Shedding of Escherichia coli O157:H7 in dairy cattle housed in a confined environment following waterborne inoculation

A study of Escherichia coli O157:H7 transmission and shedding was conducted with bull calves housed in individual pens within a confined environment. For comparative purposes, the numbers and duration of E. coli O157:H7 shedding in naturally infected calves were monitored after a single purchased calf (calf 156) tested positive prior to inoculation. During the next 8 days, the calves in adjacent pens and a pen directly across a walkway from calf 156 began to shed this serotype O157:H7 strain. Five of the eight calves in this room shed this O157:H7 strain at some time during the following 8 weeks. The numbers of E. coli O157:H7 isolates shed in these calves varied from 60 to 10(5) CFU/g of feces, and the duration of shedding ranged from 17 to >31 days. The genomic DNAs from isolates recovered from these calves were indistinguishable when compared by using XbaI digestion and pulsed-field gel electrophoresis. Inoculation of calves with 1 liter of water containing ca. 10(3) to 10(4) CFU of E. coli O157:H7/ml resulted in shedding in 10 of 12 calves (trial 1, 4 of 4 calves; trial 2, 6 of 8 calves). The inoculated calves shed the inoculation strain (FRIK 1275) as early as 24 h after administration. The duration of shedding varied from 18 to >43 days at levels from 10(2) to 10(6) CFU/g of feces. The numbers of doses necessary to initiate shedding varied among calves, and two calves in trial 2 never shed FRIK 1275 after four doses (ca. 10(6) CFU per dose). Results from this study confirm previous reports of animal-to-animal and waterborne dissemination of E. coli O157:H7 and highlight the need for an effective water treatment to reduce the spread of this pathogen in cattle.     

Shedding of Escherichia coli O157:H7 in Dairy Cattle Housed in a Confined Environment following Waterborne Inoculation

A study of Escherichia coli O157:H7 transmission and shedding was conducted with bull calves housed in individual pens within a confined environment. For comparative purposes, the numbers and duration of E. coli O157:H7 shedding in naturally infected calves were monitored after a single purchased calf (calf 156) tested positive prior to inoculation. During the next 8 days, the calves in adjacent pens and a pen directly across a walkway from calf 156 began to shed this serotype O157:H7 strain. Five of the eight calves in this room shed this O157:H7 strain at some time during the following 8 weeks. The numbers of E. coli O157:H7 isolates shed in these calves varied from 60 to 10⁵ CFU/g of feces, and the duration of shedding ranged from 17 to >31 days. The genomic DNAs from isolates recovered from these calves were indistinguishable when compared by using XbaI digestion and pulsed-field gel electrophoresis. Inoculation of calves with 1 liter of water containing ca. 10³ to 10⁴ CFU of E. coli O157:H7/ml resulted in shedding in 10 of 12 calves (trial 1, 4 of 4 calves; trial 2, 6 of 8 calves). The inoculated calves shed the inoculation strain (FRIK 1275) as early as 24 h after administration. The duration of shedding varied from 18 to >43 days at levels from 10² to 10⁶ CFU/g of feces. The numbers of doses necessary to initiate shedding varied among calves, and two calves in trial 2 never shed FRIK 1275 after four doses (ca. 10⁶ CFU per dose). Results from this study confirm previous reports of animal-to-animal and waterborne dissemination of E. coli O157:H7 and highlight the need for an effective water treatment to reduce the spread of this pathogen in cattle.     

Growth Curve and Distribution of Rous Sarcoma Virus (Bryan) in Japanese Quail

On primary infection with the Bryan strain of Rous sarcoma virus (RSV), the growth curve of the virus in the brain of Japanese quail was similar to that observed in chicks and turkey poults. Infectious virus disappeared from the brain after inoculation. After an eclipse period during which no virus was detectable, infectious virus began to appear at 2 days and reached maximal titers in the brain samples at 7 days after inoculation. When Japanese quail were infected intracerebrally with RSV, relatively high titers of virus were recovered from brain tissue but not from liver, lung, kidney, or blood of moribund birds. Only tumors produced in the wing web of quail infected subcutaneously yielded high titers of virus. Other tissues yielded no virus, even though wing web tumors appeared as early as in chicks similarly infected. RSV could be propagated in the wing web of quail for at least 14 passages without any loss of infectivity. On the other hand, serial passage in quail brain resulted in a progressive loss of infectivity until virus was completely lost.     

