Volume 12, Number 8—August 2006
Dispatch
West Nile Virus Epizootiology, Central Red River Valley, North Dakota and Minnesota, 2002–2005
Jeffrey A. Bell*, Christina M. Brewer*, Nathan J. Mickelson*, Gabriel W. Garman*, and Jefferson A. Vaughan*
Table 2
Epizootiology of West Nile virus (WNV) within the central Red River Valley of North Dakota and Minnesota during the first 4 years of its introduction into the region*
| Year | Primary transmission season† | Thermal accumulations (degree-days)‡ | Vector abundance§ | Human cases in ND¶ | Seasonal MIR# | Passerine seroprevalence |
|---|---|---|---|---|---|---|
| 2002, introductory | 92 days (11 Jun–10 Sep) | 1,067 | 230 | 17 | 0.0 (n = 5,871) | No birds tested |
| 2003, epidemic | 92 days (11 Jun–10 Sep) | 1,022 | 21 | 617 | 5.7 (n = 5,432) | 17% (n = 82) |
| 2004, cold | 51 days (7 Jul–1 Sep) | 371 | 9 | 20 | 0.0 (n = 1,245) | 58% (n = 52) |
| 2005, equilibrium? | 84 days (20 Jun–11 Sep) | 867 | 29 | 86 | 1.3 (n = 3,123) | 57% (n = 143) |
*ND, North Dakota; MIR, minimum infection rate.
†Time between first and last appearances of host-seeking Culex tarsalis mosquitoes in Mosquito Magnet traps.
‡Based on developmental threshold temperature of 14.3°C for WNV growth in Cx. tarsalis (14).
§Average number of Cx. tarsalis mosquitoes captured per trap-night in Grand Forks, ND.
¶Data from North Dakota Department of Public Health (15).
#No. of WNV-infected Cx. tarsalis mosquitoes per 1,000.
