3a - Epidemiological investigation of a multistate leptospirosis outbreak linked to pet rats (Rattus norvegicus forma domestica) in Germany, 2022–2023

Background : Leptospirosis is a bacterial infection that can be acquired through contact with the urine of infected rodents. In August 2023, the Bavarian Health and Food Safety Authority received reports of two severe human leptospirosis cases in Hesse, Germany, linked to pet rats from a Bavarian breeder. We initiated an investigation to determine the existence of an outbreak, assess the source, and establish control measures to prevent further cases.

Methods : We alerted health and veterinary authorities at the breeder’s county of residence and reviewed notified leptospirosis cases to evaluate potential links with the outbreak. We identified households that documents showed had potentially adopted infectious rats from the breeder, informed them about the infection risk, and sent each household an online questionnaire to assess risk factors. The national consultant laboratory for leptospirosis offered households free urine tests to assess acute infections in rats and serology tests (IgG/IgM) for household members. Results : Our investigation revealed two additional severe, hospitalised cases connected to the breeding site: one person who adopted a rat (symptom onset 06/2023), and the breeder (symptom onset 06/2022), who had not disclosed breeding of rats as possible infection source. We contacted 38 adopting households, of which 11 (29%) responded to our survey. Participants reported risk factors such as close physical contact with rats, bites, or exposure to rat urine. Of 56 rat urine samples, 9 yielded positive results. Serological testing of 30 household members revealed four additional cases of Leptospira infection (3 persons with IgM, 1 with IgM/IgG).

Conclusions This outbreak underlines infection risks to humans posed by pet rats as carriers of Leptospira and a need for awareness among owners. We recommend owners consider testing rats before adoption.