From the Polynesian rats accompanying Hawaii’s first settlers to the more invasive black and Norway rats introduced by Europeans, rodents have been a nuisance in the Islands for centuries. Beyond the damage these pests do to our environment, they also carry diseases harmful to residents and visitors.
In Hawaii, there are three major rat-borne illnesses to be aware of: leptospirosis, murine typhus and rat lungworm disease. While these pesky critters are a reservoir for infection, they don’t typically directly transmit them directly to humans. A bite from a rat won’t get you sick, but contact with their urine, fleas or feces might.
Here are facts behind Hawaii’s three most common rat-borne illnesses.
Leptospirosis: The infection lurking in fresh water
If you’ve lived in Hawaii for more than a few months, you’ve likely heard of the bacterial infection called leptospirosis. These bacteria can be found in Hawaii’s streams and waterfalls as it’s rampant in fresh water. Leptospirosa, the bacteria that causes leptospirosis, gets into fresh water from the urine of infected animals, including rats.
“Every freshwater area in the state is a risk,” says Sarah Park, MD, the head of the Disease Outbreak Control Division for the State of Hawaii in Honolulu.
Infection risks are higher during and after heavy rain, when contaminated soil is washed into waterways, says Dr. Park. You can contract leptospirosis from contaminated water entering the body—through swallowing, open wounds or even water going up your nose.
Some leptospirosis symptoms to watch out for include:
Good news if you enjoy kayaking down the Wailua River or dipping your toes in Likelike Falls: Taking a dip doesn’t guarantee an infection. Of the estimated 100 to 200 cases of leptospirosis that occur annually in the United States, about half occur in Hawaii. Meaning, the risk of infection is still relatively low. In fact, in 2017, there were 1.75 cases reported per 100,000 residents. Even better, the disease is treatable with antibiotics such as penicillin or doxycycline.
There are simple ways to lower your risk of infection, too. “If you are going to go in the water, make sure any cuts and wounds are covered,” says Park. “When you get out wash with soap and water, clean water. Try not to dunk your face and if you do, try not to swallow any of that water.”
Around the home, try to control rodents by trapping or poisoning them and removing any nests. Be sure to wear protective clothing such as boots and long pants when doing any yardwork that may be in contaminated soil. You can also protect pets and farm animals by vaccinating them against the infection.
Next time you’re looking at those tantalizing waterfalls, weigh your options and know the risks. If you want to keep yourself infection-free, it’s best to avoid rivers and streams entirely after major rainfall, no matter how tempting.
Beware of Typhus-spreading ukus
Typhus may sound like a bygone illness your great-grandfather may have had, but murine typhus is alive and well in Hawaii. This bacterial infection is spread by fleas, or ukus as we say in Hawaii, and carried by rats. Other rodents like mongooses and even household pets like cats and dogs can also host the fleas that spread murine typhus.
Symptoms of murine typhus are similar to the flu and leptospirosis and can include:
- Fever
- Body aches
- Nausea
- Loss of appetite
- Stomach pain
- Vomiting
- Cough
The notable difference between typhus and other infections is the potential for a rash that would appear around day five of infection. Most individuals get sick within two weeks of exposure and can recover without treatment, though some cases are more severe.
It’s hard to say exactly how prevalent murine typhus is in Hawaii as a diagnosis requires two blood tests, is often mistaken for a viral infection and because patients may be unaware they received flea bites. In 2017, there were 0.56 cases reported per 100,000 residents, but infection rates may have been higher.
“We suspect that a lot of our doctors are just empirically treating [the infection] with antibiotics,” says Park, meaning that some doctors aren’t testing for murine typhus before writing a prescription.
Despite the potential lack of testing, it has been reported every year in Hawaii since the Department of Health began tracking the illness, with most cases reported in Maui County. Like leptospirosis, murine typhus is easily treated with antibiotics, usually doxycycline.
Typically people get exposed to flea bites during a hike or other outdoor adventure, according to Park. Wearing long clothes and using bug spray during hikes or trips to the park may help curb the risk of infection. Because household animals like cats and dogs can spread disease, it’s best to keep pets up to date with flea prevention treatments.
Protect yourself against parasites
Angiostrongyliasis, or rat lungworm disease, made national headlines in 2017 when an outbreak caused 18 confirmed, and 3 suspected cases of the parasitic infection. The disease may result in eosinophilic meningitis, a parasitic form of meningitis that can cause severe headache, stiffness in the neck, fever, vomiting, light sensitivity and a tingling or painful sensation in skin. Some people who contract angiostrongyliasis will never show symptoms. Generally, only those who develop eosinophilic meningitis will show major symptoms.
As the name suggests, rats host the adult form of the roundworm that causes rat lungworm disease, but people usually catch it from slugs or snails. Infected rats pass parasite larvae in their stool where snails and slugs pick them up and pass them along. Most individuals get rat lungworm from direct contact with snails or slugs, including eating them, or from unwashed produce where the gastropods were present.
Some tips to prevent infection, according to Park, include:
- Wash your lettuce leaf by leaf
- Keep small keiki from touching slugs and snails or putting them in their mouths
- Don’t drink from garden hoses where slugs may reside
There is no specific treatment for rat lungworm disease, although the parasite cannot grow or reproduce in humans and will eventually die. Despite alarmist news headlines from the 2017 outbreak, rat lungworm infection is very rare. During that outbreak there were only 21 confirmed and probable cases for Hawaii’s 1.4 million residents.
Stay informed, stay healthy
If you suspect you have any of these conditions, schedule an appointment with your doctor. He or she may conduct blood tests for leptospirosis or murine typhus. Rat lungworm is harder to diagnose as there is no blood test to identify the parasite. Locally, doctors can confirm cases of rat lungworm with a polymerase chain reaction (PCR) test to look for the parasite in a patient’s DNA, cerebrospinal fluid or other tissue. More commonly though, physicians will conduct a medical history to assess risk of exposure and compare against symptoms of eosinophilic meningitis along with a test for the presence of eosinophils (a type of white blood cell) in spinal fluid.
“Unfortunately, we'll never get rid of the rats,” says Park. Her advice to everyone in the state to prevent infection: “Be aware of the risk and know the signs and symptoms.”
