Cryptosporidium parvum infection in experimentally infected mice: infection dynamics and effect of immunosuppression

The effect of mouse strain, age, sex, and the size of infective dose on the susceptibility to infection with the coccidium Cryptosporidium parvum Tyzzer, 1912 was determined using several murine models. Mice were infected with C. parvum oocysts originally of cervine origin, maintained by repeat passage in calves. All mice in the experimental groups proved susceptible to infection, though this resulted asymptomatic in all cases. C. parvum infection in BALB/c and Porton mice exhibited some variation. BALB/c mice demonstrated a longer prepatent period than Porton mice. They also produced a greater oocyst output over the patent period, though the differences were not statistically significant. Differences were observed between mice infected at either 3 or 4 weeks of age. Prepatent period was shorter in those mice infected at 3 weeks of age, reaching 100% infection rate by day 7 post-inoculation. The patent period was longer in younger mice showing that age at time of infection can modify the oocyst shedding profile. However, no sex related differences in the course of infection were observed. The effect of different infective doses of oocysts was analysed. The three doses used (10(4), 10(5), 10(6)) proved infective for all mice, there were no statistical differences in either prepatent or patent periods, or in the oocyst shedding profiles. Experimental cryptosporidiosis was also induced in cyclophosphamide-immunosuppressed mice. Cyclophosphamide was orally administered by stomach tube at a dose of 50 mg/kg/day starting 10 days before the intragastric inoculation of 10(6) oocysts of C. parvum per mouse and continuing until the end of the experiment. Immunosuppressed mice had a shorter prepatent period, remained infected longer and shed more oocysts than immunocompetent mice. Immunosuppression produced high mortality rates; during the course of the experiment 44% of immunosuppressed-infected and 30% of immunosuppressed-uninfected mice died. There were no deaths in the untreated groups. Differences in the clinical course of the infection were also observed between immunosuppressed and immunocompetent mice; however, some mice recovered without immunosuppression withdrawal.

Characterization of secretory IgA responses in mice infected with Cryptosporidium parvum

Mice inoculated at 5, 21 and 28 days of age with 10(6) or 10(7) Cryptosporidium parvum oocysts became infected but did not exhibit any clinical signs of disease. Specific IgA antibodies were detected in faecal extracts from all infected mice by an indirect immunofluorescent assay. These antibodies first appeared between 11 and 37 days post-infection (dpi) and persisted until the end of the experiment at 55 dpl. They appeared earlier in older mice than in newborn mice. Reduction and resolution of oocyst shedding was not directly related, however, to IgA antibody levels in infected mice. Reactive C. parvum antigens were identified by immunoblotting techniques using faecal and serum samples from infected mice. IgA copro-antibodies reacted specifically with two antigens of 26 and 33 kDa, which were also identified by IgG antibodies in mouse serum. The role of these antibodies in the resolution of infections and the subsequent protection against challenge is unknown.

Infectivity of a Cryptosporidium species isolated from a domestic cat (Felis domestica) in lambs and mice

Two neonatal lambs were inoculated orally with purified Cryptosporidium species oocysts isolated from a farm cat. Oocysts first appeared in the faeces of the two lambs three and 10 days after infection. Two distinct sizes of oocysts were observed in the faeces of both the cat and the lambs, the smaller measuring approximately 5.0 x 4.5 microns and the larger measuring approximately 6.0 x 5.0 microns in diameter. The smaller type predominated. Histological examination of the alimentary tract of the lambs revealed endogenous stages of Cryptosporidium in the epithelial borders of the ileum. In addition, Cryptosporidium oocysts were detected in impression smears from the jejunum, ileum, caecum and colon. Suspensions of 10(3) oocysts from the faeces of the farm cat were inoculated into each of 10 newborn mice and 10(4) oocysts from the two experimentally infected lambs were inoculated into each of 20 newborn mice. Cryptosporidium oocysts were detected in gut homogenates from 19 of the 20 mice inoculated with oocysts from the lambs but in none of the mice inoculated with oocysts from the cat.

