Influence of inoculation dose, inoculation schedule, chicken age, and host genetics on disease susceptibility and development of resistance to Eimeria tenella infection

Various parasite- and host-related factors influencing disease susceptibility and development of protective immunity against Eimeria tenella infection were investigated in two inbred strains of chickens. Chickens that received a primary inoculation of 10(3), 10(4), or 10(5) oocysts showed a significant reduction in packed cell volume and produced significantly more oocysts than chickens inoculated with fewer oocysts. Younger chickens were as susceptible as older chickens to identical parasite doses. However, upon a secondary inoculation 5 weeks following primary inoculation, FP chickens 1 to 21 days old at the time of primary inoculation developed resistance to reinfection, whereas SC chickens less than 3 weeks old at the time of primary inoculation were highly susceptible to secondary infection. Flow cytometric analysis of spleen lymphocytes showed a substantial reduction in T-cell number in 1-day-old SC but not FP chickens. Furthermore, 1-week-old SC chickens showed depressed mitogenic responses to concanavalin A compared with 1-week-old FP chickens. There was no significant difference between SC and FP chickens in speen B-cell number, regardless of age.     

Spatial variation in the parasite communities and genomic structure of urban rats in New York City

Brown rats (Rattus norvegicus) are a globally distributed pest. Urban habitats can support large infestations of rats, posing a potential risk to public health from the parasites and pathogens they carry. Despite the potential influence of rodent‐borne zoonotic diseases on human health, it is unclear how urban habitats affect the structure and transmission dynamics of ectoparasite and microbial communities (all referred to as “parasites” hereafter) among rat colonies. In this study, we use ecological data on parasites and genomic sequencing of their rat hosts to examine associations between spatial proximity, genetic relatedness and the parasite communities associated with 133 rats at five sites in sections of New York City with persistent rat infestations. We build on previous work showing that rats in New York carry a wide variety of parasites and report that these communities differ significantly among sites, even across small geographical distances. Ectoparasite community similarity was positively associated with geographical proximity; however, there was no general association between distance and microbial communities of rats. Sites with greater overall parasite diversity also had rats with greater infection levels and parasite species richness. Parasite community similarity among sites was not linked to genetic relatedness of rats, suggesting that these communities are not associated with genetic similarity among host individuals or host dispersal among sites. Discriminant analysis identified site‐specific associations of several parasite species, suggesting that the presence of some species within parasite communities may allow researchers to determine the sites of origin for newly sampled rats. The results of our study help clarify the roles that colony structure and geographical proximity play in determining the ecology of R. norvegicus as a significant urban reservoir of zoonotic diseases. Our study also highlights the spatial variation present in urban rat parasite communities, indicating that rats across New York City are not reservoirs for a homogenous set of parasites and pathogens. As a result, the epidemiological risks may be similarly heterogeneous for people in urban habitats.     

Lewis rats are not susceptible to oral infection with Mycobacterium avium subsp. paratuberculosis

Pathogenesis studies of Mycobacterium avium subsp. paratuberculosis infection in ruminants are hampered by the long incubation time of the disease. A laboratory animal model with a shorter incubation time would facilitate research in this field. Although small rodents are usually considered to be resistant to M.a. paratuberculosis infection, several susceptible murine strains have been found. To our knowledge, there are no detailed reports with regard to susceptibility in rats. The Lewis rat is a valuable model for inflammatory bowel disease studies as well as autoimmune diseases involving mycobacteria as inducing agents. In this study Lewis rats were used to investigate their potential as a small laboratory animal model for paratuberculosis.In total 28 female Lewis rats were orally inoculated with M.a. paratuberculosis. The rats were first inoculated at 3 weeks of age, and 12 more inoculations followed in increasing intervals during the 3 months to follow. Eight control rats received a sham inoculation. Over 9 months, two rats from each group were sacrificed at regular intervals and immunological and histopathological examinations were performed on the gastrointestinal tract, the liver and the spleen.None of the rats developed lesions which were indicative of mycobacterial infection as determined by histology with HE and Ziehl-Neelsen staining. The bacteria could not be recultured from samples taken from the gut, the liver or the spleen. The immunological tests however, showed that bacteria had entered via the intestinal tract. From this study it appears that Lewis rats are resistant to oral inoculation with M. a. paratuberculosis, and not suitable as a model to study the immunopathogenesis of paratuberculosis as it occurs in ruminants.     