Experimental infection of calves and adult cattle with Escherichia coli O157:H7.

Preweaned calves and adult cattle were inoculated with 10(10) CFU of Escherichia coli O157:H7 strain 3081, a calf isolate which produces Shiga-like toxin, to define the magnitude and duration of fecal shedding of E. coli O157:H7 for each age group. Fecal samples of eight of eight, eight of eight, three of eight, and two of eight calves were positive at 2, 7, 14, and 20 weeks, respectively. In contrast, nine of nine, two of nine, and one of nine steers were positive at 2, 7, and 14 weeks, respectively. The magnitude of shedding (CFU per gram) by individual animals at any one time postinoculation varied widely within each age group but was greater for calves as a group. The differences in shedding patterns between adults and calves were statistically significant. After inoculation, 25 of 29 animals remained healthy and 4 of 17 calves had transient diarrhea. Histologic sections of the brain, kidney, jejunum, ileum, cecum, and colon taken at necropsy from nine calves either 3, 14, or 18 days postinoculation or three adults either 2, 3, or 4 days postinoculation were normal. E. coli O157:H7 was recovered from the alimentary tracts of all of the animals necropsied, and there was no evidence of spread to the liver, spleen, or kidneys. Four calves that had ceased shedding were reinfected when inoculated again with the same strain. E. coli O157:H7 was recovered from none of five and two of five adults inoculated with 10(4) and 10(7) CFU, respectively.(ABSTRACT TRUNCATED AT 250 WORDS)     

Phage Typing Scheme for Salmonella braenderup

A phage typing scheme for Salmonella braenderup based on both phage sensitivity and lysogenicity patterns is presented. Three S. braenderup symbiotic phages (br A, br B, and br C) were used in the phage sensitivity test, and three indicator strains were used for the lysogenicity test. The 424 strains examined were grouped in 15 of 64 possible types within this scheme. The most frequent types were: A(1) (32%), G(5) (21%), F(2) (14%), and H(1) (8%). All of the strains isolated successively from the same person belonged to the same type, as did the strains isolated from groups of individuals related to a common source.     

Prolonged viral shedding and antibody persistence in patients with COVID-19

SARS-CoV-2 as a new global threat has affected global population for one year. Despite the great effort to eradicate this infection, there are still some challenges including different viral presentation, temporal immunity in infected individuals and variable data of viral shedding. We studied 255 COVID-19 suspected individuals to assess the viral shedding duration and also the antibody development against SARS-CoV-2 among the cases. Real Time RT-PCR assay was applied to determine the virus presence and SARS-CoV-2 antibodies were evaluated using SARS-CoV-2 IgM and IgG kits. 113 patients were confirmed for COVID-19 infection. The patients were followed until negative PCR achieved. The median viral shedding among studied population was obtained 34.16 (±17.65) days which was not significantly associated with age, sex and underlying diseases. Shiver and body pain were found in prolonged form of the infection and also patients who had gastrointestinal problems experienced longer viral shedding. Moreover, IgG was present in 84% of patients after 150 days. According to this data, the median viral shedding prolongation was 34.16 days which indicates that 14 days isolation might not be enough for population. In addition, IgG profiling indicated that it is persistent in a majority of patients for nearly 6 months which has brought some hopes in vaccine efficacy and application.     

