Changes

Jump to navigation Jump to search

Classical Swine Fever (view source)

Revision as of 19:10, 9 August 2010

9,196 bytes added ,  19:10, 9 August 2010
→‎Treatment
Line 49: Line 49:     
==Treatment==
 
==Treatment==
−
====Control====
+
 
−
*'''NOTIFIABLE''' disease
+
The control policy for CSF depends on the incidence and prevalence of the infection in
−
*'''Vaccination''' (live attenuated) in endemic countries:
+
the domestic and wild pig populations, respectively. In countries with CSF endemic in
−
**Parts of EU are using vaccinated bait to control spread in wild boar population
+
domestic pigs it is common practice to vaccinate against the disease, thereby, avoiding
−
**Vaccination does not curtail spread: marker vaccine needed to distinguish virus exposure from vaccine-induced antibody
+
serious losses. However, the simultaneous eradication of ®eld virus is improbable because
 +
serological methods are no longer applicable for the detection of ®eld virus infections. It
 +
is acknowledged that ®eld virus may be hidden under a `blanket' of general vaccination.
 +
Taking this risk into account, importing countries in general do not allow the introduction
 +
of pigs or pig products from countries that vaccinate against CSF. The preventive
 +
measures adopted by the EU for trade with Third Countries stipulate that live pigs and
 +
fresh pig meat can only be imported from regions or countries where no CSF has
 +
occurred for 12 months and no vaccination against CSF was applied during the same
 +
period. Nevertheless a policy of consistent and systematic prophylactic vaccination in
 +
endemic situations may ultimately lead to a favourable starting point for a non
 +
vaccination policy and the eradication of the virus. After the cessation of general
 +
vaccination, eventual local outbreaks of residual ®eld virus must be dealt with by strict
 +
measures to ensure prevention of virus spread and eradication of the virus.
 +
Based on the above mentioned disadvantages of vaccination and a cost bene®t analysis
 +
the EU banned vaccination against CSF at the end of the 1980s. Whereas most
 +
neighbours of the EU have also adopted a similar policy, vaccination is allowed and
 +
mostly routinely applied by many Central and Eastern European countries (Edwards
 +
et al., 2000). In some of the latter countries only sick or clinically suspect animals are
 +
destroyed in case of CSF outbreaks whereas all other animals of the infected herd, herds
 +
in the neighbouring area and contact herds are vaccinated.
 +
In case of an outbreak of CSF, all EU Member States and the other Western European
 +
countries execute eradication measures according to the Council Directive 80/217/EEC
 +
(Anonymous, 1980; Edwards et al., 2000). These are based on stamping out
 +
(depopulation) of infected pig herds and possibly infected contact or (partially)
 +
neighbouring herds, epidemiological investigations, clinical and virological investigations,
 +
movement restrictions for live pigs, pig meat and other vectors which can transmit
 +
CSF within zones surrounding the infected farm and restrictions on contact farms outside
 +
these zones (Anonymous, 1980). Especially in areas with dense pig populations very
 +
high numbers of pigs had to be destroyed in the course of the eradication measures
 +
dealing with the outbreaks mentioned above. Only a minority of animals were killed due
 +
to direct involvement with the infection. Most of the pigs had to be killed because of
 +
welfare measures. The direct and indirect costs of recent CSF outbreaks in several EU
 +
Member States so far amount to several billion Euro, and in the course of the CSF
 +
epidemic in the Netherlands in 1997 approximately 10 million pigs were destroyed
 +
(Saatkamp and Horst, 2000; Stegeman et al., 2000). Whereas in areas with a low density
 +
pig population, the present control policy works very well it may well be questioned
 +
whether it is sustainable in areas with a high density of pigs. There is a general consensus
 +
that a number of measures must be introduced in order to reduce the vulnerability of
 +
regions at risk, e.g., structural changes in the pig industry including trade. However,
 +
implementation of appropriate programs might be dif®cult. Several parties, notably some
 +
V. Moennig / Veterinary Microbiology 73 (2000) 93±102 99
 +
national farmers' associations requested the reintroduction of a general or at least
 +
regional vaccination.
 +
In principle, emergency vaccination is in agreement with EU legislation (Anonymous,
 +
1980). Requirements related to emergency vaccination campaigns against CSF virus have
 +
been de®ned in the document `Guidelines for a Classical Swine Fever Emergency
 +
Vaccination Programme' (Anonymous, 1994). However, by using conventional vaccines
 +
and applying the mentioned guidelines, the Scienti®c Veterinary Committee of the
 +
Commission has calculated that vaccinated animals would be excluded from the market
 +
for up to 600 days (Anonymous, 1997). This is economically unacceptable and so far
 +
emergency vaccination has never been used.
 +
With the development of a ®rst generation marker vaccine against CSF the possibility
 +
