Preliminary observations on rinderpest in pregnant cattle

A Kabete 'O' strain of rinderpest virus enhanced in virulence was inoculated subcutaneously into four cows which were between six and eight months pregnant. All the cows developed clinical signs of rinderpest from the third day after inoculation and shed high titres of virus in their ocular and vaginal secretions during the course of the clinical disease. Three of the cows died of rinderpest on the third day after the onset of fever but no virus was isolated from their fetuses which were examined post mortem. The fourth cow showed complete clinical and virological recovery by the eighth day after the onset of fever and aborted an eight-and-a-half-month-old fetus on the 12th day after it recovered. Rinderpest virus was demonstrated in a wide range of the aborted fetal tissues. Virus was also detected in the maternal vaginal discharges up to 24 hours after abortion. The only gross pathological change observed was a severe necrotising placentitis.     

Coagulation changes in African swine fever virus infection

Pigs were infected with highly virulent (Tengani '62), with moderately virulent (DR '79) African swine fever (ASF) virus, or with virulent hog cholera (HC) virus. Changes in platelet counts, selected coagulation assays and concentrations of factor VIII-related antigen (VIIIR:Ag) were monitored. Permeability of aortic endothelium was studied after the injection of Evan's blue dye on various days after infection with DR '79 ASF virus. Virulent ASF virus caused prolongation of the activated partial thromboplastin time (APTT), 1-stage prothrombin time, and thrombin clotting time as early as postinoculation day (PID) 4. These changes became progressively more severe until death. Both virulent HC and DR'79 viruses induced an increase APPT and thrombin clotting time at PID 3 to 4, only occasionally did the prothrombin time increased significantly (P less than 0.01). The APPT began to decrease on PID 7 and 8, but only DR'79-infected pigs lived long enough to regain a normal APTT. Infection by ASF viruses caused acute thrombocytopenia after PID 6 and platelet counts of HC virus-infected pigs decreased progressively from the onset of fever to levels of 1 to 2 X 10(5)/mm3 at PID 6 to 7. All ASF virus-infected pigs had an increase in VIIIR:Ag beginning at PID 3, with maximum increases at PID 6 to 7. Hog cholera virus infection did not cause consistent changes in levels of VIIIR:Ag. Pigs infected with DR'79 virus did not have increased vascular permeability to Evan's blue dye during infection; however, there was markedly decreased staining of the aorta after pigs became thrombocytopenic.     

传染性法氏囊病病毒变异株的致病性

传染性法氏囊病病毒变异ＧＣ９０２株可引起１０日龄ＳＰＦ鸡胚肝脏坏死和脾脏明显肿大及较高的死亡率。接种２周龄ＳＰＦ雏鸡,同时设标准Ｉ型强毒ＣＪ８０１株和标准变异株强毒１０８４Ａ株接种对照,该毒株接种后第３天才出现法氏囊粘膜浆膜出血、个别黄化、质硬等病变,且于第４天法氏囊明显萎缩变小,至接种后２０天法氏囊仍严重萎缩;接种后第２天引起脾脏显著肿大,于第１２天时大小恢复正常。试验结果表明,该ＧＣ９０２株对ＳＰＦ雏鸡的致病性与标准变异株基本一致,仅有一定的差异,但明显不同于标准Ｉ型强毒株的致病性。     

Response of calves to exposure with swine influenza virus

In calves inoculated with live swine influenza virus (SIV) A/sw/IL/75 (H1N1) intranasally, SIV was isolated for 7 days, and respiratory tract disease was observed. Antibody was detected in serum of inoculated calves from postinoculation day 9, and virus-neutralization antibody was demonstrated on postinoculation days 14 and 21. The primary response was low, but readily differentiated from the secondary response after calves were challenge exposed with homologous SIV. Pneumonic lesions were observed at necropsy, and histopathologic changes in airways and lungs were consistently found. Fluorescent staining revealed viral activity in epithelial cells of airways. The virus was transferred to healthy calves housed with inoculated calves.     

Immune responses in swine given lipid-conjugated pseudorabies viral antigens.

