West Nile virus update--United States, January 1-July 22, 2008

This report summarizes 2008 West Nile virus (WNV) surveillance data reported to CDC through ArboNET as of 3 a.m. Mountain Daylight Time, July 22, 2008. A total of 14 states have reported 43 cases of human WNV illness to CDC. A total of 26 (54%) cases for which such data were available occurred in males; median age of patients was 46 years (range: 12-80 years). Dates of illness onset ranged from January 17 to July 10; none of the cases were fatal.

West Nile virus update--United States, January 1-November 13, 2007

This report summarizes 2007 West Nile virus (WNV) surveillance data reported to CDC through ArboNET as of 3 a.m. Mountain Standard Time, November 13, 2007. A total of 43 states had reported 3,304 cases of human WNV illness to CDC. A total of 1,803 (55%) cases for which such data were available occurred in males; median age of patients was 51 years (range: 1 month-97 years). Dates of illness onset ranged from January 8 to November 6; a total of 93 cases were fatal.

West Nile virus update--United States, January 1-October 16, 2007

This report summarizes 2007 West Nile virus (WNV) surveillance data reported to CDC through ArboNET as of 3 a.m. Mountain Daylight Time, October 16, 2007. A total of 42 states have reported 3,022 cases of human WNV illness to CDC. A total of 1,646 (55%) cases for which such data were available occurred in males; median age of patients was 51 years (range: 15 months-97 years). Dates of illness onset ranged from January 8 to October 9; a total of 76 cases were fatal.

West Nile virus update--United States, January 1-September 11, 2007

This report summarizes 2007 West Nile virus (WNV) surveillance data reported to CDC through ArboNET as of 3 a.m. Mountain Daylight Time, September 11, 2007. A total of 38 states have reported 1,395 cases of human WNV illness to CDC. A total of 770 (56%) cases for which such data were available occurred in males; median age of patients was 49 years (range: 15 months-96 years). Dates of illness onset ranged from January 8 to September 7; a total of 38 cases were fatal.

Spectrum of infection and risk factors for human monkeypox, United States, 2003

For the 2003 monkeypox virus (MPXV) outbreak in the United States, interhuman transmission was not documented and all case-patients were near or handled MPXV-infected prairie dogs. We initiated a case-control study to evaluate risk factors for animal-to-human MPXV transmission. Participants completed a questionnaire requesting exposure, clinical, and demographic information. Serum samples were obtained for analysis of immunoglobulin G (IgG) and IgM to orthopoxvirus. When data were adjusted for smallpox vaccination, case-patients were more likely than controls to have had daily exposure to a sick animal (odds ratio [OR] 4.0, 95% confidence interval [CI] 1.2-13.4), cleaned cages and bedding of a sick animal (OR 5.3, 95% CI 1.4-20.7), or touched a sick animal (OR 4.0, 95% CI 1.2-13.4). These findings demonstrate that human MPXV infection is associated with handling of MPXV-infected animals and suggest that exposure to excretions and secretions of infected animals can result in infection.

West Nile virus update--United States, January 1--august 14, 2007

This report summarizes 2007 West Nile virus (WNV) surveillance data reported to CDC through ArboNET as of 3 a.m. Mountain Daylight Time, August 14, 2007. A total of 27 states have reported 444 cases of human WNV illness to CDC. A total of 241 (54%) cases for which such data were available occurred in males; median age of patients was 48 years (range: 2-96 years). Dates of illness onset ranged from March 25 to August 5; 15 cases were fatal.

Occupational risks during a monkeypox outbreak, Wisconsin, 2003

We determined factors associated with occupational transmission in Wisconsin during the 2003 outbreak of prairie dog--associated monkeypox virus infections. Our investigation included active contact surveillance, exposure-related interviews, and a veterinary facility cohort study. We identified 19 confirmed, 5 probable, and 3 suspected cases. Rash, headache, sweats, and fever were reported by > 80% of patients. Occupationally transmitted infections occurred in 12 veterinary staff, 2 pet store employees, and 2 animal distributors. The following were associated with illness: working directly with animal care (p = 0.002), being involved in prairie dog examination, caring for an animal within 6 feet of an ill prairie dog (p = 0.03), feeding an ill prairie dog (p = 0.002), and using an antihistamine (p = 0.04). Having never handled an ill prairie dog (p = 0.004) was protective. Veterinary staff used personal protective equipment sporadically. Our findings underscore the importance of standard veterinary infection-control guidelines.