Gallid-1 herpesvirus infection in the chicken. 3. Reinvestigation of the pathogenesis of infectious laryngotracheitis in acute and early post-acute respiratory disease

Specific-pathogen-free chickens were infected via the trachea when 4 weeks old with 2000 plaque-forming units (PFU) of the virulent Australian infectious laryngotracheitis (ILT) virus strain CSW-1. Titers of ILT virus in the trachea were greatest (10(7.0) PFU/ml in washings, 10(6.0) PFU/g of tissue) 2-4 days postinfection (PI). Infectivity then declined rapidly, to become undetectable by 7 days PI, although highly localized areas of ILT antigen in the tracheal epithelium were occasionally observed by fluorescent antibody staining at 7 and 8 days PI. Tracheal organ cultures established 7 and 8 days PI provided no evidence of latent ILT virus infection at this immediate post-acute stage of pathogenesis. ILT virus was not isolated from peripheral blood leukocytes or lymphoid organs (spleen, bursa, thymus). ILT virus was found in the trigeminal ganglia and/or brain in 14 of 36 chickens (40%) examined between 4 and 7 days after intratracheal inoculation, but it was not in these tissues in five chickens examined at 8 days PI. Virus was also detected at 6 days PI in the trigeminal ganglia in one of five chickens infected by the conjunctival route. These data indicate that the early pathogenesis of ILT (CSW-1) infection frequently involves the tissues of the nervous system. In acute ILT in 4-week-old chickens, interferon-alpha/beta activity was not detectable in serum or tracheal exudates within 14 days PI, but tracheal washings contained significant virus-neutralizing activity by 7 and 8 days PI. In 3-day-old chickens infected via the trachea with 200 PFU of ILT CSW-1, the clearance of ILT virus from the trachea was similar to that observed in 4-week-old chickens, but ILT virus spread systemically to the livers of 20% by 5-7 days PI.     

Quantitative studies of the distribution pattern for <Emphasis Type="Italic">Salmonella</Emphasis> Enteritidis in the internal organs of chicken after oral challenge by a real-time PCR

This research was undertaken to identify and understand the regular distribution pattern for Salmonella Enteritidis (S. enteritidis) in the internal organs of chicken after oral challenge over a 3 wk period. We used a real-time, fluorescence-based quantitative polymerase chain reaction (FQ-PCR) to detect genomic DNA of S. enteritidis in the blood and the internal organs, including heart, liver, spleen, kidney, pancreas, and gallbladder, from chicken after oral challenge at different time points. The results showed that the spleen was positive at 12 h post inoculation (PI), and the blood was at 14 h PI. The organism was detected in the liver and heart at 16 h PI, pancrea was positive at 20 h PI, and the final organ to show a positive results were the kidney and gallbladder at 22 h PI. The copy number of S. enteritidis DNA in each tissue reached a peak at 24 h–36 h PI, with the liver and spleen containing high concentrations of S. enteritidis, whereas the blood, heart, kidney, pancreas, and gallbladder had low concentrations. S. enteritidis populations began to decrease and were not detectable at 3 d PI, but were still present up to 12 d PI in the gallbladder, 2 wk for the liver, and 3 wk for the spleen without causing apparent symptoms. The results showed that the liver and spleen may be the primary sites for S. enteritidis setting itself up as a commensa over a long time after oral challenge. Interestingly, it may be the first time reported that the gallbladder is a site of carriage for S. enteritidis over a 12 d period. This study will help to understand the mechanisms of action of S. enteritidis infection in vivo.     