Effect of the thyroid on faecal shedding of E. coli O157:H7 and Escherichia coli in naturally infected yearling beef cattle

AIMS: To determine if thyroid function affects faecal shedding of Escherichia coli O157:H7. METHODS AND RESULTS: Eight yearling cattle (n = 4 per treatment group), previously identified as shedding E. coli O157:H7, received either 0 or 10 mg 6-N-propyl-2-thiouracil (PTU) kg(-1) BW day(-1) for 14 days to reduce serum concentrations of the thyroid hormones, T(3) and T(4). Animals were monitored daily for changes in faecal shedding of E. coli O157:H7 and E. coli (EC) for the 14-day treatment period and an additional 7 days post-treatment. Body weight was measured weekly and serum concentrations of T(3) and T(4) were determined every 3 days. No differences in faecal shedding of E. coli O157:H7 were observed during the 14-day treatment period. However, compared with control animals, a greater percentage of PTU-treated cattle ejected E. coli O157:H7 on day 16 (100 vs 25%) and 18 (75 vs 0%) of the post-treatment period. Serum T(3) was lower in PTU-treated cattle during the 14-day treatment period and greater on day 18 of the post-treatment period. CONCLUSION: Cattle with chemically altered thyroid hormones had similar shedding patterns of faecal E. coli O157:H7 and EC during the 14-day treatment period. However, faecal shedding of E. coli O157:H7 tended to be greater, and serum concentrations of T(3), were greater for PTU-treated cattle immediately following the termination of PTU treatment. SIGNIFICANCE AND IMPACT OF THE STUDY: Short-term chemical inhibition of thyroid hormones had minimal effects on faecal shedding of E. coli O157:H7 in naturally infected cattle. However, a hyperthyroid state as observed postdosing might play a role in the seasonal shedding of E. coli O157:H7 in cattle.     

Antifertility effect of gossypol in male Japanese quail

Conventionally housed 130-160 g adult male Japanese quail were given gossypol acetic acid (gossypol) im at 25 mg/kg in 0.5 ml of 10% EtOH for 12 and 24 days (Groups 1 and 2), respectively. One day after treatment was terminated they were allowed to mate with laying females individually for 20 days. Fertility was 0% from mating of the Group 1 birds on days 1-2 and increased to 25, 35, 55 and 65% on days 3-6 after cessation of gossypol treatment. At day 11, fertility was 80 vs 84% in controls, whereas hatchability was 70% for both. By comparison, eggs from Group 2 mated quail were infertile for up to 20 days after the termination of gossypol treatment. In a parallel experiment, the percent testes to body weight ratio in control and 7, 14, 21, and 28-day gossypol-treated quail was 2.5, 2.2, 1.8, 0.5, and 0.2%, respectively. In 12 vs 24-day treated birds, 7, 14, 21, and 28 days after gossypol treatment, the ratios were 1.0 vs 0.5%, 2.0 vs 0.8% and 2.8 vs 1.9%, respectively. The decreased fertility and hatachability, and testicular atrophy resulting from gossypol given to male quail was dose-time related. Furthermore, the androgen-dependent cloacal gland was drastically reduced in size by the treatment with gossypol. The mode of action of gossypol in male quail is different than it is in mammals in that the testicular size of mammals remains unchanged with long-term gossypol treatment. It is concluded that quail may be a useful avian animal model for investigating the antifertility effects of gossypol.     

Type 1 pili enhance the invasion of Salmonella braenderup and Salmonella typhimurium to HeLa cells.

The relationship between type 1 pili-associated adhesion and invasion to HeLa cells by Salmonella braenderup and S. typhimurium was studied. When the clinical isolates of these strains were grown in L-broth, they showed both type 1 pili formation and mannose-sensitive adhesion to HeLa cells. On the other hand, the type 1 pili-defective mutants, which were obtained either by repeated subcultures on L-agar plates or by the transposon Tn1-insertion mutagenesis of the S. braenderup and S. typhimurium strains, concomitantly lost mannose-sensitive adhesion to HeLa cells. When the HeLa cells were incubated with Salmonella, the type 1 piliated strains invaded the HeLa cells with much higher infection rate than did the type 1 pili-defective strains. The invasion of type 1 piliated strains to HeLa cells was markedly inhibited in the presence of D-mannose. The infectivity of the strain, which lost type 1 pili but still had mannose-resistant adhesion, was slightly higher than that of the strains defective in both mannose-sensitive and mannose-resistant adhesion. These results suggested that type 1 pili have a role in enhancing the invasion of S. braenderup and S. typhimurium to HeLa cells.     