Prevalence of specific anti-Cryptosporidium IgG, IgM and IgA antibodies in cat sera using an indirect immunofluorescence antibody test

Sera from 258 healthy and sick domestic and feral cats were screened for specific anti-Cryptosporidium antibodies using an indirect immunofluorescence antibody test (IFA). Sera were positive for IgG, IgM and IgA antibodies in 192 (74%), 84 (32%) and 67 (26%) samples, respectively. Antibody was not detected at dilutions of 1:10 and 1:20 or greater in any of eight specific pathogen-free kittens. IgM and IgA antibody classes were more prevalent in sick than in healthy domestic cats. The presence of IgM and/or IgA antibodies indicated early infection. However, these antibody classes were present in sera from cats either positive or negative for Cryptosporidium infection by faecal examination. Pronounced polar fluorescence was observed in the sporozoites in positive samples under fluorescence microscopy. The higher prevalence of specific anti-Cryptosporidium antibodies and the absence of Cryptosporidium oocysts in faecal samples from some IFA-positive animals suggests that detection of these antibodies in sera from cats could be helpful for the diagnosis of feline cryptosporidiosis.

Neutralisation of Cryptosporidium parvum sporozoites by immunoglobulin and non-immunoglobulin components in serum

Sporozoites of Cryptosporidium parvum were incubated in 1:10 dilutions of immune or non-immune, heat-inactivated lamb serum specimens or serum fractions. The infectivity of treated sporozoites was assessed by inoculating them, per rectum, into five-day-old rats followed by histological examination of their intestines at either three or five days after infection. The infectivity of sporozoites treated with heat-inactivated whole sera was greatly reduced. This neutralisation had both specific and non-specific components. The former was associated with the IgG fraction of hyperimmune serum raised against sporozoites and the latter with a heat-stable, non-dialysable component present in both IgG-depleted hyperimmune serum and uninfected gnotobiotic serum.

Comparison of staining and concentration techniques for detection of Cryptosporidium oocysts in cat faecal specimens

Modified Ziehl-Neelsen (MZN), auramine-phenol (A-P) and fluorescein isothiocyanate-labelled (FITC-labelled) monoclonal antibody (MAb) techniques were compared for detection of Cryptosporidium parvum oocysts in cat faecal specimens inoculated with known numbers of C. parvum oocysts. Of the three techniques, the FITC-labelled MAb technique detected more oocysts than the MZN and A-P techniques (P < 0.05), but A-P was more efficient than MZN (P < 0.05). Comparison of sucrose flotation, zinc sulphate (ZnSO4) flotation and formol-ether (F-E) sedimentation techniques revealed that F-E was the most efficient of the three (P < 0.05) for concentration of C. parvum oocysts from cat faecal specimens. On average, the F-E technique recovered 37% of oocysts from the original sample, whereas the sucrose and ZnSO4 flotation techniques recovered 33% and 11%, respectively. The findings of this study suggest that MZN and A-P staining are both useful for screening C. parvum oocysts in cat faecal materials containing 10(6) oocysts or more, but FITC-labelled MAb should be used when the number of oocysts is low. Also, the F-E sedimentation technique is recommended for concentrating oocysts in cat faecal specimens.

Cryptosporidium infection in cats: prevalence of infection in domestic and feral cats in the Glasgow area

A clinical and post mortem survey of domestic and feral cats in the Glasgow area revealed that 19 of 235 (8.1 per cent) were infected with Cryptosporidium species. More kittens than adults were infected (P less than 0.01), and of 51 of the cats which had diarrhoea, four also had cryptosporidium infection. Of seven domestic cats with cryptosporidium infection, two were also positive for feline immunodeficiency virus. There was no significant difference between the prevalence of cryptosporidium infection in domestic and feral cats. Cryptosporidium oocysts were detected in faecal and mucosal impression smears stained with auramine-phenol and modified Ziehl-Nielsen techniques. Endogenous developmental stages of cryptosporidium were found in the microvillus region of enterocytes of eight of 19 positive cats in sections stained with haematoxylin and eosin. The results suggest that cryptosporidium infection is common among young and newborn kittens, and that the disease is usually asymptomatic.