The immune response was compared in pigs given inactivated pseudorabies virus (PRV) antigens (with or without adjuvant) or PRV antigens covalently conjugated with a fatty acid (lauric acid) to enhance delayed-type hypersensitivity. The pigs were given 2 inoculations, 14 days apart, and were challenge exposed 28 days after the 1st inoculation. Pibs inoculated with PRV antigens, with or without adjuvant, had significant virus-neutralizing (VN) antibodies before challenge exposure, but the pigs inoculated with lipid-conjugated PRV antigens had no detectable VN antibodies, with the exception of 1 pig. All inoculated pigs were positive by the microimmunodiffusion test at postinoculation day 14 and remained positive throughout the experiment. The inoculated pigs had delayed-type hypersensitivity reactions when skin tested a postinoculation day 25; the pigs inoculated with lipid-conjugated PRV antigens had a more pronounced reaction. Inoculated pigs had mild respiratory signs on the 3rd through the 6th days after challange exposure, with no observable difference in severity between the inoculated groups. The control pigs had acute signs of PRV, and 3 or 4 pigs died 5 to 8 days after challenge exposure. The average VN titers of the different inoculated groups of pigs were nearly equal 2 weeks after challenge exposure. Results indicated that both humoral antibodies and cell-mediated immunity have a role in PRV infections in swine.     

Mechanism of thrombocytopenia in African swine fever

Pigs were inoculated with an African swine fever (ASF) isolate of moderate virulence, and the changes in the number of circulating blood platelets during infection were correlated with the appearance of antiviral antibody and fluctuations in total plasma hemolytic complement concentrations. Thrombocytopenia was detected by postinoculation days (PID) 7 and 8, and antiviral antibody was detected by PID 7, using an indirect immunofluorescence technique. The total hemolytic complement concentration was moderately and transiently decreased from PID 5 to 9, but was consistently low from PID 18 to 26. Pigs inoculated with an ASF virus isolate of greater virulence had a decrease in platelet counts on PID 6 and 7, and the total plasma hemolytic complement levels decreased in all pigs by PID 6 to 7. Antibody to ASF virus was not detected in pigs inoculated with the more virulent isolate. Pigs sensitized to ASF viral antigen with an inactivated-virus vaccine or by previous infection with ASF were challenge exposed. Sensitized pigs became clinically ill and thrombocytopenic by 24 to 72 hours earlier than did inoculated, nonsensitized pigs. Vaccinated pigs inoculated with homologous virus had lower blood virus concentrations than did nonvaccinated pigs. African swine fever virus-sensitized pigs inoculated with heterologous virus had a higher fatality rate than did nonsensitized pigs, and the pigs died peracutely, with only a few gross lesions in evidence. In vitro experiments demonstrated that ASF virus antigen induced platelet aggregation in platelet-rich plasma from recovered, nonviremic pigs. Viral antigen, antibody, or complement was not demonstrable on the surface of platelets from pigs inoculated with ASF virus isolate, by direct immunofluorescence testing.     

Pathogenesis of swine vesicular disease in pigs.

Pigs exposed to swine vesicular disease virus developed vesicular lesions by postinoculation day 2. Lesions first appeared on the coronary band and then on the dewclaw, tongue, snout, lips, and bulbs of the heels. The onset of viremia coincided with febrile response and the appearance of vesicles. Virus was isolated from the nasal discharge, esophageal-pharyngeal fluid, and feces as early as postinoculation day 1. Greater amounts of virus were isolated from samples collected during the first week of infection, and lesser amounts from samples collected during the second week. The appearance and the distribution of specific fluorescence in various tissues indicated that during the development of swine vesicular disease virus infection, the epithelial tissues were initially involved, followed by a generalized infection of lymph tissues, and subsequently, a primary viremia. Seroconversion was detectable as early as postinoculation day 4. A mild nonsuppurative meningoencephalomyelitis throughout the CNS was observed in both inoculated and contact-exposed pigs. The olfactory bulbs were most severely and were frequently affected, particularly in contact pigs. The most severe brain lesions were found in pigs 3 to 4 days after the onset of viremia; contact pigs showed more severe brain lesions than inoculated pigs. Microscopic changes were also found in the coronary band, snout, tongue, and heart.     

Immunogenicity and safety of an attenuated Bordetella bronchiseptica vaccine in pigs

