Giulio de leo dipartimento di scienze ambientali universit degli studi di parma italy
Download
1 / 28

Giulio De Leo Dipartimento di Scienze Ambientali Università degli Studi di Parma - Italy - PowerPoint PPT Presentation


  • 425 Views
  • Uploaded on

EEE - ICTP Trieste April 13-15 2005 “ To cull or not to cull, this is the problem ”: undersired effects of animals removal to eraticate diseases in widlife populations (the adaptive dynamics of CSF in wild boars) Giulio De Leo Dipartimento di Scienze Ambientali

loader
I am the owner, or an agent authorized to act on behalf of the owner, of the copyrighted work described.
capcha
Download Presentation

PowerPoint Slideshow about ' Giulio De Leo Dipartimento di Scienze Ambientali Università degli Studi di Parma - Italy' - johana


An Image/Link below is provided (as is) to download presentation

Download Policy: Content on the Website is provided to you AS IS for your information and personal use and may not be sold / licensed / shared on other websites without getting consent from its author.While downloading, if for some reason you are not able to download a presentation, the publisher may have deleted the file from their server.


- - - - - - - - - - - - - - - - - - - - - - - - - - E N D - - - - - - - - - - - - - - - - - - - - - - - - - -
Presentation Transcript
Giulio de leo dipartimento di scienze ambientali universit degli studi di parma italy l.jpg

EEE - ICTP

Trieste April 13-15 2005

“To cull or not to cull, this is the problem”:undersired effects of animals removal to eraticate diseases in widlife populations(the adaptive dynamics of CSF in wild boars)

Giulio De LeoDipartimento di Scienze Ambientali

Università degli Studi di Parma - Italy

Thanks to A.Dobson and M. Pascualand to the NCEAS WG on Seasonality and Infectious diseases


Slide2 l.jpg

c :hunting rate [t-1]

If the case of no culling (c=0):

It can be proven that it is possible to eradicate the disease if: c > r [1- 1/Ro]

Let’s take the Classical Swine Fever (CSF) as a reference disease


Basics of classical swine fever csf or hog cholera l.jpg
Basics of Classical swine fever (CSF) or Hog Cholera

  • A highly contagious disease due to a RNA virus, Family TOGAVIRIDAE, Genus Pestivirus;

  • It is a List A disease in the OIE Classification of Diseases

  • Suidae are the sole natural hosts;


Basics of classical swine fever csf or hog cholera4 l.jpg
Basics of Classical swine fever (CSF) or Hog Cholera

  • Infected animals may shed large amounts of virus for 20 - 40 days through oronasal and lacrimal secretions, urine and feces

  • The direct contact between infected and susceptible animals is the principle means of viral transmission;


Basics of classical swine fever csf or hog cholera epidemiology l.jpg
Basics of Classical swine fever (CSF) or Hog CholeraEpidemiology

  • CSF causes high morbidity and mortality (up to 90%) during the first epidemic wave…

    but low virulent strains can be isolated in wild boars in the following endemic phase;

    • Acute infections

    • Chronic infections /endemic phases


Csf distribution oei 1995 1997 l.jpg
CSF distribution(OEI 1995-1997)



Why people care about csf in eu l.jpg
Why people care about CSF in EU?

  • Wild boars are blamed to be the reservoir of CSF


Ue damages from csf between 1993 and 2000 l.jpg

Country

N. Swines removed (       = 1 milion specimen)

NL

10

Germany

2

Spaain

1

Belgium

< 1

Italy

< 1

UE Damages from CSF between 1993 and 2000

A 100 kg pig ~ €150,00


Which is easier to say than to do it l.jpg
which is easier to say than to do it…

  • The EU supports a program to eradicate the virus from wild boar mainly based on reducing population density through culling

  • What to cull?

  • Where to cull?

  • When to cull?

  • How to cull?