West Nile virus update--United States,January 1-July 24, 2007

This report summarizes 2007 West Nile virus (WNV) surveillance data reported to CDC through ArboNET as of 3 a.m. Mountain Daylight Time, July 24, 2007. A total of 19 states have reported 122 cases of human WNV illness to CDC. A total of 68 (56%) cases for which such data were available occurred in males; median age of patients was 48 years (range: 15 months-96 years). Dates of illness onset ranged from March 25 to July 18; three cases were fatal.

West Nile virus viremia in eastern chipmunks (Tamias striatus) sufficient for infecting different mosquitoes

Chipmunks might play a role in enzootic WNV cycles and be an amplifying host for mosquitoes that infect humans.

In eastern chipmunks (Tamias striatus) inoculated intramuscularly with 10^1.5 to 10^5.7 PFU of West Nile virus (WNV), serum titers developed sufficient to infect Aedes triseriatus (Say), Ae. vexans (Meigen), and Culex pipiens (L.). Mean titers (95% confidence interval) of 8 chipmunks were 10^{3.9(3.3–4.5)}, 10^{6.7(6.4–7.0)}, and 10^{5.8(4.1–7.5)} PFU/mL on days 1–3 postinoculation (p.i.) and 10^5.8 PFU/mL in 1 chipmunk on day 4 p.i. Mean estimated days that WNV titers were >10^4.8 and >10^5.6 were 1.7 (1.1–2.3) and 1.4 (1.0–1.6). The longest period of viremia >10^4.8 PFU/mL was 3–4 days. WNV antigen was detected in the small intestine of 2 chipmunks and the kidneys of 4 chipmunks by immunohistochemistry. WNV also was detected in urine, saliva, and feces of some chipmunks. These data suggest chipmunks might play a role in enzootic WNV cycles and be an amplifying host for mosquitoes that could infect humans.

West Nile virus infection in tree squirrels (Rodentia: Sciuridae) in California, 2004-2005

West Nile virus (WNV) transmission generally involves a mosquito vector and an avian reservoir host, with mammals as incidental hosts. Although most mammalian WNV infections cause low or no morbidity or mortality, tree squirrels are susceptible to WNV-associated neurologic disease with infection prevalence comparable to that in dead birds. Positive species included fox squirrel (Sciurus niger), western gray squirrel (S. griseus), and eastern gray squirrel (S. carolinensis). Kidney tissue (dissected and swabbed), and oropharyngeal (oral) swab samples from tree squirrels submitted by California vector control and rehabilitation agencies were tested by reverse transcription-polymerase chain reaction; cycle threshold values were similar for all three samples, ranging from 21.9 to 26.5. Kidney tissue was more sensitive than oral swabs for detecting WNV in squirrels. Three of 36 live neurologic tree squirrels had viremia approximately 5 log(10) plaque-forming units/mL or greater, similar to WNV-infected birds. Tree squirrels are useful in WNV surveillance and provide localized evidence of WNV transmission to mammals.

Fox squirrel (Sciurus niger) associations with West Nile virus

Tree squirrels (Sciurus spp.) have been recently shown to be commonly exposed to West Nile virus (WNV). Many characteristics of WNV infections in tree squirrels are unknown. To better understand WNV associations in fox squirrels (S. niger), we conducted mark-recapture sampling (N = 72) and radio telemetry to study the longitudinal seroprevalence, seroconversions, and ectoparasites of these animals during 2005-2006 in northern Colorado. Five seroconversions were documented during this study. The majority of seroconversions occurred during the late summer/fall months. However, one seroconversion was documented over the time period of February to late March 2005. Fleas (Orchopeas howardi) were tested for WNV RNA using real-time PCR techniques. No WNV RNA positive fleas (N = 33) were detected. In addition, urine samples (N = 17) opportunistically collected from fox squirrels were negative for WNV RNA. Results indicate that seroconversions can be observed in fox squirrels during low WNV transmission years.

