Early in the winter of 1968, an outbreak of acute respiratory disease was seen in a herd of swine in Osaka, Japan. The isolation of virus from diseased swine, the identification of the virus and serological investigation were tried. Clinical symptoms: The onset of disease was sudden. Anorexia and extreme weakness were first to appear and followed by fever and prostration. Diseased animal were crowded together to lie down and coughed when they were moved and handled. The first onset was found in pigs in a pen. Some of pigs kept in the other 13 pens of the same herd showed the same symptoms three days after the first onset. After all, 245 of 535 pigs of the herd were involved, in spite of the very short period of illness varying from 5 to 10 days. Isolation of virus: Viruses agglutinating chick erythrocytes were isolated from throat or nasal swab specimens of three pigs which had been inoculated into the allantoic cavity of 10 day-old chick embryos. They were identified as those of Hong Kong influenza virus by the cross hemagglutination inhibition (HI) test. Serological survey: Thirty convalescent serum samples were tested for HI antibody against swine influenza virus (A/Swine/S15/31) and five strains of human influenza virus. No antibody against swine influenza virus (A/Swine/S15/31) was detected. All the sera, however, inhibited he hemagglutination of Hong Kong influenza virus (A/Aichi, 2/68) and the isolated virus, A/Swine/Wadayama/69. Therefore, the isolated virus was considered to be the same as, antigenically similar to, A/Aichi, 2/68 virus. Many kinds of bacteria were also isolated from throat and nasal swabs of five pigs inspected for virus. Hemophilus, Staphylococcus, Corynebacterium and Klebeiella were isolated from all the pigs.
A total of 341 stillborn and dead neonatal piglets were collected from 233 sows in the field throughout Japan during a period from 1970 to 1974. Virus isolation was made from the brain and internal organs of these piglets by use of porcine kidney cell cultures and mice. Porcine parvovirus (PPV) was recovered from 31 stillborn piglets of 22 litters and 6 dead neonatal piglets of 4 litters in porcine kidney cell cultures. The dams of these 37 piglets had farrowed some time between August and November every year, except one which farrowed in April. The virus was isolated from almost all the principal organs and placental tissue of infected fetuses. It was onfirmed by a serological survey that all the dams of those 37 piglets had been infected with this virus during the period of pregnancy. A stillbirth rate of farrowed young was 57.2% in 21 sows from which PPV was recovered. The average number of normal young delivered was 4.4 per litter. The average number of abnormal piglets per sow was 5.9. No abnormal piglets showing nervous symptoms were farrowed from these 21 sows. The average gestation period was 113.7 days in these sows. Japanese encephalitis virus (JEV) was recovered from 8 stillborn pigltes of 8 litters and 6 dead neonatal piglets of 5 litters in both cell cultures and mice in almost the same season as PPV. A stillbirth rate of farrowed young was 73.8% in 10 sows which gave birth to young harboring JEV. The average number of normal young delivered was 2.8 per litter. The average number of abnormal piglets per sow was 7.9. Distinct nervous symptoms were manifested by 32 abnormal living piglets farrowed by those 10 sows. The average gestation period was 114.6 days in these sows. From the results mentioned above it was presumed that infection with PPV might be responsible for the occurrence of swine stillbirth. The rate of stillbirth caused by PPV was lower than that by JEV. Nevertheless, it should be emphasized that studies on the distinction of stillbirth by PPV from that by JEV and on the prevention of stillbirth caused by PPV are very important.
In Japan, over a period from 1971 to 1973, a sero-epizootiological survey was performed by using the hemagglutination-inhibition test in order to investigate the infection of swine in the field with a porcine parvovirus (PPV) and the relationship between stillbirth among gilts and the PPV infection. It was presumed that the epizootic season of PPV might extend from July to September. It was almost the same as the epidemic season of Japanese encephalitis virus (JEV). Few sows were infected with PPV in winter. A fast spread of PPV among pigs reared in a contaminated district was observed in the epizootic season. There was a tendency that pigs advanced in age in months showed a higher possession rate of PPV antibody than younger pigs; that is, pigs 5 to 6 months old exhibited a possession rate of 7.7-28.6%, pigs 7 to 10 months old 48.9-66.7%, and pigs 11 to 16 months old 83.8-100 In Fukushima Prefecture, the pre-breeding possession rate of PPV antibody was lower in gilts bred in February to July (5.9-33.3%, or 20.6% on the average) than in those bred in the other months (57.1-85.7%, or 75.6% on the average). The average annual possession rate was 37.4%. In the same prefecture, the infection rate during the period of pregnancy was higher in gilts in bred in March to July (38.5-81.3%, or 68.5% on the average) than in those bred in the other months (0-25.0%, or 12.0% on the average). The average annual infection rate was 48.2%. The same results were obtained in Ibaraki Prefecture. In 7 prefectures, 808 gilts bred in April to August in 1971 exhibited a pre-breeding possession rate of PPV antibody of 30.8% and an infection rate of 57.8% during the period of pregnancy. In Fukushima Prefecture, the pre-breeding possession rate of PPV antibody was higher in sows which had delivered once or twice before than in gilts. Sows bred in June, July, and the other months exhibited a possession rate of 44.4%, 83.3%, and 100%, respectively. The average annual possession rate was 94.3%. Sows bred in June, July, and the other months exhibited an infection rate of 55.6%, 20.0%, and 0%, respectively, during the period of pregnancy. The average annual infection rate was 6.2%. Over a period from 1971 to 1973, 880 gilts bred in April to August were immunized by two inoculations of Japanese encephalitis live virus vaccine (the S-strain) for the prevention of still-birth caused by JEV. They were divided into two groups after the enzootic period of PPV. The first group consisted of gifts which had been infected with PPV during the period of pregnancy. The second group consisted of gilts which had not been infected with PPV during the period of pregnancy. The results of delivery young were obviously better in the second group than in the first group. The average number of normal young delivered was by 1.1 per litter larger, and the average number of stillborn piglets by 0.8 per litter smaller in the second group than in the first group. In the first and the second group, a stillbirth rate of farrowed young was 19.0% and 9.3%, respectively. From the results mentioned above, it was presumed that PPV infection might induce stillbirth mostly in gilts which had been bred in spring and summer. The stillbirth rate was about 10% in these gilts.
