https://thebulletin.org/2025/02/the-bird-flu-outlook-has-only-gotten-worse/
“After delay, CDC releases data signaling bird flu spread undetected in cows and people,” https://www.npr.org/sections/shots-health-news/2025/02/13/nx-s1-5296672/cdc-bird-flu-study-mmwr-veterinarians
“The USDA is scrambling to rehire officials working to curb the spread of bird flu after firing them,” https://fortune.com/2025/02/19/usda-rehiring-workers-curb-bird-flu-after-firing/
“Canada announces avian flu vaccine buy as USDA confirms first H5N1 detections in rats,”https://www.cidrap.umn.edu/avian-influenza-bird-flu/canada-announces-avian-flu-vaccine-buy-usda-confirms-first-h5n1-detections
“As bird flu continues to spread, is there a vaccine for humans?” https://www.usatoday.com/story/life/health-wellness/2025/02/18/bird-flu-spread-vaccine/78612616007/
Finally, here’s the excerpt from Chapter 7, The Fed and the Flu: Parsing Pandemic Economic Shocks, pp. 141–44.
The flea that carries the plague becomes active in a narrow temperature range between 59 and 68 degrees. The cooler period that lasted until around 550 provided it the opportunity to expand its range as the black rats that were its hosts sailed on ships and hid in carts that clattered across the empire on Roman roads. Without that period of climate cooling, the flea would have stayed put and the plague with it.15 The Justinian Plague is an early reminder that climate change can create new opportunities for pathogens to find new human networks to infect.
The bacterium Yersinia pestis is responsible for one of the deadliest illnesses in human history. The Plague of Justinian, like the medieval Black Death, originated in China and spread to Europe, Africa, and the Middle East via the Silk Road.16 Y. pestis made its way from the port city of Pelusium in the Nile Delta inland across Egypt, eastward to Palestine, and then westward to Syria and Mesopotamia. It reached Alexandria and then, in 542 CE, Constantinople, where massive grain tributes — 240 metric tons from Egypt alone — were stored in immense warehouses that provided harborage and boundless sustenance for rats, which reproduce to the limits of their food supply. As plague gripped the city, deaths in Constantinople came to top 10,000 per day, according to Procopius. The plague swept across Persia, southern Arabia, Palestine, Syria, Asia Minor, Italy, North Africa, Gaul, Spain, and the British Isles. It penetrated even rural Bavaria.17
The disease would come in three forms, depending on how it was contracted. If the pathogen was breathed in, pneumonic plague would result. It would affect the lungs and result in a bloody discharge from the mouth and nose. If the disease was contracted via an infected flea bite, bubonic plague developed, accompanied by buboes, or swollen lymph nodes, that would burst, emitting a bloody discharge. Gangrene would often occur in the fingers, arms, feet, lips, and toes. The plague could also develop into septicemic plague when the infection entered the bloodstream. This form of the infection would result in bleeding beneath the skin, rotting of flesh, vomiting of blood, and a profusion of blood from every body cavity.18
During the Black Death in the Middle Ages, both pneumonic and septicemic plague had a mortality rate of 100%; only the bubonic form, with a roughly 60% mortality rate, offered any hope of survival.19 We cannot be certain that an earlier strain of Y. pestis would have had the same mortality rate seen during the later Black Death period; however, the first-hand reports we do have recount a horrendous toll, which may have been more dire in the cities than in the countryside. Kyle Harper has estimated that the population of the Roman world plunged by half.20
As an imaginative exercise, consider that should a pandemic of similar virulence and scope happen today, the U.S. population would plummet to what it was in 1953. Though an estimate of the size of the demographic decline caused by the Justinianic Plague and succeeding outbreaks is the stuff of best guesses rather than hard data, archeological evidence of abandoned towns corroborates the heavy death tolls reported by witnesses of the time, such as Procopius, John of Ephesus, and Gregory of Tours.
Notes
15. William Rosen, Justinian’s Flea: The First Great Plague and the End of the Roman Empire (New York: Penguin Books, 2007), 200. Kindle edition.
16. G. Morelli, Y. Song, C.J. Mazzoni, M. Eppinger, P. Roumagnac, D.M. Wagner, M. Feldkamp, B. Kusecek, A.J. Vogler, Y. Li, Y. Cui, N.R. Thomson, T. Jombart, R. Leblois, P. Lichtner, L. Rahalison, J.M. Petersen, F. Balloux, P. Keim, T. Wirth, J. Ravel, R. Yang, E. Carniel, and M. Achtman. “Yersinia pestis genome sequencing identifies patterns of global phylogenetic diversity,” Nature Genetics 42, no.12 (2010): 1140–3.
17. Kyle Harper, The Fate of Rome: Climate, Disease, and the End of an Empire (Princeton: Princeton University Press, 2017), 224–227.
18. “Plague,” Mayo Clinic, April 20, 2023, https://www.mayoclinic.org/diseases-conditions/plague/symptoms-causes/syc-20351291.
19. Anna Rovid Spickler, “Plague,” Iowa State University, 6, https://www.cfsph.iastate.edu/Factsheets/pdfs/plague.pdf.
20. Harper, Fate of Rome, 263.
Dear readers: this is a sample of how our new book has documented history from antiquity through and including COVID.
