Seroprevalence of foot-and-mouth disease in large ruminants in periurban dairy farms near Islamabad, Pakistan
Article Category: Brief communication (Original)
Published Online: Jan 31, 2017
Page range: 123 - 127
DOI: https://doi.org/10.5372/1905-7415.1002.472
Keywords
© 2016 Umer Farooq, Aman Ullah, Hamid Irshad, Asma Latif, Khalid Naeem, Aamer Bin Zahur, Zaheer Ahmad, Luis L. Rodriguez
This work is licensed under the Creative Commons Attribution-NonCommercial-NoDerivatives 3.0 License.
Foot-and-mouth disease (FMD) is a highly contagious and economically important viral disease of cloven-hoofed ruminants caused by a member of the genus Aphthovirus of the family Picornaviridae. FMD virus (FMDV) exists as seven serotypes (O, A, C, Asia 1, SAT 1, SAT 2, and SAT 3). FMDV replicates rapidly and spreads among ruminants in contact with those infected through aerosols [1]. The disease has a serious impact on the economic condition of farmers and subsequently suppresses agricultural development, altering trade patterns and food security [2]. FMD is enzootic in Pakistan and most of the outbreaks are reported in buffaloes and cattle with prevalent serotypes being O, A, and Asia-1 [3]. Disease outbreaks are reported throughout the year [4]. Losses are estimated to be PKR 6.0 billion (USD 100 million) annually (Zulfiqar M. 2003. Draft Report for Development of National Disease Control policy for foot-and-mouth disease in Pakistan under the FAO Project “Support for emergency prevention and control of main trans-boundary animal disease in Pakistan Rinderpest, FMD, PPR”). FMD is an important threat to trade and commodity markets worldwide [5].
FMD in humans is very rare [6]. No cases in humans were reported during the large outbreak of FMD affecting animals in the United Kingdom in 2001, despite increased surveillance [7]. FMD in humans is associated with the consumption of unpasteurized milk, dairy, or unprocessed meat products from infected animals, or as a result of direct contact with infected animals (e.g. in farmers and veterinarians) [8]. To our knowledge, no person-to-person transmission in humans has ever been reported.
Buffaloes and cattle are an integral part of Pakistan’s national herd and their population is 32.7 and 36.9 million, respectively (Pakistan Economic Survey 2014. Edited by Ministry of Finance, Government of Pakistan). Subsequent to acute infection with FMDV these ruminants experience a long persistent asymptomatic infection [1, 9, 10], with continuous circulation of the infective serotype and emergence of new variants [11-13].
The role of carrier animals in the spread of FMD virus is controversial. Evidence for the direct transmission from African buffaloes to cattle in Zimbabwe was reported in 1980 and 1990 [14]. Experimental transmission from buffaloes to cattle has also been documented [14] and it was proposed that transmission occurred through sexual contact between African buffaloes and cattle [15]. The presence of the virus in the esophageal–pharyngeal fluid of cattle indicates that FMDV may be transmitted to other species. The prolonged persistence and replication of FMDV in host animals can lead to genetic variation in the field by generation of new viral variants [16-18].
Antibodies against viral nonstructural proteins (NSP) are produced in animals after the use of impure vaccines or in case of infection [19, 20]. NSP fractions are usually removed from FMDV vaccines during preparation. Therefore, the presence of antibodies to NSP in serum samples, usually indicates ongoing viral activity. Detection of an antibody response to the nonstructural polyprotein 3ABC using enzyme-linked immunosorbent assay (ELISA) seems to be the most reliable indicator of infection. The indirect ELISA used in the present study can detect 3ABC antibodies, the levels of which are higher than other NSPs [21]. The 3ABC ELISA has already been used in ruminants to differentiate between infected and vaccinated animals [23, 24]. Indirect ELISA for FMDV NSP is simple to perform and suitable for large scale serological surveillance in countries like Pakistan.
The objective of the present study was to determine the seroprevalence of antibodies against NSP of FMDV in buffalo and cattle in periurban dairy colonies of large ruminants in Pakistan. The information obtained from the present study would aid in understanding the extent of FMDV circulation in large ruminants under field conditions and the role of these large ruminants in FMD outbreaks.