A study of the distribution patterns and levels of Salmonella enteritidis in the immune organs of ducklings after oral challenge by serovar-specific real-time PCR

The objective of this study was to understand the distribution patterns and levels of Salmonella Enteritidis (SE) in the immune organs of ducklings after oral challenge. We conducted serovar-specific real-time polymerase chain reaction (PCR) for SE to detect the genomic DNA of SE in the blood and immune organs, including the bursa of Fabricius, thymus, spleen, and Harderian gland, from ducklings after oral challenge at different time points. The results showed that SE was consistently detected in all the samples. The Harderian gland and spleen tested positive at 8 hr postinoculation (PI). The organism was detected in the blood, bursa of Fabricius, and thymus at 10 hr PI. The copy number of SE DNA in each tissue reached a peak at 24-36 hr PI. The spleen, blood, and Harderian gland contained high concentrations of SE, whereas the thymus and bursa of Fabricius had low concentrations. SE populations began to decrease and were not detectable at 2 days PI, but they were still present up to 9 days PI in the spleen, without producing any apparent symptoms. To validate these results, the indirect immunofluorescent antibody (IFA) technique was used, and the IFA results were similar to those of the fluorescent quantitative-PCR. In conclusion, the results provided insight into the SE life cycle in the immune organs; furthermore, the Harderian gland and spleen were determined to be the primary sites of invasion among the immune organs of normal ducklings after oral SE challenge. This study will help in understanding the pathogenesis of SE infection in vivo and may help in the development of a live Salmonella vaccine in the future.     

The histopathogenesis of paralytic rabies in six-week-old C57BL/6J mice following inoculation of the CVS-11 strain into the right triceps surae muscle

A fatal encephalomyelitis was developed after intracerebral and hind limb inoculation of in 6-week-old C57BL/6J mice by the inoculation of fixed rabies virus (CVS-11 strain), intracerebrally and into hind. After the intracerebral inoculation, virus antigens were detected in the cerebral cortex and hippocampus at 2 days postinoculation (PI), and later spread centrifugally to thalamus, brain stem, cerebellum, spinal cord and spinal ganglia. At 4 days PI, severe apoptosis and DNA fragmentation were observed in the hippocampus and cerebral cortex. All mice infected intracerebrally were dead without limb paralysis at from 10 to 11 days PI. In contrast, mice infected with virus intramuscularly were persistently observed virus antigens in the myocytes at the site of inoculation from 2 days PI. At 4 days PI, the antigens were demonstrated in the spinal dorsal root ganglia, spinal cord and muscle spindles without their detection in the cerebrum and hippocampus. There were no apoptosis in the spinal cord and dorsal root ganglia, however hind limb paralysis was found in all infected mice. Hind limb paralysis was progressed to quadriparalysis, and mice were dead from 11 to 13 days PI. From 4 days PI, necrosis of neuron was observed in the the spinal and dorsal ganglia with infiltration of lymphocyte. This study suggested that the necrosis of spinal neurons was more important to cause the paralysis of hind limb rather than the severe cerebral infection and apoptosis in C57BL/6J mice infected with CVS-11 strain. The virus primarily replicated in the muscles was ascended the spinal cord via afferent fibers and retrogradely invaded the cerebrum, and with subsequent spread to muscle spindles.     

The role of serum and biliary antibodies and cell-mediated immunity in the clearance of S. typhimurium from chickens

The development of three parameters of immunity in response to a non-lethal infection of $\text{Salmonella typhimurium}$ in adult chickens has been examined. Intravenous inoculation of 1 × 10⁶ organisms established infection in the liver, spleen and intestinal tract of all birds; the organism persisted in these sites until day 9 of the infection, after which it was cleared rapidly from all sites. High levels of agglutinating and haemagglutinating antibodies were found in serum and bile 5 days after infection; they peaked at days 7 to 10, and detectable antibody was still present in both fluids 6 weeks after infection. The presence of this antibody did not appear to cause a significant reduction in organism numbers in any of the sites examined. Cell mediated immunity was detected at day 14. It is suggested that cell mediated immunity is responsible for clearance of the organisms from the tissues.     

