| Summary: | 博士 === 國立中興大學 === 獸醫學系暨研究所 === 97 === In the study, pathology, microbiology and molecular immunology were applied to study two foot-and-mouth virus strains (FMDV), O/Taiwan/97 and O/Taiwan/99, isolated from epizootics of FMD in Taiwan in 1997 and 1999, respectively. The results including pathogenesis and the mechanism of infection and clinical symptoms in different cloven-hoofed animal species can be applied to develop prevention strategies and clinicalil diagnose FMD.
Specific pathogen free (SPF) pigs were inoculated intradermally at the front-right heel bulb with 0.5 ml of a 106.0 tissue culture infectious dose (TCID50) of FMDV O/Taiwan/97. Symptoms of depression and inappetence appeared at 1 DPI and had subsided by 7 DPI. Vesicles developed in the epidermis of non-inoculated metacarpals joints at 1 DPI, and in the mouth and snout at 2 DPI. Viraemia was detected at 1 DPI and persisted till 3 DPI. The virus was undetectable when the neutralizing antibody (NA) developed at 4 DPI. However, the virus was isolated from the skin from 1 to 12 DPI, from feces from 2 to 8 DPI, and from 95 % oesophageal-pharyngeal (OP) fluid at 8 HPI. No virus was isolated from the skin or visceral organs at 15 DPI and the virus was not detectable from the OP fluid from 12 DPI till 400 DPI. Using a reverse transcriptase-polymerase chain reaction, viral RNA was detected at the inoculation site at 1 DPI till 21 DPI. Neutralizing antibody emerged at 4 DPI and the geometric mean NA titre was 1:861 and 1:1097 at 21 and 301 DPI, respectively. The regrowth of hoof began at 21 DPI; however, remnants of old hoof were still presented at the end of this study. These results suggest monitoring pig’s hooves for residual lesions should be applied to the FMD diagnosis.
The clinical features and the activity of serum enzymes in the pigs infected with the porcinophilic FMDV and SVD were studied. The results showed four enzyme activities released from the damaged muscles, including creatine kinase (CK), lactate dehydronase (LDH), aspartate aminotransferase (AST), and alanine aminotransferase (ALT) had significant changes in the group of pigs infected with FMDV. On the other hand, in the group of pigs infected with SVDV, the activities of AST, ALT, and LDH were found to be slightly increased. Thus, we suggest early and differential diagnosis of FMD and SVD can be accomplished by measuring the activities of CK, LDH, AST, and ALT.
On the other hand, when the suckling piglets borne by a sow free from antibodies to FMDV were infected intra-orally with the viral suspension containing 5 × 10 8.0 TCID50/ml. The piglets started to die from 24 HPI and only one piglet survived until the end of this experiment. The activities of LDH and CK rose significantly at 12 HPI. Generally, typical “tiger heart” lesions were found in the piglets at 56 HPI, but were not visible in those died by 24 HPI. The virus was recovered from the visceral organs and epithelial tissues of the piglets died after 30 HPI. Using ISH and IHC, the viral RNA and specific FMD antigens were localized within the myocytes and epithelium cells of the piglets. Nevertheless, the virus was recovered from one piglet that died at 24 HPI. The virus coult not be isolated from the piglets died at 30, 42, 48, 56, and 72 HPI with prominent myocardial lesions. The results shown the activities of LDH and CK may serve as early indicators of FMD infection in piglets. This study also provided details of the pathogenesis of FMD in suckling piglets.
In order to study the pathogenicity of O/Taiwan/99 strain (O Kimen strain) of FMDV, the virus was inoculated into healthy cloven-hoofed livestocks reared in Taiwan. Transmission of the virus among the same species of animal or between different species of animal by contact exposure was also studied. In pigs, vesicle formations in the skin were noted, and the lesions were similar to those induced by pig-adapted FMD virus (O /Taiwan/ 97) in a previous study. The infection was transmitted to the cohabitaing pigs. In dairy goats, the virus was isolated from feces and oesophageal-pharyngeal fluid (OPF). In dairy cows, a high dose of the virus, 107.3 TCID50/ml, induced vesicle formations in the muzzle and feet, and serum neutralizing antibody titer was 1: 512 at 7 DPI. The infection was transmitted to the contact-exposed mate. In Taiwan yellow cattle, virus was isolated from feces and infection was transmitted to cohabitant pigs. In steers, the virus was isolated from OPF. In Taiwan buffalo, there were not typical clinical symptoms, and the virus was isolated from feceal swab, blood, nasal swab and OPF. However, cows and pigs were not infected in cohabitation.
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