Experimental Immunization of Sows with Cell-cultured TGE Virus

Five sows were inoculated with a cell-cultured, cytopathic strain of the virus of transmissible gastroenteritis (TGE). Two sows were inoculated intramuscularly, and three by the intramammary route. The response was measured by the neutralizing antibody titers in the serum and the milk, and by the protection against experimental challenge of piglets nursing the sows. There were no marked differences in the serum or milk antibody titers resulting after the two methods of inoculation, although milk titers at the time of challenge were higher after intramammary inoculation. Piglets nursing sows inoculated by the intramammary route were protected to a greater extent than those nursing sows inoculated intramuscularly.     

Experimental Immunization of Sows with Inactivated Transmissible Gastroenteritis (TGE) Virus

Four sows were immunized with inactivated TGE virus. The virus was either propagated in pig kidney cell cultures, or obtained from the intestines of experimentally infected gnotobiotic pigs, and inactivated by treatment with β-propiolactone. The inactivated virus preparations were administered to sows by intramammary inoculation. Two sows received two inoculations; the other two sows received three inoculations of inactivated virus. The antibody responses in the serum and milk were determined and piglets nursing the sows were experimentally challenged with virulent TGE virus. Three inoculations of the virus preparation stimulated much higher levels of serum and milk antibody than did two inoculations. A schedule of three inoculations of sows with inactivated TGE virus was effective in stimulating protection against TGE for piglets nursing these sows.     

Clinical evaluation of transmissible gastroenteritis virus vaccines and vaccination procedures for inducing lactogenic immunity in sows

Two federally licensed attenuated live transmissible gastroenteritis (TGE) virus vaccines (an IM vaccine and an oral-IM vaccine) and 1 nonlicensed nonattenuated live TGE virus vaccine were evaluated and compared in sows free of TGE virus-neutralizing antibodies. Litters from the sows were challenge exposed at 3 and 5 days of age, and results were combined according to the vaccine administered to the sows. The survivability of pigs suckling sows vaccinated with the nonattenuated vaccine was significantly (P less than 0.01) greater than that of pigs suckling sows vaccinated with the IM attenuated vaccine, significantly (P less than 0.05) greater than that of pigs suckling sows vaccinated with the oral-IM attenuated vaccine, and significantly (P less than 0.05) greater than that of pigs suckling sows that had not been vaccinated. The differences, however, between survivability of litters from sows vaccinated with the IM attenuated vaccine or the oral-IM attenuated vaccine and that of litters from the sows not vaccinated were not significant (P greater than 0.10). The nonattenuated TGE vaccine, although giving a higher level of protection than the attenuated vaccine, was eventually overwhelmed. Dexamethasone did not increase the incidence of diarrhea, and levamisole did not potentiate the lactogenic immunity in sows after given their first dose of the nonattenuated vaccine. Survivability in litters suckling sows that developed diarrhea after given their first dose of the nonattenuated vaccine was not greater than that in litters suckling sows that did not develop diarrhea. The best results were obtained when 3-day-old suckling pigs were challenge exposed with virulent TGE virus.     

Vaccination of pregnant sows against transmissible gastroenteritis with two attenuated virus strains and different inoculation routes

Summary

Two attenuated transmissible gastro‐enteritis (T. G. E.) virus strains were used for vaccination experiments in sows.

Four different experiments were carried out (see Table 1). In each experiment, 9 sows were vaccinated during pregnancy and 3 sows served as controls. They were kept together in one farrowing house. The sows were due to farrow at about the same time. The sows and their litters were challenged shortly after farrowing by exposing 3 piglets of 2 control litters to virulent TGE virus.

The following vaccination schedules were used (see Table 1): twice intramuscularly with TGE‐vac (a commercially available TGE‐vaccine), one oral administration followed by an intramuscular vaccination with an attenuated TGE Purdue (Pu) strain, twice orally with Pu strain in enteric coated capsules, and one direct intra intestinal administration followed by 2 intramuscular vaccinations or 3 intramuscular vaccinations with the Pu strain.

