Kajian Presensi dan Vaksinasi Penyakit Jembrana pada Sapi Bali di Wilayah Kabupaten Sarolangun, Jambi

Abstract

Penyakit Jembrana (JD) adalah penyakit pada sapi Bali yang disebabkan oleh infeksi lentiviral, dan merupakan penyakit prioritas nasional. Beberapa tahun terakhir wabah maupun kasus sporadik terjadi di beberapa wilayah Sumatra; pengawasan lalu lintas sapi serta vaksinasi diterapkan sebagai upaya pencegahan dan pengendalian penyakit. Penelitian ini bertujuan untuk menelaah infeksi virus Jembrana (JDV) guna menentukan status penyakit dan mengaji efektivitas vaksinasi dengan mengukur laju seroproteksi dan durasi imunitas. Kajian dilakukan di dua desa bertetangga di Kecamatan Air Hitam, Kabupaten Sarolangun, Provinsi Jambi, Sumatra selama delapan bulan mulai Agustus 2019 sampai dengan Maret 2020. Konfirmasi kehadiran JDV difokuskan di Desa Bukit Suban yang diduga pernah terjangkit JD. Sebanyak 36 sapi Bali yang lama tinggal tanpa riwayat vaksinasi JD dijadikan obyek kajian; serum, buffy coat dan plasma dikoleksi. Disamping itu, limpa dan hati berasal dari kasus probable yang terjadi selama masa studi juga turut diperiksa sebagai accidental sampling. Presensi virus dilakukan dengan mendeteksi gen gag pada DNA proviral maupun RNA viral menggunakan metode polymerase chain reaction (PCR) dan reverse transcriptase PCR (RT-PCR) teknik konvensional dan dilanjutkan dengan sekuensing. Sementara itu, kajian vaksinasi dilakukan pada 36 sapi Bali pendatang di Desa Pematang Kabau yang berbatasan dengan desa diduga tertular tersebut dan merupakan desa target ring vaccination. Vaksinasi dilakukan menggunakan vaksin JD-Vet® sebanyak dua dosis dengan interval waktu injeksi satu bulan. Observasi klinis dan pengambilan sampel darah pada saat sebelum vaksinasi (H0), dua minggu (H44) dan dua bulan (H90) pascavaksinasi kedua. Titer antibodi spesifik JD ditentukan dengan metode enzyme linked immunosorbent assay (ELISA). Seluruh kegiatan lapang dilakukan beriringan dengan pelaksanaan program vaksinasi oleh Pelayanan Kesehatan Hewan di Puskeswan Air Hitam, Kabupaten Sarolangun. Hasil ELISA menunjukkan bahwa 55,56% (20/36) sapi lama tinggal Desa Bukit Suban seropositif tetapi pemeriksaan PCR tidak mendeteksi adanya genom JDV. Semua sapi kajian tetap hidup sampai akhir masa studi, tetapi kasus probable JD dilaporkan terjadi pada beberapa ekor sapi lain di bulan Desember 2019. Segmen gen gag berhasil diamplifikasi pada sampel limpa sapi kasus tersebut dengan sekuen nukleotida yang menunjukkan homologi 91,32–94,79% dari sekuen JDV terdahulu. Hal ini mengindikasikan bahwa wilayah Sarolangun endemik JD dengan adanya kasus sporadis yang masih terjadi. Kasus terindikasi JD belum pernah dilaporkan di Desa Pematang Kabau sebelum dan selama penelitian ini dilakukan. Semua sapi Bali pendatang kajian tidak ada yang menunjukkan gejala sistemik maupun lokal. Hasil ELISA pada awal dimulainya studi (H0) menunjukkan bahwa sebagian besar (88,89%) seronegatif dan 11,11% seropositif. Hal tersebut mengindikasikan bahwa sapi berasal dari daerah endemik. Vaksinasi sapi dengan status awal seropositif tidak berdampak pada peningkatan titer antibodi sebaliknya sapi-sapi tersebut mengalami penurunan titer antibodi bahkan menjadi seronegatif pada H90. Sementara itu, 32 ekor sapi Bali pendatang dengan status awal seronegatif memberikan tanggapan positif yang signifikan terhadap vaksinasi (P<0,05). Sebagian besar sapi (71,88%) mengalami serokonversi pada hari ke-14 pascavaksinasi kedua (H44); 40,63% termasuk kategori seropositif kuat dan 31,25% seropositif lemah. Namun demikian pada H90 tingkat seropositivitas ini menurun signifikan menjadi 28,13% dan hanya menyisakan 15,63% sapi seropositif kuat. Kajian lapang ini menunjukkan bahwa vaksin aman, tetapi belum mampu menginduksi antibodi yang memadai dan memiliki durasi kekebalan yang relatif pendek. Beberapa hal yang mungkin mempengaruhi diantaranya konsentrasi antigen dalam vaksin, jenis ajuvan ataupun perlunya booster vaksinasi tambahan. Penentuan status kekebalan prevaksinasi penting dilakukan melalui penegakan aturan lalu lintas sapi Bali di lapangan. Secara keseluruhan, kajian ini menunjukkan bahwa wilayah Kabupaten Sarolangun adalah daerah endemik JD dan menggaris bawahi pentingnya vaksinasi di desa yang belum tertular serta perlunya evaluasi kembali program vaksinasi. Efektivitas vaksin dalam melindungi sapi dari infeksi JDV tidak dapat dikaji dalam penelitian ini karena tidak adanya kasus JD yang dilaporkan di lokasi vaksinasi. Kajian lebih lanjut pada jumlah sapi yang lebih banyak dan cakupan wilayah yang lebih luas masih diperlukan untuk memvalidasi temuan kajian terbatas ini guna mengembangkan program vaksinasi yang lebih efektif.

