WSSV - White spot syndrome virus · 2015-05-13 · WSSV - White spot syndrome virus. RCN Marine Disease Modeling and Transmission Workshop – May 2015

Hosts of WSSV bull Shrimp

ndash Penaeusbull monodonbull semisulcatus

ndash Farfantepenaeusbull aztecusbull duorarum

ndash Fenneropenaeusbull chinensisbull indicusbull merguensisbull penicillatus

ndash Marsupenaeusbull japonicus

ndash Litopenaeusbull vannameibull stylirostrisbull setiferus

ndash Metapenaeus ensis

ndash Exopalaemonbull orientalis

ndash Macrobrachium sppndash Palaemon styliferuusndash Palaemonetes pugio

bull Crabndash Calappa lophosndash Charybdis

bull feriatabull natotor

ndash Helice spndash Portunus

bull pelagicusbull Sanguineolentus

ndash Callinectes sapidus

ndash Armasus cinereumndash Scylla serratandash Sesarma sppndash Sommanniathelpusa spndash Thalamita spndash Uca sppndash Menippe adina

bull Lobsterndash Panuluris

bull longipesbull ornatusbull argus

bull Crayfishndash Procambarus clarkiindash Cherax quadricarinatus

RCN Marine Disease Modeling and Transmission Workshop ndash May 2015

0

100

200

300

400

500

600

700

800

900

1000

0 3 6 9 12 15 18 21

Num

ber o

f shr

imp

Day

Weight 3 gDensity 550m3

Dose 003 bwfinal survival 000 003max daily mortality 10 06

WSSV Litopenaeus vannamei

RCN Marine Disease Modeling and Transmission Workshop ndash May 2015

Armasus cinereum

Uca panacea

Callinectes sapidus

Litopenaeus setiferus

Uca speciosa

Local decapods exposed to WSSV (China)

0 5 10 15 20 25 30Day

00

01

02

03

04

05

06

07

08

09

10

Surv

ival

RCN Marine Disease Modeling and Transmission Workshop ndash May 2015

Salt marshes

RCN Marine Disease Modeling and Transmission Workshop ndash May 2015

Mississippi sound

Jourdan

Biloxi

Pearl

Wolf

Lake Pontchartrain

RCN Marine Disease Modeling and Transmission Workshop ndash May 2015

Prevalence of WSSV in decapods of Ms Sound

Blue crab (Callinectes sapidus) (83 n=12)

Purple marsh crab (Sesarma reticulatum) (100 n=20)

Gulf mud fiddler crab (Uca longisignalis) (500 n=72)

Panacea sand fiddler crab (U panacea) (108 n=1404)

Mudflat fiddler crab (U rapax) (230 n=88)

Spined fiddler crab (U spinicarpa) (357 n=98)

Red-jointed fiddler crab (U minax) (227 n=22)

Squareback marsh crab (Armasus cinereum) (267 n=30)

Daggerblade grass shrimp (Palaemonetes pugio) (94 n=1244)

White shrimp (Litopenaeus setiferus) (200 n=40)

RCN Marine Disease Modeling and Transmission Workshop ndash May 2015

Modeling WSSV in communities of decapods

RCN Marine Disease Modeling and Transmission Workshop ndash May 2015

WSSV life cycle diagram

λ Host recruitmentβ TransmissionLiveχ TransmissionDeadα MortalityWSSVμ MortalityNaturalδ DecayCarcassη ConsumptionCarcass

δ η

Susceptible Infected Dead

β

χ

λ

micro

α micro

( ) ( )( )( ) ( )( ) ( ) ( )( )

( ) ( )( ) ( ) ( )( )

1

1

1

1 1 1

1 1 1 1 1 1

1 1 1 1 1 1

t t

t t

I Dt t t

I Dt t t t

t t t t

S S S

I I S I

D D I D

β χ λ micro

β χ α micro

α micro η δ

+

+

+

= minus sdot minus minus minus + minus

= + sdot minus minus minus minus minus minus sdot minus sdot

= + minus minus sdot minus sdot minus minus minus sdot minus sdot

RCN Marine Disease Modeling and Transmission Workshop ndash May 2015

( )1-

t t t tS S S Iβ

+= sdot sdot

RossKermack-McKendrick

1- (1 )(1 ) t

t t tIS S S β+

= sdot minus minusReed-Frost

Black-Singer

Transmission terms - Force of infection λprobability of infection after contact

RCN Marine Disease Modeling and Transmission Workshop ndash May 2015

( )1 1 Iλ β= minus minus

( )Iλ β= sdot

Force of InfectionProbability of infection after contact with all infecteds

Ross

Reed-Frost

RCN Marine Disease Modeling and Transmission Workshop ndash May 2015

1 2 3 4 5 6 7

1 11 12 13 14 15 16 17

2 21 22 23 24 25 26 27

3 31 32 33 34 35 36 37

S S S S S S S

I SI SI SI SI SI SI SI

I SI SI SI SI SI SI SI

I SI SI SI SI SI SI SI

( )1-

t t t tS S S Iβ

+= sdot sdot

RossKermack-McKendrick

If β is probability of transmission after one S contacts one IThen SI is number of contacts between every S and every I

May have more infects than susceptiblesSome transmissions are to the same susceptible

RCN Marine Disease Modeling and Transmission Workshop ndash May 2015

2(1 )βminus

1 βminusβ 1 βminusβ

21 (1 )βminus minus

3 Ways to become infected1 amp not 2 βlowast(1minusβ)ornot 1 amp 2 (1minusβ)lowastβor1 amp 2 βlowastβ

Only 1 way to remain uninfected1 amp 2 (1- β)lowast(1minusβ)

βlowast(1minusβ) + (1minusβ)lowastβ + βlowastβ

1- (1 )(1 ) t

t t tIS S S β+

= sdot minus minusReed-Frost

Black-Singer

RCN Marine Disease Modeling and Transmission Workshop ndash May 2015

Epidemic models ndash parameter estimates

( ) ( )( )( ) ( )( )

( ) ( )( )

1

1

1

1 1 1

1 1 1

1 1 1

t t

t t

I Dt t t

I Dt t t t

t t t t

S S S

I I S I

D D I D

β χ

β χ α

α η δ

+

+

+

= minus sdot minus minus minus

= + sdot minus minus minus minus sdot

= + sdot minus minus minus sdot minus sdot

RCN Marine Disease Modeling and Transmission Workshop ndash May 2015

If t = 1 and I0 = 1

1

0

1 ss

β

= minus

The proportion infected after exposure to one infected shrimpβ

Parameter estimates ndash transmission (β χ)

1 (1 (1 ) )tIt t tS S S β+ = minus sdot minus minus

Solve for β

1

1

0

0

ln(1) 1 exp

tSS

Iβ

= minus

RCN Marine Disease Modeling and Transmission Workshop ndash May 2015