All sows, except most of those treated with enteric coated capsules, seroconverted demonstrably (Table 2). The geometric mean seroneutralization (SN) titer log 2 varied from 4.1 to 7.5 after the first vaccination and from 7.6 to 10 after the second vaccination.

None of the vaccination schedules resulted in an effective lactogenic immunity. The morbidity in the piglets was 100% within 3 to 5 days after challenge. The mortality rate varied from 44 to 80% in litters from vaccinated sows and from 71 to 100% in litters from control sows (see Table 3). Clinical signs were observed in 33,3% of the control sows and in 36% of the vaccinated sows.

No correlation was found between the titer of SN antibodies in the sera of the piglets and their survival rate (Table 4).

A rapid decrease in antibody concentration was observed, during the first week of lactation in milk samples collected from 4 orally and intramuscularly vaccinated sows (Table 5).     

Vaccination of pregnant sows against transmissible gastroenteritis with two attenuated virus strains and different inoculation routes

Summary Two attenuated transmissible gastro-enteritis (T. G. E.) virus strains were used for vaccination experiments in sows. Four different experiments were carried out (see Table 1). In each experiment, 9 sows were vaccinated during pregnancy and 3 sows served as controls. They were kept together in one farrowing house. The sows were due to farrow at about the same time. The sows and their litters were challenged shortly after farrowing by exposing 3 piglets of 2 control litters to virulent TGE virus. The following vaccination schedules were used (see Table 1): twice intramuscularly with TGE-vac (a commercially available TGE-vaccine), one oral administration followed by an intramuscular vaccination with an attenuated TGE Purdue (Pu) strain, twice orally with Pu strain in enteric coated capsules, and one direct intra intestinal administration followed by 2 intramuscular vaccinations or 3 intramuscular vaccinations with the Pu strain. All sows, except most of those treated with enteric coated capsules, seroconverted demonstrably (Table 2). The geometric mean seroneutralization (SN) titer log 2 varied from 4.1 to 7.5 after the first vaccination and from 7.6 to 10 after the second vaccination. None of the vaccination schedules resulted in an effective lactogenic immunity. The morbidity in the piglets was 100% within 3 to 5 days after challenge. The mortality rate varied from 44 to 80% in litters from vaccinated sows and from 71 to 100% in litters from control sows (see Table 3). Clinical signs were observed in 33,3% of the control sows and in 36% of the vaccinated sows. No correlation was found between the titer of SN antibodies in the sera of the piglets and their survival rate (Table 4). A rapid decrease in antibody concentration was observed, during the first week of lactation in milk samples collected from 4 orally and intramuscularly vaccinated sows (Table 5).     

Induction of lactogenic immunity to transmissible gastroenteritis virus of swine using an attenuated coronavirus mutant able to survive in the physicochemical environment of the digestive tract.

A transmissible gastroenteritis (TGE) coronavirus mutant (188-SG), selected as attenuated and resistant to acidity and proteases of the digestive tract of adult pigs, was used as vaccine ("Nouzilly strain") in sows to protect suckling piglets against a challenge exposure carried out with a highly virulent TGEV strain. The pregnant sows were immunized once (42-49 days before farrowing) or twice (42-49 and 7-15 days before farrowing) by the oral, intramuscular or conjunctival route with the 188-SG strain. Sows exposed to virulent TGEV in the field and experimentally infected sows (two oral inoculations during pregnancy) were used as positive controls leading to high protection. The neutralizing antibody response to vaccination and/or infection was studied in serum and milk. No protection against mortality was observed in the litters of (1) the nine seronegative, susceptible sows, with piglet mortality of 65/70, (2) the seven once orally vaccinated sows, with mortality of 44/54, (3) the seven sows vaccinated twice by the conjunctival route, with mortality of 55/76. Moderate protection was observed in (1) the eight sows vaccinated intramuscularly twice with piglet mortality of 36/90, (2) the seven orally and intramuscularly vaccinated sows with piglet mortality of 31/51. In of 3 contrast, improved protection was observed in (1) the 10 sows vaccinated twice orally, with piglet mortality of 23/95, (2) the four naturally infected sows with piglet mortality of 6/41, (3) the six sows experimentally infected with virulent TGEV with piglet mortality of 1/59. No correlation was found between neutralizing antibodies titers in serum and milk and protection rate of the piglets. The results indicate that relative protective lactogenic immunity against TGEV is induced only by repeated ingestion of the attenuated 188-SG strain of TGEV.     

