# Presentation: 914932

## Mosquito field infection rates and transmission risk are related to avian and mosquito host competence 

- William K. Reisen
- Center for Vectorborne Diseases
- School of Veterinary Medicine
- University of California, Davis

- 2005 National Conference on West Nile Virus in the United States

- WNV

- Culex

- Scrub jay

## Support for research in California

- National Institutes of Allergy and Infectious Diseases, NIH
- Centers for Disease Control and Prevention
- Office of Global Programs, NOAA
- California Department of Health Services
- University-wide Mosquito Research Program
- Coachella Valley MVCD
- Greater Los Angeles Co VCD
- Sacramento/Yolo MVCD
- Kern MVCD

## Feb 2004

**Missing:**  Marc Kennsington [COAV], Scott Hallam & Leah Korserof
-  [Kern]; Aaron Brault, Chris Barker and Bruce Eldridge [Davis], Scripps Group, UC San Diego

- Hugh
- Lothrop

- Stan
- Wright

- Bob Chiles

- Vince
- Martinez

- Emily Green

- Barbara
- Cahoon

- Steve
- Lewis

- Bill
- Reeves

- Mark
- Palmer

- Sarah
- Wheeler

- Ying Fang

- Brian
- Carroll

- SandyGarcia

- Marzi
- Shafii

- Nicole
- Kahn

- WKR

- Jenn
- Wilson

- Veronica
- Armijos

## Talk Content

- Mosquito species infected in nature
- Mosquito vector competence
- Avian host competence
- Incidence of human infection

## Gonotrophic cycle and biological WN virus transmission

- BLOOD DIGESTION
-         [>3 days]

- OVIPOSIT

- HOST-
- SEEK

- HOST-SEEK

- TEMPERATURE

- BLOOD FEED

- INFECTION?

- TRANSMISSION??

- Virus
- growth

**Notes:**
Example of gonotrophic cycle

Mention 3 types of transmission:
Mechanical
Horizontal
Vertical

## NA mosquito species WNV positive,ArboNet, 1999-04

- _NA mosquito species WNV positive,ArboNet, 1999-04_

## Distribution of major vectors in North America

- Circles show the locations of the largest epidemics

- Modified from Darsie & Ward
- Mosquitoes of North America

- 2002

- 2003

- 2004

## USGS CBC and BBS data showing distribution of AMCOs

- Circles show the locations of the largest epidemics

- December

- June

- Copied from USGS website
- http://www.mbr-pwrc.usgs.gov/

## Vector competence of some NA mosquitoes for WVN after feeding on a viremic chicken

- Turell et al. 2001. JME 38: 130

## Summary of vector competence characteristics of some eastern NA mosquitoes

- Turell et al. 2001. Ann NY Acad Sci 951: 317

## California mosquitoes testing positive for West Nile Virus Jan - Nov 2004

**California mosquitoes testing positive for West Nile Virus Jan - Nov 2004**

- Data from Calif Encephalitis
- Virus Surv Prog; summary by CM Barker

## Host selection patterns of some California mosquitoes

- Data from:  Reeves. 1990. Epidemiology and Control of Mosquito-borne Arboviruses in California, 1943-1987.  Calif. Mosq. Vector Control Assoc.

## 1

**Vector Competence Methods**

**Insectary at 24****±2°C**
**Adults aged 4-6 days**

**Fed on blood with**
**known dose of virus**

**Kept at 26****°C**
**For 2 wks**

**Body**

**Expectorate**

**-70****°C**

**Plaque Assay at 0, -2**
**and –4 Dilutions**

**1**

**3**

**5**

**Legs**

**Body**

**Wings**

**4**

**2**

**6**

**Legs**

## Vector competence of California mosquitoes for WNV [7 log10 PFU/ml]

- Vector competence of California mosquitoes for WNV [7 log10 PFU/ml]

- Goddard et al. 2002 EID 8: 1385

## Vector competence of California mosquitoes for WNV [ dose = 4.9 log10 pfu/ml]

- Goddard et al. EID 8 [12]

## Infection and transmission of WNVby Culex,  virus presented on pledgets*, Southern California, 2003

- *dose 5.8-7.3 log10 PFU/ml

- Reisen et al. 2005 JME [in press]

## Percent of Cx. tarsalis infected and transmitting after feeding on adult House sparrows or House finches infected with West Nile virus

- KNWR colony: % infected

- Field populations:  % infected and transmitting after feeding on House finches with different viremias

## Culex WNV vector competence:Dose response of infection

- tars = *tarsalis*
- quin = *pipiens quinquefasciatus*
- stig = *stigmatosoma*

- Refractory

- Susceptible

- Moderate?

- Reisen et al. 2005 JME [in press]

## LA Cx. p quinquefasciatus  WNV vector competence: Dose response 

## Avian host competence

## Avian Viremia Response

- Komar et al. 2000 EID 9:3

- WNV infectious doses
- used by Goddard

- Threshold used
- By Komar for
*Cx. pipiens*

## Host competence of some California birds for WNV

- Assay threshold

## Nestling MODO:

- SLEV viremia response and competence of *Cx. tarsalis*

- Nestling viremia

- Cx. tarsalis

- Mahmood et al. 2004. JME 41: 965

## Acquired cross-immunity protects House finches and lowers viremia titers

- Assay threshold

- First infection

- Challenge

- Reisen unpubl.

## Natural experiment:  3 areas in southern California with different densities of corvids

- Few AMCOs moderate WESJs

- Few corvids, except ravens

- High AMCOs, moderate WESJs

## Distribution of most effective hosts in California based on CBC data

## Distribution of most effective hosts in California based on BBC data [http://www.mbr-pwrc.usgs.gov/]

- American crow

- Western scrub jay

- House finch

- House sparrow

## Infection rates for Culex species tested from southern California, May – Sep 2004

- MLE Calculated from Biggerstaff:  http://www.cdc.gov/ncidod/dvbid/westnile/software.htm

## Incidence of WNV cases [CNS + fever] among human populations, California 2004

- Data from: http://westnile.ca.gov/2004_maps.htm

## What will happen in 2005?Possible epicenter in Central California

- AMCO BBS distribution

- Dec 2004

- Distribution of positive
- Dead birds, chickens,
- Mosquito pools

- WNV epicenter?