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New foot-and-mouth strain spreads across Gaza Strip
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On April 19, sick animals were detected in Rafah — a town on the border between the coastal Palestinian territory of the Gaza Strip and Egypt. As reported by the Food and Agriculture Organization of the United Nations, these cases were diagnosed as an outbreak of foot-and-mouth disease, caused by a new strain, SAT2, which had been detected in February in Egypt and Libya.
Highly contagious among animals
Foot-and-mouth disease (FMD) is not considered to be a public health problem. Foot-and-mouth disease virus (FMDV) infections in humans are very rare, with approximately 40 cases diagnosed since 1921. Vesicular lesions and influenza-like symptoms can be seen; the disease is generally mild, short-lived and self-limiting. Please note that FMD is not related to hand-foot-and-mouth disease, a condition seen only in humans.
Arnon Shimshony
FMD is the most contagious disease of mammals and has a great potential for causing severe economic loss in susceptible cloven-hoofed animals. It is caused by a virus of the genus Aphthovirus and family Picornaviridae. There are seven serotypes of FMDV, namely O, A, C, Asia1 and South African Territories (SAT) serotypes SAT1, SAT2, SAT3. Infection with any one serotype does not confer immunity against another. Within serotypes, many strains can be identified by biochemical and immunological tests.
Indeed, the introduction of the African FMDV serotype SAT2 into Egypt and Libya in February caused grave concern because the target animal species in both countries, primarily cattle, buffalo, sheep and goats, had never been in contact nor vaccinated against this exotic virus strain and were fully vulnerable.
Although the Libyan outbreak remained localized, the virus spread rapidly in Egypt, severely affecting the densely populated delta region and eventually infecting livestock in all of Egypt’s governorates. The disease was characterized by severe signs, primarily in cattle and buffalo, despite their earlier vaccination against serotypes A and O. The clinically affected animals were counted in six-digit figures. High mortality was observed in young animals, and by late April, the death toll topped 20,000.
After peaking, the disease continued during May, albeit in a slower pace; mass SAT2 vaccination has been applied. The issue became subject to public debates; the media showed pictures of dead animals thrown in front of government offices by protesting farmers. Meat prices soared, with FMD becoming one of the main factors blamed as the cause of the current economic crisis.
Movements of animals from the Nile Delta eastward through the Sinai Peninsula and north into the Gaza Strip have been deemed the highest risk for the spread of the disease into the wider Middle East region. The Food and Agriculture Organization of the United Nations (FAO) has recently indicated that if FMD SAT2 reaches deeper into the Middle East, it could spread throughout vast areas, threatening the Gulf countries — even southern and eastern Europe, and perhaps beyond.
Susceptible animals
Of the domesticated species, cattle, pigs, sheep, goats and water buffalo are susceptible to FMD. Infection of susceptible animals with FMDV can lead to the appearance of vesicles on the feet, in and around the oral cavity, and on the mammary glands of females. The vesicles rupture and then heal.
One of the first signs of disease in milking cows is a sudden drop in milk yield. Mastitis is a common sequel of FMD in dairy cattle. Vesicles can also occur at other sites, such as inside the nostrils and at pressure points on the limbs — especially in pigs. FMDV is exhaled by the sick animal and discharged in saliva, milk and excretions.
Besides direct contact and aerosols, it spreads easily and indirectly via contaminated hay, stalls, trucks and clothing. The rapid spread into large proportions of the animal population is behind the serious economic implications. Suspected cases are notifiable and may cause trade restrictions on national and international levels.
Identification and control measures
The severity of clinical signs varies with the strain of virus, the exposure dose, the age and breed of animal, the host species and the immunity of the animal. The signs can range from a mild or unapparent infection to one that is severe. Death may result in some cases. Mortality from a multifocal myocarditis is most commonly seen in young animals and may exceed 50% in severe outbreaks. The convalescence period is extended, which contributes to serious economic loss.
FMD is present throughout Asia, Africa and South America. However, Europe, North America, Australia and New Zealand are free of disease. In case FMD is suspected in such a country, the suspected animals and their contacts are culled, with no vaccination applied.
Countries that are officially recognized as FMD-free, prohibit imports of live animals and unprocessed animal products (such as meat and dairy products) from infected countries. On their part, many infected countries apply preventive mass vaccinations.
FMD vaccines are inactivated; the protection conferred by such vaccines is relatively short-lived and will protect only against the homologous virus strain. After the primary vaccination, which should be repeated after several weeks, the animals undergo at least one annual vaccination throughout their life. If more than one serotype circulates within the country or region, multivalent vaccines are used.
Early and accurate diagnosis of FMD in samples from suspected cases is of the highest importance to enable the timely application of control measures. In vaccinating countries, the earliest identification of exotic types, not covered by the vaccine strains in use, is of the utmost importance.
The world reference laboratory for FMD (WRLFMD) in Pirbright, United Kingdom, provides the needed support to identify virus strains in samples from suspected cases and confirm results of national laboratories. WRLFMD carries out vaccine matching tests and genotyping of the circulating strains.
Gaza Strip outbreak
During 2012, samples from the FMD outbreak in Egypt, Libya and the Palestinian Autonomous Territories were received by the WRLFMD. Serotype SAT2 was isolated from each set of samples and subjected to reverse transcription polymerase chain reaction and sequencing of the VP1 gene.
Genotyping revealed that the virus belonged to topotype VII (there are 14 SAT2 topotypes), known to circulate in sub-Saharan Africa. It was found that there were either two independent introductions or a single introduction of two lineages into Egypt, all presumably from one or more sub-Saharan African countries; there was one independent introduction into Libya. The strain in the Gaza Strip was identical to one of the Egyptian lineages.
Besides these recent cases due to serotype SAT2, a new FMDV serotype A lineage was also detected in Egypt in 2012. The FMD situation in Egypt has become extremely complex with the presence of at least five distinct FMDV lineages between 2010 and 2012, requiring at least three different vaccine virus strains.
The spread of SAT2 into the Middle East is of great concern to countries in the region and to European nations because further spread may be possible. For example, in January 1962, FMDV SAT1 was introduced into Bahrain from East Africa. Within a few months, it had spread to Iran, Iraq, Israel, Jordan, Lebanon, Syria, Turkey and Greece. The virus persisted in Iran until 1964 and Turkey until 1965.
So far, the undertaken steps in the Gaza Strip and in neighboring Israel have prevented a further spread of the SAT2 virus strain. In Gaza, all cattle were vaccinated with an emergency SAT2 vaccine supplied by the FAO. Israel created a buffer zone along its borders with the Gaza Strip and Egypt, in which all susceptible animals were vaccinated and severe restrictions on animal movements were applied.
The situation is still rather precarious and high alertness is maintained.
Clearly, close monitoring of the FMD situation in the region is now needed to define risks of future outbreaks, as well as to ensure that control measures (vaccines and diagnostic tests) are appropriate for the virus strains that are circulating. Countries in the region are encouraged to submit samples to the WRLFMD for genetic and antigenic characterization.