Relationship among transmissible gastroenteritis virus antibody titers in serum, colostrum, and milk from vaccinated sows, and protection in their suckling pigs

We studied the antibody responses to transmissible gastroenteritis (TGE) in serum, colostrum, and milk from sows vaccinated with 2 attenuated (1 IM and 1 oral-IM) and 1 nonattenuated live vaccines and the relationship of these responses with the survivability of the sow's suckling pigs after challenge exposure with virulent TGE virus. Contrary to previous studies, the anti-TGE virus-neutralizing geometric mean titers (GMT) in the milk of sows vaccinated with attenuated vaccines at 3 and 5 days of lactation were similar to that found in the colostrum. Colostral and serum antibody titers were highest in sows given 2 injections of the IM attenuated vaccine. Half of the sows given the oral-IM attenuated vaccine did not seroconvert after 2 oral doses. Only sows vaccinated with the nonattenuated live vaccine had milk GMT that remained high for 21 days after farrowing. The linear relationship between colostral GMT and percentage of survivability of suckling pigs challenge exposed at 3 days of age was significant (P less than 0.05), although the relationship between serum GMT and percentage of survivability and the relationship between milk GMT and percentage of survivability were not significant (P greater than 0.10). The linear relationship between colostral (P less than 0.10) or pre-challenge exposure milk (P less than 0.05) GMT and percentage of survivability of suckling pigs challenge exposed at 5 days of age was significant.(ABSTRACT TRUNCATED AT 250 WORDS)     

Intrafetal inoculation of swine with transmissible gastroenteritis virus.

Fetuses in 3 sows were inoculated (intramuscularly) with transmissible gastroenteritis (TGE) virus on 95th, 77th, and 74th days of the gestation. At 15, 14, and 37 days later (or days when pigs were obtained by hysterectomy), there was evidence of intestinal localization of virus, with villous atrophy and subsequent repair. All intrafetal-inoculated pigs became serologic-positive for TGE. A noninoculated pig shown to be seropositive for TGE at 15 days of age (after hysterectomy) was resistant to challenge exposure with virulent TGE virus given on the 32nd day, in contrast to 3 seronegative littermates that developed typical disease when challenge exposed.     

Mild transmissible gastroenteritis in pigs suckling vaccinated sows

A strain of transmissible gastroenteritis (TGE) virus of low virulence was isolated from 14-day-old pigs suckling sows vaccinated with an attenuated TGE vaccine. Diarrhea developed in suckling pigs approximately 14 days after farrowing in 4 farrowings; however, none of these pigs died from diarrhea. Diarrhea ceased after the 4th farrowing, when vaccination of sows was discontinued. Experimentally, both the field isolate and the vaccine strain were infective and in some instances lethal for 2-day-old pigs exposed orally; however, neither strain was as virulent as the Purdue strain.     

