Murine Typhus in Hawaii: When the Mice Come Into Play

Case Study
By Alan Tice, MD

Synopsis: Life in paradise is still not without risk.

It seems this year was a good one for rodents. An unusually wet winter and spring in Hawaii led to exuberant growth of grasses and vegetation that support the replication and survival of mice and rats on several of the Hawaiian islands. It was not until late summer when the fields began to dry out that the explosion of the vermin population was recognized. They headed into town to look for food—and brought their fleas with them. There were reports of mice brazenly moving into homes and of traps being filled or overflowing nightly. Terminex was overwhelmed. Some swimming pools had to be cleaned daily to get rid of the dozens or sometimes hundreds of mice trapped in them. The situation seemed the worst on Maui, where there have been problems before but not as bad.

The mice and rats created a special problem for my patient, a young man in prior excellent health, who lives on Molokai but works on Kahoolawe 4 days a week cleaning up debris on the island which was used as a practice bombing run since World War II. Goats primarily populate it at this point. After returning from work on the island, he noted myalgias and malaise and a headache along with a chill. His symptoms gradually got worse over the next few days and he began to run a fever. He visited a local urgent care center but was told he had a viral syndrome and was sent home without therapy. When his headaches worsened and his fevers persisted for a week, he came to Honolulu for more advice. Evaluation found a well-nourished and developed man who was miserable and had a temperature of 103°. He had mild meningismus and a little photophobia but no conjunctival hemorrhages. His chest was clear but his liver was enlarged and tender. No rash was noted. Labs showed a WBC of 13,000 and liver function studies 5 times upper limit of normal. On specific questioning, he had noted an increase in the number of mice around his home and at work. He even remembered being bitten by one on Kahoolawe. He was given a prescription for doxycycline and began to feel better within a day and was able to go back to work in 4 days.

His serologies for leptospirosis were negative, but when other cases of murine typhus were reported from Maui, his blood was tested for murine typhus and was found to be strongly positive with a more than 4-fold increase in IgG titers over 3 weeks.

Murine typhus is an unusual infection and probably often overlooked. There were up to 5000 cases reported per year in Hawaii during World War II but it almost disappeared after a DDT campaign was instituted. Only a few dozen cases are now reported to the health department each year, and those are mainly from Maui, where the endemic focus was established before. An endemic focus has also been identified in Kauai with a report of 5 cases in 1998.1 The risk continues with exposure to rats and mice, but the outbreaks occur when there is migration of the pests into the residential areas. The primary carrier is Rattus rattus. The vector is usually Xenopsylla cheopis but the cat flea, Ctenocephalides felis, can carry the pathogen as well. Either flea spreads the infection to humans through bite wounds contaminated with flea feces, although dried feces can apparently cause an inhalation form as well. The flea is a life-long host of the rickettsia once it is infected.

Rickettsia typhus commonly presents with myalgias, a severe headache, persistent fevers, and often a fine macular rash. Pneumonitis and meningoencephalitis may also occur, sometimes with devastating results if the appropriate antibiotic is not used early. Hepatitis is common. Mild thrombocytopenia and leukocytosis are often present but seldom a clinical problem. Infections may occur in many places, often in port cities and tropical areas. Outbreaks have been reported in Texas and California but it can be found almost any place in the world where a population of rats can exist.

Mice were certainly a problem in Hawaii this year but a fall overflow has been reported in California as well, although no specific diseases have been attributed to it. There is also an apparent increase in hantavirus infections in Peru, again likely related to a rise in the rodent population. The differential diagnosis for murine typhus in Hawaii is primarily leptospirosis, which is endemic in most of the fresh water in Hawaii and even contaminates the seawater on occasion when there is a lot of rainfall. Dengue is also of concern in Hawaii but the recent epidemic seems to be over. The differential in the rest of the world is very great and includes meningococcemia, measles, typhoid fever, syphilis, toxic shock syndrome, Kawasaki disease, Rocky Mountain Spotted Fever, Colorado Tick fever, and various viral infections. A careful and detailed history plus knowledge of the local disease epidemiology may be extremely useful.

Local measures such as rat traps, pesticides, and exterminators have all been advocated by the health department and have apparently been effective over the last few weeks. No further cases have been reported and the rodent population seems to be declining.

Dr. Tice, Infections Limited, PS, Tacoma, WA; Infectious Disease Consultant, John A. Burns School of Medicine, University of Hawaii, Honolulu, HI, is Associate Editor of Infectious Disease Alert.

Reference

1. Manea SJ, et al. Clinical and epidemiological observations regarding the 1998 Kauai murine typhus outbreak. Hawaii Med J. 2001;60:7-11.