Comparative microscopic lesions in reoviral and staphylococcal tenosynovitis

Experimental inoculation of 1-day-old male broiler chickens with avian reo-virus or Staphylococcus aureus caused tenosynovitis of the gastrocnemius and digital flexor tendons. Reovirus inoculation by either the oral or footpad route initiated a diffuse lymphocytic infiltration in the peritendineum, synovial membrane, and epitenon from 1 to 5 weeks postinoculation (PI). Heterophils were not a predominant feature of the inflammatory response, but when present they were localized with fibrin in and around synovial spaces. The prevalence of microscopic tendon lesions was less common with staphylococcal infection than with reovirus infection. With staphylococcus, lesions were localized to the synovial space and membranes and were characterized by heterophils and fibrin but few lymphocytes. Synovial cell hyperplasia and bursal atrophy were common in both groups. From 10 to 20 weeks PI, both groups developed progressive tendon fibrosis. These results indicate that tenosynovitis due to inoculation with reovirus or staphylococcus may be differentiated histologically from 1 through 5 weeks PI. After 10 weeks, this may not be possible, because diffuse fibrosis was the major lesion with both. Perhaps fibrosis predisposes older, heavier broilers to tendon failure and rupture.     

Adenosine deaminase activity in serum, erythrocytes and lymphocytes of rats infected with Leptospira icterohaemorrhagiae

Leptospirosis is a systemic disease of humans and domestic animals, mainly dogs, cattle and swine. The course of human leptospirosis varies from mild to severe fatal forms and the most severe form of human leptospirosis is principally caused by Leptospira interrogans serovar icterohaemorrhagiae (L. icterohaemorrhagiae). The enzyme adenosine deaminase (ADA) plays an important role in the production and differentiation of blood cells. The aim of this study was to evaluate the activity of ADA in serum, erythrocytes and lymphocytes of rats infected with L. icterohaemorrhagiae, as compared with non-infected rats. Twenty-four adult rats, divided into two uniform groups (A and B) were used for the enzymatic assays. The animals in Group B were inoculated intraperitoneally with 2×10(8) leptospires/rat, and the rodents in Group A (control) were not-inoculated. Blood collection was performed on days 5 and 15 post-infection (PI) and the blood used to assess the ADA activity. The infection by L.icterohaemorrhagiae altered erythrocyte count, hemoglobin concentration and hematocrit, causing a decrease in all these parameters on day 15 PI. Lymphocytes decreased significantly on day 15 PI, and ADA activity in serum was inhibited in infected rats on days 5 and 15 PI and its activity in erythrocytes were increased on day 5 PI. On day 5 PI, we found an increase in ADA activity in erythrocytes of infected rats. No correlation was observed between hematocrit and erythrocyte ADA activity on days 5 and 15 PI. The ADA activity was inhibited in rats infected on day 15 PI. A positive correlation (r(2)=60) was also observed between the number of lymphocytes and ADA activity in lymphocytes on day 15 PI (P<0.05). In conclusion, our results showed that the ADA activity is altered in serum, lymphocytes and erythrocytes in experimental infection by L.icterohaemorrhagiae in rats, concomitantly with hematological parameters.     

Dynamics and responsiveness of T-lymphocytes in secondary lymphoid organs of rabbits developing immunity to Eimeria intestinalis

Primary infection with Eimeria intestinalis confers very effective immunity against further infections in rabbits. This study was designed to determine the onset of the immune response in primary-infected rabbits and to characterise the immune status of protected rabbits. Variations in kinetics of CD4+ and CD8+ T-cell subpopulations were followed after primary infection at the intestinal sites of penetration (duodenum) and development (ileum), in mesenteric lymph nodes (MLN) and in the spleen. The response against the parasite was measured by specific lymphocyte proliferation in the spleen and MLN and by determining specific IgG titres in serum. The mucosal immune response was strong after primary infection and was characterised by (i) transient increase in the percentages of intestinal CD4+ lymphocytes and MLN CD8+ lymphocytes 14 days PI and (ii) strong increase in the percentages of intestinal CD8+ lymphocytes from 14 days PI persisting throughout further infections. Extensive infiltration of the lamina propria with CD8+ lymphocytes was observed 14 days PI. The specific proliferative response started between 7 and 14 days PI in MLN but remained undetectable in spleens for up to 21 days, in contrast to “immunised” rabbits. The fact that systemic immune responses were low after primary infection, in contrast to indicators of mucosal immune responsiveness, suggests that protection of rabbits against E. intestinalis infection is due to an effective mucosal immune response, and that systemic responses that increase after successive infections are only reflections of repeated encounters with parasite antigens.     