妊娠母猪免疫高致病性猪繁殖与呼吸综合征疫苗对仔猪免疫功能的影响

规模化猪场猪繁殖与呼吸综合征病毒（PRRSV）呈持续性感染,给养猪业造成的损失最为严重。部分规模化猪场未实施切实的猪繁殖与呼吸综合征疫苗免疫,呈慢性和潜伏感染,作者现场对妊娠母猪接种高致病性猪繁殖与呼吸综合征（HP-PRRS）减毒活疫苗（TJM-F92株）,旨在从体液免疫、细胞免疫、非特异性免疫功能角度探讨妊娠母猪接种疫苗后对仔猪免疫功能的影响。选取妊娠60 d母猪随机分为A、B 2组,A组母猪接种HP-PRRS减毒活疫苗（TJM-F92株）,B组母猪接种等量生理盐水,2组所产仔猪于10、20、30日龄时检测PRRSV、猪瘟病毒（CSFV）、猪伪狂犬病病毒（PRV） 母源抗体,以MTT法测定外周血T、B淋巴细胞转化率、以琼脂平板法测定血清溶菌酶含量、以Griess试剂法测定NO含量。试验结果表明,妊娠母猪免疫HP-PRRS减毒活疫苗（TJM-F92株）后,其所产10日龄仔猪PRRSV母源抗体水平显著高于对照组仔猪（P＜0.05）,仔猪CSFV阻断抗体极显著增高（P＜0.01）,20日龄仔猪PRV感染抗体显著下降（P＜0.05）;免疫组和对照组所产仔猪的T、B淋巴细胞转化率及NO、溶菌酶含量均无显著差异（P＞0.05）。提示,妊娠母猪免疫HP-PRRS减毒活疫苗（TJM-F92株）,对所产仔猪非特异性免疫功能和T、B免疫功能均无免疫抑制作用,仔猪抗PRRSV母源抗体、抗CSFV阻断抗体均显著增高且PRV感染抗体降低。     

Quantitative transmissible gastroenteritis virus shedding patterns in lactating sows.

To test the role of sows in spreading transmissible gastroenteritis (TGE), 11 sows were intravenously, intranasally, or intramammarily inoculated with virulent virus within 5 days of farrowing. Six of the sows were separated from their offspring, and 5 were allowed to nurse their litters. All sows became clinically ill with sign of anorexia, depression, and fever that persisted until postinoculation day 4 or 5. They shed virus through milk, nasal secretions, and feces, with individual variations occurring in degree and duration of shedding in the 1st week after inoculation. Of 40 pigs separately fed milk samples from the 6 inoculated sows, 19 pigs (47.5%) became sick in 24 to 40 hours, and virus was isolated from them at necropsy. Of 43 pigs in the 5 litters that nursed exposed dams, all became sick with typical signs of TGE, and 29 (67.4%) died in 2 to 9 days. Sows given the single intramammary inoculation of virus developed statistically significant higher levels of TGE virus-neutralizing antibodies than did sows inoculated intravenously or intranasally.     

Upper respiratory infection of lactating sows with transmissible gastroenteritis virus following contact exposure to infected piglets.

Ten breeding sows were left in direct contact with their newborn piglets that had been experimentally infected with transmissible gastroenteritis (TGE) virus. All sows became infected with the virus. The sows developed fever and showed mild clinical signs of the disease for a few days. The sows excreted virus in the nasal secretion, feces, and milk during the acute febrile phase of illness. Virus was isolated from the nasal secretion of one sow as early as 20 hours after contact exposure to the infected piglets. At necropsy, the virus was more frequently isolated from the tissues of the upper respiratory tract than from small intestines; this finding indicated that the TGE coronavirus replicated in the upper respiratory tract and induced an acute respiratory infection in susceptible adult swine. Neutralizing antibody was present in the sera 8 sows after 12 to 36 days during the convalescent period. From these results, we conclude that susceptible sows in direct contact with ill piglets can become infected and by excreting virus can serve as a source of TGE virus for other susceptible pigs on the premises.     

