Which factors influence the outcome of experimental infection with Cystoisospora suis?

For reliable predictions of clinical and parasitological outcome of experimental infections with parasites, different models must be evaluated for possible influences of infection time point, infection dose and host-specific parameters such as breed or litter size. To address these issues for Cystoisospora (syn. Isospora) suis, the causative agent of porcine neonatal coccidiosis, 181 piglets from 90 litters (hybrid crosses of different breeds) were included in a retrospective study to evaluate differences in time point and dose of infection in four different experimental models ((1) 1,500 oocysts on the 4th day of life, d.o.l.; (2) 1,000 oocysts, 4th d.o.l.; (3) 1,000 oocysts, 1st d.o.l.; (4) 5,000 oocysts, 4th d.o.l.). The target variables body weight gain, faecal consistency and oocyst excretion were evaluated during the acute phase of infection (5-10 days post infection), and the influences of the dependent variables breed or litter size were estimated. Despite differences in the time course of excretion and faecal consistency, neither the average amount of excretion nor the average faecal consistency differed among models, breeds or litters of different size. High individual variability was seen in all four models as described earlier for higher infection doses. When infections on the 1st vs. 4th day of life were compared, no differences in averages could be found, in contrast to previous observations on the influence of age. Other, not yet defined, variables appear to have a greater impact on the outcome of infection than doses and time points in the tested range, despite the reliable outcome of infection with high excretion rates and signs of clinical disease.

Prevalence of Eimeria bovis and Eimeria zuernii in German cattle herds and factors influencing oocyst excretion.

The present study was designed to investigate the prevalence of the pathogenic coccidia species Eimeria bovis and Eimeria zuernii in shed-reared animals in German dairy and fattening facilities. Samples were obtained from 65 cattle farms distributed randomly across all the regions of Germany regardless of the occurrence of clinical problems. The samples were obtained rectally. Faecal consistency and the total number of oocysts per gram of faeces (OPG) were determined, along with the OPG values for E. bovis and E. zuernii. A questionnaire was completed for each farm to record information about herd size and management, along with individual animal data. Eimeria oocysts were detected in 62 of these farms, which give a prevalence of 95.4%. The farm prevalence of the pathogenic species was 76.9% for E. bovis and 83.1% for E. zuernii. The number of oocysts excreted could not be correlated significantly with farm type or farm management but depended on the floor type, the age of the calves and the time after rehousing. Furthermore, there was a positive correlation between OPG and the observation of diarrhoea. E. zuernii had a greater influence on the occurrence of diarrhoea than E. bovis. This study confirms that herd management frequently does not meet the requirements of effective coccidia control despite the fact that the pathogenic coccidia E. bovis and E. zuernii are ubiquitous in German cattle populations.

Necrotic enteritis due to simultaneous infection with Isospora suis and clostridia in newborn piglets and its prevention by early treatment with toltrazuril.

In this study, 51 piglets originating from five different sows were included in the investigations. The animal source of all sows had a history of Clostridium perfringens type A (ß2) infection. The piglets of three sows (n = 31) were experimentally infected with Isospora suis within the first 4 h after birth and were randomly assigned to the treatment group or the sham-dosing group. The piglets of the two remaining sows (n = 20) served as I. suis-uninfected controls. Twelve hours post-infection, the animals in the treatment group (n = 15) were treated with toltrazuril (20 mg/kg BW, Baycox® 5% suspension). During an observation period of 14 days faecal consistency, faecal oocyst counts, faecal germ counts, mortality, body weight development and clinical status were recorded. One piglet per study group and litter was necropsied, and intestinal tissue samples were taken for histopathological investigations and in situ hybridisation on study days (SDs) 3 and 14. I. suis-infected but untreated piglets showed clinical disease resulting in liquefaction of faeces and decreased body weight development. In 59.2% of the observations, I. suis-infected but untreated piglets showed abnormal faecal consistencies whereas only 12.0% or respectively 4.4% of the faecal samples had a pasty consistency in the I. suis-infected-treated or in the control animals. The mean body weight at the end of the study was 3.37 kg in the I. suis-infected but untreated piglets while the average body weight in the I. suis-infected-treated animals was calculated as 4.42 kg and the control animal's mean body weight was 4.45 kg. Moreover, mortality, occurring between SDs 8 and 14, in this study group was 38.5% (n = 5), with 30.8% (n = 4) died from necrotic enteritis. In contrast, no piglets died in the I. suis-uninfected control group or in the toltrazuril-treated study group. The results of this study corroborate the hypothesis that simultaneous infection with I. suis and C. perfringens type A soon after birth leads to distinct interactions between the two pathogens and result in an increase in clinical disease, mortality and metabolically active C. perfringens type A.