Xenogenic oogenesis of chicken (Gallus domesticus) female primordial germ cells in germline chimeric quail (Coturnix japonica) ovary

In present study, chicken primordial germ cells (PGCs) were transferred into quail embryos to investigate the development of these germ cells in quail ovary. Briefly, 2 microl of chicken embryonic blood (stage 14) or about 100 purified circulating PGCs were transferred into quail embryo. Contribution of chicken PGCs were detected in gonads of chimeric quail embryos (stage 28) by immunocytochemical staining of cell surface antigen SSEA-1, and by in situ hybridization (ISH) with female chicken specific DNA probe. As a result, 52.0+/-43.2 (n=18) and 42.7+/-27.3 (n=17) chicken PGCs were found in the gonads of chimeric quail embryo that was injected with chicken embryonic blood (stage 14) and about 100 purified circulating PGCs, respectively. Furthermore, the ovaries of 81.8% (9/11) 12 days post incubation (dpi) chimeric quail embryos were observed with a mean of 457.6+/-237.1 female chicken PGCs-derived oogonia scattered in ovarian cortex area. In 9 out of 12 newly hatched and one week old chimeric quail chicks, on average of 2883.0+/-1924.1 primary oocytes and 3 follicles derived from chicken PGCs were found, respectively. The present results suggest that chicken female PGCs are able to migrate, colonize, proliferate and differentiate into oogonia, primary oocytes in chimeric quail ovary.     

Comparative evaluation of different immunoassays for the detection of Taenia solium cysticercosis in swine with low parasite burden

Seven swine were experimentally infected with Taenia solium eggs and blood samples from each animal were periodically collected. At the end of the experiment (t140) the animals did not show clinical aspects of cysticercosis or parasites in tongue inspection. All animals were slaughtered and cut into thin slices in searching for cysts. The number of cysts found in each animal varied from 1 to 85. Enzyme-linked immunosorbent assay (ELISA) tests for antibody (Ab) detection and for antigen (Ag) detection were performed, which presented respectively 71 and 57% of positivity. By immunoblot (IB), using 18/14(T. crassiceps Ag) or lentil-lectin-purified glycoproteins from T. solium Ag (LLGP) as Ag, five (71%) and six (86%) animals were positive, respectively. The association between Ag-ELISA with any IB (18/14 or LLGP) allowed the detection of all animals at 140 days post-experimental infection (days p.e.i.). The use of IB 18/14 combined to the Ag-ELISA allowed the detection of all animals since 70 days p.e.i., and the association between IB LLGP and Ag-ELISA allowed the detection of all animals since 112 days p.e.i. While all animals could be considered healthy by conventional screening tests, the use of immunoassays for detecting Ab and Ag showed better accuracy; therefore it would be more useful than usual clinical examination for screening cysticercosis in slightly infected pigs.     