Lesions of transmissible gastroenteritis virus infection in experimentally inoculated pigs suckling immunized sows

Intestinal lesions of transmissible gastroenteritis (TGE) virus infection in conventionally reared pigs suckling either nonvaccinated, vaccinated, or previously infected sows were studied by scanning electron microscopy, light microscopy, and immunofluorescent microscopy for TGE viral antigen. Pigs were inoculated with virulent TGE virus when they were 5 or 21 days old and were euthanatized shortly after the onset of diarrhea or 96 hours after inoculation if no diarrhea developed. Pigs inoculated when they were either 5 or 21 days old and suckling nonvaccinated sows developed severe lesions, including swelling and necrosis of enterocytes and severe villus atrophy. Pigs inoculated when they were 5 days old and suckling sows vaccinated with attenuated vaccines developed less-severe villus atrophy, and those suckling sows immunized by exposure to nonattenuated TGE virus developed moderate or no villus atrophy. Pigs inoculated when they were 21 days old and suckling sows vaccinated with attenuated vaccines had severe villus atrophy, whereas those suckling sows immunized by exposure to nonattenuated virus had more-moderate villus lesions. Villus atrophy was inhibited to various degrees in pigs suckling immunized sows, depending in part on the antibody titer in the colostrum and milk.     

Active oral immunization of suckling piglets to prevent colonization after weaning by enterotoxigenic Escherichia coli with fimbriae F18

Immunoprophylaxis of porcine oedema disease and post-weaning diarrhoea caused by strains of Escherichia coli expressing fimbriae F18 is an unsolved problem. The study was designed to examine whether vaccination with a live F18ac vaccine of unweaned pigs born to sows with F18ac antibody in the colostrum requires preformed fimbriae in the vaccine, and whether protection against the heterologous fimbrial variant F18ab is induced as well. Genetically susceptible pigs were vaccinated orally on three consecutive days, beginning 10 days before weaning with 10(11) CFU of an F18ac culture. Challenge with a dose of 10(7) CFU of E. coli F18 on three consecutive days was initiated 9 or 11 days after weaning. Eighteen pigs given the fimbriated F18ac vaccine and challenged with a strain of the homologous fimbrial variant were protected against colonization; mean faecal viable counts of the challenge strain were >3 log10 lower than those from the 17 non-vaccinated control pigs. The vaccinated pigs developed a significant rise of F18ac IgA serum antibodies. The 23 pigs which had received the non-fimbriated vaccine showed no significant protection and exhibited much lower serum F18ac IgA ELISA reactivities. Eighteen pigs vaccinated with the fimbriated F18ac and challenged with an F18ab strain had faecal viable counts nearly as high as those from 16 non-vaccinated control pigs. It is concluded that only oral vaccines having preformed fimbriae induce protection limited to the homologous fimbrial variant.     

猪乳中抗猪瘟IgA、IgG、IgM抗体动态变化规律研究

以猪瘟弱毒疫苗免疫空怀母猪,待母猪分娩后,分别收集10 d内的乳汁,以建立的间接ELISA方法检测猪瘟IgA、IgG、IgM水平,并观察各种抗体动态变化规律。试验结果表明,猪初乳中的IgA、IgG、IgM抗体效价均在分娩当天达到最高值,随后迅速下降,7 d后抗体水平与常乳基本一致。对照组母猪仅在分娩当天检测到较低的抗体水平。     

Efficacy of the classical swine fever (CSF) marker vaccine Porcilis Pesti in pregnant sows

