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Scrub typhus now endemic in South America
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New findings published today in the New England Journal of Medicine suggest that scrub typhus — a disease that kills approximately 140,000 people each year in the Asia-Pacific region — may now be endemic in South America.
“The cases of scrub typhus, found off of Chile’s mainland, expand our understanding of the epidemiology of scrub typhus and suggest that there may be a much wider global distribution than previously understood,” study researcher Thomas Weitzel, MD, from the Universidad del Desarrollo, Chile, said in a press release.
Scrub typhus, which is caused by the bacteria Orientia tsutsugamushi, is transmitted through the bite of larval mites, or chiggers. “The microorganism then spreads through the lymphatic fluid and blood, causing systemic manifestations that include fever, rash, and laboratory abnormalities such as elevated levels of C-reactive protein and liver enzymes,” Weitzel and colleagues wrote. According to the CDC, epidemic typhus may be fatal in 20% to 60% of untreated cases, necessitating prompt treatment.
O. tsutsugamushi has until recently been limited to a region called the “tsutsugamushi triangle,” extending from Pakistan in the west to far eastern Russia in the east to northern Australia in the south. In 2006, however, two cases of infection with Orientia spp. were identified outside of this region — the first occurring in the Middle East and another in southern Chile. In January 2015 and earlier this year, three autochthonous cases were discovered on Chiloé, an island located off the coast of mainland Chile with approximately 155,000 inhabitants. According to the researchers, the cases included a 38-year-old female homemaker, a 40-year-old male construction worker and a 55-year-old male farmer. One of the hospitals on the island that identified the cases — the Hospital Ancud — was taking part in a study of rickettsial infections, of which scrub typhus is one group. Indirect immunofluorescent antibody assays and enzyme-linked immunosorbent assays confirmed the serologic status of the three cases. In addition, samples from the first case were flown to the Mahidol Oxford Tropical Medicine Research Unit in Thailand and the Lao-Oxford-Mahosot Hospital Wellcome Trust Research Unit (LOMWRU) in Laos for further serologic and molecular analysis and were confirmed to be positive for O. tsutsugamushi.
Paul Newton
Although the distribution, reservoirs and vectors of the disease remain unknown in southern Chile, the presence of O. tsutsugamushi infections 12,000 km from the tsutsugamushi triangle suggests that the pathogen is now endemic in this part of the Western Hemisphere, according to the researchers.
“Scrub typhus is a common disease, but a neglected one,” Paul Newton, BM BCh, DPhil, MRCP, director of the LOMWRU, said in the release. “Given that it is known to cause approximately a million clinical cases and kills at least 140,000 people each year, this evidence of an even bigger burden of disease in another part of the world highlights the need for more research and attention to it.” – by John Schoen
References:
CDC. Rickettsial (Spotted & Typhus Fevers) & Related Infections (Anaplasmosis & Ehrlichiosis). http://wwwnc.cdc.gov/travel/yellowbook/2016/infectious-diseases-related-to-travel/rickettsial-spotted-typhus-fevers-related-infections-anaplasmosis-ehrlichiosis. Accessed September 7, 2016.
Weitzel T, et al. N Engl J Med. 2016;doi:10.1056/NEJMoa1603657.
Disclosure: Please see the full study for a list of all authors’ relevant financial disclosures.
Perspective
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Peter J. Hotez, MD, PhD
Scrub typhus historically has been confined to the “tsutsugamushi triangle,” and it is not generally thought of as a New World problem. So, the fact that researchers found it on the Pacific Coast of Chile suggests the possibility that it may have moved from east to west across the Pacific. This reminds me of one other disease that has done the same in recent years: Zika. Zika went from French Polynesia to Easter Island and then entered into the New World. The question is: Is this coincidental? Is this part of a larger trend of migration of disease across the Pacific Ocean into the New World?
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