The immunogenicity and safety of an attenuated Bordetella bronchiseptica vaccine for swine atrophic rhinitis (AR) was evaluated in 22 hysterectomy-produced, colostrum-deprived pigs and 18 conventional pigs. None of 8 pigs inoculated at 7 days of age intranasally with greater than or equal to 3 X 10(5) colony-forming units (CFU) of vaccinal strain/pig and 2 of 5 pigs inoculated at 7 days of age intranasally with 3 X 10(4) CFU of the vaccinal strain/pig developed AR after intranasal challenge exposure with a virulent strain at postinoculation week (PIW) 3. The remaining 3 vaccinated pigs and 4 nonvaccinated pigs developed AR. Thirteen pigs were inoculated intranasally with 3 X 10(6) to 3 X 10(9) CFU of the vaccinal strain at 7 days of age. At PIW 12, the pigs were killed and necropsied. None of the pigs had clinical signs of AR and/or pneumonia. Virulence was studied by transmission of vaccinal strain through 3 serial growing passages on the nasal mucosa of a litter of hysterectomy-produced colostrum-deprived pigs. Inoculum (nasal swab samples from 2 pigs 4 days after inoculation with 10(8) CFU of vaccinal strain at 5 days of age) was inoculated into the nasal cavity of 2 nonvaccinated pigs. This procedure was repeated 3 times. After the 1st passage, the vaccinal strain was recovered on postinoculation day 4, but after postinoculation day 4, the vaccinal strain was not recovered until the end of the 3rd passage. Turbinate atrophy or pneumonia was not recognized in these inoculated pigs. The vaccinal strain provided immunogenicity without ill effects.     

Detection of rinderpest virus antigens in vitro and in vivo by direct immunofluorescence

Cell-culture attenuated and virulent strains of rinderpest virus (RV) were inoculated on to bovine kidney cell cultures. A direct immunofluorescent antibody test detected RV antigens in cell cultures within one to three days after inoculation whereas RV cytopathic effects usually took three to nine days to develop. Cells containing RV antigens were also detected in impression smears and frozen sections of tissues collected from RV infected animals at post mortem examination, and in smears of lymph node biopsies taken from cattle with clinical rinderpest. These techniques may offer additional methods for rapid diagnosis of rinderpest.     

Vesicular exanthema of swine and San Miguel sea lion virus: experimental and field studies in otarid seals, feeding trials in swine

The naturally occurring disease caused by San Miguel sea lion virus in fur seals was characterized by small fluid-filled vesicles 1 to 25 mm in diameter on the nonhaired portions of the flippers. Early epithelial lesions contained multifocal sites of cell lysis. The resultant microvesicles enlarged and coalesced, forming grossly visible macrovesicles. Mature vesicles progressed to involve all layers of the epithelium but did not involve the underlying dermis. Intradermal inoculation of vesicular exanthema of swine virus type A48 or San Miguel sea lion virus type 2 into otarid (fur) seal pups caused plaque-like lesions around inoculated coronary bands. These swellings regressed without rupture by 96 hours postinoculation. One seal inoculated with San Miguel sea lion virus had a linear lingual erosion at ten days postinoculation. Virus was isolated from this site and from two uninoculated sites, the tonsil and testicle. Contact controls showed no evidence of infection. Virus was isolated in low titers from some sites of inoculation and draining lymph nodes from seals infected with vesicular exanthema of swine virus. Virus was recovered more easily, in higher titers, and from more tissues, from seals infected with San Miguel sea lion virus. Inoculated seals tested after four to ten days seroconverted. Feeding swine seal tissues from the inoculation experiments resulted in seroconversion in swine which were fed tissues from seals infected with vesicular exanthema of swine virus but not in those which were fed tissues from seals infected with San Miguel sea lion virus.     

Vaccination of newborn pigs with an attenuated strain of transmissible gastroenteritis virus.

Clinical signs of transmissible gastroenteritis were not observed in newborn pigs orally inoculated with the high-passaged vaccinal transmissible gastroenteritis virus (TO-163 strain). Vaccinal viral multiplication in digestive tract of newborn pigs fed colostrum before inoculation and kept at 21 to 22 C was diminished, but was not diminished in those fed colostrum and kept at 10 to 11 C. Other groups of newborn pigs inoculated with the attenuated vaccinal virus and kept at 18 to 22 C or at 31 to 34 C were challenge exposed with virulent intestinal virus on the 1st, 2nd, . . ., or 6th postinoculation (PI) days. In the groups kept at 18 to 22 C, 2 of 7 inoculated pigs challenge exposed with virulent virus on the 3rd PI day, 4 of 7 pigs exposed on the 4th PI day, and all of the pigs exposed on and after the 5th PI day survived the exposure. In the groups kept at 18 to 22 C, the attenuated vaccinal virus was distributed mainly in the respiratory organs and lymphatic tissues. On the contrary, in the groups kept at 31 to 34 C, all of the pigs died in 2 to 5 days after challenge exposure, and the attenuated vaccinal virus was scarcely detected in any of the pigs.     