Collection of blood samples from animals was approved by the Animal Welfare Committee of the National Agricultural Research Centre, Islamabad (07 October 2010), and the U.S. Department of Agriculture (Project No. 1940-32000-057-58). A cross-sectional survey was conducted during 2011-12 of periurban dairy farms near Islamabad. Sample size was calculated using an online sample size tool for cluster surveys available at
Serum samples were examined for the presence of antibodies against FMD virus NSP using an indirect ELISA (Chekit FMD-3ABC bo-ov EIA Kit, Idexx Laboratories, Westbrook, ME, USA). The assay was performed as described by [25] following the manufacturer’s instructions. Briefly, the test sera, and positive and negative control sera, were diluted 1:100 with buffer. Diluted sera (100 μL) was dispensed in FMDV NSP antigen precoated microtitration plate wells and incubated for 60 min at 37°C. After washing the wells, 100 μL of anti-ruminant IgG peroxidase conjugate was dispensed into the microtitration plate wells, and incubated for 60 min at 37°C. After washing, 100 μL of 3,3′,5,5′-tetramethylbenzidine chromogenic substrate was added into each well of the microtitration plate. The plate was incubated at room temperature for 15 min in darkness and then 100 μL of stop solution was added into each well. The absorbances of each well were determined using an ELISA plate reader with a 450 nm filter.
The data obtained were analyzed using a χ2 test and multiple logistic regression.
The seroprevalence of FMD in the large ruminants in Islamabad Capital Territory was 46% (n = 293, 95% CI 42.18-49.95). The seroprevalence was significantly (χ2 = 21.46;
Seroprevalence of foot-and-mouth disease (FMD) in large ruminants in periurban dairy farms in Islamabad Capital Territory
| Age group | Animals with FMD virus nonstructural protein antibody-positive serum | |
|---|---|---|
| Buffalo ( | Cattle ( | |
| Young | 10/99 (10%) | 4/23 (17%) |
| Adult | 275/485 (57%) | 4/29 (14%) |
| Total | 285/584 (49%) | 8/52 (15%) |
The risk of FMD seropositivity increased significantly with age (χ2=72.71;
The sex of the animal was not significantly associated with the status of the FMD serology (OR 0.58, 95% CI 0.17–1.95,
Seroprevalence of FMD in buffaloes and cattle in the present study suggests active viral activity. The overall seroprevalence of antibodies against FMDV NSP in large ruminants was 46%. Other studies have similarly reported a high seroprevalence of FMDV NSP antibodies in large ruminants. Kibore et al. [26] reported 52.5% seroprevalence in cattle in Kenya, Mwiine et al. [27] reported 39.48% seroprevalence in cattle in Uganda, and Megersa et al. [28] reported 48.1% seroprevalence in cattle in Ethiopia. By contrast, other workers have found higher and lower FMD seroprevalence in cattle. Olabode et al. [29] reported 75.11% seroprevalence of FMD in Nigerian cattle, whereas the seroprevalence in Ethiopian cattle in various regions was reported as 21.59% [30] and 8.01% [31]. These differences in seroprevalence might be the result of species differences, i.e., cattle rather than buffalo, spatial and temporal variations, and differences in husbandry practices. In Laos, FMD seroprevalence in buffalo was reported as 32.2%, and 26.5% in cattle [32], which is remarkably lower than in our present study.
Our data suggest that there is a strong association between age of animal and risk of being seropositive for FMD. Similarly, other studies have also found a higher seroprevalence of FMDV NSP antibodies in adult animals than in young animals [26, 29]. Kibore et al. [26] reported higher seroprevalence of FMD in adult cattle (>2 years old) than in calves <1 year to 2 years old. A study of Ethiopian cattle found a higher seroprevalence of FMD in adult cattle than in young animals [28]. As the age of the animal increases the chances of exposure to disease increases compared with young animals who are likely to have less prior exposure [33].
Animals are brought to the periurban dairy colonies of ICT from all over the country, and most animals traveled hundreds of kilometers. There is a possibility that these dairy colonies may act as hub for the persistence and transmission of FMD virus to other areas.
The passage of viruses in susceptible populations may give rise to new variants. Variant information is lacking in the present study. Persistence of FMDV in cattle may generate new variants, which have differences in their viral capsid protein VP1 sequence [16]. To characterize this variation, a study to isolate the FMDV from the animals kept at periurban dairy colonies in Islamabad and to analyze the molecular differences between the viruses is required, and may be useful for vaccine development.
The present study shows the high seroprevalence of FMDV in buffalo and cattle in periurban dairy farms near Islamabad and suggests a role for these large ruminants in the persistent transmission of FMD in Pakistan.