doi:10.5455/vetworld.2013.122-125 Epidemiological investigation of bluetongue virus antibodies in sheep in Iran 1

AbstractAim: Bluetongue is a non-contagious, infectious viral disease of domestic and wild ruminants; which is believed to have originated in Africa. The epidemiology of Bluetongue virus infection is poorly defined in many parts of the world, including a wide range of Asia and the Middle East. This paper reports the results of a Bluetongue serological survey in sheep from some provinces of Iran during 2008-2009. Material and Methods: A total of 996 sheep sera were collected from 8 provinces in Iran and tested for Bluetongue virus specific using c-ELISA. Results: The results showed that the Bluetongue virus seroprevalence of sheep over the entire study areas was 34.93%, with the highest and lowest prevalence seen in West-Azerbaijan (64.86%) and Qom (12.1%) areas respectively. Conclusion: The results demonstrated a high prevalence of Bluetongue antibodies in Iranian sheep, giving serological evidence of extensive exposure to Bluetongue virus infection in some provinces of the country. Keywords:


Introduction
distribution of BTV coincides with the distribution of competent Culicoides insect vectors and climatic Bluetongue virus (BTV) belongs to the genus conditions promoting their proliferation [5,6].Even Orbivirus in the family Reoviridae.The virus particle though an orbivirus, direct transmission of BTV from is non-enveloped, icosahedral in shape, and consists of vertebrate to vertebrate transplacentally and through a double-layered protein coat.At least 26 serotypes of semen has been demonstrated.Nonetheless, such the virus have been identified [1,2].Bluetongue (BT) is transmission mechanisms are rare [7].on the Office international des epizootics (OIE) list of In the Mediterranean region, BT was reported notifiable multi-species diseases because of its first from Cyprus and Israel in 1943 but is thought to substantial economic impact and potential for rapid have occurred in the region as early as 1924.Six spread.Infection with BTV can cause severe serotypes, namely BTV-2, -4, -6, -9, -10 and -16, hemorrhagic disease with high mortality rates in sheep recurred at varying temporal intervals.BT is enzootic and deer [3].In sheep, the clinical signs may include in Turkey, Syria, Israel and Egypt, thus making these fever, excessive salivation, depression, dyspnea and countries a potential source of virus for the Westward panting.Initially, animals have a clear nasal discharge, located regions.There is evidence that outbreaks of BT which becomes muco-purulent and dries to a crust are mediated by the transportation of infected midges around the nostrils at a later stage.The muzzle, lips, and from enzootic to non-enzootic areas by winds that ears become hyperemic, and the lips and tongue may seasonally prevail, and that this is the principal manner swell severely.The tongue gets cyanotic and protrudes by which a fractured, but persistent cycle of BT is from the mouth occasionally.The coronary bands on perpetuated around the Mediterranean Sea [8]. the hooves are often hyperemic and painful, with Diagnostics tests are a major component of the progression to lameness and sloughing when driven.
success of any surveillance system.A variety of Pregnant ewes may abort their fetuses, or give birth to serological tests are capable of detecting BTV specific "dummy" lambs [4].In sheep, the severity of disease antibodies.These include agar gel immunodiffusion varies with breed, virus strain, and environmental (AGID), haemagglutination-inhibition (HI), complement stresses, and morbidity rate can be as high as 100% in fixation (CF), serogroup-specific blocking or compthis species.Mortality rates are usually 0-30%, but can etitive enzyme-linked immunosorbent assays (c-ELISA), reach 70% in highly susceptible animals [4].
and serotype-specific serum neutralization (SN) tests Hematophagous Culicoides insects transmit BTV [9].Non-serological diagnostic tools include BTV from infected to susceptible ruminants, thus the global isolation, antigen and genome identification, RT-PCR c-ELISA: BTV antibodies in sera were detected using a is extensively used since it is rapid, can identify the commercial group specific competitive ELISA kit serotype of the BTV strain [10]; and detects viral (VMRD Inc., Pullman, USA).The assay is based on a nucleic acid for up to 6 weeks and 6 months post-competition for binding to a VP7 antigen coated on the infection in experimentally infected sheep and cattle solid phase of the ELISA plate, between test sera accordingly [11,12].
antibodies and anti-VP7 MAb.Strong color The OIE manual of diagnostic tests and vaccines development following addition of substrate indicates for terrestrial animals recommends AGID, c-ELISA little or no blockage of monoclonal antibody binding and RT-PCR as prescribed tests for international trade.
and thus the absence of BT antibody in sample sera.However, AGID is known for cross-reactions with Weak color development due to inhibition of the other Orbiviruses such as epizootic haemorrhagic monoclonal antibody binding to the antigen on the disease virus (EDHV) [13], thus its use has declined solid phase indicates the presence of bluetongue over time and replaced with the easier to use, rapid, antibodies in sample sera.highly sensitive and specific c-ELISA [14,15].

