MMWR Week 35 | August 29- September 4, 2021

MMWR Week 35 Summary

• 19 mosquito pools from Wilco have been tested by DSHS from week 35
• 1 mosquito pools tested positive for WNV this week.
  • Located in Granger
• There have been 0 reported human cases of West Nile disease in Wilco in 2021
  • There have been 0 human cases of SLE, Zika, CHIKV or Dengue in 2021
• Average number of mosquitoes/trap include:
  • Culex spp: 24

Wilco: Williamson County
DSHS: Texas Department of State Health Services
WNV= West Nile virus; CHIKV= chikungunya virus; SLE= St. Louis encephalitis
Arbovirus= Arthropod-borne virus

Figure 1. WILCO Mosquito Trap Map, 2021

Williamson County Region WNV Positive Year to Date Summary

• There has been a total of 7 positive mosquito pools in 2021
  • Granger (6) Taylor (1)
• There have been no reported human cases of WNV

WNV= West Nile virus; WNND= West Nile neuroinvasive disease

Table 1. Cumulative Data for Williamson County, Weeks 33-35

* Weekly Vector index (VI) added beginning MMWR Week 31
1. MLE= Maximum Likelihood Estimate or the estimate of the mosquito infection rate per mosquito species calculated using a Maximum Likelihood Estimation (MLE). Biggerstaff, Brad J. PooledInfRate, Version 4.0: a Microsoft® Office Excel© Add-In to compute prevalence estimates from pooled samples. Centers for Disease Control and Prevention, Fort Collins, CO, U.S.A., 2009
2. Vector Index is a measure of infectivity that accounts for vector species composition, vector species population density, and vector species infection rates. The VI reflects the MLE adjusted for Culex quinquefasciatus abundance. 

Figure 2. Average Number of Female Culex quinquefasciatus per Trap and WNV Vector Index by Week: 2021 Season (Through Week 35)

Note: A vector index of 0.50 is the historical threshold associated with larger local epidemics of WNV illnesses in humans. Vector index is calculated on a county-wide level due to limited number of traps.

Table 2. Central Texas West Nile Virus Activity as Reported by DSHS as of September 4, 2021

1. Mosquito surveillance not routinely conducted in this county.
 

WNV= West Nile virus; WNF= West Nile fever; WNND= West Nile neuroinvasive disease

PVD= presumptive viremic blood donors are people who had no symptoms at the time of donating blood through a blood collection agency, but whose blood tested positive when screened for the presence of WNV. Some PVDs may develop symptoms after donation.

Table 3. Other Central Texas Arbovirus* Activity as Reported by DSHS as of September 4, 2021

1. Mosquito surveillance not routinely conducted in this county
CHIKV= Chikungunya virus; DENV= Dengue virus; SLEV= St. Louis encephalitis virus; ZIKV= Zika virus
*All reported CHIKV, DENV, and ZIKV human cases are travel-related

For Additional Information Please Visit the Links Below:
Department of State Health Services
Arbovirus Activity Reports
Texas West Nile Virus

Williamson County and Cities Health District 
Integrated Vector Management Home Page 

Centers for Disease Control and Prevention 
West Nile virus
Integrated Mosquito Management

Environmental Protection Agency 
Insect Repellent Information