Wednesday, March 16, 2011

New Viral Illness in China Linked to Ticks

New Viral Illness in China Linked to Ticks

By Charles Bankhead, Staff Writer, MedPage TodayPublished: March 16, 2011Reviewed by Robert Jasmer, MD; Associate Clinical Professor of Medicine, University of California, San Francisco.

A previously unrecognized severe febrile illness in China has been traced to a novel bunyavirus, possibly transmitted by ticks, Chinese investigators reported.
Characterized by severe fever and thrombocytopenia, the illness had an initial case fatality rate of 30%.
Since June 2009, investigators have documented the presence of the virus in 171 patients from six regions in central and northeastern China, and the infection proved fatal in 12% of cases.
The virus invaded multiple cells, but primarily thrombocytes and leukocytes. Multi-organ failure developed rapidly, as reflected by elevated liver enzymes, creatine kinase, and lactate dehydrogenase.
A causal relationship between the virus and the illness has yet to be established. However, epidemiologic, clinical, and laboratory data strongly implicate the virus in the febrile illness, the researchers reported online in the New England Journal of Medicine.
"Our finding that [the bunyavirus] is the probable cause of a previously unknown severe febrile disease is one of the fruits of heightened surveillance of infectious diseases in China," De-Xin Li, MD, of the Chinese Center for Disease Control and Prevention in Beijing, and co-authors wrote in conclusion.
"More research is needed to determine the extent to which this disease occurs in regions outside its area of identification."
Identification of the illness evolved from observations of an emerging infectious disease in two rural provinces of central China from late-March to mid-July 2009. In addition to severe fever and thrombocytopenia, gastrointestinal symptoms and leukocytopenia were common manifestations of the illness.
Called severe fever with thrombocytopenia syndrome (SFTS), the illness's symptoms resembled those of anaplasmosis, but neither bacterial DNA nor antibodies to Anaplasma phagocytophilum were isolated from blood samples of most patients.
Instead, investigators isolated a novel phlebovirus of the Bunyaviridae family, which they have designated SFTS bunyavirus.
The virus was isolated for the first time in June 2009 from a 42-year-old man from Henan Province. During 2010, 11 additional strains were isolated from patients in the acute phase of the illness.
Analysis of partial or complete viral genomic sequences showed that SFTS virus was related to the five prototypical viruses of Bunyaviridae: orthobunyavirus, hantavirus, nairovirus, phlebovirus, and tospovirus. The authors reported that SFTS virus belongs to the Phlebovirus genus and is distantly related to the other four genera.
The investigators performed serologic analysis of a group of 35 patients who had SFTS virus infection during acute and convalescent phases of the illness, confirmed by reverse transcriptase-polymerase chain reaction.
"An elevation in the antibody titer by a factor of four or seroconversion was observed in all 35 patients, as seen especially on microneutralization," the authors wrote. "These results indicated that high levels of neutralizing antibodies were generated during the convalescent phase."
All 35 seropositive samples had confirmation of SFTS virus infection by viral RNA sequencing and 11 by virus isolation.
From June 2009 through September 2010, the bunyavirus was isolated from 171 of 241 hospitalized patients who met the case definition of SFTS. During 2010, 148 of 154 laboratory-confirmed cases of SFTS occurred from May to July.
Three-fourths of the patients were older than 50, more than half were women, and all but four were farmers living in wooded and hilly areas and working in fields before the illness.
The bunyavirus was not detected in serum samples of 200 age-matched healthy controls from endemic areas, 180 healthy controls from nonendemic areas, or 54 patients with suspected hemorrhagic fever with renal syndrome.
Mosquitoes and ticks were found in the homes of most of the patients. The investigators found no viral RNA in any of 5,900 mosquitoes tested but did isolate viral RNA from 10 of 186 (5.4%) ticks of the species Haemaphysalis longicornis found on domestic animals belonging to patients.
Viral RNA sequences from the ticks were not identical but were closely related to the SFTS virus isolated from patients.
The study reflects the type of rapid and aggressive response that is required to the increasing number of emerging infectious diseases worldwide, Heinz Feldmann, MD, of the National Institute for Allergy and Infectious Diseases in Hamilton, Mont. and the University of Manitoba in Winnipeg, wrote in an accompanying editorial.
"To date, we still have an alarming number of cases of infectious disease without a laboratory diagnosis," Feldmann wrote. "Even clusters of cases or outbreaks sometimes go undiagnosed for long periods."
"Such a scenario is not unusual and occurs more often in countries with weak public health infrastructures," he added.
A concerted, coordinated effort is needed to ensure responses that are "secure and safe but also rapid and targeted, with the primary goal of immediately supporting public health while providing the best treatment for the affected patient."
Neither Li and co-authors nor Feldmann had relevant disclosures.

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