Role of peptidergic neurons in ocular herpes simplex infection in mice

Peptide-containing nerve fibers (peptidergic fibers) abundantly innervate the mammalian cornea. We investigated their role in ocular herpes simplex infection in mice by using capsaicin, which causes degeneration and permanent loss of peptidergic neurons in neonates and temporary peptide depletion in adult animals. The corneas of neonatally denervated BALB/c mice were observed for capsaicin-induced keratitis at 11-14 wk of age and were then infected bilaterally with herpes simplex virus 1 (HSV-1); trigeminal (TG) ganglia were cocultivated 6 wk later to establish the rate of latent infection. We also applied capsaicin eye drops to adult BALB/c mice that had been infected with HSV-1 6 wk earlier, and measured viral shedding before, and 3 days and 2 months after, administration of capsaicin drops; TG ganglia of these animals were cocultivated at 3 days and 2 months after capsaicin application. Neurotrophic keratitis was found in 81% of neonatally denervated animals; mortality rate due to HSV-1 infection was reduced from 80% in the controls to 24% in the capsaicin-treated group, and recovery of latent virus by cocultivation was reduced by 50%. Viral shedding could not be produced by capsaicin eye drops in adult animals infected with HSV-1. However, recovery of latent virus was significantly reduced in TG ganglia sampled 3 days and 2 months after capsaicin drops were instilled. Our findings suggest 1) that peptidergic fibers play a crucial role in the establishment of trigeminal HSV-1 latency and 2) that reactivation of latently infected ganglia can be inhibited by topical capsaicin.     

Studies on two strains of Plasmodium cynomolgi in New World and Old World monkeys and mosquitoes

Infections that cause the Gombak and Smithsonian strains of Plasmodium cynomolgi were induced in Macaca mulatta, Aotus lemurinus griseimembra, Aotus nancymai, and Saimiri boliviensis monkeys. Transmission of the Gombak strain to Aotus spp. monkeys was obtained by the injection of sporozoites dissected from the salivary glands of experimentally infected Anopheles dirus and by the bites of infected An. dirus and Anopheles farauti mosquitoes. Two S. boliviensis monkeys were infected via the injection of sporozoites dissected from An. dirus. Prepatent periods in New World monkeys ranged from 14 to 44 days, with a median of 18 days. The Smithsonian strain was transmitted via sporozoites to 1 A. lemurinus griseimembra and 9 A. nancymai monkeys. Prepatent periods ranged from 12 to 31 days.     

The 106-kilobase plasmid of Salmonella braenderup and the 100-kilobase plasmid of Salmonella typhimurium are not necessary for the pathogenicity in experimental models

Among 1.041 clinical isolates (77 serovars) of Salmonella which had been derived from cases with acute enterocolitis, 601 (58%) contained one or more plasmids. Large serovar-specific plasmids were seen in 95 of 307 isolates (31%) of Salmonella typhimurium, in 34 of 34 isolates (100%) of Salmonella enteritidis and in 36 of 38 isolates (94.7%) of Salmonella braenderup: the sizes of which were 100, 60 and 106 kilobases (kb), respectively. In order to determine the role of these plasmids in pathogenicity for enterocolitis, the plasmids were eliminated from some strains of S. braenderup and S. typhimurium and the pathogenicity of the plasmid-less strains was compared with that of the parent strains by invasiveness to HeLa cells, fluid accumulation in the rabbit ligated ileal loop, lesion of mucosal tissue and the Sereny test. The virulence of all the plasmid-less strains was as strong as that of the plasmid-bearing strains in these pathogenicity assay systems. We therefore concluded that the 106-kb plasmid of S. braenderup and the 100-kb plasmid of S. typhimurium are not necessary for their pathogenicity in the experimental models: invasiveness to HeLa cells, fluid accumulation in the rabbit ligated ileal loop, and Sereny test.     

Reticuloendotheliosis Virus Nucleic Acid Sequences in Cellular DNA

Reticuloendotheliosis virus 60S RNA labeled with (125)I, or reticuloendotheliosis virus complementary DNA labeled with (3)H, were hybridized to DNAs from infected chicken and pheasant cells. Most of the sequences of the viral RNA were found in the infected cell DNAs. The reticuloendotheliosis viruses, therefore, replicate through a DNA intermediate. The same labeled nucleic acids were hybridized to DNA of uninfected chicken, pheasant, quail, turkey, and duck. About 10% of the sequences of reticuloendotheliosis virus RNA were present in the DNA of uninfected chicken, pheasant, quail, and turkey. None were detected in DNA of duck. The specificity of the hybridization was shown by competition between unlabeled and (125)I-labeled viral RNAs and by determination of melting temperatures. In contrast, (125)I-labeled RNA of Rous-associated virus-O, an avian leukosis-sarcoma virus, hybridized 55% to DNA of uninfected chicken, 20% to DNA of uninfected pheasant, 15% to DNA of uninfected quail, 10% to DNA of uninfected turkey, and less than 1% to DNA of uninfected duck.     