Experimental rotavirus infection in three-week-old pigs

Thirteen 3-week-old pigs that had been allowed to nurse for the first 16 to 18 hours after birth were orally inoculated with 1 x 10(6.5) TCID50 of porcine rotavirus. All developed diarrhea, anorexia, and vomiting by postinoculation (PI) hour 30. These signs had abated by PI day 6. Villus blunting in the small intestine was most severe in the jejunum and ileum of pigs euthanatized between PI days 3 and 5. Villi had returned to nearly normal length by PI day 6, although fused villi were seen in a few locations in the distal portion of the jejunum and in the ileum. Virus was detected in the feces of inoculated pigs by isolation in cell cultures and by electron microscopy during the 7-day course of the experiment. There was 1 extraintestinal virus isolation from the lung of 1 pig at PI day 2. Infection and disease developed in the presence of serum-neutralizing antibody obtained by nursing seropositive sows. There was no significant change in neutralizing antibody titers in the 3-week-old pigs over the course of the experiment. In this experimental work, a model to study rotavirus infection in 3-week-old pigs has been developed.     

Pathogenesis of porcine reproductive and respiratory syndrome virus infection in mid-gestation sows and fetuses.

Two experiments were undertaken to evaluate whether porcine reproductive and respiratory syndrome (PRRS) virus was able to cross the placenta and infect midgestation fetuses following intranasal inoculation of sows and whether PRRS virus directly infected fetuses following in utero inoculation. In experiment 1, eight sows between 45 and 50 days of gestation were intranasally inoculated with PRRS virus (ATCC VR-2332), and four control sows were inoculated with uninfected cell culture lysate. Virus inoculated sows were viremic on postinoculation (PI) days 1, 3, 5, 7 and 9, shed virus in their feces and nasal secretions, and became leukopenic. Sixty-nine of 71 fetuses from principal sows euthanized on PI day 7, 14 or 21 were alive at necropsy and no virus was isolated from any of the fetuses. Two principal sows that farrowed 65 and 67 days PI delivered 25 live piglets and three stillborn fetuses. The PRRS virus was isolated from two live piglets in one litter. In experiment 2, laparotomies were performed on five sows between 40 and 45 days of gestation and fetuses were inoculated in utero with either PRRS virus alone, PRRS virus plus a swine serum containing PRRS antibodies, or uninfected cell culture lysate. Three sows were euthanized on PI day 4 and two sows on PI day 11. Viral replication occurred in fetuses inoculated with virus alone and was enhanced in fetuses inoculated with virus plus antibody. No virus was isolated from control fetuses.(ABSTRACT TRUNCATED AT 250 WORDS)     

Transplacental infection of porcine fetuses following experimental challenge inoculation with encephalomyocarditis virus.

Ten multiparous sows were inoculated between 46 and 50 days of gestation with a fetal swine isolate of encephalomyocarditis virus (EMCV) to investigate the ability of the virus to cause transplacental infection and fetal death. Four sows (group 1) were inoculated IM with EMCV MN-25 that had been passaged 4 times on baby hamster kidney-21 line cell monolayers. Two sows were euthanatized at postinoculation (PI) day 23, and the other 2 sows at PI day 44. An additional 6 sows (group 2) were inoculated IM with the same virus that had been passaged 5 additional times in pigs. Two sows were euthanatized at 14 days, and the remaining 4 sows at PI day 28. Clinical signs were not observed in any of the sows, whereas all sows seroconverted to EMCV. In group 1, only 2 of 50 fetuses were mummified. Virus was not recovered, although EMCV antibodies were detected in the 2 mummified fetuses. In group 2, the 2 sows that were euthanatized at PI day 14 had 26 normal fetuses and there was no evidence of fetal infection. However, in the 4 sows euthanatized at PI day 28, 20 of 48 fetuses were mummified, hemorrhagic, or edematous. Encephalomyocarditis virus was recovered from 21 of 48 fetuses. Transplacental infection and fetal deaths in pregnant sows was achieved following infection with EMCV passaged in pigs.     