The efficacy of the classical swine fever (CSF) subunit marker vaccine Porcilis Pesti based on baculovirus expressed envelope glycoprotein E2 of CSF virus (CSFV) was evaluated in pregnant sows. Ten gilts were vaccinated with one dose of marker vaccine, followed by a second dose 4 weeks later. Four gilts remained unvaccinated and received a placebo at the same times. Thirty-three days after the second vaccination all animals were artificially inseminated. Neither local or systemic reactions nor an increase of body temperature were observed after vaccinations. All gilts showed a normal course of pregnancy. Thirty-five days after first vaccination all animals developed E2 specific neutralising antibodies with titres in the range of 5.0 and 7.5 log(2). No antibodies to CSFV-E(rns) were found in ELISA.On day 65 of gestation (126 days after the first immunisation) all sows were infected intranasally using 2ml (10(6.6) TCID(50)/ml) of the low virulent CSFV strain "Glentorf". After challenge in two of the unvaccinated control sows a slight transient increase of body temperature was observed, whereas leukopenia was demonstrated in all control animals. In addition all controls became viraemic. Vaccinations with the CSFV subunit vaccine protected the animals from clinical symptoms of CSF. In two sows a moderate decrease of leukocyte counts was detected on day 5 post infection. In contrast to the unvaccinated control sows in none of the vaccinated animals virus was isolated from the nasal swabs or the blood.Approximately 40 days after challenge all sows were killed and necropsy was done. The sows and their offspring were examined for the presence of CSFV in blood, bone marrow and different organs. No virus was found in any of the sows. In contrast, in all litters of the control sows CSFV was found in the blood as well as in the organ samples. Nine out of 10 litters of the vaccinated sows were protected from CSFV infection. Blood samples, lymphatic organs and bone marrow of these animals were all virologically negative. When sera were tested for CSFV-antibodies all sows had developed E(rns)-specific antibodies but no CSFV-specific antibodies were found in any of the progeny.It was concluded that vaccination with CSF subunit marker vaccine Porcilis((R)) Pesti protected 90% of the litters from viral infection when sows were challenged mid-gestation using the CSFV-strain "Glentorf".     

猪瘟母源抗体衰减及保护水平分析

为分析仔猪体内猪瘟母源抗体的衰减规律及母源抗体保护水平,测定了断奶时母猪和仔猪抗体水平,并监测仔猪母源抗体水平至81日龄;分别对12头81日龄仔猪（来自5头母猪）和25头35日龄仔猪（来自5头母猪）进行了攻毒试验,并用RT—nPCR进行了跟踪检测,对7头攻毒耐过猪用兔体中和法测定了中和效价。结果表明,母猪抗体水平不均衡会导致仔猪群体母源抗体水平不均衡;仔猪群体抗体到60日龄时仍然有67％（12／18）的个体用ELISA检测阻断率在50％以上：81日龄攻毒组有3头（3／12）耐过,35日龄攻毒组能全部耐过（25／25）,但有2头（2／25）在攻毒27d后仍然呈PCR阳性,此时中和抗体水平从低于1：4到1：16不等,推测中和抗体水平1：8～1：16是母源抗体保护的临界线。     

Cell-mediated immune responses of suckling pigs inoculated with attenuated or virulent transmissible gastroenteritis virus

Two litters of suckling pigs seronegative for transmissible gastroenteritis (TGE) virus were orally inoculated with live attenuated (P115) or virulent (M5C) strains of TGE virus. A third seronegative litter (controls) was given cell culture fluids from uninfected cells. Lymphocytes were collected from blood, spleen, mesenteric lymph nodes, and Peyer patches of euthanatized pigs at 0 day and approximately weekly until 26 days after exposure and at approximately 45 days after exposure. Sera were tested for virus-neutralizing antibody titers by use of plaque reduction. Lymphocytes were tested in a lymphocyte proliferation assay for uptake of [3H]thymidine after incubation with the homologous or the heterologous strain of inactivated TGE virus or uninfected cell culture fluids. Only pigs inoculated with virulent TGE virus developed clinical signs of TGE and shed virus. However, all pigs inoculated with TGE virus seroconverted at 6 days after exposure. Responses of lymphocytes from all sources from TGE virus-inoculated pigs peaked between 6 and 14 days after exposure. Pigs inoculated with virulent TGE virus had higher lymphocyte proliferative responses and neutralizing antibody titers than did pigs inoculated with attenuated TGE virus. Cessation of virus shedding coincided with the peak of lymphocyte proliferative responses. The highest responses were with intestinal lymphocytes (mesenteric lymph nodes and Peyer patches) from pigs inoculated with virulent TGE virus. The responses of intestinal lymphocytes from pigs inoculated with attenuated virus were not significantly different from those of pigs inoculated with cell culture fluid. Lymphocytes collected from all sources, except blood from M5C-inoculated pigs, had significantly (P less than 0.05) higher responses to the homologous than to the heterologous TGE virus stimulation.(ABSTRACT TRUNCATED AT 250 WORDS)     

