Naturally acquired bovine besnoitiosis: Disease frequency, risk and outcome in an endemically infected beef herd.

The recent spread of bovine besnoitiosis warrants further epidemiological investigations to improve the knowledge on disease development. Thus, a 4-year longitudinal open cohort study was conducted in the first German cattle herd naturally infected with Besnoitia besnoiti. At seven herd-visits between 2008 and 2012, fourteen breeding bulls (>1.5 years) and 131 females (>1 year) were examined clinically and serologically. In females, clinical and serological prevalences, incidence and remission rates were determined. In addition, the association of age, antibody levels and number of visible parasitic cysts with clinical and serological outcome was investigated. The seroprevalence (89.4%-100%) and serological incidence rate (140.5 per 100 animal-years) were considerably higher than the clinical prevalence (23.5%-36.6%) and clinical incidence rate (16.7 per 100 animal-years). Of 33 new clinical and 12 new serological cases, only 6.7% (3/45) attracted attention with clinical signs of acute bovine besnoitiosis. The apparent serological remission rate (1.9 per 100 animal-years) was considerably lower than the clinical remission rate (37.3 per 100 animal-years). A median cyst score of <1 and mean immunofluorescent antibody test (IFAT) titre of ≤1,600 over the entire observation period was significantly associated with a negative clinical outcome at the end. Overall cyst score was not significantly associated with serological outcome and age had no significant influence on clinical and serological outcome. Within 4 years, there was a significant reduction in cyst scores and IFAT titres in the same animals, leading to eight clinically and serologically negative animals in the end. Two initially negative animals achieved clinical and apparent serological remission in about 2.5 years. In bulls, the time between herd entry and seroconversion was 7-30 months and the serological incidence rate was nearly identical to the rate in females (142.0 per 100 animal-years). This shows that a high B. besnoiti prevalence leads to infection of bulls within a short time period.

Naturally acquired bovine besnoitiosis: Differential distribution of parasites in the skin of chronically infected cattle.

Bovine besnoitiosis is caused by Besnoitia besnoiti, an apicomplexan parasite closely related to Toxoplasma gondii and Neospora caninum. In the acute stage of besnoitiosis, cattle suffer from pyrexia, swollen lymph nodes, anorexia and subcutaneous edema. In the chronic stage, tissue cysts are formed in a variety of tissues including the skin. Knowledge about the distribution of tissue cysts of different parts of the skin of infected animals is scarce. Four chronically infected cattle were euthanized and skin samples were taken from a total of 77 standardized cutaneous locations per animal. Portions of the dermis were taken, from which DNA was extracted and examined by real-time PCR. Cycle of transition (Ct) values reflecting the amount of parasite DNA in the samples were determined. For statistical analysis, samples were attributed to 11 larger skin regions ('OuterHindlegDistal', 'Rump, ForelegMiddle', 'NoseFrontEars', 'CheekEye', 'SideLowerPart', 'ForelegDistal', 'SideUpperPart', 'LegsInner', 'VentralHeadNeck', 'DorsalNeckWithersBackTail'). While all samples revealed a positive result in three female cattle, only 63.6% (49/77) of the samples of a bull showed positive results. For statistical analysis, a Ct value of 45 was assumed for samples with a negative result. The dams showed median Ct values of 16.1, 17.5 and 19.4, while in skin samples of the bull a median Ct value of 37.6 was observed. To determine the differences in DNA concentrations between different locations of the skin of the animals, a relative Ct (relCt) was determined by subtracting for each animal indv the MedianCtindv from each sample Ct. Analyses of the relCt values showed that the highest relative parasite DNA concentrations were observed in the categories 'OuterHindlegDistal', 'Rump', 'ForelegMiddle' and 'NoseFrontEars'. The relCt values in these categories differed statistically significantly from those determined for the categories 'VentralHeadNeck' and 'DorsalNeckWithersBackTail'. The analysis showed clear differences in the distribution and the detectability of parasite DNA in the skin of cattle infected with B. besnoiti. In all four animals, samples from the 'Rump' region (Regio fermoris) showed high parasite DNA concentrations. Because this region is also easily accessible for veterinarians, this skin location appears to be optimal for taking skin biopsies for detection or isolation of B. besnoiti.

