Dynamic Simulation Modeling of Dynamic Simulation Modeling of Mosquito Populations with Climate DataMosquito Populations with Climate Data

Andrew Andrew ComrieComrie & Cory Morin& Cory MorinUniversity of ArizonaUniversity of Arizona

Why Model Mosquitoes & Climate?Why Model Mosquitoes & Climate?

http://upload.wikimedia.org/wikipedia/commons/4/48/Aedes_aegypti_biting_human.jpg

Disease impacts of climate change are poorly Disease impacts of climate change are poorly understood, oversimplifiedunderstood, oversimplifiedMosquito vectors responsible for a huge disease burdenMosquito vectors responsible for a huge disease burdenFew empirical/statistical mosquito models, poor Few empirical/statistical mosquito models, poor mosquito data series, mosquito data series, no dynamic modelsno dynamic models

Climate Change Impacts are UnderwayClimate Change Impacts are Underway

Bryan Christie/Scientific American August 2000 (in Epstein PR & Mills E, 2005)

Disease: Coupled Natural & Social SystemsDisease: Coupled Natural & Social Systems

National Research Council, 2001

Epidemiologic Triangle of DiseaseEpidemiologic Triangle of Disease

A A multimulti--factorialfactorial relationship between hosts, relationship between hosts, agents, vectors and environment

HostHost((egeg, Human), Human)

EnvironmentEnvironment((egeg, Climate), Climate)

AgentAgent((egeg, Pathogen), Pathogen)

VectorVector

Start with coupling Start with coupling between climate between climate

and mosquito and mosquito populationspopulations

agents, vectors and environment

Modeling Malaria & Climate ChangeModeling Malaria & Climate Change22ººF simple F simple increase vs. increase vs. more complex more complex empirical empirical modelmodel

http://www.exploratorium.edu/climate/global-effects/data/risk6-3.jpg

AZ

Hatched = currentRogers & Randolph Science 2000

Abrupt Climate Change & DengueAbrupt Climate Change & Dengue

Increased Increased dengue risk dengue risk based on based on projected projected humidity humidity changeschangesOversimplified?Oversimplified?

1990

2085

Hales et al. Lancet 2002

Mosquitoes: Mosquitoes: Aedes AegyptiAedes AegyptiCharacteristicsCharacteristics

Urban, Container Breeding Urban, Container Breeding MosquitoMosquitoTropical HabitatTropical HabitatDengue Fever VectorDengue Fever Vector

Dengue FeverDengue Fever100 Million Cases a Year 100 Million Cases a Year WorldwideWorldwide4 Serotypes without Cross 4 Serotypes without Cross Immunity Immunity Dengue Hemorrhagic Fever Dengue Hemorrhagic Fever from Multiple Infections

Picture taken from http://www.interet-general.info/IMG/Aedes-Aegypti-2.jpg

from Multiple InfectionsPicture from http://www.cdc.gov/ncidod/dvbid/dengue/map-distribution-2005.htm

West Nile West Nile VirusVirus

http://www.cdc.gov/ncidod/EID/vol11no08/images/05-0289a_1b.gif http://diseasemaps.usgs.gov/wnv_us_human.html

2006

Mosquitoes: Mosquitoes: Culex QuinquefasciatusCulex Quinquefasciatus

CharacteristicsCharacteristicsUrban MosquitoUrban MosquitoFeeds on Humans and Feeds on Humans and AnimalsAnimalsWest Nile Virus VectorWest Nile Virus Vector

West Nile VirusWest Nile VirusArrived in Arizona in Arrived in Arizona in 20032003150 Cases with 10 150 Cases with 10 Deaths in 2005Deaths in 2005Symptoms: Mild FeverSymptoms: Mild Fever--EncephalitisEncephalitis

Image taken from http://www.lahey.org/Medical/

InfectiousDiseases/WestNileVirus.asp

Dynamic Modeling of MosquitoesDynamic Modeling of Mosquitoes

Create climateCreate climate--driven model based on ‘first principles’driven model based on ‘first principles’

InputsInputsTemperature, Precipitation, Daylight (Monthly)Temperature, Precipitation, Daylight (Monthly)Evaporation Derived (Hamon’s Equation) Evaporation Derived (Hamon’s Equation) Irrigation/Land Cover Irrigation/Land Cover

