Kissing Bugs, Ticks, and Fleas: Disease Vectors in the Southwestern U.S.

Aabstract & Commentary

By Stan Deresinski, MD, FACP, Clinical Professor of Medicine, Stanford, Associate Chief of Infectious Diseases, Santa Clara Valley Medical Center, is Editor for Infectious Disease Alert.

Sources: Reisenman CE, et al. Infection of kissing bugs with Trypanosoma cruzi, Tucson, Arizona, USA. Emerg Infect Dis. 2010;16:400-405; Williamson PC, et al. Borrelia, Ehrlichia, and Rickettsia spp. in ticks removed from persons, Texas, USA. Emerg Infect Dis. 2010;16:441-446; Adjemian J, et al. Murine typhus in Austin, Texas, USA, 2008. Emerg Infect Dis. 2010;16:412-417.

Synopsis: Epidemiologists and clinicians must be alert to tick-borne, flea-borne, and triatomine-borne infections in the United States.

Vector-borne diseases remain a danger in the United States, a problem highlighted by recent studies in Arizona and Texas. Reisenman et al detected DNA of Trypanosoma cruzi in 68 of 164 (41.5%) triatomine insects (kissing bugs) collected in Tucson, AZ.

Separately, 144 (15.9%) of 903 ticks representing 11 individual species were removed from persons in Texas from 2004-2008, submitted for examination, and were found to contain DNA of at least one of the following pathogenic genera: Borrelia, Ehrlichia, or Rickettsia. Amblyomma americanum and Dermacentor variabilis were the most frequently identified ticks, and spotted fever group Rickettsia were the most frequently detected bacteria. Borrelia spp. was detected in a Dermacentor tick, while one Ixodes scapularis yielded a DNA sequence with 99% identity with that of B. burgodorferi. Ehrlichia chafeensis DNA was detected in four Amblyomma ticks.

From March to October 2008, 33 human cases of confirmed murine typhus were identified in Austin, TX, clustered in the central portion of the city. Hospitalization was required for 23 (70%) of the patients, whose mean age was 39 years (range 7 to 64 years); nine received intensive care, but none died. One-half received antibiotics, but only 13 received doxycycline; the mean interval from symptom onset to receipt of antibiotics was eight days (range 1 to 19 days). Only 46% had a rash. Nineteen of 56 (33.9%) animals, including dogs, cats, opossums, raccoons, and rats were seropositive for Rickettsia typhi, but none of the fleas examined contained DNA of this organism.

Commentary

T. cruzi has previously been identified in triatomines in south Texas as well as Arizona. Despite this, only seven authocthonous cases of Chagas disease have been reported in the United States, most recently a case from New Orleans reported in 2006. None have been identified in Arizona, despite the findings reported by Reisenman et al. While this may be, at least in part, the result of lack of diagnostic acumen, other reasons may also account for this. The authors note that the triatomines in southern Arizona live in association with sylvatic animal reservoirs and appear to have a low capacity for adaptation to human habitats. These and other factors, together with generally better housing conditions than in regions with recognized Chagas disease, do not provide the crevices in walls and ceilings preferred by the insects.

The Texas Department of Health Services (TDHS) web site lists four tick-borne diseases in the state: Lyme disease, ehrlichiosis, relapsing fever, and Rocky Mountain spotted fever.1 They state that fewer than 10 cases of ehrlichiosis are reported annually.1 There were 105 confirmed cases of Lyme disease reported in 2008, yielding an incidence of 0.4 per 100,000 population.2 TDHS reports that the incidence of Rocky Mountain spotted fever is < 1 per million population per year,1 while CDC indicates that in 2001-2002 it was < 2 per million.3 Another tick-borne disease which may be acquired in Texas is relapsing fever. Between 6 and 10 cases of relapsing fever, which in Texas is due to B. turicatae and is often associated with spelunking, were reported in that state between 1977 and 2000.4

Although the investigators were unable to detect DNA of R. typhi, the etiologic agent of murine typhus, in fleas captured from animals in proximity to human cases, fleas are the vector of this rickettsial infection. Other pathogens transmitted by fleas in the United States include R. felis, Bartonella, and Yersinia pestis.5 Murine typhus occurs in Hawaii and California, in addition to Texas, and is likely underdiagnosed everywhere. One serological study in Texas found a seroprevalence of approximately 13% in asymptomatic children tested.6 Murine typhus is a readily treatable disease, and lack of early diagnosis and treatment may be associated with severe complications.

These seemingly exotic diseases should be on the radar of physicians in the southwestern U.S. Alertness to the potential for emergence of Chagas disease in the United States must also be maintained.

References

1. http://www.dshs.state.tx.us/idcu/health/tick_borne_disease/

2. http://www.cdc.gov/ncidod/dvbid/lyme/ld_rptdLymeCasesbyState.htm

3. http://www.cdc.gov/ticks/diseases/rocky_mountain_spotted_fever/statistics.html

4. Dworkin MS, et al. Epidemiologhy of tick-borne relapsing fever in the United States. Am J Trop Med Hyg. 2002; 66:753-758.

5. McElroy KM, et al. Flea-associated zoonotic diseases of cats in the USA: bartonellosis, flea-borne rickettsioses, and plague. Trends Parasitol. 2010 Feb 23. [Epub ahead of print]

6. Purcell K, Fergie J, Richman K, Rocha L. Murine typhus in children, south Texas. Emerg Infect Dis. 2007;13:926-927.