Serologic Evidence of Zoonotic Infections by Brucella canis in Southern Chile: A Neglected Emerging Disease.

UNLABELLED: Brucella canis infections are poorly understood in humans and difficult to diagnose, with low blood culture yields. Serological diagnosis was introduced in Chile in 2017.

AIM: To report a clinical series diagnosed by serological methods.

METHODS

Multicenter study in southern Chile of cases admitted in three hospitals in two regions. Diagnosis was made by Rapid Slide Agglutination Test with 2-mercaptoethanol (ME-RSAT).

RESULTS

Ten cases were identified between 2020 and 2024 (7 males, median age 54.5 years). Of these, 4 resided in rural areas, and 9 reported exposures to dogs. The cases presented as prolonged fever in 4 patients (40%), spondylodiscitis in 2 (20%), myopericarditis, meningoencephalitis, febrile hepatitis, and cervical lymphadenopathy with weight loss (10% each). Blood cultures were performed in 9 patients, all of which were negative (median incubation time 5 days). All 10 patients received treatment. Two were treated with doxycycline alone, while the remaining 8 received combination therapy. In 3 of the 10 cases, combination therapy was used to prevent relapse after a self-limiting episode of fever, myopericarditis or cervical lymphadenopathy. Histological analysis was available for 4 cases and 2 presented granulomas. The 7 patients who received treatment during the acute phase showed improvement. However, three of them developed chronic pain, and one patient required a disability pension. Additionally, the patient with hepatitis experienced three relapses. Human leucocyte antigen (HLA) typing showed a high relative frequency of the HLA B*07 allele. Epidemiological information reveals that most cases of brucellosis in Chile are due to B. canis, and are concentrated in southern regions.

CONCLUSIONS

B. canis infections are emerging, appear to be pleomorphic, with prolonged morbidity and risk of relapse and sequelae. A zoonotic exposure to dogs, even in the past, can help to in suspecting them, and diagnosis is primarily serological. They respond to treatments recommended for other Brucella species and may be associated to some HLA alleles.