An outbreak of encephalomyocarditis-virus infection in free-ranging African elephants in the Kruger National Park

A cluster of four deaths in late December 1993, marked the onset of an outbreak of disease of African elephants (Loxodonta africana) in the Kruger National Park (KNP) in South Africa, which has an estimated population of 7,500 elephants. Mortalities peaked in January 1994, with 32 deaths, and then declined steadily to reach pre-outbreak levels by September, but sporadic losses continued until November. During the outbreak altogether 64 elephants died, of which 53 (83%) were adult bulls. Archival records revealed that, in addition to the usual losses from known causes such as poaching and intraspecific fighting, sporadic deaths from unexplained causes had, in fact, occurred in widely scattered locations from at least 1987 onwards, and from that time until the perceived outbreak of disease there had been 48 such deaths involving 33 (69%) adult bulls. Carcases had frequently become decomposed or had been scavenged by the time they were found, but seven of eight elephants examined early in 1994 had lesions of cardiac failure suggestive of encephalomyocarditis (EMC)-virus infection, and the virus was isolated from the heart muscles of three fresh carcases. The results of tests for neutralizing antibody on 362 elephant sera collected for unrelated purposes from 1984 onwards and kept frozen, indicated that the virus had been present in the KNP since at least 1987. Antibody prevalences of 62 of 116 (53%) 18 of 139 (13%) and seven of 33 (21%) were found in elephants in three different regions of the KNP in 1993 and 1994. Studies had been conducted on myomorph rodents in the KNP for unrelated purposes since 1984, and trapping attempts were increased during the perceived outbreak of disease in elephants. There was a striking temporal correlation between the occurrence of a population explosion (as evidenced by markedly increased catch rates per trap-night) and a surge in prevalence of antibody to EM virus in rodents, and the occurrence of the outbreak of disease in elephants.

Isolation of encephalomyocarditis virus from dormice (Myoxus glis) in Italy

Two isolates of encephalomyocarditis (EMC) virus (ZRC 276RA/90 and ZRC 292RA/90) were isolated from two dormice (Myoxus glis) in Tuscany, Italy. The two isolates were lethal for laboratory mice and caused a rapid cytopathic effect characterized by rounded and wrinkled cells in both baby hamster kidney cells (BHK21) and African green monkey kidney cells (Vero). We found neutralizing antibodies against EMC virus in 408 (77%) of 529 domestic pigs (Sus scrofa scrofa) and in 165 (49%) of 338 wild boars (S. scrofa ferus majori) in Tuscany.

Encephalomyocarditis (EMC) virus infection in the common vole, Microtus arvalis

Encephalomyocarditis (EMC) virus infection in the common vole was examined for the first time. Sixteen 8-week-old males inoculated intraperitoneally with 10(5) plaque-forming units (pfu)/animal of the D variant of EMC virus were killed 3 and 7 days after inoculation (3 and 7 DAI). Viral replication was detected in the brain (10(5) pfu/g), heart (10(4) pfu/g) and pancreas (10(7) pfu/g) of all 8 animals at 3DAI. It was found in the pancreas (10(3) pfu/g) of all 8 animals and in the brain (10(4) pfu/g) of 2 of 8 animals at 7 DAI. Histopathological changes were observed in the brain (mild mononuclear cell infiltration around capillaries and sporadic pyknosis of neurons), heart (minimal myocardial necrosis) and pancreas (prominent acinar cell necrosis with inflammatory exudation) at 3DAI. At 7 DAI, replacement of necrotic tissues by mesenchymal cells and regeneration of acinar cells were conspicuous in the pancreas. Throughout the experimental period, no evidence for diabetogenic effect was found.

Social isolation modifies the response of mice to experimental Mengo virus infection

To investigate the effects of social isolation on host resistance male mice were housed either individually (IH) or in groups of four or five (GH). All animals were infected with MengoM,L virus. Incubation time (INCUB), duration of illness (ILL), death rate (DR), histopathological changes, and serum corticosterone levels (CORT) were recorded. First, the effect of IH starting 4 days prior to infection was studied in 5 different inbred strains. Next, the effect of different IH length was examined, and the role of T-cells was investigated by comparing euthymic (+/+) and athymic (nu/nu) NMRI mice. Finally, the effects of the infection on CORT in IH and GH mice were compared in C57BL/6 mice. The major findings were: 1. IH significantly increased ILL in all but the DBA/2 strain, whereas DR was not affected except in C57BL/6. 2. Longer IH (starting 35 [DBA/2] or 10 [NMRI] days prior to virus inoculation) significantly shortened INCUB and prolonged ILL, but IH starting on the day of virus inoculation [DBA/2] significantly prolonged INCUB and shortened ILL. 3. NMRI nude mice exhibited an unaltered DR accompanied by a tremendously prolonged INCUB. 4. Investigations in C57BL/6 mice revealed a significant rise of CORT after infection. This increase was higher in IH compared to GH mice. It is suggested that IH attenuates T-cell mediated inflammatory processes and/or increases macrophage activation, which in turn results in a prolonged course of the disease.

Reproductive failure in sows following experimental infection with a Belgian EMCV isolate

In this study, a transplacental infection with fetal death was demonstrated following inoculation of pregnant sows with a Belgian encephalomyocarditis virus (EMCV) isolate. Eight multiparus sows were inoculated between 60 and 92 days of gestation with this EMCV-isolate to investigate its ability to cause reproductive failure in sows. Virus persistence and antibody titre in their offspring were also studied. Only the two sows inoculated at 60 days of gestation showed premature farrowing, but all sows seroconverted to EMCV. Virus was recovered from the offspring of all sows at the time of farrowing, but not from every piglet born. One month after birth EMCV could be isolated from all the piglets examined. These results can help in a better understanding of the spread of the disease in piggeries.

Experimental encephalomyocarditis virus infection in pigs

A field isolate of Encephalomyocarditis (EMC) virus was inoculated intravenously into 8 pigs. Four animals died at post inoculation day (PID) 2, the remaining being sacrificed at PID 5, 7, 11 and 15. Two control, in-contact pigs were sacrificed at PID 19. Virus was isolated from leucocytes and nasal swabs until PID 4, from rectal swabs until PID 2 and, in the pigs found dead at PID 2, from several organs. EMC virus was further isolated from brain and spleen of the pig sacrificed at PID 7. One of the 2 control pigs became infected: virus was isolated from nasal swabs at days 6 and 7 and from leucocytes at day 4 of the experiment. Serum-neutralizing (SN) antibody was detected in the injected pigs starting from PID 4; two days later, it was also revealed in the infected, in-contact control. To our knowledge, this is the first report of an experimental transmission of EMC virus infection in pigs by contact exposure.