Novel tools for the diagnosis and differentiation of acute and chronic bovine besnoitiosis.

Diagnosis of acute bovine besnoitiosis is a major diagnostic problem. We developed diagnostic tests to serologically diagnose and differentiate acute and chronic cases of bovine besnoitiosis using affinity purified antigens of Besnoitia besnoiti tachyzoites in immunoblots and in both, a conventional ELISA and an avidity ELISA. Sera of acutely and chronically infected cattle were investigated using these tests. Acutely infected cattle initially recognised an antigen of 74 kDa relative molecular mass, followed by reactions with increasing intensity against 81 and 28 kDa antigens. In addition, faint reactions against antigens with 36, 37, 39 and 42 kDa molecular mass started soon after seroconversion and increased over time. An antigen of 45 kDa molecular mass was transiently recognised early after infection but not or only weakly in the chronic stage. At least two antigens, the 39 and the 42 kDa antigens, seem to be located on the surface of B. besnoiti tachyzoites as determined by biotinylation. Affinity purified antigen was used to establish an APure-BbELISA which showed excellent sensitivity (100%) relative to a serological reference system in naturally, most likely chronically, infected cattle. Specificity was also high (99.8%) as determined in cattle from herds with Neospora caninum-associated abortions. The antibody levels in APure-BbELISA were correlated with the parasite load in the skin or the mucous membrane of the vestibulum vaginae as determined by real-time PCR. In acute cases of bovine besnoitiosis (confirmed by the detection of low avidity IgG in the APure-BbELISA) first specific antibodies were detected by ELISA in all animals except one, at the same time or earlier than in the serological reference system. The detection of parasite DNA in skin by real-time PCR was clearly superior to serological analysis in detecting infected cattle during acute besnoitiosis.

Dynamics of shiga-toxin producing Escherichia coli (STEC) and their virulence factors in cattle.

Starting at birth, twenty Holstein calves were housed individually, in groups of five and finally in one large freestall while fecal samples were collected weekly for 25 weeks. From each sample, twenty isolates of Escherichia coli were screened for 6 virulence markers including shiga-toxin 1, 2, intimin, enterohemolysin, the fimbrial antigen efa1 and the adhesin saa. Dynamic models of transmission of E. coli were used to model the transmission of different virulotypes between calves and the loss of the same virulotypes from the calves. It was found that, once E. coli encoding shiga-toxins in combination with enterohemolysin were transmitted and established in a calf, they tended to be eliminated less efficiently compared to E. coli without this combination of virulence markers. It was concluded that the presence of certain combinations of virulence markers coincided with persistence of E. coli in the bovine gastrointestinal tract. In addition, the combinations of stx with either eae or ehxA in E. coli have a greater impact on the loss rates than on the transmission rates.

Microsatellite typing and avidity analysis suggest a common source of infection in herds with epidemic Neospora caninum-associated bovine abortion.

Neosporosis is an important cause of reproductive failure in cattle worldwide. Two different abortion patterns associated with Neospora caninum infection have been observed in cattle herds: endemic and epidemic abortion outbreaks. The endemic pattern is characterized by an abortion problem in a herd persisting for several months or years, and is assumed to be caused by reactivation of a chronic infection. In epidemic outbreaks, abortions concentrate within a short period of time, most likely due to a recent point source exposure of naïve animals to N. caninum. The aim of the study was to characterize five N. caninum-associated epidemic abortion outbreaks in Germany by serological and molecular techniques, including a p38-avidity-ELISA and typing of N. caninum in clinical samples by multilocus-microsatellite analysis. DNA extracts from the brain of 18 N. caninum infected fetuses from epidemic abortion outbreaks were characterized using 10 N. caninum-microsatellite markers. Nested-PCR protocols were developed to amplify the marker regions MS1B, MS3, MS5, MS6A, MS6B, MS7, MS12 and MS21 from clinical samples for subsequent analysis by capillary electrophoresis. Microsatellites MS2 and MS10 were analyzed by previously reported sequencing techniques. Most dams which had aborted showed a low-avidity IgG response to the N. caninum p38-antigen, and in three of the five studied herds, the majority of the dams at risk, which had not aborted, had also low-avidity responses suggesting that infection with N. caninum had recently occurred in most animals. A common microsatellite pattern prevailed in all fetuses from each individual epidemic outbreak. This pattern was unique for each herd. Although the number of epidemic abortion outbreaks analyzed was limited, the observation of a common microsatellite pattern, accompanied by a low-avidity IgG response against N. caninum in the dams, supports the hypothesis of a recent infection from a common point source. The genetic diversity of N. caninum observed among these outbreaks may indicate that not a particular N. caninum genotype but the horizontal infection route determines the occurrence of epidemic abortions.