Efficacy of sulfonamides and Baycox(®) against Isospora suis in experimental infections of suckling piglets.

Sulfonamide treatment of piglets against neonatal coccidiosis has frequently been suggested in the literature. In order to evaluate the efficacy of sulfonamides against experimental Isospora suis infections in suckling piglets (oral infection with 1,500 sporulated oocysts of I. suis per piglet on the fourth day of life), two trials were conducted. In trial I, oral sulfadimidine (group Sulfa-Oral) was applied in doses of 100 mg/kg of body weight (BW) 1 day before infection and 75 mg/kg BW daily for the following 5 days, and sulfamethoxypyrimidine (SMP) was applied parenterally in daily doses of 75 mg/kg BW for the same time period. In trial II, SMP was applied parenterally in doses of 75 mg/kg BW (a) from the day of infection daily for 7 days (SMP-Standard), (b) for 2 days starting on the day of infection (SMP-Early), (c) for 3 days starting 2 days post-infection (d.p.i.; SMP-Middle), (d) for 2 days starting 5 d.p.i. (SMP-Late), and (e) every other day from the day of infection until 6 d.p.i. (SMP-Alternating), as well as (f) orally in doses of 75 mg/kg BW from the day of infection for 7 days (SMP-Oral). The sulfonamide-treated groups were compared to a toltrazuril-treated group (single oral treatment with Baycox® 5% suspension, 20 mg/kg BW 2 d.p.i.) and to a water-treated Control group. Each group consisted of seven to nine piglets. The parameters evaluated were oocyst excretion and fecal consistency/diarrhea from 4 to 15 d.p.i. Sulfa-Oral, SMP-Early, and SMP-Late had no significant effect in reduction of oocyst excretion and diarrhea, whereas treatment for 3-7 days with SMP reduced both parasite shedding and diarrhea significantly. Oral treatment with SMP was comparable to parenteral application. Baycox® in a single application had the most pronounced effect and completely suppressed oocyst excretion and diarrhea during the examination period. It could be shown that repeated application of sulfonamides, provided that the appropriate time period after infection is covered, can in principle be used to control piglet coccidiosis; however, the amount of work required is considerable, and the practicability is poor. Due to the short half-life of sulfonamides in pigs and the lack of predictability of the time point of infection, an efficient application of sulfonamides to control piglet coccidiosis under field conditions appears unlikely. Baycox®, on the other hand, applied once during the prepatent period of infection, had a lasting effect and can be used to most effectively control I. suis.

Prevalence of Eimeria bovis and Eimeria zuernii in German cattle herds and factors influencing oocyst excretion.

The present study was designed to investigate the prevalence of the pathogenic coccidia species E. bovis and E. zuernii in shed-reared animals in German dairy and fattening facilities.Samples were obtained from 65 cattle farms distributed randomly across all the regions of Germany, regardless of the occurrence of clinical problems. The samples were obtained rectally. Faecal consistency and the total number of oocysts per gram of faeces (OPG) were determined for Eimeria spp., along with the separate OPG values for Eimeria (E.) bovis and E. zuernii. A questionnaire was completed for each farm to record information about herd size and management together with individual animal data. Eimeria oocysts, regardless of the kind of Eimeria spp., were detected in 62 of these farms, which gives a prevalence of 95.4 %. The farm prevalence of the pathogenic species was 76.9 % for E. bovis and 83.1 % for E. zuernii. The average oocyst excretion level was 2,950 OPG in terms of total Eimeria spp. oocyst excretion, 700 OPG for E. bovis and 1,500 OPG for E. zuernii.The number of oocysts excreted could not be correlated significantly with farm type or farm management but depended on the floor type which influences the infection pressure, on the age of the calves and the time after rehousing. In general, higher oocyst excretion rates were found in calves kept on litter compared to rearing on slatted floor. Younger calves and calves sampled early after housing shed higher amounts of oocysts than older calves and calves stabled a longer period before sampling, respectively. Furthermore, there was a positive correlation between OPG and the observation of diarrhoea, defined as observation of a loose to liquid faecal consistency. Excretion of E. zuernii oocysts was more closely linked to the occurrence of diarrhoea than E. bovis oocyst excretion. This study confirms that the pathogenic coccidia E. bovis and E. zuernii are ubiquitous in German cattle populations and a significant cause of diarrhoeal disease in calf rearing.

