Aedes aegypti in Washington, DC—Overwintering in the extreme range?

Andy Lima—Fairfax County Health DepartmentDisease Carrying Insects Program

Virginia Mosquito Control Association—February 13th, 2014Andrew.Lima@fairfaxcounty.gov

Winter Storm Pax

This does not look

good.

Snowed In…

Potted plant saucers at semi-abandoned homePicture taken on 2/2/13

2’ x 2’

Picture taken on 2/2/2013

5’Evil may lurk where you least suspect it…

Welcome to the Bassment.

Aedes aegypti (Linnaeus) biology• Container-inhabiting• Urban habitats

– Especially those without running water

• Dessication-resistant eggs – Require diapause period

for hatching• Short flight range

– ¼ mile• Humans are preferred

host Center for Disease Control Public Health Image Library

Importance of the Yellow fever mosquito, Aedes aegypti

• Primary vector of:

– Yellow Fever • (urban cycle)

– Dengue Fever

– Chikungunya virusE. A. Goeldi (1905) Os Mosquitos no Pará. Memorias do Museu Goeldi. Pará, Brazil.

Ae. aegypti was likely the primary vector of Yellow fever outbreaks as far north as New York, Philadelphia, and Boston from the 1690s to 1820s.

Ae. aegypti in the Americas• Aedes aegypti may currently

be more widespread and abundant than any time in the past (Halstead 2008)– 1948 – 1962

• Ae. aegypti eliminated from 21 countries in the Americas

– 1970• range limited to SE U.S.,

Caribbean, and NE S.A.– 2008

• reclaimed all lost territory and now ranges from Argentina in the south the U.S. in the north

• Reemergence of Dengue from 1980s through present (2014)– Increasing in tropics/subtropics

PAHO/WHO 2002

WHO 2003

Distribution of Aedes aegypti in the Americas, 1930s, 1970, and 1998 (CDC)

Why don’t we see more Ae. aegypti in Washington, D.C.?

• Tropical/subtropical– Common only in S. Florida

and some parts of other Gulf Coast states

• Autochthonous Dengue tranmission in Florida Keys/south Florida since 2009

• Parts of southern Texas, Arizona, and New Mexico

• Local transmission in Suffolk County, NY in 2013

– Ae. albopictus???

• Eggs not known to overwinter in temperate latitudes

Why don’t we see them more?

• Competition with other container-exploiting mosquito species (like Ae. albopictus) also affects Ae. aegyptirange

• How do they overwinter in the extreme range?– Eggs?– Larvae?– Adults?

• Populations surviving continuously underground?

– Blood-feeding?

competition

Distribution of Aedes aegypti in the U.S. (Darsie and Ward 2005)

Temperature as a limit to distribution

• Northern and southern limits strongly correlated with temperature• “normal” range of Ae. aegypti

• January isotherm of 50° F• “extreme” northern range in the U.S. (Christophers 1960)

– January isotherm of 35° F– July isotherm of 75° F

• Avg of 36° F and 79.8° F, respectively in DC during the past 30 years• Current literature lacking for cool temperatures

– most information from 1900s through 1930s• Currently unknown whether range restriction is more closely

related to low winter temperatures or insufficiently high and long summer temperatures (Eisen and Moore 2013)

VA counties with records of Ae. aegypti

Ae. aegypti collections in DC,MD, and VA, 2003 - 2011

Year # Locations Positive for Ae. aegypti

2003 102004 42005 22006 22007 22008 62009 32010 02011 3

Collected in 16 locations between 2003 and 2011-Mostly military installations

-Transportation of supplies from overseas?

Study Objectives

1) Investigate the potential for overwintering Ae. aegyptiin a Capitol Hill neighborhood in SE Washington, D.C.

2) Examine genetic relatedness between years to make inferences about overwintering

Collection Methods• Passive sampling during

random visits to DC– 2011

• 10/22, 10/25– 2012

• 9/26– 2013

• 7/13, 8/25, 10/19, 11/15, 11/22

• No standardized collection protocol

• Initial collection was a cup-swatted adult

• Collected larvae using a pipette, turkey baster, dipper cup, or whatever else was around.

• Larvae placed in WhirlPaks, Ziploc bags, tupperwarecontainers.

• Larvae killed with hot water and stored in 70% ethyl alcohol

Locations of Ae. aegypti collections in Capitol Hill neighborhood of SE D.C., 2011 - 2013

Square fountain

Garbage can

2-tier birdbathPotted plant saucers

(2013 only)

U.S. Capitol

U.S. Supreme Court

Union Station

Library of CongressAe. aegypticollections

2011, 2012, 2013

Capitol Hill scenery

Larval abundance from Capitol Hill containers, 2011 - 2013

Cx. pipiens (251)

Ae. albopictus (127)

Ae. aegypti (59)

Cx. restuans (42)

An. punctipenis (3)

Oc. triseriatus (1)

• In close proximity to:

– Library of Congress (0.17 miles)