Mucosal and systemic isotype-specific antibody responses and protection in conventional pigs exposed to virulent or attenuated porcine epidemic diarrhoea virus

Eleven-day-old conventionally reared piglets were inoculated orally with two different doses of the cell-culture adapted strain CV-777 of the porcine epidemic diarrhoea virus (PEDV) or the virulent isolate of the same strain and challenged with the same virulent PEDV 3 weeks later. Pigs inoculated with the two doses of the attenuated virus did not show any typical sign of the disease, and virus shedding was not frequent. In contrast, 31% of pigs exposed to the virulent PEDV developed diarrhoea and virus shedding was demonstrated in 100%. At different postinoculation day (PID) and postchallenge day (PCD) virus-specific antibody-secreting cells (ASC) in gut associated lymphoid tissues (duodenum and ileum lamina propria and mesenteric lymph nodes) and systemic locations (blood and spleen) were assessed by enzyme-linked immunospot (ELISPOT). Only a small response was detected in the groups inoculated with attenuated PEDV, whereas in the group previously exposed to the virulent virus on PID 21 a large number of IgG and IgA ASC was detected. Isotype-specific antibody responses in serum were investigated by ELISA. IgG responses were detected in all groups, although the highest response corresponded to the group inoculated with virulent virus and only this group showed an IgA response. The pigs exposed to virulent PEDV were completely protected against the challenge with a higher dose of the same virulent virus on PID 21 and none of them shed the virus. The pigs inoculated with the attenuated strain were partially protected against the challenge, and 25% of the low dose- and 50% of the high dose-exposed pigs did not shed virus after challenge. All the pigs from a control group, not previously exposed to the virus, excreted the virus in faeces. A strong positive correlation was established between protection and the ASC responses detected in gut associated lymphoid tissues and blood at the challenge day and also between protection and serum isotype-specific antibody titers on that day. In addition, the IgA and IgG ASC responses detected in the blood on PID 21 also correlated with the responses found in the gut associated lymphoid tissues. The ASC and serum antibody responses after the challenge corresponded to a secondary immune response in the groups inoculated with attenuated virus, whereas a primary response was evident in the control group. No increase was seen in any of the parameters studied in the pigs inoculated with virulent PEDV.     

Improved isolation of rinderpest virus in transformed bovine T lymphoblast cell lines.

Bovine T lymphoblast cell lines transformed by the protozoan Theileria parva were compared with bovine kidney (BK) and Vero cells for their ability to isolate various strains of rinderpest virus from tissues and infected secretions. All of the strains of rinderpest virus that were tested, including attenuated cell-culture, caprinised and lapinised vaccines, and both mild and virulent pathogenic strains, readily induced syncytial cytopathic effect (cpe) in T lymphoblasts. The cpe could often be detected within one day of inoculation of lymphoblasts, whereas it took three to 14 days to appear in Vero and BK cells. Using lymphoblasts it was possible to reisolate rinderpest virus from nine of 42 swabs collected from three cattle experimentally infected with an isolate from a recent outbreak of mild disease whereas the same swabs yielded only one reisolate on BK cells. It was also possible using the lymphoblasts to detect infectious virus in the ocular, nasal and oral secretions of goats and rabbits infected with caprinised and lapinised virus, respectively. Peste des petits ruminants virus appeared to grow as rapidly as rinderpest virus in the lymphoblasts whereas canine distemper virus readily induced cpe on first passage but less readily on subsequent passage. Measles virus induced relatively little cpe when inoculated into lymphoblasts and did not appear to passage in these cells. The lymphoblasts are easy to maintain in culture and since they rapidly recovered 11 isolates from 37 diagnostic samples could prove useful in laboratories carrying out rinderpest diagnosis.     

Moderately virulent African swine fever virus infection: blood cell changes and infective virus distribution among blood components

Blood samples of pigs infected with a moderately virulent African swine fever virus (ASFV) isolate, obtained from the Dominican Republic (DR-II), were monitored temporally for viremia, infective ASFV association with major blood components, differential changes in blood cell composition, and plasma antibodies to ASFV. After intranasal/oral virus inoculation, pigs underwent acute infection and illness that resolved. Acute illness began on postinoculation day (PID) 4 and continued to PID 11, and pigs were febrile, with maximal infective ASFV titers detected in blood. By PID 11, initial antibody titers to ASFV antigens were detected in plasma. The WBC numbers were maintained near preinoculation counts; however, lymphocyte counts decreased slightly with a compensatory increment in neutrophil and monocyte numbers. From PID 11 to PID 25, rectal temperatures gradually returned to preinoculation values, titers of viremia began to decrease, plasma antibody to ASFV antigens increased to peak titers, and WBC numbers increased slightly. Percentages of lymphocytes returned to preinoculation values, neutrophil percentages decreased to slightly below preinoculation values, monocyte percentages were mildly increased, and eosinophil percentages were unaffected. From PID 25 to PID 46, titers of viremia further decreased, and plasma titers of antibodies to ASFV antigens remained high. In pigs with DR-II viremia (PID 4 to PID 46), most viral infectivity (greater than 95%) was RBC associated. Plasma contained less than 1% infectivity, and less than 0.1% of virus was in the WBC fraction (monocytes, lymphocytes, and granulocytes). After PID 46, viremia was no longer detectable.     