Governing ProcessesGoverning ProcessesDevelopment Rates (Rueda 1990, Sharpe 1977) Development Rates (Rueda 1990, Sharpe 1977) Death Rates (Conway 1974, Kasule 1996)Death Rates (Conway 1974, Kasule 1996)Reproductive Rates (Christophers 1960) Reproductive Rates (Christophers 1960) Larval/Pupa Capacity (Christophers 1960)Larval/Pupa Capacity (Christophers 1960)Water Flux (sources and sinks)Water Flux (sources and sinks)

Conceptual ModelConceptual Model

Dynamic Mosquito Simulation Model Dynamic Mosquito Simulation Model ((DyMSiMDyMSiM))

Model BaseModel Base SubSub--Model DetailModel Detail

Implemented in Stella® softwareImplemented in Stella® software

DyMSiMDyMSiM: Sample Equations/Code: Sample Equations/CodeDays_with_No_Water(t) = Days_with_No_Water(t - dt) + (No_Water - Water_Day) * dtINIT Days_with_No_Water = 0INFLOWS:No_Water = if Total_Water=0 then 1 else 0OUTFLOWS:Water_Day = if Total_Water>0 then Days_with_No_Water else 0Water(t) = Water(t - dt) + (Rain + Irrigation1 - Evaporation - Infiltration) * dtINIT Water = 0INFLOWS:Rain = Prec*Area:_PermiableIrrigation1 = Irrigation*Area:_PermiableOUTFLOWS:Evaporation = ((2.1*Day_Light^2*(.6108*EXP((17.27*ATemp)/(237.3+ATemp))))/(ATemp+273.2)/10)*Area:_PermiableInfiltration = Area:_Permiable*PermiabilityRateWater1(t) = Water1(t - dt) + (Rain_in_Containers + Irrigation2 - Evaporation1 - Spill) * dtINIT Water1 = 0INFLOWS:Rain_in_Containers = Prec*Area:_ContaintersIrrigation2 = Irrigation*Area:_ContaintersOUTFLOWS:Evaporation1 = ((2.1*Day_Light^2*(.6108*EXP((17.27*ATemp)/(237.3+ATemp))))/(ATemp+273.2)/10)*Area:_ContaintersSpill = if Water1> Area:_Containters*Hight_Container then Water1-(Area:_Containters*Hight_Container) else 0AdltDeath = if Mos>AdltMinPop then if ATemp<AdltTempMin or ATemp>AdltTempMax then 1 else AdltDeathRate else 0AdltDeathRate = .14AdltMinPop = 2AdltSize = -0.0147*History(ATemp, Time-10)+ 2.1127AdltTempMax = 40AdltTempMin = 5Area = 40468564Area:_Containters = Percent_Contain*AreaArea:_Permiable = Percent_Perm*AreaArea_Perminant = Area*Percent_PermanantATemp = Temp+TempDifferenceDay_Light = If TIME>0 and TIME<32 then 10.083 else if TIME>31 and TIME<61 then 10.6 else if TIME>60 and TIME<92 then 11.52 else if TIME>91 and TIME<122 then 12.52 else if TIME>121 and TIME<153 then 13.45 else if TIME>152 and TIME<183 then 14.12 else if TIME>182 and TIME<214 then 14.22 else if TIME>213 and TIME<245 then 13.73 else if TIME>244 and TIME<275 then 12.82 else if TIME>274 and TIME<306 then 11.85 else if TIME>305 and TIME<336 then 10.88 else 10.2 Dept = 5EggsLaid = (46.5*AdltSize)Food = 1Food_or_ecological_rating = .5Genotrophic_cycle = if Food =1 and ATemp> 20 then (.00898*((ATemp+273.15)/(298.15))*EXP(15725.23/(1.987)*(1/(298.15)-1/(ATemp+273.15))))/(1+EXP(1756481.07/(1.987)*(1/(447.17)-1/(ATemp+273.15))))*24 else 0Hight_Container = 20Irrigation = if IR_Index=1 then IR_1 else if IR_Index=2 then IR_2 else 0IR_1 = if ATemp>Temp_Thresh then IR_Ammount else 0 IR_2 = if TIME>Julian_Start and TIME<Julian_Stop then IR_Ammount else 0 IR_Ammount = .1IR Index = 0

DyMSiMDyMSiM DynamicsDynamics

DevelopmentDevelopmentDegree Day Model: Members of each cohort proceed Degree Day Model: Members of each cohort proceed through development stages at a rate governed by through development stages at a rate governed by temperaturetemperature