– U.S. Capitol (0.3 miles)– Congressional offices

(0.32 miles)– Union Station (0.6 miles)

Habitat type Total # Ae. aegypti collected (2011 - 2013)*

Square Foutain 132-tier birdbath 38

Potted plant saucers 6Garbage can 2

Collection Dates # Ae. aegypti collected10/22/2011 610/25/2011 209/26/2012 177/13/2013 68/25/2013 110/19/2013 811/22/2013 1

Total # of Ae. aegypti collected from Capitol Hill neighborhood of Washington, D.C. (2011 – 2013) by habitat type

Total # of Ae. aegypti collected from Capitol Hill neighborhood of Washington, D.C. (2011 – 2013) by date

*22 randomly selected individuals used in genetic analysis

Ae. aegypti testing methods—University of Notre Dame

• DNA extracted from ethanol-preserved mosquitoes

• Aedes aegypti individuals confirmed using microsatellite PCR primers

• Primers for COI mitochondrial gene used to obtain 710 basepair amplicon

• Amplicons sequenced and aligned to determine haplotype similarity

• Haplotype tree constructed for COI sequences from 22 field-collected Ae. aegypti– GenBank COI sequence for Ae.

albopictus was used as outgroup

Phylogenetic tree showing relatedness among haplotypes in Capitol Hill samples to select haplotype sequences in GenBank.

Haplotype: a segment of DNA containing closely linked gene variations that are inherited as a unit

Results / Discussion

• Ae. aegypti larvae collected from a total of (4) locations on the same block during summer 2011, 2012, and 2013

• Ae. aegypti larvae collected from (2) locations during all three summers

• Recovery of same (2) haplotypes over all three years from (2) locations suggests the population overwintered

Year

avgmeteorolgicalwinter temp, °F (Dec - Feb)

warmest winter

ranking (since 1871)

warmest winter

ranking (since 1981)

# days mean

temp ≤ 32

# days min

temp ≤32

# days max

temp ≤ 32

2012 43.4 3 1 6 28 1

2013 41.4 12 6 7 27 4

2014 (through 2/9/14) 37.5 56 22 17 44 7

30-year avg. 38.2

Climate data for meteorological winter (December – February) at National Airport, 1871 – 2014

*Of the 14 years where winter temps have been greater than 41°F, (6) have been in the past 25 years

41.5

44.3 44.6

42.2

42.9

41.542

41.6

42.543.2 43.4

41.4

37.5

27

29

31

33

35

37

39

41

43

45M

ean

Win

ter T

empe

ratu

re (F

)

Year

Mean winter temperature at National Airport, 1871 - 2014

Average winter Temperature (F) Linear (Average winter Temperature (F))

30-year avg. (38.2° F)

Survival at low temperatures• Ae. aegypti adults are most

active at 82 F– Below 62 F they are sluggish

and stop feeding– Below 68 they cease mating– Below 32 F they quickly die

• Most lab data indicate that consistent temperatures of about 50° F are lethal to larvae and adults– Eggs capable of surviving

lower temperatures • Less cold tolerance than Ae.

albopictus

Photo taken on 2/8/14

Brrr…ice.

Survival after freezing?! • 11/22/2013

– (1) aegypti larva and (46) Cx. pipiens collected from 2-tiered birdbath

• Samples froze solid in my car from 11/24 – 11/25 for more than 24 hours

• The single aegypti larva and most of the Culexthawed and survived

Bad [lateral] hair day.

“pitchfork” comb scales

Strong thoracic spines

Questions remain

• Overwintering life stage is unknown– Tunnels beneath Capitol

Hill?– Egg survival in containers

during mild winters of 2012 and 2013?

– How will below-average 2014 winter temps affect the population?

– Hidden containers in protected areas?

• Does this population have more cold tolerance than aegyptiin the normal range?– Where did they come

from in the first place?– Effect of origin on cold

tolerance?

Future Studies• Will there be any Ae. aegypti in

summer 2014?• Winter 2014 has been relatively cold through

December and January, with largest snowfall totals in more than 3 years

• Include larger sample of sequences from GenBank to examine geographic origin of population

• Use microsatellite markers to infer relatedness of population across years

– Are they siblings?• Further sampling in 2014 to try and

determine the mode of overwintering

– Egg diapause or continuously breeding population?

– Hidden larval sources that can be sampled?

• Need for more current studies on Ae. aegypti cold tolerance

Acknowledgements• University of Notre Dame

– Dr. David Severson (dseverso@nd.edu)– Diane Lovin (lovin1@nd.edu)

• Clarke– Lauren Lochstampfor– Patrick Patterson

• FCDH—Disease Carrying Insects Program– Joshua Smith– John Orr

• Dr. Bruce Harrison• Dr. David Gaines• Army Public Health Command

– Ben Pagac, Alexandra Spring • All military data

• DC Department of Health– Maria Hille

• The BASSment– DJ Brian Wheeler

E. A. Goeldi (1905) Os Mosquitos no Pará. Memorias do Museu Goeldi. Pará, Brazil.

Questions?