An epidemic of hand, foot and mouth disease occurred in Hokkaido in the summer of 1970. From 153 patients, 74 fecal samples, 124 throat swabs, and a sample of vesicular fluid were collected. A total of 79 Cox A 16 viruses and 25 unidentified viruses were isolated from them by inoculation into primary monkey kidney cells. In addition 61 Cox A16, 17 Cox A4, 27 Cox A5, 63 Cox A6, and 9 Cox A10 viruses were isolated from them by inoculation into suckling mice. Of 45 patients from whom both fecal and throat samples had been collected, Cox A 16 was isolated singly from 7 patients, Cox A 16 and some other tipes were in combination from 34 patients, and Cox A viruses other than Cox A 16 were from 3 patients. Cox A 5 (from 2 patients) Cox A 6 (from 3 patients), Cox A 10 (from 2 patients) were regarded as causative a-gents, in addition to Cox A 16. A rise of antibody against each of these viruses was as follows: Cox A 16 (16.7%), Cox A 5 (16.7%), Cox A 6 (11.4%), Cox A 2 (2.8%), Cox A 4 (2.8%), Cox A 10 (2.8%) when examined in 42 paired sera (of which 7 paired sera were tested only for Cox A 16 and Cox A 5). A simultaneous rise of antibody against 2 types was seen in 4 paired sera. From virological and serological findings, it was suggested that Cox A 5, Cox A 6, and Cox A 10 viruses might be able to play a role as causative agents in an outbreak of hand, foot and mouth disease.
Swine vesicular disease (SVD) caused by enterovirus broke out for the first time in Japan in November, 1973. It occurred originally in a region producing breeding swine in Kanagawa Prefecture and prevailed up to the next month. Then an antibody survey was conducted to clarify the degree of infiltration of this virus among swine. Incidentally, antibody against SVD virus was detected in it from the sera of some swine which were considered to be free from the outbreak of SVD. These sera included those collected before the present outbreak and those harvested from swine produced and raised on farms in a region geographically apart from the site of the outbreak. SVD virus is antigenically very well identical with Coxsackie virus B5 (CB-5), which is human enterovirus. Serum samples were collected from swine in the field and examined for the presence of antibody against CB-5 virus. Then studies were made on the relationship between this antibody and that against SVD virus with the following results. 1. Serum samples were collected from swine all over Japan at three points of time; that is, prior to the outbreak of SVD and 1 and 5 months after the termination of this outbreak. Serum positive for SVD antibody was detected at every point of time. The coefficient of correlation between the two types of antibody, however, was considerably low, or 0.34, 0.31, and 0.34 before and 1 and 5 months after the outbreak, respectively. 2. When serum samples were collected from swine apparently infected on farms involved in the outbreak of SVD and examined for the two types of antibody, there was a very high correlation (r=0.74-0.85) between the antibody titers of these two types. 3. The coefficient of correlation was low, or 0.44, in serum samples collected from swine manifesting only indistinct signs of infection and from those which had withstood the infection without showing any symptom on farms involved in the outbreak of SVD. It was also low, or 0.53, in serum samples (antibody titer, <44.0) harvested from swine which seemed to be in the ascending stage of antibody. From these results, it was suggested that there might be an inapparent infection of swine in Japan with such type of virus as mentioned above which would not cause the production of vesicles, but that of low-titer antibody. As such virus, CB-5 virus, which was antigenically identical with SVD virus, or any other unknown virus was presumed to exist.
The organ culture method described by Pinkel was modified to use fragments 4×3×3mm in size, a Millipore filter membrane, THWPO 1400, as the supporting screen, and an autologous rabbit kidney capsule as the covering. It was applied to the cultivation of rabbit lymph node tissue. More than 50% of the cultured fragments retained the architecture characteristic of the lymph node in their dorsal regions. Such well maintained area occupied 1/2-3/4 of the thickness of each fragment, where lymphoid follicles with germinal centers were observed up to 4 weeks of cultivation. The cultured fragments supported the multiplication of the lapinized strain of rinderpest virus, which had been reported to be unable to grow in ordinary rabbit cell cultures. The rabbit minimum infective dose of the cultured fragment reached as high a level as 104/ml and occasionally 105/ml. Infective virus and specific antigen remained in cultured fragments over a period of cultivation ranging from 2 to 39 days. The susceptibility of the cultured fragments to the lapinized strain of rinderpest virus was 1/60 to 1/200 of that of intact rabbits. Neither inclusion body nor syncytium was recognized in the infected cultured fragments examined so far.