Risk Factors for Human Lice and Bartonellosis among the Homeless, San Francisco, California, USA - Volume 20, Number 10—October 2014 - Emerging Infectious Disease journal - CDC
Volume 20, Number 10—October 2014
CME ACTIVITY - Research
Risk Factors for Human Lice and Bartonellosis among the Homeless, San Francisco, California, USA
The human body louse (Pediculus humanus humanus) has played a key historical role in the transmission of diseases such as trench fever, epidemic typhus, and louseborne relapsing fever (1,2). Because of the emergence of pesticide-resistant head lice (P. humanus capitis) (3), lice continue to be part of the human landscape. Head lice are not implicated in the transmission of disease-causing agents, but they do have social and economic effects because of the school days missed by children with infestations (3). Like head lice, pubic lice (Pthirus pubis) are not known to transmit pathogens (4). Although diseases are not transmitted by all lice species, heavy louse infestations can cause pruritus, secondary infections from scratching, and anemia (5,6).
A combination of conditions, including poor clothing hygiene, lack of resources, and cold weather, put certain human populations, such as homeless persons, more at risk of harboring lice and for louseborne diseases (2). Research suggests that environments frequented by homeless persons (e.g., homeless shelters, where there is close body-to-body contact and where clothing hygiene is lacking) promote louse transmission (2,5). The number of homeless persons is not trivial. A single night count by the Annual Homeless Assessment Report (AHAR) estimated 649,917 homeless persons in the United States in 2010; of that total, 5,823 (0.9%) were in San Francisco (7). Given the large number of homeless persons in the United States, human lice of all species and the diseases they may carry are a health concern for this population.
Of concern is the potential for body lice to transmit Bartonella quintana, the bacterium that causes trench fever, the most common louseborne disease in some urban homeless persons (8). Trench fever is characterized by severe frontal headache, dizziness, conjunctival congestion, shin pain, and lymphadenopathy, accompanied by a relapsing fever lasting 4–8 days at a time. Life-threatening complications, such as endocarditis and bacillary angiomatosis, can occur (1,9). The only known vector of B. quintana is the body louse, although recent studies suggest head lice may also vector disease agents (10–12). B. quintana proliferate in body lice 4 days after ingestion and are continuously excreted in feces for >3 weeks (13). B. quintana can be transmitted to a human host when an infected louse feeds on an uninfected human and excretes B. quintana-infected feces onto their skin (1). The bacteria are rubbed into open mucous membranes or scratched into the skin through the bite wound (5), resulting in B. quintana infection 15–25 days later (1). Although B. quintana are principally infective to humans, macaque monkeys and the lice that infest them can maintain and circulate a strain of B. quintana(14).
In a previous study of head and body lice from homeless persons in San Francisco, we determined that 33.3% of body lice samples and 25% of head lice samples, which were pooled by host, were positive for B. quintana (12). To better characterize body and head lice transmission and to gauge the risk for B. quintana infection, we evaluated San Francisco homeless persons to determine presence of head and body lice, assess habits that may increase the risk of acquiring lice, and collect lice to test for B. quintana infection.
Ms Bonilla is a senior public health biologist with the California Department of Public Health involved with the surveillance, prevention, and control of vectorborne diseases, and is the manager of the state-wide tickborne disease program in California. Some of her special interests include the prevention and control of vectors (such as lice, bed bugs, and scabies mites) and vectorborne disease in urban settings.
We thank first the numerous physicians, nurses, and medical students who worked with us and alongside of us at San Francisco Homeless Connect. We also thank the following people and agencies for taking time to work on this project or who made this project possible: Jaynia Anderson, Ervic Aquino, Rachel Bouttenot, Laura Diaz, Tina Feiszli, Leslie Foss, Long Her, Timothy Howard, Vicki Kramer, Mike Niemela, Kerry Padgett, Mary Joyce Pakingan, Erin Parker, Robert Payne, Ed Powers, Tiaquandra Reddick, Katherine Shimabukuro, James Suchy, Inger Vilcins, Jane Koehler, Allean Husted, Stan Husted, staff from the San Francisco Public Health Department, and staff from Alameda County Vector Control District.
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Suggested citation for this article: Bonilla DL, Cole-Porse C, Kjemtrup A, Osikowicz L, Kosoy M. Risk factors for human lice and bartonellosis among the homeless, San Francisco, California, USA. Emerg Infect Dis. 2014 Oct [date cited]. http://dx.doi.org/10.3201/eid2010.131655