Immune response of pigs inoculated with virulent pseudorabies virus and pigs inoculated with attenuated or inactivated pseudorabies virus vaccine before and after challenge exposure

Pseudorabies virus (PRV) antibodies, detectable by indirect radioimmunoassay (IRIA), serum-virus neutralization test (NT), or microimmunodiffusion test (MIDT) were developed within 8 days after pigs were inoculated with virulent PRV or attenuated PRV vaccine. Indirect radioimmunoassay and NT titers in pigs inoculated with virulent PRV were developed at the same rate, with IRIA titers being higher than NT titers. Pigs inoculated with attenuated or inactivated PRV vaccine developed peak mean prechallenge NT antibody titers of 4 and 1 (reciprocals of serum dilutions), respectively. Pigs inoculated with attenuated PRV vaccine had peak mean prechallenge IRIA antibody titers of 6, whereas pigs inoculated with inactivated PRV vaccine had mean IRIA antibody titers of 64. Challenge exposure of swine inoculated with attenuated or inactivated PRV vaccine elicited quantitatively equivalent responses, as measured by IRIA or NT, which were higher than prechallenge titers. There were no false-positive IRIA, NT, or MIDT results obtained when sera from nonvaccinated, nonchallenge-exposed pigs were tested. It appears that the PRV infection status of a seropositive swine herd could be ascertained by serologically monitoring several representative animals from a herd, using the NT. If 2 or more tests of representative animals at 14-day intervals were done and the mean NT titer was 4 or less, it could be concluded that the herd was vaccinated against, but not infected with, virulent virus.     

Specificity of the indirect enzyme-linked immunosorbent assay for detection of pseudorabies virus antibodies in pigs exposed to bovine herpesvirus-1

Six 5-week-old pigs were inoculated intranasally (IN) with 10(7.6) TCID50 of bovine herpesvirus-1 (BHV-1). Three of the pigs also were inoculated IV with a similar dose of BHV-1. Clinical responses were not observed in these 6 pigs before oronasal challenge exposure with 10(7.8) TCID50 of virulent pseudorabies virus (PRV) at postinoculation day 42. Two pigs inoculated IN with BHV-1 and challenge exposed with PRV remained healthy, whereas the remaining 4 pigs developed severe clinical signs of pseudorabies and were moribund at postinoculation day 50 (8 days after challenge exposure). Anti-BHV-1 antibodies were demonstrable by ELISA in all 6 pigs and by serum neutralization (SN) in 5 pigs before challenge exposure with PRV. Anti-PRV antibody was not detected by ELISA or SN before challenge exposure to PRV. After challenge exposure to PRV, pigs with humoral antibody to BHV-1 responded anamnestically, and anti-PRV antibody activity was demonstrable by ELISA and SN in the 2 surviving pigs.     

Experimental infection of calves with epizootic hemorrhagic disease virus.

OBJECTIVE: To determine whether experimental inoculation with a field strain of epizootic hemorrhagic disease virus serotype-2 (EHDV-2) suspected of causing clinical disease in naturally infected cattle would cause clinical disease in calves. ANIMALS: 8 calves. PROCEDURE: A strain of EHDV-2 isolated from a white-tailed deer that died of hemorrhagic disease was passaged twice in deer and used to inoculate 6 calves SC and ID; the other 2 calves were used as controls. Physical examinations, CBC, lymphocyte blastogenesis assays, and coagulation assays were performed; rectal temperature, interferon production, and serum neutralizing antibody responses were measured; and virus isolation was attempted every other day for 21 days after inoculation and then every fourth day for another 30 days. Calves were euthanatized on postinoculation day 51, and necropsy was performed. RESULTS: Calves inoculated with EHDV-2 became infected, as evidenced by development of viremia and seroconversion. However, the virus did not cause detectable clinical disease, clinicopathologic abnormalities, or gross lesions. Viremia was prolonged despite development of a serum neutralizing antibody response. A white-tailed deer inoculated with the same EHDV-2 strain developed clinical signs of epizootic hemorrhagic disease, demonstrating that the inoculum was virulent. CONCLUSION: Calves experimentally infected with EHDV-2 developed viremia and seroconverted but did not develop detectable clinical disease.