Moreover, the c-ELISA has been reported to detect
The simplicity, sensitivity, specificity and rapidity BTV antibodies from the 7th to 10th day post infection of the c-ELISA made it ideal for use as a high [16].Although the SN test is in general recognized as throughput test in the study.the most sensitive and specific serological test for the A combined BT seroprevalence among the detection of BTV antibodies in ruminants [17], its provinces comprising the 2007-2008 sero surveillance application in routine diagnosis impractical since the was 34.93% (348/996 positive sera) (Table -1).test is too cumbersome, time-consuming and involves Prevalence of specific antibodies to BTV ranged testing for at least 24 serotypes per sample [15].between 12.1% and 64.86% among the provinces.In Iran, approximately 37.4%, 34.1% and 24.7% West-Azerbaijan had the highest number of positive of the livestock comprise sheep, goats and cattle sheep (64.86%), while Qom displayed the lowest respectively.Diseases of livestock are a threat to the infection rates (12.1%).wellbeing of the animal and human populations, and could have a devastating impact on the economy.

Incidences of BTV occurrence have been documented
Iran is located in South West Asia.It is bound by in Iran, Pakistan, Saudi Arabia, Oman, Turkey, Yemen, Azerbaijan, Armenia, Turkmenistan and the Caspian India, Kuwait and the Middle East [18][19][20][21][22][23][24][25][26] in the past, Sea to the North, Afghanistan and Pakistan to the East, but only a few studies from the region have been Iraq to the West, Turkey to the North-West, the Gulf of published recently.
Persian and Oman Sea to the South (Figure1).There is The aim of this study was thus to estimate the a possibility that BTV can be transmitted by infected prevalence of BTV antibodies in sheep from different animals from neighboring countries which cross the provinces of Iran during 2007-2008.borders into Iran.never affected.This is attributed mainly to climate and samples were tested, or signal increased BTV infection the northern expansion of the major old world vector, rates.East-Azarbaijan province in the North-West part Culicoides imicola, which is an Afro-Asiatic species of of Iran was previously reported to have a seropositivity biting midge [27].

BTV exists throughout many parts of the world
of 76.44% [35], while our study showed a reduced rate Our study revealed a BT seroprevalence of 34.93% of 39.89% for the same area.Sero-surveillance studies in sheep in Iran.Considering that no vaccination have nonetheless indicated a general increase in BT against BT is practiced, the findings clearly indicate antibody levels in the North-West parts of the country that BTV infections occur in the country [28].Higher [6].seropositivity were recorded for India (62.69%),Saudi Previous studies employing BT c-ELISA have Arabia (54.1%) and Pakistan (48.8%) accordingly [19, indicated seroprevalence of 51.6%, 45.9%, 2.13% and 26, 29], while lower prevalence rates of 21.4% and 100% for sheep, cattle and camel in the central 29.5% were reported for Kazakhstan and South-(Isfahan), West (Kurdistan) and South-East (Kerman) Eastern Turkey respectively [7,21].Iran is thus imme-of Iran respectively [31,36,37,38].diately adjacent to the unstable BT zone involving
BTV seroprevalence has never been reported in The economy of the area is based on agriculture many areas of Iran encompassing Ardabil, Khuzestan, and domestic ruminants come into contact when Qom and Fars.As far as we know, this is the first study grazing on extensive semi-arid rangeland pastures investigating the prevalence of antibodies to BTV in [30,31].When taking into consideration the seasonal sheep in these provinces of the country.Our results movements of different live animals, it is suggested demonstrated a high prevalence of BT antibodies in that risk-based control measures be adopted [19].Iran's sheep in Iran, providing serological evidence of strategic location in the South-East of Europe makes it exposure to BTV.In the absence of animal movement an important potential source of BTV strains and restrictions in the region and within the country, animal serotypes that may spread to adjacent countries transportation possess a huge risk for BT outbreaks.[27].The distribution and intensity of infection in Consequently, a well-defined control strategy for regions of the continents is determined by the climate, preventing and controlling BTV spread should not only geography and altitude, since these factors affect the be based on vaccination and vector eradication but also occurrence and activity of the Culicoides vectors.The include restriction of animal movements between presence of susceptible mammalian hosts also play an countries in the region, and within Iran.BTV is important role [27].Climate is a major risk factor as widespread in some areas of Iran with the possibility of Culicoides require warmth and moisture for breeding endemic icy, warranting further research.and calm, and warm humid weather for feeding [27].A cold winter or a dry summer can markedly reduce Author's contribution vector numbers and risk of disease occurrence.
SMA implemented the study design and test samples.Moisture may be in the form of rivers and streams or MK analyzed the data, drafted and revised the manuscript.irrigation; but, rainfall is the predominant influence Both authors read and approved final manuscript.and rainfall in the preceding months is a major determinant of BTV infection.Optimal temperatures

Figure 1 .
Figure 1.Map of Iran showing the location of areas where the present study was conducted

Table - 1
. Prevalence of BTV antibodies in sheep from 8 provinces in Iran between 2007-2008