Jembrana disease (JD) is a national priority disease, caused by lentiviral infection amongst Bali cattle. In recent years, outbreaks and sporadic cases have occurred in several areas of Sumatra; traffic control of cattles and vaccination are implemented as an effort to prevent and control disease. This study aims to examine Jembrana Disease Virus (JDV) infection to determine disease status and assess the effectiveness of vaccination by measuring seroprotective rate and duration of immunity. Eight-month length study was conducted in two neighboring villages in the Air Hitam Sub-District, Sarolangun District, Jambi Province, Sumatra, from August 2019 to March 2020. Confirmation of the presence of JDV focused on Bukit Suban Village where probable JD has been reported. A total of 36 Bali cattle that have called resident Bali cattle without a history of JD vaccination were used as objects of study. Serum, buffy coat and plasma were collected. In addition, the spleen and liver from probable JD cases that occurred during the study period were also examined as accidental sampling. Viral presence was carried out by detecting the gag gene in proviral DNA and viral RNA used the polymerase chain reaction (PCR) and the conventional reverse transcriptase PCR (RT-PCR) technique and continued with sequencing. Meanwhile, a vaccination study was conducted on 36 newly arrived Bali cattle in Pematang Kabau Village, which borders the infected village and is the target village for ring vaccination. Vaccination was carried out using two doses of JD-Vet® vaccine with one month interval of injection. Clinical observations and blood sampling at the time before vaccination (D0), two weeks (D44) and two months (D90) after the second vaccination. JD-specific antibody titers were determined by enzyme linked immunosorbent assay (ELISA). All field activities were carried out in line with the implementation of the vaccination program by the Animal Health Service at the Air Hitam Health Center, Sarolangun District. The ELISA results showed that 55,56% (20/36) of the resident Bali cattle in Bukit Suban Village were seropositive but PCR examination did not detected the presence of the JDV genome. All study cattle were still alive until the end of the study period, but probable cases of JD were reported in several other cattle in December 2019. The gag gene segment was successfully amplified in the spleen sample from a cattle with nucleotide sequence showed homology of 91,32–94,79% of the previous JDV sequences. This indicates that the Sarolangun area is endemic to JD with sporadic cases still occurring. Cases indicated for JD had never occurred and were reported in Pematang Kabau Village before and during this study. None of the newly arrived Bali cattle showed systemic or local symptoms. ELISA results at the start of the study (D0) showed that most (88,89%) were seronegative and 11,11% were seropositive. This indicating that the cattle comes from an endemic area. Vaccinated cattle with initial seropositive status instead of increasing antibody titers, on the other hand, these cattle experienced a decrease in antibody titers and became seronegative at D90. Meanwhile, the newly arrived Bali cattle with initial seronegative status (32 cattle) gave a significant positive response to vaccination (P<0,05). Most of the cattle (71,87%) were seroconverted on day 14 after the second vaccination (D44); 40,63% belong to the category of strong seropositive and 31,25% weakly seropositive. Furthermore, at D90 this level of seropositivity decreased significantly to 28,13% and only 15,63% of cattle were strongly seropositive. This field study shows that the vaccine is safe, but has not been able to induce adequate antibodies and has a relatively short duration of immunity. Several things that may affect include the concentration of antigen in the vaccine, the type of adjuvant or the need for a second booster vaccination. It is important to determine the status of prevaccination immunity through enforcement of traffic rules for Bali cattle in the field. Overall, this study shows that the Sarolangun district is an endemic area for JD and underscores the importance of vaccination in uninfected villages and the need for re-evaluation of the vaccination program. The effectiveness of the vaccine in protecting cattle from JDV infection could not be assessed in this study because there were no reported cases of JD at the vaccination area. Further studies on larger cattle numbers and wider area coverage are required to validate the findings of this limited study to develop more effective vaccination programmes.