Molecular comparison of Neospora caninum oocyst isolates from naturally infected dogs with cell culture-derived tachyzoites of the same isolates using nested polymerase chain reaction to amplify microsatellite markers.

Neospora caninum infection is an important cause of bovine abortion. The infection can be transmitted transplacentally or by ingestion of oocysts shed by definitive hosts. There are few reports of dogs naturally shedding N. caninum oocysts and only some oocyst isolates were transferred into cell culture. The aim of the present study was to analyse N. caninum oocysts from the faeces of naturally infected dogs using a microsatellite-based typing technique and to compare them with cell culture-derived tachyzoites of the same isolates. To this end, N. caninum oocysts from six naturally infected dogs were inoculated into gamma-interferon knockout mice. After these mice had developed disease, tissue samples or peritoneal washings from necropsied mice were transferred into cell culture. Nested-PCR techniques were developed for the sensitive and specific amplification of N. caninum microsatellite-containing regions (MS1B, MS2, MS3, MS4, MS5 and MS10). DNA was extracted from oocysts and cell culture tachyzoites of each isolate, followed by amplification and sequence analysis of microsatellite-containing regions. Each parasite isolate examined yielded a unique microsatellite genotype, while no differences were revealed when data for N. caninum oocysts were compared with cultured tachyzoites of the same isolate. Our technique may allow the typing of clinical samples and different strains of N. caninum at the molecular level. This method may prove useful for the identification of infection sources in molecular epidemiological studies.

Characterization of a repetitive DNA fragment in Hammondia hammondi and its utility for the specific differentiation of H. hammondi from Toxoplasma gondii by PCR.

Hammondia hammondi and Toxoplasma gondii are closely related protozoan parasites. Both species use felids as definitive hosts and a broad spectrum of warm-blooded animals as intermediate hosts. Morphologically and serologically, the two parasites are difficult to differentiate. While T. gondii is an important pathogen of humans and a broad range of other vertebrates, disease has not yet been associated with H. hammondi infection. The aim of the present study was to identify and characterize a repetitive DNA fragment in H. hammondi and to evaluate its suitability for diagnostic purposes. With two primers considered to be specific for a 529 bp repetitive DNA fragment in T. gondii, weak products were amplified by polymerase chain reaction (PCR) from genomic DNA from H. hammondi oocysts. These amplicons (of approximately 150, 300 and 450 bp) were sequenced. The 292 bp consensus sequence of these three fragments revealed 84% identity with parts of the 529-bp repeat in T. gondii. Based on this sequence, a pair of primers was selected which amplified products of 98 and 630 bp from genomic DNA from H. hammondi oocysts but not from DNA from T. gondii. The 630-bp product was purified and cloned into a plasmid vector and the consensus sequence determined from seven randomly selected clones; comparison of this sequence with those available in current databases for T. gondii revealed an 84.0-88.1% identity over a length of 529 bp. The sequence data obtained was used for the development of a sensitive PCR which is entirely specific for H. hammondi and incorporates an internal control. The sequence data for the repetitive DNA element of H. hammondi provides a foundation for the design of primers specific to T. gondii, and the future optimisation of conventional and real-time PCR assays for the specific diagnosis of toxoplasmosis in definitive and intermediate hosts.