Production of quail (Coturnix japonica) germline chimeras by transfer of gonadal primordial germ cells into recipient embryos

The possibility of producing quail germline chimeras by the transfer of gonadal primordial germ cells (gPGCs) into recipient embryos was investigated. Japanese quail of the black (D: homozygous for the autosomal incomplete dominant gene D) and wild-type plumage (WP: d+/d+) strains were used as donors and recipients, respectively. Gonadal cells were retrieved from the gonads of 5-day-old D embryos, and gPGCs were enriched by magnetism-activated cell sorting. Fresh (noncultured) gPGCs or those isolated after culture for 3 days with gonadal stromal cells present in the mixed cell population were introduced into the dorsal aorta of 2-day-old recipient WP embryos. Hatchability of the recipient embryos was 23.7% (31/131) and 34.4% (31/90) for those transfused with cultured or noncultured gPGCs, respectively. Of the hatched quail, 28 acquired sexual maturity; among these animals, 7.1% (1/14) and 21.4% (3/14) of those that received cultured or noncultured gPGCs, respectively, were proved to be germline chimeras. The percentage of germline transmission to the donor-derived gametes in the chimeras that received cultured and noncultured gPGCs were 1.9 and 2.2-4.7%, respectively. In conclusion, quail gPGCs retrieved from 5-day-old embryos were thus transmitted in the germline after their transfer to quail embryos of a different strain. This property of the gPGCs was not adversely affected by culture for up to 3 days.     

The strain-specific dynamics of Escherichia coli O157:H7 faecal shedding in cattle post inoculation

This study reports analysis of faecal shedding dynamics in cattle for three Escherichia coli O157:H7 (ECO157) strains (S1, S2 and S3) of different genotype and ecological history, using experimental inoculation data. The three strains were compared for their shedding frequency and level of ECO157 in faeces. A multistate Markov chain model was used to compare shedding patterns of S1 and S2. Strains S1 and S2 were detected seven to eight times more often and at 10⁴ larger levels than strain S3. Strains S1 and S2 had similar frequencies and levels of shedding. However, the total time spent in the shedding state during colonization was on average four times longer for S1 (15 days) compared to S2 (4 days). These results indicate that an ECO157 strain effect on the frequency, level, pattern and the duration of faecal shedding may need to be considered in control of ECO157 in the cattle reservoir.     

Long-Term Shedding of Influenza Virus,Parainfluenza Virus,Respiratory Syncytial Virus and Nosocomial Epidemiology in Patients with Hematological Disorders

