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Leptospirosis Epidemiology

By Jonas Wilson, Ing. Med.

The spirochete bacterium Leptospira is a very common disease-causing microorganism for both humans and animals. It can be an occupational or recreational hazard for those who come into frequent contact with the urine or urine-contaminated media (e.g., water, food, and soil) of infected animals.

Rodents play an imperative role in the spread of the disease. Leptospires gain entry into the body through the mucosa or open wounds in the skin and quickly acquire access to the bloodstream where they disseminate in various body tissues and organ systems.

About 9 in every 10 people affected develop symptoms that are mild and flu-like. These include headache, fever, and muscle pains. A small percentage of these people, approximately 10%, may go on to develop more severe leptospirosis called Weil’s disease and have problems, such as pneumonitis, pancreatitis, hepatitis, meningitis, and even death due to internal hemorrhaging and multiple organ failure.

Global Distribution

Leptospirosis is believed to be the most widespread zoonosis globally. It is found all over the world, but has a higher prevalence in countries that are located in tropical and subtropical regions. Leptospires have been shown to be able to survive longer in climatic conditions that are humid and hot. Persons living in or travelling to countries such as India and China or regions such as the Caribbean, Central, and South America, South East Asia, or the African continent should be aware of the higher potential of exposure risk and contracting leptospirosis.

It is found in both urban and rural areas and is particularly hazardous for those employed in sectors, such as farming, crop harvesting, sewers, military, and veterinary clinics. In addition to these, outdoor activities, such as camping, sailing, canoeing, rating, and swimming in potentially contaminated fresh water bodies (e.g., ponds, lakes, and rivers) also put people at risk. Natural disasters, such as flooding may also be linked to potential leptospirosis outbreaks, particularly if the drinking water becomes contaminated with water from the flood.

Leptospirosis in Numbers

The number of people affected by the condition worldwide is not very well documented. However, it is believed to range from somewhere between 0.1 and 1 per 100,000 people per year in the temperate zones. This number increases to about 10 or more per 100,000 people per year in tropical regions and may surge to well over 100 per 100,000 in events such as hurricanes and heavy flooding, which may cause outbreaks. Notwithstanding these estimates, it is believed that cases worldwide may also be underreported due to being overlooked or mistaken for other conditions.

Epidemiological Patterns

Faine defined three epidemiological patterns of the disease. The first of the three tends to occur in temperate climatic conditions. In this pattern, few serotypes are implicated and people become infected by direct contact with an animal that is infected. Farming of pigs and cattle puts people at particular high risk. To lower one’s risk of exposure, animal immunization is suggested.

The second epidemiological pattern is found in wet tropical regions and has many more serovars implicated and involves more animal reservoirs, including dogs and other pets. Rodent populations need to be controlled to limit animal and ultimately human infection. Moreover, occupational and recreational hygiene to avoid exposure, such as the use of protective gear, should be employed to reduce exposure risk.

The third epidemiological pattern is seen in urban environments. Its global significance is small and it is rarely seen in the developed world. However, it becomes important in circumstances where the urban infrastructure has been compromised by events such as natural disasters or war.

Reviewed by Susha Cheriyedath, MSc

Further Reading

Last Updated: Sep 22, 2016

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