DeathDeathImmature mosquitoes: Based on temperature and Immature mosquitoes: Based on temperature and water availabilitywater availability

When population exceeds capacity, youngest die firstWhen population exceeds capacity, youngest die firstAdults: Daily survival rates from markAdults: Daily survival rates from mark--releaserelease--recapture studies and temperaturerecapture studies and temperature

ReproductionReproductionAdult mosquitoes will feed and mate at certain Adult mosquitoes will feed and mate at certain temperatures, water is required for egg layingtemperatures, water is required for egg laying

ExperimentsExperimentsThree runs for a “typical” oneThree runs for a “typical” one--acre areaacre area

Tucson daily data, 1950Tucson daily data, 1950--20052005AedesAedes AegyptiAegypti

Urban Urban vsvs NonNon--Urban RunsUrban RunsClimate = same for both runsClimate = same for both runsUrban = 2 x amount of impermeable land + Urban = 2 x amount of impermeable land +

small areas of permanent watersmall areas of permanent water

Urban Areas with/without Heat Island EffectUrban Areas with/without Heat Island EffectLand cover settings held constantLand cover settings held constantSimulate a 3Simulate a 3°°C rise in temperature over last 55 years C rise in temperature over last 55 years (+0.27(+0.27°°C every 5 years)C every 5 years)Also a proxy for climate changeAlso a proxy for climate change

Urban Urban vsvs NonNon--UrbanUrban

•• Urban areas >> nonUrban areas >> non--urban (more impermeable urban (more impermeable sfcsfc, standing water), standing water)

•• Population explosions in particular yearsPopulation explosions in particular years

A Closer Look at NonA Closer Look at Non--UrbanUrban

NonNon--urban population responds often, but with small numbers relativeurban population responds often, but with small numbers relative to to urban population explosionsurban population explosions

19551955 19641964 19831983

1954 1954 vsvs19551955

Temps = similarTemps = similar

PrecipPrecip totalstotals = = similarsimilar

PrecipPrecip timingtiming = = pricelesspriceless

Urban Mosquitoes in 1983Urban Mosquitoes in 1983

1983 summer = unremarkable; TS in October = major flooding 1983 summer = unremarkable; TS in October = major flooding and mosquito population explosion in urban areasand mosquito population explosion in urban areas

Urban Urban vsvs NonNon--Urban by MonthUrban by Month

In semiIn semi--arid (waterarid (water--limited) limited) TucsonTucson, moist urban environments , moist urban environments increase the number of mosquitoes and extend the survival seasonincrease the number of mosquitoes and extend the survival season

Urban with/without Heat IslandUrban with/without Heat Island

3°C linear increase leads to slightly reduced population3°C linear increase leads to slightly reduced population

Urban with/without Heat Island by MonthUrban with/without Heat Island by Month

The heat island effect:The heat island effect:(i) reduces mosquitoes during Summer (evaporation), but (i) reduces mosquitoes during Summer (evaporation), but (ii) increases numbers in Spring and early Winter (temperature)(ii) increases numbers in Spring and early Winter (temperature)

Model LimitationsModel Limitations

““All Models are Wrong, Some are Useful” All Models are Wrong, Some are Useful” --George BoxGeorge BoxThe model only accounts for climate and land The model only accounts for climate and land use factors. The following variables are not use factors. The following variables are not consideredconsidered

Predation, Pesticides, Food Availability, Human Predation, Pesticides, Food Availability, Human Behaviors, MigrationBehaviors, Migration

AssumptionsAssumptionsAll mosquitoes will react similarly to stressorsAll mosquitoes will react similarly to stressorsAll female mosquitoes are fertileAll female mosquitoes are fertileAll female mosquitoes take a blood mealAll female mosquitoes take a blood meal

What Do These Results Tell Us?What Do These Results Tell Us?

Precipitation Precipitation timingtiming, and not necessarily , and not necessarily seasonal amount, accounts for major seasonal amount, accounts for major urban mosquito population explosionsurban mosquito population explosionsUrban areas are key to enabling mosquito Urban areas are key to enabling mosquito breeding in semibreeding in semi--arid locationsarid locationsWarming temperatures (urban or climate Warming temperatures (urban or climate change) are projected to extend the change) are projected to extend the season when mosquitoes can surviveseason when mosquitoes can survive