Drawbacks of culling 1 2 as reported by the italian wildlife national service infs l.jpg

b

Ro

Culling rate [y-1]

1

Culling rate [y-1]

Drawbacks of culling (1/2)as reported by the Italian Wildlife National Service (INFS)

  • It may push hosts out of their natural home range, thus fostering disease spread

~ 20% increase of culling rate

~ 60% reduction of population density

with respect to constant b


Drawbacks of culling 2 2 l.jpg
Drawbacks of culling (2/2)

  • It may push hosts out of their natural home range, thus fostering disease spread

  • If culling is focused mainly on old (low susceptible) hosts, it may change population age structure in favor of more susceptible yearlings

  • Given the existence of multiple strains of CSF (Biagetti et al. 2001), a change in host density may foster the selection of less virulent but more persistent strains, thus making culling more costly and ineffective

  • Research questions:

    • Is it possible?

    • If positive, under which conditions?

    • Which are the consequences?


A simple two strains competition model l.jpg

m

c

m

m

c

c

I2

I1

a1

a2

A simple two-strains competition model

S

  • Hosts I1 infected with a Low Virulent Strain (LVS)

     smalla1

  • Hosts I2 infected with a High Virulent Strain (HVS)

     largea2

b2

b1

b12

highly virulent strain

(large a2)

low virulent strain

(small a1)

b12is the super-infection coefficient


The new equations lvs vs hvs l.jpg
The new equations (LVS vs. HVS):

S' =G(S) -b1I1S - b2I2S- cS

I1' =b1I1S- (a1+ m + c)I1-b12I1I2

I2' = b2I2S- (a2+ m+ c) I2+ b12I1I2

  • Assumptions on the LVS vs. HVS

  • Disease induced mortality (virulence)

    • a1 << a2

  • Transmission rate

    • b1b2b12 0


  • Basic epidemiological implications of the above assumptions l.jpg
    Basic epidemiological implications of the above assumptions

    • Basic Reproductive rate (LVS vs. HVS)

    • Threshold density for disease eradication

    • KT1<KT2

     LVS can persist in a very sparse population


    Further epidemiological implications l.jpg
    Further epidemiological implications

    • If there is no super-infection(b12=0)

    • LVS always outcompetes HVS


    If there is super infection b 12 0 l.jpg

    • If LVS outcompetes HVS

    • If LVS and HVS coexist

    • If HVSoutcompetes LVS

    where

    If there is super-infection (b12 >0)


    Further epidemiological implications19 l.jpg
    Further epidemiological implications

    • If hog population density K (as well b12)is sufficiently high, thenHVS can coexist with, or even outcompete LVS

       decreasing population density by culling migh increase the chance ofLVSto outcompeteHVS


    Slide20 l.jpg

    Epidemiology of classical swine fever in wild boars of Eastern SardiniaLVSHVSfrom a field survey by Guberti (1998)and Artois et al. (2002)


    Slide21 l.jpg

    Prevalence at the equilibrium as a function of culling rate, when the two strains are isolated

    Removal rate



    Slide23 l.jpg

    Total Prevalence for two competing strains


    Number of infected individuals l.jpg
    Number of infected individuals for two competing strains


    The si 2 r model susceptible infected recovered l.jpg

    m for two competing strains

    c

    S

    m

    m

    b2

    b1

    I2

    I1

    c

    c

    a1

    a2

    b12

    LVS

    (small a1)

    HVS

    (large a2)

    g1

    g2

    R

    m

    c

    The SI2R model(Susceptible-Infected-Recovered)


    Conclusions l.jpg
    Conclusions for two competing strains

    • It is possible that the reduction of host density by culling may indeed foster the selection of less virulent strains

    • This in turn would reduce the threshold host density for disease eradication

    • If this happens, the harvesting effort required to completely eradicate the disease will be higher than initially expected

    • If culling effort is not large enough, the net effect of this policy is to increase both prevalence and the number of infected hosts

    • The harvesting effort required for the eradication of the least virulent strains may be unrealistically high (or too costly)


    Further developments l.jpg
    Further developments for two competing strains

    • Analyse pop.dynamics by using a stochastic (possibly spatially explicit, seasonal) version of the model

    • Introduce age structure and age-depedent epidemiological parameters


    ad