Failure of imidocarb dipropionate to clear experimentally induced Ehrlichia canis infection in dogs

The recommended treatment for canine ehrlichiosis is tetracycline or its analog doxycycline, although recent reports have documented ineffective clearing of Erchlichia canis after doxycycline administration. Imidocarb dipropionate is used as an alternative treatment to tetracycline or is used in conjunction with doxycycline. The effectiveness of imidocarb dipropionate in clearing Ehrlichia species from the blood and tissues of dogs with E. canis infection has not been thoroughly evaluated. Fifteen dogs were experimentally infected with E. canis. Ten dogs were treated with imidocarb dipropionate (6.6 mg/kg, IM, 2 injections given 2 weeks apart). Five infected control dogs were not treated. Blood samples from all 15 dogs were E. canis DNA positive by PCR assay by 3 weeks after inoculation (PI), and E. canis antibodies were detected by IFA assay by 1 week PI. Blood platelet counts in all dogs were below the reference interval by 4 weeks PI. E. canis DNA was detected in bone marrow and splenic aspirates by PCR assay 4 weeks PI but not before infection. Bone marrow aspirates were E. canis DNA positive by PCR assay in 14/15 dogs, and splenic aspirates were E. canis DNA positive by PCR assay in 13/15 dogs. Blood samples from all treated and control dogs remained positive for E. canis DNA by PCR assay, and platelet counts remained below preinoculation values 13 weeks PI (6 weeks after 2nd treatment). As administered in this study, imidocarb dipropionate did not clear experimental E. canis infection in dogs.     

The early pathogenesis in chicken inoculated with non-pathogenic serotype 2 Marek's disease virus.

A newly cloned serotype 2 Marek's disease virus (MDV), strain ML-6, was inoculated via the nasal cavity in specific-pathogen-free chicks to examine early virus replication and the expression of Marek's disease (MD)-related antigens. Following inoculation, viral intracellular antigens (VIAs) were detected in lymphoid organs (bursas and spleens) between 5 and 14 days post inoculation (PI), in feather follicles between 14 and 30 days PI, and in lungs at 3 days PI by the immunohistopathological staining of avidin-biotin-peroxidase complex method. But, very few VIAs were expressed in the thymuses between 5 and 14 days PI. However, MD tumor-associated surface antigens were not detected in any organs. Viruses were isolated from separated spleen cells at 14 and 30 days PI. Fluorescent antibodies of convalescent sera were also detected after 10 days PI. As most of the VIAs were detectable in B-cells in bursas and spleens. B-cells were considered to be the main first target cells for the serotype 2 MDV infection.     

In vitro and in vivo characterization of avian reoviruses. III. Host factors affecting virulence and persistence

