Virus Top Twenty For August 2006
This report summarizes West Nile virus (WNV) surveillance data reported to CDC through ArboNET as of 3 a.m. Mountain Daylight Time, August 15, 2006. A total of 26 states had reported 388 cases of human WNV illness to CDC (Figure, Table). A total of 214 (56%) cases for which such data were available occurred in males; median age of patients was 49 years (range: 2--91 years). Dates of illness onset ranged from January 6 to August 10; a total of 13 cases were fatal. A total of 68 presumptive West Nile viremic blood donors (PVDs) have been reported to ArboNET during 2006. Of these, 20 were reported from Nebraska; 18 were reported from Texas; five were reported from California; four were reported from Utah; three each were reported from Oklahoma and South Dakota; two each were reported from Idaho, Iowa, Kentucky, and Mississippi; and one each was reported from Arizona, Colorado, Minnesota, Nevada, North Dakota, Wisconsin, and Wyoming. Of the 68 PVDs, 10 persons (median age: 43 years [range: 18--59 years]) subsequently had West Nile fever.
Virus Top Twenty for August 2006
West Nile virus (WNV) transmission through blood transfusion was first reported in 2002 (1,2), prompting rapid implementation of nationwide screening of blood donations for WNV by 2003 (3,4). Screening strategies were developed using minipool nucleic acid-amplification testing (MP-NAT) based on six or 16 pooled donor samples. To improve sensitivity of WNV detection, blood-collection agencies (BCAs) later implemented enhanced screening by individual donation NAT (ID-NAT), most often used when a given trigger threshold of positive MP-NAT results is reached during the WNV transmission season (5,6). This approach has been effective, resulting in the detection and interdiction of approximately 1,400 potentially infectious blood donations during 2003--2005 and a reduction in recognized transfusion-transmission events (7). A total of 23 confirmed WNV transfusion-transmitted cases were reported in 2002, before screening was implemented; six probable or confirmed cases were detected in 2003 after MP-NAT screening was initiated, one was detected in 2004, and none were detected in 2005 (7). This report describes the first WNV transfusion-transmission cases detected since the initiation of enhanced screening strategies using ID-NAT triggering. In 2006, two immunosuppressed patients had onset of West Nile neuroinvasive disease (WNND) after receiving blood products from a single infected donor despite a negative MP-NAT result at the time of donation. Although risk for transmission has been substantially reduced as a result of routine MP-NAT and triggered ID-NAT screening, clinicians should be reminded that transfusion-transmitted WNV infections can still occur, and that immunosuppressed patients are more likely to have onset of WNND.
Monthly distribution of confirmed bluetongue virus 8 (BTV-8) outbreaks in northern and central Europe from August 17, 2006, through February 1, 2007. After January 1, 2007, few BTV cases were reported; those that were probably involved animals that had been infected, but not detected, in 2006.
Moreover, in relation to the demonstrated overwintering ability of the virus in northern Europe, small numbers of adult Culicoides spp. were captured in animal housing during the winter period (November 25, 2006, to March 9, 2007) (i.e., females of C. obsoletus complex, males of C. obsoletus, C. scoticus, and C. dewulfi) (25). Whether the occurrence of these midges and the possibility of their activity extending over the winter in such climatically protected locations can explain the persistence of virus from 1 vector transmission season to the next (13) or whether they represent newly emerged midges from nearby breeding sites is not known (25). Several hypotheses have been formulated to explain the overwintering ability of BTV: by persistence within surviving adult vectors themselves, transovarial transmission through the vector, or prolonged/persistent infection in viremic or aviremic vertebrate hosts (13,25,26).
While prior H5N1 strains have been known, they were significantly different from the 2006 strain of H5N1 on a genetic level, making the global spread of this new strain unprecedented. The 2006 strain of H5N1 is a fast-mutating, highly pathogenic avian influenza virus (HPAI) found in multiple bird species. It is both epizootic (an epidemic in non-humans) and panzootic (a disease affecting animals of many species especially over a wide area). Unless otherwise indicated, "H5N1" in this article refers to the highly pathogenic 2006 strain of H5N1.
By April 2006, scientists had concluded that containment had failed due to the role of wild birds in transmitting the virus and were now emphasizing far more comprehensive risk mitigation and management measures.
In April 2006 a swan, that had been found dead in Scotland eight days earlier, tested positive for the deadly H5N1 strain of avian influenza (bird flu). While the virus didn't pose a huge threat to humans experts feared the virus could change and gain the ability to make humans ill and in its new form trigger a flu pandemic, putting millions of lives at risk. This led to many wildlife areas being cordoned off and the population questioning if they could still eat chicken and wondering if their budgie would survive the outbreak.