Efficacy of the antipoxvirus compound ST-246 for treatment of severe orthopoxvirus infection

Efficacy of the new antipoxvirus compound ST-246 was evaluated as treatment of monkeypox (MPX) virus infection in a ground squirrel model of the disease. Ground squirrels were given a lethal dose of MPX virus and were then treated orally at various times post-inoculation (pi) with 100 mg/kg/day of ST-246. Morbidity and mortality, clinical laboratory results, viral load, and pathology of placebo and treatment groups were compared. All animals that started treatment with ST-246 on days 0, 1, 2, and 3 pi survived lethal challenge with MPX virus; 67% of animals treated on day 4 pi also survived. In contrast, 100% of the placebo group died. Most of the ST-246-treated animals showed no evidence of clinical disease or alteration of baseline clinical laboratory values and had minimal histopathologic changes. These results suggest that ST-246 is a promising candidate for early treatment of severe orthopoxvirus infection.

Comparative pathology of North American and central African strains of monkeypox virus in a ground squirrel model of the disease

The first human cases of monkeypox (MPX) were recognized in central Africa in 1970. Since then, sporadic outbreaks of the disease have occurred in central and west Africa. In 2003, an outbreak of human MPX occurred in the United States after importation of infected rodents from west Africa. Clinical features of the 2003 outbreak were less severe than accounts of the disease among people in central Africa. The reasons for this observed difference are unknown. In this study, the clinical and pathologic characteristics of experimental infection with representative central African and North American MPX virus strains were compared in a ground squirrel model of the disease. The results indicate that the US 2003 virus, which phylogenetically is a member of the west African MPX virus clade, was less virulent than central African MPX virus strains.

Qualitative assessment of risk for monkeypox associated with domestic trade in certain animal species, United States

In 2003, US officials identified several human monkeypox cases and traced the virus exposure to infected captive prairie dogs. The virus was likely introduced through a shipment of imported African rodents, which were kept with other mammals, including prairie dogs, in a pet distribution facility in the Midwest. To prevent the further introduction and spread of the virus, federal agencies restricted the importation of African rodents and restricted the domestic trade or movement of prairie dogs and certain other rodents. In this qualitative assessment of the risk for monkeypox associated with the 2003 outbreak, we conclude that the probability of further human infection is low; the risk is further mitigated by rodent import restrictions. Were this zoonotic disease to become established domestically, the public health effects could be substantial.

West nile virus activity--United States, January 1-November 7, 2006

This report summarizes West Nile virus (WNV) surveillance data reported to CDC through ArboNET as of 3 a.m. Mountain Standard Time, November 7, 2006. A total of 41 states and the District of Columbia had reported 3,830 cases of human WNV illness to CDC.

West Nile virus activity--United States, January 1-October 10, 2006

This report summarizes West Nile virus (WNV) surveillance data reported to CDC through ArboNET as of 3 a.m. Mountain Daylight Time, October 10, 2006. A total of 41 states and the District of Columbia had reported 3,135 cases of human WNV illness to CDC. A total of 1,717 (55%) cases for which such data were available occurred in males; median age of patients was 50 years (range: 3 months-99 years). Dates of illness onset ranged from January 6 to September 25; a total of 97 cases were fatal.

Experimental infection of fox squirrels (Sciurus niger) with West Nile virus

Tree squirrels (Sciurus spp.) have exhibited high seroprevalence rates, suggesting that they are commonly exposed to West Nile virus (WNV). Many characteristics of WNV infections in tree squirrels, such as the durations and levels of viremia, remain unknown. To better understand WNV infections in fox squirrels (S. niger), we subcutaneously inoculated fourteen fox squirrels with WNV. Peak viremias ranged from 10(4.00) plaque-forming units (PFU)/mL of serum on day 2 post-infection (DPI) to 10(4.98) PFU/mL on 3 DPI, although viremias varied between individuals. Oral secretions of some fox squirrels were positive for WNV viral RNA, occasionally to moderate levels (10(3.2) PFU equivalent/swab). WNV PFU equivalents in organs were low or undetectable on 12 DPI; gross and histologic lesions were rare. The viremia profiles of fox squirrels indicate that they could serve as amplifying hosts in nature. In addition, viral RNA in the oral cavity and feces indicate that this species could contribute to alternative WNV transmission in suburban communities.

West Nile virus activity--United States, January 1-September 12, 2006

This report summarizes West Nile virus (WNV) surveillance data reported to CDC through ArboNET as of 3 a.m. Mountain Daylight Time, September 12, 2006. A total of 36 states and the District of Columbia had reported 1,634 cases of human WNV illness to CDC. A total of 921 (57%) cases for which such data were available occurred in males; median age of patients was 51 years (range: 3 months-95 years). Dates of illness onset ranged from January 6 to September 10; a total of 52 cases were fatal.

