Leptospirosis is caused by spirochetes belonging to the genus Leptospira. This is a zoonotic disease, meaning that it is transmitted from animals to humans. Leptospirosis is largely acquired from contaminated animal urine (in urban areas, particularly that of rats).
The early stages of leptospirosis are characterized by fever, chills, headache, and other common symptoms. However, its progression can lead to renal failure, jaundice, and even hemorrhagic pneumonitis. The case fatality rate ranges from 5-40%.
If It’s a Rural Disease, then Why is it Impacting Urban Populations?
Although leptospirosis can affect humans worldwide, it is most common in tropical and rural settings. In developed countries, it remains a rare disease; if it’s ever mentioned, it’s mostly related to household pets. However, in Dr. Ko's study, leptospiral antibodies have been found in up to 30% of selected urban populations. In fact, three cases of leptospirosis have been reported in Baltimore (which doesn’t sound like much, but for this disease it is), indicating that it might be more of an underlying urban problem than we think.
Dr. Ko’s studies particularly focus on Brazil. From the 1960s-90s, Brazil experienced a large demographic shift which caused a 350% increase in urban settlement. This led to the creation of urban slums where the lack of sanitation and rodent problem easily led to a leptospirosis outbreak.
In a 1923 study of yellow fever in Brazil, leptospirosis was found to be a sporadic rural disease that mostly affected livestock. However, this large shift from rural to urban settlements in crammed slums overrun with rodents have created hotspots for leptospiral infection.
“The factors are pathogen and disease specific,” says Dr. Ko, “Dengue, Zika, and Chikungunya are diseases that are transmitted by a mosquito Aedes aegypti that has expanded in abundance due to urbanization and climate (breeding spots proliferating due to lack of refuse collection, eggs laid in plastics after rainfall, and adults hatching from larvae which go on to transmit these pathogens). Yellow fever and malaria are different diseases with different factors that enable transmission in Brazil.”
Leptospirosis is often misdiagnosed for more common diseases like Dr. Ko mentioned above. But, with the use of surveillance tools and interviews of over 3,000 residents of Brazilian slums, Dr. Ko and his team were able to identify the causes of increased leptospiral outbreaks, which are largely due to the environmental scene and infrastructure of these slums. Open sewers, refuse, and inadequate flood water drainage are the perfect place for bacteria to live. In addition, low socioeconomic status was found to independently contribute to the spread of infection.
Leptospirosis doesn't just affect Brazil. Outbreaks of similar size have been seenin Nicaragua, El Salvador, and other more tropical environments. Because of this, I was curious as to why Dr. Ko chose to focus his studies on Brazil.
“I was going to work in Haiti but, because of the military coup, I had to find another place to work. My friends at the Brazilian Ministry of Health invited me. There’s similar problems of social inequity, urbanization, and the growth of informal settlements that existed there as in Haiti.”
The findings related to the environment/infrastructure of Brazilian slums, as well as the socioeconomic component, indicate that the prevention of leptospirosis will need to address social factors that produce health disparities in urban slum communities. Although it’s easier said than done, governments and health organizations can start by producing greater efforts to improve sanitation in these communities. Educating its residents on how they can practice better sanitation skills, as well as expanding healthcare and diagnostic tests to test for infectious diseases such as leptospirosis, are all goals that the public health community needs to continue to work towards.
Dr. Ko’s Work:
2008 PLoS Neglected Trop Dis Reis 2-4-e228 Impact of environment and social gradient on leptospira infection