A deep dive into an outbreak of tularemia linked to contaminated must and wine that led to several complicated infections, requiring extended durations of treatment.
Tularemia is a zoonotic disease that continues to teach us a lot about the transmission of pathogens between humans and animals. The often-rare disease is brought on by the bacteria Francisella tularensis, which consists of 2 subspecies, Holarctica, which is frequently seen in the Northern hemisphere, and tularensis, which is mostly commonly detected in North America. Unfortunately, due to its rarity and non-specific symptoms, tularemia is commonly mistaken for other diseases.
Outbreaks of the disease tend to be smaller events, clustered around wild-life exposures or inhalation of contaminated dust/aerosols. However, since tularemia outbreaks tend to be an infrequent occurrence, when one does happen, there is always intrigue.
A recent article in the International Journal of Infectious Diseases sheds light on a cluster of cases associated with a grape harvest. Although this might sound like a trip to Napa Valley gone wrong, this German outbreak provides details on the variety of mechanisms of transmission that tularemia exhibits, including tick/deer fly bites, handling infected animals, laboratory exposures, inhalation of contaminated dust, or even contaminated food and water.
The initial case in the German outbreak occurred in a 46-year-old patient who attended a wine tasting and subsequently experienced a severe fever and swollen lymph nodes, which spiraled into severe tonsillopharyngitis. Submandibular lymph node swelling increased and, after a consultation with an ear, nose, and throat physician, an antibody test for F tularensis was ordered and returned positive. Despite 500 mg of ciprofloxacin twice a day for 2 weeks, lymph node swelling worsened and hospitalization was required.
In addition to the initial case, there were 5 other patients infected following consumption of must (grape juice) or wine from the same vineyard. Three male and 2 females, ranging in age from 3 to 41 years, experienced symptoms beginning 4 to 24 days after exposure. Nearly all of the ill experienced cervical lymphadenopathy and pharyngitis, as well as fever and general malaise. Serological confirmation of tularemia led to appropriate treatment and symptoms resolved within 23 to 45 days.
The epidemiological investigation pinpoints the likely source of transmission as must from a vineyard in the area of Rhineland-Palatinate, Germany. In the must-making process, grapes are collected by an automatic harvest machine and then pressed to produce juice without filtering out extraneous materials. The investigators note that “consumption of fresh must with the highest genomic equivalents of F tularensis ssp. Holarctica was significantly associated with the development of disease.”
In the past, outbreaks of tularemia have been linked to contaminated food and water and, in this case, it is highly likely that when the grapes were collected by the automatic harvest machine, they were contaminated by an infected rodent or rabbit.
This tularemia outbreak is not the first linked with consumption of grapes in a German vineyard. In October 2016, 6 grape harvesters acquired tularemia after exposure to grape must that was later found to be contaminated with wood mice DNA.
The investigators on the latest report heavily emphasized that not only is tularemia very infectious, but also that the treatment process can be complicated. The recommended duration of treatment is often 14 days, but complications and continuation of symptoms seen in this outbreak led the authors to advise upwards of 21 days of treatment.
Overall, this outbreak sheds light on yet another route of transmission for this zoonotic disease, but also provides an example of how to manage an outbreak when recommended treatment may not be sufficient to resolve symptoms.