Foot-and-mouth disease virus O/ME-SA/Ind 2001 lineage outbreak in vaccinated Holstein Friesian cattle in Saudi Arabia in 2016

Abstract

Background: Foot-and-mouth disease virus (FMDV) is a highly contagious viral infection of large ruminants. Despite the massive application of vaccines against FMDV, several outbreaks are still being reported in Africa and Asia.

Aim: To perform molecular characterization of FMDV in an outbreak among a cattle herd Saudi Arabia in 2016. This herd had been vaccinated with a polyvalent FMDV vaccine.

Methods: To investigate this outbreak, we collected specimens from 77 animals showing typical clinical signs of FMDV. Specimens including sera, nasal swabs, and tissues (tongue, coronary bands, hooves, and hearts) were collected. We tested the collected cattle sera for the presence of FMDV antibodies with commercial ELISA kits. In addition, we tested the swabs for the presence of the most common FMDV strains (O, A, Asia-1 and SAT-2) with RT-PCR using serotype-specific oligonucleotides.

Results: Serology showed that 22% of the tested sera were positive. Molecular testing of the examined swabs confirmed that 24% of the tested animals were positive. Our sequencing analysis confirmed that the circulating strains of FMDV belonged to FMDV serotype O. The phylogenetic tree based on the FMDV-VP-1 gene revealed high nucleotide identity between the circulating strains and the Bangladesh strain (99%). These strains were distinct (shared 89% nucleotide identity) from the FMDV-O strains used for the preparation of the vaccine administered to the animals in this herd. Moreover, they had 7% nucleotide difference between the FMDV-O strains reported in Saudi Arabian in 2013.

Conclusion: More in-depth molecular characterization of these FMDV strains is warranted.

Keywords: Cattle; PCR; Saudi Arabia; foot-and-mouth disease; pathology; serotype O.

Figure 1.

Clinical and pathological pictures of some FMDV infected cattle in Eastern Saudi Arabia in 2016. (A) Note the hyperemic and slightly eroded areas on the muzzle and inner side of the lower lip (asterisk) with two vesicles on the nares (arrows). (B) Ruptured vesicles on the dental pad (arrows). (C) Sloughed hard palate leaving an ulcerated surface (arrow). (D) Single vesicle on the side of the tongue. (E) Large ulcerated areas on the dorsal surface of the tongue (asterisk) and on the hard palate (arrow). (F) Multiple vesicles on the coronary band (arrows). (G) Ruptured coronary band vesicles. (H) Ulcerated areas on the skin above the coronary band (arrows). (I) Focal gray area of myocardial necrosis (arrow).

Figure 2.

Histopathological pictures of some FMDV-infected cattle in Eastern Saudi Arabia in 2016. H&E-stained sections from animals showing clinical signs of FMDV (Bar =50 µm). (A) The epithelium of the coronary band shows acanthosis (asterisk) with elongation of rete ridges (arrows). (B) A higher magnification of the previous images demonstrates intracellular edema in the cells of stratum spinosum (arrows). (C) Note the presence of prominent intercellular bridges (arrow) with dissociation of keratinocytes (asterisk). (D) Multiple microvesicles are seen within the epidermis of the coronary band (arrows). (E) A focal area of coagulative necrosis (arrow) is located within the epidermis. (F) The lingual epithelium is ulcerated (double-headed arrow) and covered with cellular and karyorrhectic debris (asterisk). (G) The lamina propria of the tongue is moderately infiltrated with inflammatory cells, mostly lymphocytes (arrow). (H) The cardiomyocytes exhibit a hypereosinophilic cytoplasm with a loss of striation. (I) A focal area of the myocardium is replaced with lymphocytes.

Figure 3.

Agarose gel electrophoresis of some RT-PCR-tested nasal swabs from cattle for FMDV in 2016 in Eastern Saudi Arabia. Some RT-PCR results of selected specimens collected from the nasal swabs of FMDV-infected animals. Lane (M) DNA marker, (100 bp); lane (1) empty well; lanes (2–13) purified PCR products of the partial FMDV VP-1 gene. The positive amplicons are 641 bp in length.

Figure 4.

Molecular identification of circulating FMDV strains in a large ruminant herd in Eastern Saudi Arabia in 2016. The maximum likelihood phylogenetic tree of circulating FMDV strains in Eastern Saudi Arabia in 2016 in a dairy herd. This phylogram shows the classification of the identified FMDV strains in the current study compared with the other seven FMDV serotypes. The reported sequences in the present study are clustered together with other serotype O FMDV sequences, especially those from Bangladesh.

Figure 5.

Phylogenetic analysis of the identified FMDV O strains detected in a large ruminant herd in Eastern Saudi Arabia in 2016. The maximum likelihood phylogenetic tree of circulating strains in Eastern Saudi Arabia in 2016 in a dairy herd. The tree was constructed based on the sequences of circulating FMDV serotypes in this herd. The identified serotype shared some variations with the common vaccine strains used in the vaccination of the dairy herd under study, especially the FMDV O strain isolated from cattle in Saudi Arabia in 1993.