Xishan Biology

Introduction to Pathogens

Leptospira

Introduction to Pathology

 

Leptospira, belonging to the family Leptospiraceae, is a slender, motile, filamentous bacterium commonly referred to as leptospires. These bacteria typically measure between 6 and 20 micrometers in length and 0.1 to 0.2 micrometers in width, featuring dense, regular, and numerous spiral structures. Notably, one or both ends of the bacterial cell often curve into hook-like shapes. Leptospira are obligately aerobic organisms and thrive best when cultured at 30°C on media supplemented with bovine serum, along with vitamins B1 and B12.

Figure 1: Electron micrograph of Leptospira bacteria

Epidemiology

 

Leptospirosis is considered the most widespread animal-borne infectious disease in the world, and it also qualifies as a zoonotic disease. The illness typically occurs in warm, humid tropical regions, where stagnant water with neutral or slightly alkaline pH is commonly found. Humans usually contract the infection through direct or indirect contact with infected animals—or by coming into contact with contaminated soil, water, or irrigation ditches that have been exposed to excretions from carrier animals. After infection, some individuals remain asymptomatic, while others develop leptospirosis. Livestock such as cattle, pigs, and dogs, as well as wild animals like cats, dogs, and rodents, can all transmit the disease. Among these, rodents—particularly species like the black-striped field mouse, yellow-haired rat, yellow-breasted rat, and brown house rat—are the most common reservoirs. Infection often leads to lymphocytic infiltration and cellular damage in rats. Leptospirosis in dogs peaks during the summer and autumn months, with the incidence rate positively correlated with rainfall levels. In poorly maintained kennels, the prevalence of the disease tends to be even higher. Interestingly, male dogs are more susceptible than females, and puppies are particularly vulnerable, often experiencing more severe symptoms. According to estimates from the World Health Organization (WHO), there are approximately 1 million severe cases of leptospirosis in humans each year. Notably, France ranks as the country with the highest infection rate among European nations.

Figure 2: Transmission of Leptospirosis

Clinical symptoms

 

Leptospira bacteria can enter the body through skin and mucous membranes, spreading via the bloodstream to vital organs such as the liver and kidneys. In humans, initial symptoms of leptospirosis typically resemble those of the flu—fever, nausea, headache, vomiting, and diarrhea. Many mild cases remain asymptomatic, while severe infections may lead to jaundice, kidney failure, liver failure, meningitis, or even pulmonary hemorrhage, with mortality rates as high as 10% to 20%. Animals, on the other hand, often carry Leptospira without showing clinical signs themselves, yet they can develop chronic kidney infections and shed large amounts of bacteria in their urine. Dogs, in particular, are susceptible to infection by multiple serogroups of Leptospira, including the Canicola and Bratislava groups. The Pomona group, meanwhile, tends to target either the kidneys or the liver, whereas the Icterohaemorrhagiae and Australis groups more commonly cause liver-related diseases. During acute infection, dogs usually exhibit fever and shivering, followed by symptoms like vomiting, diarrhea, and peripheral vascular collapse. Other signs may include coughing, irregular heart rhythms, vomiting blood, nosebleeds, and widespread skin hemorrhages. In severe cases, dogs can also experience coagulation disorders and extensive vascular damage, ultimately leading to death.

Figure 3: Pathogenesis of Leptospira

Prevention and removal

 

Controlling leptospirosis can be somewhat challenging due to the variability in serovars, reservoir animals, and transmission conditions of the bacteria. Dog kennels can implement preventive measures by isolating rodents and vaccinating dogs, while livestock and humans can also protect themselves through vaccination. Currently, two inactivated vaccines for human use are available on the market, whereas vaccines for livestock and veterinary use typically depend on the locally prevalent serovars. Commonly used disinfectants for environmental sanitation include 1% sodium hypochlorite solutions and quaternary ammonium compounds. According to guidelines from the Center for Food Safety and Public Health (CFSPH), pasteurization is an effective method for eliminating Leptospira bacteria.

Diagnosis and Treatment

 

Diagnosis in dogs typically involves hematological tests, urine analysis, imaging studies, and more. Alternatively, leptospires can be cultured from blood, cerebrospinal fluid, or urine (though culturing is quite challenging), or detected using PCR technology and immunological methods—where antibody titers in convalescent-phase serum are at least four times higher than those in the early phase. For severe cases, treatment usually relies on penicillin-based, tetracycline-based, or azithromycin-based antibiotics.

References

 

1. Binns, et al. "Leptospirosis: A Global Public Health Story." Asia Pacific Journal of Public Health (2016).

2. Levett, Paul N. "Leptospirosis." Clinical Microbiology Reviews 14.2 (2001): 296.

3. Foster, Timothy J., and J. A. Geoghegan. "Staphylococcus aureus – Molecular Medical Microbiology (Second Edition) – Chapter 37." *Molecular Medical Microbiology* (2015): 655–674.

4. Troìa R., et al. "Prospective evaluation of rapid point-of-care tests for the diagnosis of acute leptospirosis in dogs." Veterinary Journal 237 (2018): 37-42.

5. Liu Shan. Diagnosis and Treatment of 8 Cases of Canine Renal Failure Caused by Leptospira. Diss. Nanjing Agricultural University.

6. Djelouadji, et al. "Overview of Laboratory Methods for Diagnosing Leptospirosis and Identifying and Typing Leptospires." (2017).

 

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