Abstract
Dogs are highly susceptible to the leptospiral infection, notably stray and sheltered dogs. Unsanitary conditions often observed in dog shelters may predispose the introduction and spread of leptospires among sheltered populations, potentially increasing the chances for the inadvertent adoption of asymptomatically infected animals. The present work describes a longitudinal study using a multidisciplinary approach for the identification of chronically infected dogs and the characterization of potentially pathogenic strains circulating among stray and sheltered dog populations in São Paulo, Brazil. A total of 123 dogs from three populations were included. The initial evaluation consisted of blood and urine quantitative PCR testing (qPCR), the detection of specific antibodies by microscopic agglutination test (MAT), physical examination and hematological and serum biochemistry analyses. The qPCR-positive dogs were prospectively examined, and reevaluations also included culture from urine samples. Positive qPCR samples were subjected to 16S rRNA and secY gene phylogenetic analysis. The recovered strains were characterized by Multilocus Sequence Typing, polyclonal serogroup identification and virulence determination. Leptospiruria was detected in all populations studied (13/123), and phylogenetic analysis revealed that 10 dogs had L. interrogans infection. Three dogs (3/13) had L. santarosai infection. The secY phylogenetic analysis revealed that the L. santarosai sequences clustered separately from those obtained from other hosts. Ten leptospiruric dogs were reevaluated, and three dogs presented persistent leptospiruria, allowing culturing from two dogs. The strains were characterized as L. interrogans serogroup Canicola (virulent) and L. santarosai serogroup Sejroe (not virulent). Serum samples were retested by MAT using the DU92 and DU114 strains as antigens, and no increased seroreactivity was detected. Asymptomatic L. santarosai infection was observed in all populations studied, suggesting a possible role of dogs in the chain of transmission of this leptospiral species. The results suggest a genetic distinction between lineages of Brazilian L. santarosai maintained by dogs and other animal hosts. Our findings revealed that dogs could act as maintenance hosts for distinct pathogenic Leptospira, highlighting also that asymptomatically infected dogs can be inadvertently admitted and adopted in dog shelters, potentially increasing the risks of zoonotic transmission.
Highlights
Leptospirosis is a bacterial disease caused by pathogenic helical shaped spirochetes of the genus Leptospira [1]
To promote evidence-based knowledge regarding asymptomatic urinary shedding of leptospires in dogs, the present study proposes the identification of chronically infected animals and the characterization of potentially pathogenic strains circulating among stray and sheltered dog populations in São Paulo, Brazil
Dogs exhibiting asymptomatic urinary shedding of pathogenic Leptospira were successfully identified in all populations studied, and the prospective evaluation of the infected dogs has confirmed the presence of chronic carriers among these populations, allowing the culturing and characterization of circulating leptospiral strains
Summary
Leptospirosis is a bacterial disease caused by pathogenic helical shaped spirochetes of the genus Leptospira [1]. The disease is recognized as the most widespread zoonosis and has emerged as a major public health issue in much of the developing world [3]. The exposure to water and soil contaminated by the urine of infected animals is the most common route of transmission to humans and domestic animals [6], and rodents are considered the major source for human infection, a role likely attributed to its synanthropic behavior and widespread distribution [3]. Recent One Health approaches have been used to circumvent crucial epidemiological aspects of leptospirosis, and several studies have pinpointed a significant role of different mammalian hosts in its zoonotic transmission [6,7,8,9]
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