Three avian reovirus isolates (2177, 2035, and 1733) were used to determine the effect of the age of chickens at inoculation on virus virulence and persistence. Groups of specific-pathogen-free leghorns were inoculated with three different reovirus isolates of different levels of pathogenicity at 1 day, 1 week, 2 weeks, 3 weeks, or 4 weeks of age. Tissues were examined for the presence of virus and lesions at regular intervals until 8 weeks postinoculation (PI) and then again at 22 weeks PI. Isolate 1733, which is highly pathogenic, was reisolated from the thymus, trachea, liver, intestine, cecal tonsils, bursa of Fabricius, gastrocnemius tendon, and white blood cells. Microscopic lesions were observed in some tissues, including the thymus, liver, spleen, bursa of Fabricius, and gastrocnemius tendons, when sampled within a 7-day period following inoculation. This isolate persisted and produced microscopic lesions in the gastrocnemius tendons for as long as 22 weeks PI. The isolates of intermediate pathogenicity (2035) or low pathogenicity (2177) were isolated less frequently and from fewer tissues than isolate 1733. Isolate 2035 could be found in the gastrocnemius tendons as long as 7 weeks PI, whereas isolate 2177 was never isolated from the tendons, nor did it produce any notable gross or microscopic tissue changes. Birds inoculated at age 1 week or older with any of the three reovirus pathotypes were more resistant to infection than 1-day-old inoculates, as evidenced by a decrease in virus reisolations and a concurrent reduction in the severity of lesions in selected tissues.     

Bacteriologic and histologic features in mice after intranasal inoculation of Brucella melitensis

OBJECTIVE: To characterize effects of intranasal inoculation of virulent Brucella melitensis strain 16M in mice. ANIMALS: Female Balb/c mice, 6 to 8 weeks old. PROCEDURE: Studies were designed to elucidate gross morphologic lesions, bacterial burden in target organs, and histologic changes in tissues following experimental intranasal inoculation of mice with B melitensis 16M, which could be used to characterize a model for testing vaccine efficacy. RESULTS: Measurable splenomegaly was evident at 3 and 7 weeks after inoculation. A demonstrable increase in splenic colony-forming units (CFU) from infected mice increased over time with increasing dose when comparing inocula of 10(3), 10(4), and 10(5) CFU. Recovery of brucellae from the lungs was possible early in infection with 10(1), 10(3), and 10(5) CFU, but only the group inoculated with 10(5) CFU consistently yielded quantifiable bacteria. At a dose of 10 CFU, few organisms were located in the spleen. Bacteria were recovered up to 140 days after inoculation in mice given 10(3) CFU. At an inoculum of 10(5) CFU, bacterial counts were highest early in infection. Histologic examination of tissues revealed an increase in white pulp and marginal zone in the spleen and lymphohistiocytic hepatitis. CONCLUSION AND CLINICAL RELEVANCE: Changes in the spleen and liver increased with increases in dose and with increased time following intranasal inoculation with B melitensis 16M. Surprisingly, histologic changes were not observed in the lungs of inoculated mice.     

A follow-up of Beagle dogs intradermally infected with Leishmania chagasi in the presence or absence of sand fly saliva

In this study, we compare the development of infection and/or disease in Beagle dogs intradermally infected with Leishmania chagasi, in the presence or absence of Lutzomyia longipalpis saliva, with those of intravenously infected animals.Spleen samples of all the animals inoculated with parasites had positive polymerase chain reaction tests for Leishmania DNA. Positive spleen cultures for Leishmania were detected earlier (P < or = 0.018) and were more frequent (five out of the five animals) in intravenously infected animals than in the intradermally infected animals, in presence (two out of the six animals) or absence (three out of the five animals) of salivary gland lysate of L. longipalpis. Significant increase in serum antibodies against Leishmania was observed only in the intravenously infected group (P = 0.004). In addition, dogs with infection confirmed by isolation of amastigotes or detection of parasite DNA were, nevertheless, negative for anti-Leishmania antibodies up to 5 months or more after infection. Only animals of the intravenously infected group developed progressive decreases in hematocrit (Pearson r = -0.8076, P = -0.0026) and hemoglobin (Pearson r = -0.8403, P = 0.0012) during the infection period. No significant difference in the course of infection was observed between groups of intradermally infected animals. The data presented herein confirms that the intradermal inoculation of dogs with Leishmania produces an asymptomatic form of infection. It also fails to show an advantage in using L. longipalpis saliva as an infection-enhancing agent in experimental canine leishmaniasis.     

