Serological Evidence of Potential Occupational Exposure to Leptospirosis in Kentucky Horse Farm Workers and Veterinarians

Serological Evidence of Potential Occupational Exposure to Leptospirosis in Kentucky Horse Farm Workers and Veterinarians


Sera from employees and horses residing on farms affected (AF) by outbreaks of

leptospirosis in Central Kentucky since 2006 were compared to farms unaffected (UF) by

these outbreaks during this same time period. A total of six farms, three farms from each

group, were compared (4 human subjects and 4 horses) for a total of 24 horses and 24

humans. Sera from a second group, veterinarians specializing in equine medicine (EV), were

also analyzed. This group contained 24 veterinarians with a range of exposure levels from no

known past exposure to individuals exposed five days previous to collection of sera. Each

farm manager completed a survey assessing farm management of horses. In addition,

veterinarians completed a survey regarding their equine medicine experience. Enzyme-linked

immunosorbent assays (ELISA) showed an increased risk of seroconversion to Leptospira in

5 (22%) of 23 equine veterinarians compared to zero (0%) of 24 farm workers (p=0.05).

Antibody levels for both sphingomyelinase 2 (Sph2) and leptospiral immunoglobulin-like

protein A (LigA) were significantly increased (p=0.03 and p=0.05 respectively) in

veterinarians. Indirect hemoagglutination (IHA) and microscopic agglutination (MAT) titers

were negative for all individuals participating in the study. Risk for seroconversion did not

appear to be influenced by the period of time from last exposure nor age of the individual.

There is an increased risk for seroconversion to Leptospira, without the appearance of clinical

disease, in EV compared to individuals working on Central Kentucky horse farms.

Leptospirosis is a zoonotic infection of worldwide importance. Once thought to

be contained it has emerged as one of the most widespread zoonotic disease in the world

(1,2,3). It is readily spread from animal to animal and animal to man; however human-tohuman

transmission is considered rare. Leptospira spp. are found in over 160 mammals

worldwide including dogs, cats, cattle, horses and sea lions (5,6). Leptospirosis is a major

public health concern in South America and South east Asia, and is now considered a reemerging

disease in most developed countries (4). Leptospira spp. are found in over 160

mammals worldwide and vaccines at this time only exist for cattle, swine and dogs making

infection in other mammals including humans a major health concern in many countries (5,6).

Horses are incidental hosts for several serovars of Leptospira (7). The bacterium

is easily transmitted via urine and fetal membranes/fluids from horse to horse. In North

America, transmission to horses is believed to be through contact with wildlife, or through

food, water, soil infected with leptospiral bacteria. Those animals infected with leptospires will

shed the organism in their urine contaminating ground water and soil (5, 6, 7). The disease is

maintained in nature through chronic infection, shed in the animal s urine, which can last for

months to years. Veterinarians, farmers, slaughterhouse workers, butchers and sewer

workers are at risk for contracting the disease either through direct contact (urine or body

fluids) or indirect contact (contaminated water or soil) (8). Individuals working on farms are

generally considered at highest risk of contracting the disease.

The disease can be confused with common occurring infections and humans can

remain asymptomatic, therefore misdiagnosis is common. Individuals infected with Leptospira

often experience typical viral symptoms such as fever, headache, nausea, vomiting and

abdominal pain (5,7). Those that seroconvert are unaware that they have been exposed and

in individuals where the disease progresses, liver and kidney failure, and/or respiratory

complications can occur. Mortality can be as high as 25%.

MAT is considered the standard method for diagnosis of leptospirosis (5,6). IHA

is also widely used in human medicine, but test results can vary. Both are useful in detecting

only active clinical cases as titers diminish rapidly post exposure (5,9). This study was carried

out to determine the risks of seroconversion in farm workers and veterinarians on Central

Kentucky farms comparing MAT, IHA and a non-commercial ELISA tests.

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