Published Date: 2012-10-30 17:09:02
Subject: PRO/AH/EDR> Bluetongue - Europe (06): Italy (SD) serotype 1
Archive Number: 20121030.1377648
BLUETONGUE - EUROPE (06): ITALY (SARDINIA) SEROTYPE 1
A ProMED-mail post
ProMED-mail is a program of the
International Society for Infectious Diseases
Date: Mon 29 Oct 2012
Source: Press release, Animal Health Institute of Sardinia [in Italian, machine trans., edited]
Tests performed by the Animal Health Institute of Sardinia (IZS), indicating that a new outbreak of bluetongue was diagnosed in Barisardo, Ogliastra, have been confirmed. The news came from the National Reference Center for bluetongue of Teramo, after receiving blood serum samples sent by the IZS laboratories of Sassari, Sardinia where positive results were obtained. The analysis showed that the virus strain responsible for the disease is of type 1, one of the serotypes already detected in Sardinia during the period 2006-2010, the year of the last clinical episodes in our region.
"There are 24 different serotypes of bluetongue virus [BTV; see comment]; animals immune to one strain are however sensitive [susceptible] to others", said the Director-General of IZS, Antonello Usai. "Serotype 1 was responsible in the past for outbreaks in Sardinia, particularly in the provinces of Cagliari, Carbonia-Iglesias, and Villacidro-Sanluri. The fact that it is a familiar virus provides reassurance against the danger of an epidemic on our island, since the pathogen had already come into contact with sheep and has fostered an immune response; thus the animals have become less vulnerable. Furthermore, since 2007 -- says the director -- there is an ongoing vaccination campaign, which includes the use of serotype 1.
"Clinical surveillance and control systems have been put in place in collaboration with the regional veterinary services, and will address the disease risks", adds the responsible Regional Veterinary Epidemiologist of IZS, Sandro Rolesu. "Unfortunately, however, the circulation of the virus is not always controllable because Sardinia has a very large sheep population, while the environment and ecosystem are favorable to the disease vectors. So we'll continue to monitor cases, test samples of serum, and carry out entomological surveillance, in order to verify the presence of the arthropod vector and monitor the immune response of sentinel animals".
Meanwhile, the recommendation to farmers is to observe the requirements provided by the health authorities, bearing in mind that, according to international requirements, only vaccinated animals are allowed transportation.
Epidemiological situation: bluetongue disease appeared in Sardinia for the 1st time in 2000, initially in a flock in Pula [Cagliari province, at the southern tip of Sardinia, opposite Tunisia]. This was the 1st Italian case of an exotic disease of ruminants. During the following 10 years, the disease has affected 62 per cent of Sardinia's sheep farms with a loss of 650 000 heads. The 1st major epidemic in 2000-2001, accounted for nearly half of the losses, followed by the epizootics of 2001-2002, and 2003-2004. Only a handful of communities have escaped the disease. The most recent outbreak, totalling 24, were recorded in 2010. The downward spiral reflected the success of the vaccination methods applied by the regional health system.
[We are grateful to Sabine Zentis for bringing the serotyping of the current Sardinian virus to our attention.
A HealthMap/ProMED-mail interactive map of Sardinia can be seen at http://healthmap.org/r/3VBw. The location of Barisardo (Bari Sardo) is available at http://www.fallingrain.com/world/IT/14/Bari_Sardo.html.
It may be assumed that BTV-infected _Culicoides_ midges have managed to cross the distance between Algiers or Tunisia and Sardinia, as they had allegedly done several times since 2000. In the previous invasions, BTV-2, BTV-4 and BTV-1 were introduced.
As demonstrated by molecular studies (see Ref 1), the Algerian 2006 strain of BTV-1 is closely related to other BTV-1 isolates from the western Mediterranean basin (Morocco, Italy/Sardinia, Portugal, and France), representing a single, western virus lineage. In contrast, the Greek BTV-1 isolates segregate into a different group (an eastern lineage) reflecting a different geographic origin, most closely related to BTV-1 strains from India.
In 2007, BTV-1 belonging to the same western lineage was again identified in North Africa (Algeria, Tunisia, Libya, and Morocco) and in the south of the Iberian Peninsula (Spain, Portugal, and Gibraltar). This movement into Europe may have been caused by wind-borne movement of adult _Culicoides_ in a similar manner to the movement of BTV-4 from Morocco to Iberia during 2003.
BTV-2, which initially invaded Sardinia in 2000 -- causing severe losses -- was also genetically related to a western lineage, which included a Tunisian strain, BTV-2 Tunisia.
Since the start of BTV invasion to Europe, a total of 9 serotypes have been recorded. Between 1998 and 2007, 6 different serotypes (BTV-1, 2, 4, 8, 9, and 16) have been isolated and identified from epizootics occurring across Europe. Since 2008, 2 additional serotypes, BTV-6 and BTV-11 were detected in northern Europe, allegedly derived from the live attenuated vaccine strains originally developed in South Africa (see ProMED-mail archive 20090304.0888). In 2008, a novel orbivirus was detected in goats from Switzerland, initially identified as Toggenburg orbivirus, later coined BTV-25.
The Sardinian milk sheep seems to be very susceptible to BTV. The European policy regarding BTV control has been put to discussion in ref 2. The paper includes also data pertaining to the BT epizootics in Sardinia and their control, in particular the BTV-2 and BTV-4 events.
1. Cetre-Sossah C, Madani H, Sailleau C, et al: Molecular epidemiology of bluetongue virus serotype 1 isolated in 2006 from Algeria. Res Vet Sci. 2011 Dec; 91(3): 486-97; abstract available at http://www.ncbi.nlm.nih.gov/pubmed/21074232.
2. Caporale V, Giovannini A: Bluetongue control strategy, including recourse to vaccine: a critical review. Rev Sci Tech. 2010 Dec; 29(3): 573-91; abstract available at http://www.ncbi.nlm.nih.gov/pubmed/21309456. - Mod.AS]