From ANIMAL PEOPLE, June 2012:
Feral cats not to blame in Southern California murine typhus scare
SANTA ANA, California–Fear of “Typhus moggie” appeared to be receding in Orange County, California by June 1, 2012, just a few days after emerging, but anti-neuter/return bloggers had already amplified misleading claims far and wide about an alleged link of feral cats to murine typhus.
In truth there was no cause to associate either of two cases of murine typhus occurring three months apart with feral cats.
Murine typhus is a rare flea-borne disease, easily cured by antibiotics, which is entirely unrelated to typhoid fever, the once common and often deadly disease of which “Typhoid Mary” Mallon, 1869-1938, was the first known immune carrier.
Traps provided by Orange County Vector Control to catch feral cats on the grounds of the Frances E. Willard Intermediate School and El Sol Science & Arts Academy were removed three days after they were set, Santa Ana city spokesman Jose Gonzalez told Denisse Salazar of the Orange County Register.
“No cats were trapped, tested or euthanized,” Salazar reported. “The plan to corral feral cats living on the campuses was an effort to reduce the flea population and stave off the spread of typhus,” after a child who lives near the two Santa Ana schools developed murine typhus in April 2012.
Santa Ana is the Orange County seat. “An adult living in [the neighboring city of] Orange was diagnosed in January. Both have recovered,” Salazar continued.
“We are changing our focus and attacking the real problem, which are the fleas,” Gonzalez said.
Amid concern that traps had been set in schoolyards, KABC-TV reported that “the traps were placed in areas not accessible by students.”
Observed Vox Felina blogger Peter Wolf, “One wonders just how accessible the cats are.”
The cat trapping was misguided from the start, said University of California at Los Angeles School of Public Health epidemiologist Deborah L. Ackerman. Ackerman serves on the advisory board of the Stray Cat Alliance, founded by longtime southern California animal advocate Christi Metropole.
Reviewing past outbreaks, Acker-man recalled that, “An investigation of an outbreak in Los Angeles County found that of 30 people who contracted murine typhus, 87% had cats and dogs. Only 50% were exposed to free-roaming neighborhood cats.”
Within the outbreak area involved in that episode, Ackerman said, “90% of pet cats were seropositive for typhus, but only 11.5% of neighborhood cats. No cats from control areas, such as impounds at local animal shelters, were seropositive. Thus pet cats were the most likely source of infected fleas.
“A 2005 investigation of an outbreak of six cases of flea-borne typhus on one block in Pasadena,” Ackerman added, “found that three out of four households representing four out of six [human] cases had indoor/outdoor cats, and reported the presence of opossums.
“In Texas,” Ackerman said, “where outbreaks of flea-born typhus also occur, officials have found that fleas on pet dogs rather than on cats are more likely to harbor the infection.”
There were no cases of murine typhus reported in Orange County from 1993 to 2006. One case was identified in 2006; 15 were identified in 2011.
“Every year the numbers have gone up,” Orange County health department spokesperson Nicole Stanfield told NBC Los Angeles.
But there was never any clear reason to associate murine typhus with feral cats in particular.
“Murine typhus, also called endemic typhus, occurs when fleas that carry Rickettsia typhi bite a person. These pests live on animals including rats, cats, skunks, raccoons, and opossums,” explained Matthew Levison, bacterial disease moderator for the International Society for Infectious Diseases’ Program for Monitoring Emerging Diseases.
“Murine typhus is similar to epidemic or human louse-borne typhus that is caused by Rickettsia prowazekii, but murine typhus is much milder and the fatality rate in untreated cases is under 2%,” continued Levison, who was formerly chief of the Division of Infectious Diseases at the Drexel University School of Public Health in Philadelphia.
The National Institutes of Health web site Medline warns that murine typhus is characterized by very high fevers of 105 to 106 degrees Fahrenheit, which may last as long as two weeks, accompanied by abdominal pain, backache, diarrhea, and a red rash that radiates from the middle of the victim’s body. But the NIH adds that prompt antibiotic treatment will cure nearly all patients.
“Although murine typhus in the United States in the first half of the 20th century was maintained by infected rats and rat fleas,” Levison commented to ProMED participants in 2007, “absence of these infected components of the transmission cycle subsequently suggested alternate reservoirs and vectors. Sero-positivity for R. typhi in opossums and domestic cats associated with human cases of typhus, and heavy infestation of the animals with cat fleas, which readily bite humans, suggested these as alternate components of the transmission cycle in suburban environments.”
“The cat flea, Ctenocephalides felis, is an important vector [for murine typhus] both in Texas and California,” offered Tel Aviv Medical Center director of geographic medicine and clinical microbiology Steve Berger, M.D., in a July 1997 ProMED commentary. In addition, Berger noted, cat fleas can transmit “Another rickettsial disease, Rickettsia felis, with similar clinical features and cross-reactive serology. Infested fleas have been identified in Texas, California, Louisiana, and New York state.”
But Berger cautioned that, “Endemic typhus must not be confused with the more severe disease, epidemic or louse-borne typhus, last reported in the U.S. in 1922. Epidemic typhus is caused by Rickettsia prowazekii and is transmitted human-to-human by the body louse, Pediculus. A putative reservoir has been suggested in the American flying squirrel, with enzootic transmission by squirrel fleas. The epidemic typhus case-fatality rate for untreated cases is 10% to 20%. Two deaths were ascribed to endemic typhus during 1982 to 1991. Fifteen cases of sylvatic typhus, with reservoir in the flying squirrel, were reported in North Carolina, Virginia, West Virginia, Georgia, Tennessee, Massachusetts and Pennsylvania.
Sylvatic typhus is believed to erupt most often in winter, when hibernating squirrels are most vulnerable to fleas.
Murine typhus has actually approached eradication even as the U.S. cat population grew from circa 20 million in 1937, according to data collected by National Family Opinion Survey founders Howard and Clara Trumbull under the pseudonym John Marbanks, to circa 100 million today, including about 60 million indoor pet cats, 30 million free-roaming pet cats, and six to twelve million feral cats.
Between 1944 and 1953, Berger recounted, 19,663 murine typhus cases were reported in the U.S., 5,401 of them in 1944 alone, the peak year for the World War II housing shortage around rapidly expanded military installations along the West Coast and coastal Southeast.
As human living conditions improved, 1954-1964, the reported murine typhus caseload declined to just 812–and then fell to 315 between 1964 and 1973.
Both the number of pets in U.S. households and the murine typhus caseload nearly doubled from 1974 to 1983, a span when 588 cases were reported, but the advent of preventive flea treatments for household pets had already begun rapidly eliminating most reservoirs of infected Ctenocephalides felis fleas. Indeed, Los Angeles appeared to be the last major murine typhus reservoir in the U.S., with 33 reported cases in 1984-1988.
By 1990 there were just 50 reported murine typhus cases nationwide–and only 25 in 1993. As murine typhus appeared to be practically extinct in the U.S., national tracking ended in 1994–but another reservoir had become evident, as more than half of the known cases during the last five years of national tracking occurred in the Rio Grande Valley of southern Texas.
Berger received the 2011 ProMED Award for Excellence in Outbreak Reporting on the Internet. The 2010 winner was ANIMAL PEOPLE editor Merritt Clifton.
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