Age, not infection dose, determines the outcome of Isospora suis infections in suckling piglets.

Data from 13 trials involving 124 suckling piglets experimentally infected with Isospora suis were evaluated for the effects of infection dose and age on the clinical and parasitological outcome of infection in four different models, infections with 1,000 oocysts on the 1(st) day of life (d.o.l.) (model 1; 9 piglets/3 litters), 1,000 oocysts on the 4(th) d.o.l. (model 2; 25 piglets/11 litters), 1,500 oocysts on the 4(th) d.o.l. (model 3; 40 piglets/20 litters) and 10,000 oocysts on the 4(th) d.o.l. (model 4; 50 animals/10 litters). Weights were determined on the day of birth and in weekly intervals. Faecal consistency and quantitative oocysts excretion were evaluated for 2 weeks starting 4 days after infection (d.p.i.). The weight gain depression was most noticeable in model 2 (infection on the 1(st) d.o.l.), where animals only gained 2.08 x their birth weight until the 22(nd) d.o.l., compared to 2.31-2.52 x in the other groups. This correlated with the occurrence of watery diarrhoea which was found in 37 % of the samples in the acute phase (4-11 d.p.i.) in model 2 but only in 12-20 % of the samples in the other models. Median oocyst excretion peaked earlier in the models with higher infection doses but reached the highest values in model 2 (early infection). As in previous studies, this cross-sectional analysis of a larger number of animals confirms the influence of age on the outcome of isosporosis in suckling piglets, stressing the need to control the infection at an early life phase.

Study of the comparative efficacy of toltrazuril and diclazuril against ovine coccidiosis in housed lambs.

A blinded, controlled and randomised field study was conducted on a sheep farm with a known history of coccidiosis and a high prevalence mainly of the pathogenic coccidium Eimeria ovinoidalis. The efficacy of treatment with toltrazuril (Baycox 5% suspension) against natural infections with Eimeria crandallis and/or Eimeria ovinoidalis in housed lambs was investigated in comparison with diclazuril and untreated controls. Both drugs were administered either metaphylactically (i.e., in the prepatency of Eimeria spp.) or therapeutically (after onset of oocyst excretion). A total of 145 animals aged 1 to 5 days at the start of the study were included. Examination of faecal samples was performed every second day between days 13 and 49 of the study. The assessment of treatment efficacy was based mainly on total oocyst excretion and the number of E. crandallis and E. ovinoidalis oocysts (OPG) shed throughout the study. Oocyst excretion was reduced significantly in both groups treated with toltrazuril compared with the untreated control group and with both diclazuril-treated groups. The most prevalent and most severe diarrhoea was observed in the untreated control group. In this study, toltrazuril proved to be highly effective in controlling ovine coccidiosis both metaphylactically and therapeutically. The efficacy of toltrazuril was significantly higher than the efficacy of the control substance with regard to the duration and amount of oocyst excretion, both for the comparison of metaphylactic as well as therapeutic treatment.

Porcine coccidiosis--investigations on the cellular immune response against Isospora suis.