Cryptosporidium parvum: investigation of sporozoite excystation in vivo and the association of merozoites with intestinal mucus

Enteric cryptosporidiosis was studied in the small intestine of five-day-old sucking mice after infection with 10(6) Cryptosporidium parvum oocysts. It was shown that excystation and the majority of subsequent endogenous stages occurred predominantly in the ileum. During the first three days of infection the number of merozoites collected in ileal washings increased over 100-fold to approximately 10(6) merozoites per mouse on the third day. In contrast to control mice, wash fluid from infected mice contained numerous strands of dislodged mucus. Estimates of mucus in the ileal washings of infected mice were similar to those made in controls until day 4 after infection when they increased and remained high throughout the remainder of the experiment. This study describes a method whereby ileal mucus washings from C parvum infected infant mice could be used as a rich source of merozoites.

Comparative studies of Babesia spp. from white-tailed and sika deer

Babesia odocoilei from white-tailed deer (Odocoileus virginianus) in Texas (USA) and B. capreoli isolated from sika deer (Cervus nippon) in Ireland were compared morphologically and antigenically. Babesia odocoilei and B. capreoli paired pyriforms resembled each other closely when in sika deer, but B. odocoilei pyriforms in white-tailed deer were slightly different. Babesia odocoilei in white-tailed deer also differed from B. odocoilei and B. capreoli in sika deer in the frequency of its developmental forms. Indirect immunofluorescence antibody test titres showed that there was some antigen cross-reactivity, but not as much as between B. capreoli and the bovine parasite, B. divergens. The Babesia spp. from deer that we studied appear to be distinct but related species. The low infectivity of B. odocoilei for a splenectomised sika deer suggests that sika deer in North America are probably not very susceptible to this parasite in the wild.

In vitro cultivation of Cryptosporidium parvum and screening for anticryptosporidial drugs

Sporozoites of Cryptosporidium parvum which were excysted in vitro from oocysts isolated from calves or patients with acquired immune deficiency syndrome underwent development in monolayers of the mouse fibroblast cell line L929. Asexual multiplication occurred, with the maximum numbers of parasites usually being observed between 24 and 48 h after infection. Gametocytes were also found, but their numbers were relatively small compared with those of the asexual stages. A study was made of the effect on parasite development of 20 antimicrobial agents, most of which were anticoccidial or antimalarial agents. The majority of the drugs had a limited inhibitory effect on parasite development, but usually only at high concentrations. The two most active drugs were monensin and halofuginone, which reduced parasite multiplication by more than 90% at high concentrations. In the case of monensin, however, inhibition of parasite development at higher concentrations was due, at least in part, to a toxic effect of the drug on the host cells.

Analysis of the kinetics, isotype and specificity of serum and coproantibody in lambs infected with Cryptosporidium parvum

Enteric cryptosporidiosis was studied in colostrum-deprived lambs each infected at five days old with 10(6) oocysts. The prepatent period was three to five days and faecal oocyst concentration fell below detectable levels by day 16 after infection. Specific IgA, the only isotype detected by immunofluorescent assay in faecal extracts from infected lambs, was first evident on day 10 and titres continued to rise until day 16 of infection in association with declining oocyst output. Specific IgM and IgG antibodies were first detected in serum seven days after infection. No specific antibody was detected in uninfected control lambs. Immunoblotting methods showed that serum antibody and faecal IgA had similar profiles of antigen recognition. Antigens with approximate molecular weights of 180,000, 23,000 and 15,000 were consistent features on immunoblots performed with convalescent sera and faecal extracts. The results suggest that specific IgA in intestinal secretions has an important role in immunity to cryptosporidiosis.

Trial of a novel experimental Toxoplasma iscom vaccine in pregnant sheep

Fifteen vaccinated ewes (group 1) and 13 unvaccinated ewes (group 2) were each challenged orally with 2000 sporulated Toxoplasma gondii oocysts at 91 (+/- 1) days' gestation. Another four pregnant ewes acted as unvaccinated unchallenged controls. Lamb mortality in group 1 was 36.4% after a mean gestation of 141 days while in group 2 it was 64.7% after a mean gestation of 131.5 days. These differences were not statistically significant. However, substantially more specific antibody was detected in precolostral sera from live lambs from vaccinated ewes than in live lambs from unvaccinated ewes in group 2.