of an amendment of the existing EU emergency vaccination regulations seems feasible. A
 +
restricted application of a marker vaccine would require extensive serological testing in
 +
the vaccinated population in order to detect hidden ®eld virus infections. At present no
 +
marker vaccine has been licensed within the EU and EU Member States demand welldocumented
 +
data on the safety and ef®cacy of the vaccine before its potential use in
 +
emergency situations. It is understood that the criteria for the use of the marker vaccine
 +
will be very stringent. Provided that all safety requirements are met, the period of
 +
exclusion from the market could be considerably shortened at least for pig products after
 +
a CSF outbreak (Anonymous, 1997). As soon as marker vaccines are suf®ciently
 +
investigated and licensed, the `Guidelines for a Classical Swine Fever Emergency
 +
Vaccination Programme' (Anonymous, 1994) are to be amended. The possible use of an
 +
emergency vaccination with marker vaccines is expected to avoid the ethically
 +
questionable and expensive large scale pre-emptive slaughter of pigs. Thereby, the
 +
public acceptance of the eradication policy will increase and costs will decrease. Under
 +
these circumstances the use of emergency vaccination using marker vaccines could be a
 +
useful tool of the non-vaccination policy.
 +
A still unresolved problem is the control of CSF in wild boar (Laddomada, 2000).
 +
Both the prolonged persistence of virus in wildlife populations and the constant threat
 +
of domestic pig holdings in the respective areas require an ef®cient control strategy.
 +
Comprehensive information about the current situation in wild boar populations
 +
is essential and new strategies have to be devised. They have to take into account
 +
current knowledge about factors in¯uencing CSF epidemiology, e.g., wild boar
 +
behaviour; population dynamics; in¯uence of hunting strategies; in¯uence of geographic
 +
pro®les.
 +
An ef®cient surveillance system must be an integral part of the control strategy. The
 +
EU Commission has held a workshop dedicated to this topic (Anonymous, 1998) and a
 +
working group of the Scienti®c Committee on Animal Health and Animal Welfare will
 +
prepare a recommendation.
 +
===Vaccination===
 +
From the beginning of the century attempts have been made to develop vaccines
 +
against CSF. However, the safety and ef®cacy of the ®rst generations of vaccines were
 +
poor. In the 1940s ®rst experiments were made to attenuate CSFV by adapting it to
 +
rabbits (Baker, 1946; Koprowski et al., 1946). After initial setbacks, this development
 +
ultimately led to a very ef®cient and safe generation of live vaccines. Most attenuated
 +
vaccines are based on the China-strain (C-strain) of lapinized CSF virus. C-strain
 +
vaccines were and are still being used world-wide for the control of CSF in domestic pigs.
 +
It is also used at least on an experimental basis for the oral immunisation to control CSF
 +
in wild boar (Kaden et al., 2000). C-strain vaccines induce high titres of neutralising
 +
antibodies and they are safe when used on pregnant animals. Their ef®cacy is
 +
demonstrated by the observation that vaccinated pigs are protected against infections with
 +
virulent CSF virus as early as ®ve days after vaccination. The animals are immune
 +
throughout their economic life. However, with respect to today's global trade policy there
 +
is a severe disadvantage in using live attenuated vaccines against CSF: Vaccinated and
 +
®eld-virus-infected animals cannot be distinguished because the antibody pattern induced
 +
by the vaccine virus resembles that of reconvalescent animals.
 +
A way out of this dilemma may be the development and use of so-called marker
 +
vaccines, e.g., subunit vaccines consisting of single viral surface proteins, which are suf-
 +
®cient for the induction of protective immunity. At present two subunit vaccines containing
 +
the viral glycoprotein E2 are under scrutiny. The respective gene is expressed in baculoviruses
 +
grown in insect cells (Van Rijn et al., 1996). Since these cells are able to glycosylate
 +
proteins, the resulting viral glycoprotein is expressed in a `natural'way.CSF subunit vaccines
 +
are safe and so far their protective potency is promising, though inferior to live vaccines.
 +
Vaccinated animals may be distinguished from infected pigs using an ELISA based on a
 +
different viral protein as diagnostic antigen, e.g., the surface glycoprotein Erns or the
 +
nonstructural protein NS2-3. However, not all criteria for the emergency use of marker
 +
vaccines are well de®ned yet, and the technical merits of these vaccines have not yet been
 +
established. More data are expected to be available during the year 1999.
 +
Technically there is the potential for further improving CSF marker vaccines by
 +
developing, e.g., viral vector vaccines (RuÈmenapf et al., 1991; Van Zijl et al., 1991; Hooft
 +
van Iddekinge et al., 1996), DNA vaccines and molecularly altered infectious cDNA
 +
clones of CSF virus (Meyers et al., 1996, Moormann et al., 1996, Ruggli et al., 1996).
    
==Prognosis==
 
==Prognosis==
Lizzies
6,502

edits

Retrieved from "https://en.wikivet.net/Special:MobileDiff/82712"

Navigation menu