Clinical manifestations of human monkeypox influenced by route of infection

BACKGROUND

In April 2003, an outbreak of monkeypox occurred in the United States following the importation of monkeypox virus (MPXV)-infected animals in a consignment of exotic pets from West Africa. Transmission of the virus to non-African captive species, including prairie dogs, preceded human disease.

METHODS

We evaluated the influence of the route of infection on clinical illness for persons with confirmed and probable cases of human monkeypox. Exposures were categorized as being "noninvasive" (e.g., the person touched an infected animal, cleaned an infected animal's cage, and/or stood within 6 feet of an infected animal) or "complex" (e.g., invasive bite or scratch from an ill prairie dog plus potential noninvasive exposure), and associations between exposure, illness manifestation, and illness progression (i.e., elapsed time from first exposure to an ill prairie dog through various benchmarks of illness) were assessed.

RESULTS

Patients with complex exposures were more likely than patients with noninvasive exposures to have experienced pronounced signs of systemic illness (49.1% vs. 16.7%; P=.041) and to have been hospitalized during illness (68.8% vs. 10.3%; P<.001). Complex exposures were also associated with shorter incubation periods (9 days for complex exposures vs. 13 days for noninvasive exposures) and the absence of a distinct febrile prodrome.

CONCLUSIONS

The findings of this study indicate that route of infection can influence monkeypox illness manifestations.

West Nile virus activity--United States, January 1-August 15, 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. 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.

West Nile virus activity--United States, January 1-December 1, 2005

West Nile virus (WNV) is the leading cause of arboviral encephalitis in the United States. Originally discovered in Africa in 1937, WNV was first detected in the western hemisphere in 1999 in New York City. Since then it has caused seasonal epidemics of febrile illness and severe neurologic disease. During January 1-December 1, 2005, a total of 2,744 cases of WNV disease in humans were reported in the United States, an increase from 2,359 during the same period in 2004. A total of 1,165 cases were WNV neuroinvasive disease (WNND). WNV infections in humans, birds, mosquitoes, and nonhuman mammals are reported to CDC through ArboNET, an Internet-based arbovirus surveillance system managed by state health departments and CDC. During 2005, WNV transmission to humans or animals expanded into 21 counties that had not previously reported transmission and recurred in 1,196 counties where transmission had been reported in previous years. This report summarizes provisional WNV surveillance data through December 1, 2005, and highlights the need for ongoing surveillance, mosquito control, promotion of personal protection from mosquito bites, and research into additional prevention strategies.

Update: West Nile virus activity--United States, 2005

This report summarizes West Nile virus (WNV) surveillance data reported to CDC through ArboNET as of 3 a.m. Mountain Standard Time, November 1, 2005.

Transmission of monkeypox among persons exposed to infected prairie dogs in Indiana in 2003

OBJECTIVE

To describe a cluster of human monkeypox cases associated with exposure to ill prairie dogs in a home child care.

DESIGN, SETTING, PARTICIPANTS

We identified all persons exposed to 2 pet prairie dogs in County A, Indiana; performed active surveillance for symptomatic monkeypox infection; and evaluated the types of exposure that may have resulted in infection. For children who attended the child care where the animals were housed, we also measured the rate of seroconversion to monkeypox virus.

MAIN OUTCOME MEASURES

Nine (13%) of 70 persons exposed to the prairie dogs reported signs and symptoms of monkeypox. Two (40%) of 5 symptomatic child care attendees reported direct contact with the prairie dogs. Two (13%) of 15 child care attendees evaluated tested positive for IgM antibodies against orthopoxvirus; both reported symptoms consistent with monkeypox.

RESULTS

The risk of symptomatic infection correlated with the time and intensity of animal exposure, which was 100% (4/4) among family members with extensive direct contact, 19% (5/26) among the veterinarian and nonfamily child care attendees with moderate exposure, and 0% (0/40) among school children with limited exposure (P<.01).

CONCLUSIONS

Monkeypox virus was transmitted from ill prairie dogs in a child care and veterinary facilities. The risk of symptomatic infection correlated with the amount of exposure to the prairie dogs. Although most cases of human monkeypox were associated with direct animal contact, other routes of transmission cannot be excluded.

Update: West Nile virus activity--United States, 2005

This report summarizes West Nile virus (WNV) surveillance data reported to CDC through ArboNET as of 3 a.m. Mountain Daylight Time, October 25, 2005.