Porcine neonatal coccidiosis is caused by the protozoan Isospora suis and affects mainly piglets in the first three weeks of life. High morbidity with diarrhoea and reduced weight gain lead to economic losses, affecting pig-breeding worldwide. Infection causes damage of the mucosal surface in the jejunum and ileum and transient non-haemorrhagic diarrhoea. Secondary infections with other enteric pathogens may lead to increased mortality. Despite its economic and veterinary importance, the immunology of porcine isosporosis is still poorly understood. A striking feature of the infection is the rapidly increasing age resistance prohibiting the development of clinical disease in piglets older than 3-4 weeks irrespective of the immune status. It can be hypothesised that the development of the innate immune system in the first weeks of life and subsequently its interplay with the adaptive immune system is closely related to this phenomenon. Infections with I. suis induce migration of TcR-gammadelta(+) cells to the gut during primary infection and lead to induction of IFN-gamma production by TcR-gammadelta(+) cells and CD4(+) T-helper cells in blood and various lymphoid tissues. Like in other coccidial infections both innate as well as adaptive response mechanisms are activated during infection. They might be both not completely developed in the first weeks of life and therefore leaving a time frame for successful infection.

W A A V P guideline for evaluating the efficacy of anticoccidials in mammals (pigs, dogs, cattle, sheep).

This guideline is intended as an aid in the design, implementation and interpretation of studies for the assessment of drug efficacy against Eimeria in cattle and sheep, Cystoisospora in pigs and dogs, and Cryptosporidium in cattle. It deals with the most important aspects of how to conduct both experimental and field studies for dose determination, dose confirmation and assessment of field effectiveness. Also, guidance on the selection of animals, diagnostic techniques, statistical evaluation and methods for the preparation, maintenance and use of parasites is provided. The specific management conditions that may influence the course of natural infections and consequently determine treatment schemes are mentioned and suggestions for best practice in sampling and evaluation of data prior to conducting of efficacy studies are given. The guideline is also intended to assist investigators in carrying out specific studies, provide relevant information for registration authorities involved in the decision-making process, assist in the approval of anticoccidial drugs in the target species, and facilitate the world-wide adoption of standard procedures. Although currently not implemented, issues of drug resistance testing and alternative methods for drug testing are also discussed as future issues in drug testing against mammalian coccidia.

Ovine coccidiosis in housed lambs in Saxony-Anhalt (central Germany).

The course of coccidiosis in lambs and the species of Eimeria involved were investigated in Saxony-Anhalt, Germany. A field study was conducted on three farms (conventional lamb-fattening farms) with 59 lambs. A total of 1092 faecal samples were taken during a period from about two to seven weeks after birth; the Eimeria species involved were determined in 415 of these samples and morphometrical characteristics of oocysts of 12 Eimeria spp. were recorded. Subclinical to moderate clinical coccidiosis was observed on all the farms and infections with Eimeria spp. were detected in all study lambs. 12 Eimeria species were identified on two of the farms (A and C): E. ahsata, E. bakuensis, E. crandallis, E. faurei, E. granulosa, E. intricata, E. marsica, E. ovinoidalis, E. pallida, E. parva, E. punctata and E. weybridgensis. The majority of these species were also detected on farm B, with the exception of E. granulosa, E. intricata and E. punctata. To our knowledge this is the first reported occurrence of E. punctata in Germany. Specimens with 3, 4 and 5 Eimeria spp. were the most common. E. ovinoidalis predominated in the faecal samples which underwent oocyst differentiation (> 90% positive samples on each farm). This species also accounted for the generally high oocyst counts observed. Since even subclinical coccidiosis may entail economic losses in lamb-rearing and considering the high prevalence of the pathogenic species E. ovinoidalis, appropriate monitoring of the disease in these farms is advisable.

Parasitological and morphological findings in porcine isosporosis after treatment with symmetrical triazintriones.

Neonatal porcine isosporosis is known to cause serious economic losses in piglet farms by causing severe enteritis with dehydration, weight loss and reduced development in the affected animals, predominantly during the first weeks of life. In the present study, piglets experimentally infected with Isospora suis were treated with Bay Vi 9143, a symmetrical triazintrione, at different days post-infection. As shown by clinical and pathological examinations, Bay Vi 9143 is effective against the asexual and sexual stages of I. suis at all selected treatment times. However, the therapeutic use at an early stage of asexual multiplication is most effective before the onset of clinical symptoms.