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Bluetongue: Mediterranean Emergence
The Spread of Bluetongue in the Mediterranean:
1997-2002Within the context of the U.S. Institute of Medicine's definition of an emerging disease, it can be said that the dreaded Bluetongue is a viral emergent in Mediterranean ruminants. Not only is it breaking out in regions that have not previously reported* an occurrence (Algeria, Corsica, Bulgaria, Tunisia, Sardinia, Sicily, Calabria, Macedonia, Yugoslavia and Croatia), the serotypes (numbers 2, 4 and 9) found in recent outbreaks had been considered inactive.
In 1997, bluetongue was reported in Cyprus. In December 1998, it appeared in Greece for the first time in a decade. By June 1999 it was showing up in Bulgaria and Tunisia, by July in Turkey for the first time in 20 years. Greece experienced in August 1999 a fresh outbreak that continued through December. Three serotypes were in play, numbers 9 and 4 and another that resembled number 13.
In a westward movement, the disease was reported by Algeria in July 2000; again by Turkey in August; in early September by the Italian islands of Sardinia and Sicily and by the region of Calabria on the Italian mainland; by the Spanish island of Majorca in late September (after 40 years); and by the French island of Corsica in October. By early December there were additional outbreaks in Majorca and Minorca (Spain): 118 outbreaks involving 14,248 sheep in October; 166 outbreaks involving 16,605 animals including sheep, goats and cows. The latest epizootic phase featured serotype 2.
In keeping with previous years, new outbreaks in 2001 began in the late summer months. On 17 September Greece reported cases on its mainland and estimated that infection first occurred in late August. On 19 September, Bulgaria reported cases in the western part of that country. Cases in Kosovo were reported in mid-October; in Yugoslavia in November. By early December, there were suspected cases in Croatia. Thus, the most eastern focus of the disease turned northward. In a similar fashion, bluetongue advanced from the tip of Italy's boot to Tuscany, by March 2002 greatly impacting livestock markets in that country.
Bluetongue, also known as soremuzzle and pseudo foot-and-mouth disease, is caused by a orbivirus that has double-stranded RNA. The disease is ordinarily vectored by a small biting fly called the midge, which travels en masse, creating a virtual insect cloud. Thus, the spread east to west in the Mediterranean may have been facilitated by wind. There is another possibility: one Bluetongue vaccine in use in the region is based on an attenuated serotype 2 virus and it is possible for vaccine viruses to regain their ineffectivity under certain situations.
Bluetongue is an important disease of economic consequence. Control methods include (along with vaccination, quarantine and disinfection with acetic acid) wholesale slaughter of all infected animals, mostly sheep since cattle and goats rarely show clinical signs of disease. Tens of thousands of sheep have been destroyed in the Mediterranean over the past two years. The virus is thought by some to "over-winter" in cattle and lie in wait for the reappearance of the insect vector. In addition, it can be transmitted vertically to fetal calves and cause congenital deformities. In sheep, the virus produces lesions in the respiratory tract and in the vascular system, where it can lead to hemorrhage. Highest mortality rates are seen in white-tailed deer, pronghorn sheep and bighorn sheep. It does not affect humans and is not passed as a contagious disease from animal to animal.
Once, the disease was thought to be confined to the African continent. In 1948, it was confirmed in Cyprus. Outbreaks have occurred outside the Middle East and Mediterranean, including Pakistan and India. There was an outbreak in the U.S. in the early 1950s.
* Not reported does not necessarily mean that the disease has never occurred in the country. However, given the countries involved in the current outbreaks, it is likely that the disease has not occurred since reporting requirements were established by the World Animal Organization (OIE) and became effective in the late 1920s.