Serodiagnosis of ovine toxoplasmosis: an assessment of the latex agglutination test and the value of IgM specific titres after experimental oocyst-induced infections

The antibody response of 20 pregnant ewes to oocyst infection with Toxoplasma gondii was determined by the latex agglutination test (LAT) and compared with the indirect fluorescent antibody test (IFAT) and a commercially available indirect haemagglutination test (IHAT). The LAT and IFAT showed a similar rapid response with antibody first appearing by two to three weeks after infection and titres that correlated closely (r = 0.81, P less than 0.001). The IHAT response was slower and less consistent up to seven weeks after infection. The LAT response was biphasic in seven of the sheep. Sera were fractionated using a minicolumn gel filtration technique and specific IgM and IgG titres determined by LAT. IgM titres peaked three weeks after infection and IgG titres exceeded IgM titres at a mean time of 4.7 weeks after infection (range 3 to 7). Eleven sheep exhibited fetopathy with abortion/parturition 12 to 53 days after infection; in nine of them IgG titres exceeded IgM at that time. A non-specific anti-toxoplasma reaction associated with IgM antibody occurred at low titre in one sheep. The results indicate that used from a dilution of 1/64 the LAT is a sensitive, reliable and rapidly responsive serological test for toxoplasma infection in ewes and it may be utilised with sample fractionation techniques to determine IgM titres. It is suggested that the best time to examine ewe sera to assist diagnosis of toxoplasma abortion is one week after abortion. While the determination of specific IgM titres in ewe sera may assist epidemiological studies and, sometimes, diagnosis, in the majority of aborting ewe sera it is unlikely to aid diagnosis.

Titration of Toxoplasma gondii oocysts in non-pregnant sheep and the effects of subsequent challenge during pregnancy

Fifty-nine ewes, seronegative to Toxoplasma gondii, were allocated to four groups which received 2000, 200, 20 or no M1 strain toxoplasma oocysts 56 days before mating. Fifty-one of them subsequently became pregnant and were challenged with 10,000 oocysts between 78 and 83 days of gestation. Infection with 2000 oocysts induced a pyrexia, seroconversion and protective immunity in all the recipient animals. Ewes that received either 20 or no oocysts before pregnancy were susceptible to subsequent challenge and severe fetal mortality occurred. In this study 200 oocysts was the threshold value for the induction of toxoplasma infection in sheep, although not all the ewes that seroconverted to this dose were protected against further challenge.

Further studies in the use of monensin in the control of experimental ovine toxoplasmosis

Monensin was fed to 69 pregnant ewes from 81 to 84 days gestation until lambing, at an estimated rate of nil, 16.8 or 27.9 mg per head per day. Ten days after the start of this regime, groups of the ewes were dosed orally with nil, 2000 or 12,000 sporulated Toxoplasma gondii oocysts. Twenty ewes given T. gondii alone (T ewes) produced 29 lambs or aborted foetuses, 16 (55.2 per cent) of which were born dead. The 39 ewes given monensin and T. gondii (M + T ewes) produced 48 lambs or aborted foetuses, 8 (16.7 per cent) of which were born dead. The 10 ewes given monensin alone produced 12 live lambs. No difference of effect was apparent between the two doses of monensin given, nor between the two doses of Toxoplasma oocysts used. Monensin alone caused no discernible problems. Not only were proportionately more live lambs born to M + T ewes than to T ewes, but they were also heavier, possibly due to a lesser "weight" of infection within the gravid uterus. We conclude that monensin fed at about 16 mg per head per day to pregnant ewes can significantly reduce losses at lambing time due to experimentally administered T. gondii.

IFAT detection of IgG specific to toxoplasma in thoracic fluids from aborted lambs: evaluation on routine diagnostic submissions

Thoracic fluids from 171 aborted lambs from 55 flocks were examined by the indirect fluorescent antibody test for the presence of IgG specific to Toxoplasma gondii. The technique was shown to be both sensitive and specific for the diagnosis of toxoplasma abortion at a titre of 1/256, when compared with diagnoses made in the flocks and in the small number of individual fetuses in which the pathology of the cotyledons and the serology of the ewe were known.

Studies of antibody titres in experimentally induced ovine toxoplasmosis

Analysis of serological data from 63 experimentally infected sheep showed an inverse relationship between rise in toxoplasma indirect haemagglutination (IHA) titre after infection and titre at the time of infection. It was observed that, on average, sheep with a preinfection IHA titre of 1:200 or higher did not exhibit a significant rise in titre after infection. The ratio of toxoplasma antibody titres measured by the IHA and dye tests and the ratio of IHA titres in the IgM and IgG antibody fractions were shown to vary according to the duration of infection indicating that serological techniques could be developed to distinguish between latent and acute ovine toxoplasmosis.