Monitoring chronic infection with a field strain of Aleutian mink disease virus

Aleutian mink disease virus (AMDV) readily spread within farmed mink and causes chronic infections with significant impacts for welfare and economy. In the present study a currently circulating Danish AMDV strain was used to induce chronic experimental infection of farmed mink.PCR was used to detect viral DNA in full blood, organs, faeces and oro-nasal swabs weekly for the first 8 weeks and then biweekly for another 16 weeks after AMDV challenge inoculation of wild type mink. The mink (n = 29) was infected and seroconverted 2–3 weeks after AMDV inoculation and AMDV antibodies persisted during the maximum experimental period of 24 weeks. Viraemia and faecal excretion of viral DNA was detected in the mink (n = 29) at various and intermittent time intervals. Excretion of viral DNA in oro-nasal swabs was detected for 1–8 weeks in 21 mink. This highlights the risk of transmitting AMDV between infected farms.PCR was successfully used to detect viral DNA in organs 8, 16 and 24 weeks after AMDV inoculation with only minor differences between these weeks which is of diagnostic interest.This AMDV challenge model was also used to mimic natural infection of susceptible sapphire mink. Four of 6 sapphire mink were infected indirectly via the AMDV inoculated wild type mink whereas the other 2 sapphire mink remained uninfected.     

Primary infection protects pigs against re-infection with Lawsonia intracellularis in experimental challenge studies

In two separate trials pigs were experimentally infected with Lawsonia intracellularis at 5-6 weeks of age followed by antibiotic treatment and resolution of the primary infection and then re-inoculated at 12-13 weeks of age. A treatment-control group of pigs received the primary infection and antibiotic treatment only, and served as control for the antibiotic treatment of the primary infection. A challenge-control group of pigs received the second inoculation dose only at 12-13 weeks of age to control infectivity of the challenge-dose and susceptibility of pigs to L. intracellularis at this age. Pigs were monitored for shedding of L. intracellularis in faeces by PCR, and for the development of antibodies and responses of acute phase proteins in serum. The presence of L. intracellularis antigen in the intestinal mucosa was examined in post mortem samples by immunohistochemistry. In both trials primary infected pigs were protected from infection after challenge inoculation as evidenced by absence of faecal shedding of L. intracellularis, lack of changes in acute phase protein concentrations after challenge and with low levels of bacterial antigen in the intestinal mucosa of re-inoculated pigs comparable to that of the treatment-control pigs. In contrast, challenge-control pigs shed L. intracellularis in faeces, had L. intracellularis antigen extensively present within all layers of the intestinal mucosa and developed a significant acute phase protein response in serum after the experimental infection. The acute phase protein response to L. intracellularis infection was detected as an increased rise in the serum concentrations of C-reactive protein and haptoglobin from day-6 post infection, and increased serum concentrations of haptoglobin were generally seen 2-3 weeks after inoculation both at 5-6 and 12-13 weeks of age. In conclusion substantial protection against L. intracellularis infection was found in the re-inoculated pigs in contrast to the development of infection in age-matched control pigs. The acute phase protein responses reflected both the observed protection against L. intracellularis infection upon secondary challenge and that increased resistance to the infection develops with age.     

Effect of age on the immune response of cattle experimentally infected with Babesia bigemina

Two different age groups of Holstein Friesian cattle were experimentally infected with Babesiabigemina. Calves of group A (6 months old) did not show noticeable symptoms of babesiosis and had relatively low (0.6%) numbers of parasites in their red blood cells (RBCs). Group B calves (1 year old) had typical signs of the disease; parasites were found in 6.6% of their RBCs. Blood from both groups inoculated into splenectomized calves at 3, 6, 12 and 18 months following initial inoculation demonstrated the presence of B. bigemina, while after 22 months no parasites could be demonstrated.The indirect fluorescent antibody (IFA) test detected babesial antibodies at 4–5 days post inoculation (PI) and reached a maximum titre of 1 : 640 at 2 weeks PI. Following challenge at 2–3 months after initial inoculation, the antibody titre rose sharply to 1 : 2560, then decreased gradually but was still detectable 22 months PI. No correlation was found between antibody titre and the presence of the parasite hin the peripheral blood.