Respiratory viruses are a cause of upper respiratory tract infections (URTI), but can be associated with severe lower respiratory tract infections (LRTI) in immunocompromised patients. The objective of this study was to investigate the genetic variability of influenza virus, parainfluenza virus and respiratory syncytial virus (RSV) and the duration of viral shedding in hematological patients. Nasopharyngeal swabs from hematological patients were screened for influenza, parainfluenza and RSV on admission as well as on development of respiratory symptoms. Consecutive swabs were collected until viral clearance. Out of 672 tested patients, a total of 111 patients (17%) were infected with one of the investigated viral agents: 40 with influenza, 13 with parainfluenza and 64 with RSV; six patients had influenza/RSV or parainfluenza/RSV co-infections. The majority of infected patients (n = 75/111) underwent stem cell transplantation (42 autologous, 48 allogeneic, 15 autologous and allogeneic). LRTI was observed in 48 patients, of whom 15 patients developed severe LRTI, and 13 patients with respiratory tract infection died. Phylogenetic analysis revealed a variety of influenza A(H1N1)pdm09, A(H3N2), influenza B, parainfluenza 3 and RSV A, B viruses. RSV A was detected in 54 patients, RSV B in ten patients. The newly emerging RSV A genotype ON1 predominated in the study cohort and was found in 48 (75%) of 64 RSV-infected patients. Furthermore, two distinct clusters were detected for RSV A genotype ON1, identical RSV G gene sequences in these patients are consistent with nosocomial transmission. Long-term viral shedding for more than 30 days was significantly associated with prior allogeneic transplantation (p = 0.01) and was most pronounced in patients with RSV infection (n = 16) with a median duration of viral shedding for 80 days (range 35–334 days). Long-term shedding of respiratory viruses might be a catalyzer of nosocomial transmission and must be considered for efficient infection control in immunocompromised patients.     

病毒感染后的实验小鼠对植入的肿瘤细胞抑制作用的实验研究

昆明鼠或ＤＢＡ／２鼠腹腔植入Ｓ１８０肉瘤细胞。Ｐ３８８白血病细胞或Ｆｒｉｅｎｄ白血病细胞后１００％死亡。然而在小鼠感染ＰＲ８株甲型流感病毒、ＮＤＶ或Ｍ１４病毒２５天左右的恢复期腹腔接种上述三种恶性肿瘤细胞时,３０～９５％的小鼠能抑制肿瘤发生而存活。另外,自然感染鼠痘而存活的小鼠,在其感染恢复期内接种上述肿瘤细胞,小鼠的存活率可达１００％,而相应的禾感染鼠痘组小鼠１００％死于肿瘤。病毒感染恢复期小鼠的抗肿瘤作用机制是机体非特异性肿瘤免疫机能强化所致。我们的结果表明,病毒恢复期Ｔ细胞的杀肿瘤作用增强并伴有巨噬细胞数量增加及其吞噬活性增加的现象。本研究的结果提示,自然或人为地非致病病毒感染有利于机体清除变异细胞或肿瘤细胞,对肿瘤发生有一定的防护作用。     

Salmonella fecal shedding and immune responses are dose- and serotype- dependent in pigs

Despite the public health importance of Salmonella infection in pigs, little is known about the associated dynamics of fecal shedding and immunity. In this study, we investigated the transitions of pigs through the states of Salmonella fecal shedding and immune response post-Salmonella inoculation as affected by the challenge dose and serotype. Continuous-time multistate Markov models were developed using published experimental data. The model for shedding had four transient states, of which two were shedding (continuous and intermittent shedding) and two non-shedding (latency and intermittent non-shedding), and one absorbing state representing permanent cessation of shedding. The immune response model had two transient states representing responses below and above the seroconversion level. The effects of two doses [low (0.65×10(6) CFU/pig) and high (0.65×10(9) CFU/pig)] and four serotypes (Salmonella Yoruba, Salmonella Cubana, Salmonella Typhimurium, and Salmonella Derby) on the models' transition intensities were evaluated using a proportional intensities model. Results indicated statistically significant effects of the challenge dose and serotype on the dynamics of shedding and immune response. The time spent in the specific states was also estimated. Continuous shedding was on average 10-26 days longer, while intermittent non-shedding was 2-4 days shorter, in pigs challenged with the high compared to low dose. Interestingly, among pigs challenged with the high dose, the continuous and intermittent shedding states were on average up to 10-17 and 3-4 days longer, respectively, in pigs infected with S. Cubana compared to the other three serotypes. Pigs challenged with the high dose of S. Typhimurium or S. Derby seroconverted on average up to 8-11 days faster compared to the low dose. These findings highlight that Salmonella fecal shedding and immune response following Salmonella challenge are dose- and serotype-dependent and that the detection of specific Salmonella strains and immune responses in pigs are time-sensitive.