Simple technique for the direct isolation of toxoplasma tissue cysts from fetal ovine brain

A simple technique is described for the isolation of Toxoplasma gondii tissue cysts from fetal ovine brain by centrifugation on a discontinuous density gradient of 30 per cent and 90 per cent Percoll (colloidal silica solution). Brain samples from 51 aborted ovine fetuses were examined by both the Percoll and mouse inoculation techniques; eight infections were detected by the Percoll technique compared to 12 by mouse inoculation. Possible reasons for this discrepancy and the scope for improving the Percoll technique are discussed.

Ovine enzootic abortion: the acquisition of infection and consequent abortion within a single lambing season

The spread of enzootic abortion was observed in a flock of 37 unvaccinated Scottish blackface ewes, in mid-pregnancy at the start of the trial. Eight ewes were infected with the ZC 26 strain of chlamydia and allowed to run with 29 untreated controls until lambing was completed. All eight inoculated ewes aborted between 26 and 51 days after infection and chlamydial infection was demonstrated in seven of the abortions. Complement fixing antibodies were not detected in the controls until nine days after the first infected abortion, but within four weeks 69 per cent of the control ewes had developed significant complement fixation titres. Ten of the control ewes lost lambs, chlamydial infection was demonstrated in seven cases, two were undiagnosed and one was attributed to dystocia. The seven infected cases occurred between 69 and 87 days after the start of the trial and coincided with a further rise in the percentage of seropositive controls to a maximum of 90 per cent by the end of lambing.

Response of immune and susceptible ewes to infection with Toxoplasma gondii

Inocula containing 75, 250 or 1000 Toxoplasma gondii tissue cysts were used to infect seronegative gimmers and seropositive ewes in the fourth month of pregnancy. The seronegative gimmers developed typical toxoplasma infections at all dose levels. Four of them aborted and the surviving lambs showed rising indirect haemagglutination titres in the first two to three months of life indicating congenital infection. The seropositive ewes showed no response to challenge, all their lambs survived and there was no serological evidence of congenital infection. Indirect haemagglutination titres in the seropositive ewes remained unchanged throughout the experiment, titres in the gimmers rose sharply from the 10th day after infection and by three months were the same as those in the ewes.

Clinical and serological response of pregnant gimmers to experimentally induced toxoplasmosis

Thirty-five Scottish blackface gimmers in mid or late pregnancy were infected with Toxoplasma gondii by subcutaneous injection of 2000 tissue cysts. Approximately half the gimmers developed a mild febrile response between eight and 10 days after infection but were otherwise unaffected until lambing. Only seven gimmers lambed without loss; in the remainder abortions and neonatal deaths accounted for 27 of the 31 lambs born. These losses occurred predominantly among gimmers which had been infected in mid pregnancy. Antibody titres in the toxoplasma indirect haemagglutination test rose sharply after the 10th day post infection and remained high for over 200 days. The majority of abortions and neonatal deaths occurred after the 40th day post infection by which time mean indirect haemagglutination titres had exceeded 1/320.

Toxoplasmosis in rams: possible significance of venereal transmission

Three rams were infected with tick-borne fever eight months after infection with toxoplasma. There was no clinical evidence of reactivation of the latent toxoplasma infection and semen samples from the rams were not infective to mice. Semen samples from 77 apparently normal rams were tested for toxoplasma infection by passage through mice; none of the samples produced patent infections in mice. Two rams with chronic toxoplasma infection were repeatedly mated with seronegative ewes. None of the ewes showed serological evidence of acquired infection and all lambed satisfactorily.