Protection against neonatal Escherichia coli diarrhoea in pigs by vaccination of sows with a new vaccine that contains purified enterotoxic E. coli virulence factors F4ac, F4ab, F5 and F6 fimbrial antigens and heat-labile E. coli enterotoxin (LT) toxoid

The efficacy of a new vaccine against neonatal Escherichia coli diarrhoea in piglets containing purified F4ab, F4ac, F5 and F6 fimbriae and detoxified heat-labile toxin (LT) was tested in challenge experiments by the method described by the European Pharmacopoeia (3rd edn, EDQM, Council of Europe, Strasbourg, France). A group of 11 young sows from a herd without E. coli problems was vaccinated 6-8 and 2-4 weeks prior to expected farrowing and another group of nine young sows were non-vaccinated controls. Escherichia coli antibody titres were determined in serum samples taken from the sows before first vaccination and before farrowing and in colostrum samples. The newborn piglets were allowed to suckle colostrum from their mother immediately after birth. The piglets were marked with individually numbered ear tags. Approximately 12 h after birth, 118 piglets from vaccinated sows and 79 piglets from non-vaccinated control sows were challenged by oral instillation of 5 ml of a freshly prepared culture of one of the challenge strains [O8:K87:F4ab (LT+) or O149:K91:F4ac (LT+) or O9:K30:F5 or O9:K103:F6 respectively]. The challenge cultures contained as a mean 6.8x10(9) CFU/ml. After challenge the piglets were observed for 7 days and mortality and morbidity were recorded. Vaccinated sows developed significant levels of antibody titres in colostrum and serum. Control sows stayed at a low/seronegative level. The protective efficacy was excellent because 66.7-87.5% of the piglets from vaccinated sows remained without clinical signs after challenge. Only 0.0-28.0% of the piglets from non-vaccinated sows remained healthy and more than 47.1% of the piglets in this group died after challenge. It is concluded that the new vaccine is very effective in protection of piglets against neonatal E. coli diarrhoea.     

Kinetics of IgM and IgG responses to experimental and naturally acquired Rickettsia rickettsii infection in dogs

The kinetics of specific IgM and IgG antibody response was characterized in four 9-month-old Beagles after inoculation of 2 x 10(2) plaque-forming units (PFU) of Sheila Smith strain of Rickettsia rickettsii. Immunoglobulin M antibodies were first detected by indirect immunofluorescence on postinoculation (PI) day 9, peaked by PI day 20, and were no longer detectable by PI day 80. Immunoglobulin G antibodies became detectable between PI days 22 and 28, peaked by PI day 42, and decreased gradually through PI day 130. Subsequent challenges with R rickettsii on PI days 216 (2 x 10(2) PFU/dog) and 1,029 (5 x 10(4) tissue culture infective dose [TCID50]/dog) resulted in slightly different serologic responses. The initial challenge exposure failed to increase the concentration of IgG antibodies and induced only low concentrations of IgM antibodies. After the second challenge inoculation, IgM antibodies were not detectable and the concentration IgG antibodies increased slightly. Clinical abnormalities and seroconversion were documented in control dogs following each challenge exposure. Examination of acute and convalescent serum samples from 55 dogs in which Rocky Mountain spotted fever was suspected clinically suggested that sole evaluation of IgM antibodies in acute-phase serum would result in inaccurate diagnoses because of false-positive and -negative results. Use of a composite conjugate that detects IgM and IgG antibodies to R rickettsii appears to be satisfactory for diagnostic purposes; however, concurrent quantitation of IgM antibodies may facilitate serodiagnosis in a select group of dogs in which a four-fold increase in convalescent antibody titer is not detected by use of the composite conjugate.(ABSTRACT TRUNCATED AT 250 WORDS)