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Flood Water Displaces Rodents, Raises Infectious Disease Concerns

SEP 01, 2017 | CONTAGION® EDITORIAL STAFF

Rat-Bite Fever (RBF)

Rat-bite fever (RBF) is not common in the United States; however, because it is not a notifiable disease, incidence rates are unavailable, and so the true number of infections in the United States is unknown. Much as the infection’s name indicates, transmission of the RBF pathogen, Streptobacillus moniliformis bacillus, occurs when an individual is infected via bite, scratch, or even skin contact with an infected rodent. Although primarily transmitted by rats, the bacterium can also be transmitted via mice and gerbils. According to the CDC, after an incubation period of about 3 to 10 days, the infection causes non-specific symptoms, such as “fever, chills, myalgia, headache, and vomiting.” Some patients may also experience, “a maculopapular rash on the extremities 2 to 4 days after fever onset, followed by polyarthritis in approximately 50% of patients.”

If not treated, a RBF infection can lead to endocarditis, myocarditis, meningitis, pneumonia or sepsis. The mortality rate for RBF is about 7% to 13%, according to the CDC. Because it is difficult to grow S. moniliformis in culture, diagnosis, “requires specific media and incubation conditions.” Samples are taken from either blood, synovial fluid, or other body fluids. Specific methods are described by the CDC as follows: “In the absence of a positive culture, identification of pleomorphic gram-negative bacilli in appropriate specimens supports a preliminary diagnosis. S. minus does not grow in artificial media. For this reason, diagnosis is made by identifying characteristic spirochetes in appropriate specimens using darkfield microscopy or differential stains. If RBF is suspected in a severe illness or death, but a diagnosis has not been made, physicians can consider requesting diagnosis assistance from their state public health laboratories.”

Salmonellosis

Salmonellosis can be spread in many ways; however, from small mammals, the disease can be spread to humans via contact with their feces, or contact with an infected animal. Information for healthcare professionals and laboratories can be found on the CDC website.

Tularemia

Spread by the bacterium Francisella tularensis, the disease is transmitted to humans via, “tick and deer fly bites, skin contact with infected animals (such as rodents, muskrats, ground squirrels, and beavers), ingestion of contaminated water, and inhalation of contaminated aerosols or agricultural dusts,” according to the CDC. There are 6 different types to infection, depending on how the bacteria enter the body. The most common is ulceroglandular, which occurs after “a tick or deer fly bite or after handing of an infected animal. A skin ulcer appears at the site where the bacteria entered the body. The ulcer is accompanied by swelling of regional lymph glands, usually in the armpit or groin,” according to the CDC.
Diagnosis is made through special diagnostics completed in the lab. (Rapid diagnostic testing is not available.) Specimens should be collected from appropriate sample sites, depending on the type of infection. The treatment of choice for the infection is streptomycin. Alternate treatment choices are available on the CDC website.

To avoid these zoonotic-borne diseases, residents are urged to avoid rodents and their droppings as best they can and clean up / seal up areas that would attract them.
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