Experimentally induced toxoplasmosis in young rams: the clinical syndrome and semen secretion of toxoplasma

Six rams were inoculated subcutaneously with 2000 toxoplasma tissue cysts. Semen samples from these rams, and from three uninfected controls, were screened for the presence of infective forms of toxoplasma. Three of the infected rams produced infective semen, each on two occasions, between 14 and 26 days post infection (pi). Five of the infected rams showed a febrile response from the fourth to 10th days pi and their indirect haemagglutination titres rose sharply from 10 days pi; the sixth ram was seropositive before infection and showed no clinical or serological response. In the experimental infection studied there were no symptoms or haematological changes of possible diagnostic value. The production of infective semen was restricted to a brief period shortly after infection although observations were continued for over 90 days. It was concluded that venereal transmission was unlikely to be significant in the spread of ovine toxoplasmosis.

Perinatal changes in lambs infected with Toxoplasma gondii

Twenty-one lambs, born to ewes experimentally infected with Toxoplasma gondii during pregnancy, which were either stillborn or died soon after birth, were examined for pathological changes. In the brain perivascular cuffing by lymphoid cells and distinctive focal inflammation was widespread and common. In addition, focal leucoencephalomalacia, often associated with haemorrhages, was found in almost half the cases examined. The livers from 14 of the lambs displayed large accumulations of lymphoreticular cells in portal triads and foci of extramedullary haemopoietic cells were present in 10. Among other tissues examined the adrenal gland in 14 cases was infiltrated by eosinophils which were often associated with macrophages that contained pigment with the staining characteristics of lipofuscin. In bone marrow the myeloid-erythroid cell ratio was significantly less than that in control animals. It is concluded that intrauterine infection of the ovine fetus with T gondii causes characteristic neuropathological changes in the fetus and that anoxia due to cotyledonary damage plays a significant role in the cause of death.

A serological survey for Babesia in cattle in Scotland. III. The rates of acquisition and loss of antibody to Babesia and their effects on observed levels of antibody incidence

Data for age and the incidence of antibody to Babesia divergens in cattle from areas of high and low endemicity have been analysed using three simple epidemiological models to estimate the rates of gain and loss of antibody. The models adequately described the observations but did not allow for an increased recovery rate attributable to acquired immunity in older animals. The rate of loss of babesial antibody in the absence of challenge was estimated directly from data for age and the incidence of antibody in Irish bred cattle located in nonendemic areas of Scotland. These data suggested an antibody loss rate of 0.25 per annum but did not provide firm evidence for the form of the antibody loss curve. Measurements of the titre of babesial antibody supported the conclusions drawn from studies of antibody incidence. In Irish bred cattle from non-endemic areas titres declined gradually over eight to ten years, whereas in cattle from an area of high endemicity, titres did not change appreciably with age. Cattle tested within one to three months of infection exhibited high titres.

The occurrence of antibody to Babesia and to the virus of louping-ill in deer in Scotland

Sera of wild red deer from 16 localities in Scotland were tested by the indirect fluorescent antibody technique for antibody to Babesia and by the haemagglutination inhibition test for antibody to the virus of louping-ill. Babesial antibody was detected in sera from all localities in proportions ranging from 22 to 100 per cent. Antibody to louping-ill virus could not be demonstrated in sera from five of the localities and in the other 11 was found less frequently than was antibody to Babesia. Sera from male and female deer were positive for louping-ill in almost equal proportions whereas the incidence of babesial antibody was significantly lower in females than in mature males. This difference could be explained by the habits of the deer. The variable occurrence of louping-ill antibody suggested that red deer are tangential hosts for the virus.

The isolation and characterization of a Babesia from red deer (Cervus elaphus)

On three occasions, antibody positive blood from wild red deer produced overt infections with Babesia when inoculated into splenectomized red deer. One of the deer also became infected with Eperythrozoon sp. Babesia divergens, B. capreoli and the Babesia of red deer are morphologically similar and the marginal position of the parasites in the host cell is characteristic. Babesia were not seen and no antibody was formed in five out of six splenectomized bovine calves which were injected with parasitaemic red deer blood. Two of these calves when challenged with B. divergens were fully susceptible. A transient infection with the deer Babesia may have occurred in the sixth calf since antibody was detected and the animal resisted challenge with B. divergens. In indirect fluorescent antibody tests there was little or no difference in the titre of sera from naturally or experimentally infected cattle and deer when reacted with B. divergens or the red deer Babesia antigens. Despite their similarities, specific status for B. divergens and the red deer Babesia is probably justified; at present there is insufficient evidence to justify separation of the red deer Babesia from B. capreoli.