Chemotherapy of human and animal coccidioses: state and perspectives

Generation and Characterization of an Anti-diclazuril Monoclonal Antibody and Development of a Diagnostic Enzyme-Linked Immunosorbent Assay for Poultry

An anti-diclazuril monoclonal antibody (mAb) was developed for use in enzyme-linked immunosorbent assay (ELISA)-based detection of diclazuril with high sensitivity and specificity, which can be used to measure anti-coccidial drug residues. The anti-diclazuril mAb had a half-maximal inhibitory concentration of 0.449–0.517 ng/mL. The mAb cross-reactivity with toltrazuril, toltrazuril 18 sulfone, clozaril, monesin, madurmycin, and salinomycin was very minimal (< 0.1%). The detection limit of the ELISA using this mAb was 0.10 ng/mL and the sensitivity was 0.05 ng/mL. A standard curve generated in the range of 0.05–16.2 ng/mL had a linear correlation coefficient value of ≥ 0.99. The average recoveries of diclazuril from chicken and duck samples ranged from 85.0 to 102.5%.Intra- and inter-assay coefficients of variation ranged from 5.9 to 8.5% and 9.2 to 12.6%, respectively. Using the International Immunogenetics Information System^®, the VH domain of the mAb was found to be encoded by an IGHV3 family gene and had the following complementarity determining region (CDR) sequences: GFTFSRY (CDR1), SRGGS (CDR2), and GDDNYAFAY (CDR3). The VL domain was encoded by an IGKV1 family gene and had the following CDR sequences: KSSQSLLNSRTRKNYLA (CDR1), WASTRES (CDR2), and KQSYNLHT (CDR3). This study provides a method to generate anti-diclazuril mAbs and determine their variable region sequences. The diagnostic ELISA developed using this mAb may drive additional studies on the monitoring and detection of food and veterinary drug residues.

Diclazuril Inhibits Biofilm Formation and Hemolysis of Staphylococcus aureus

Biofilm formation and hemolysis induced by Staphylococcus aureus are closely related to pathogenicity. However, no drugs exist to inhibit biofilm formation or hemolysis induced by S. aureus in clinical practice. This study found diclazuril had antibacterial action against S. aureus with minimum inhibitory concentrations (MICs) at 50 μM for both methicillin-sensitive S. aureus (MSSA) and methicillin-resistant S. aureus (MRSA). Diclazuril (at 1/4× or 1/8× MICs) significantly inhibited biofilm formation of S. aureus under static or flow-based conditions and also inhibited hemolysis induced by S. aureus. The RNA levels of transcriptional regulatory genes (agrA, agrC, luxS, sarA, sigB, saeR, saeS), biofilm formation-related genes (aur, bap, ccpA, cidA, clfA, clfB, fnbA, fnbB, icaA, icaB, sasG), and virulence-related genes (hla, hlb, hld, hlg, lukDE, lukpvl-S, spa, sbi, alpha-3 PSM, beta PSM, coa) of S. aureus were decreased when treated by diclazuril (at 1/4× MIC) for 4 h. The diclazuril nonsensitive clones of S. aureus were selected in vitro by induction of wildtype strains for about 90 days under the pressure of diclazuril. Mutations in the possible target genes of diclazuril against S. aureus were detected by whole-genome sequencing. This study indicated that there were three amino acid mutations in the diclazuril nonsensitive clone of S. aureus, two of which were located in genes with known function (SMC-Scp complex subunit ScpB and glyceraldehyde-3-phosphate dehydrogenase 1, respectively) and one in a gene with unknown function (hypothetical protein). Diclazuril showed a strong inhibition effect on planktonic cells and biofilm formation of S. aureus with the overexpression of the scpB gene.

An epidemiological study of gastrointestinal nematode and Eimeria coccidia infections in different populations of Kazakh sheep

This is an epidemiological study on the gastrointestinal nematode (GIN) and Eimeria coccidia infections in Kazakh sheep and the F1 and F2 generations of Kazakh × Texel sheep crosses. A total of 7599 sheep fecal samples were collected from the Zhaosu County and Nilka County in Ili Kazakh Autonomous Prefecture in the four seasons-spring, summer, autumn, and winter of 2019. The parasite causing the infection was identified by the saturated saline floating method, and the infection intensity was calculated by the modified McMaster method. SPSS19.0 was used to evaluate the differences in the fecal egg count (FEC) of for GIN and the fecal oocyst count (FOC) value of for coccidia per sample. The results showed that there were nine types of sheep GIN infections and Eimeria coccidia in these two counties of Ililocations, with the dominant parasite species of Haemonchus contortus, Trichostrongylus spp., and Ostertagia spp as the predominant parasites in the sheep. Most of the GIN and coccidia infections in these two regions were mild and moderate. The mean log (FEC) of GIN infection in the Zhaosu area was significantly higher than that in the Nilka area, whereas the mean log (FOC) of coccidia infection in Zhaosu was significantly lower than that of Nilka. The mean log (FEC) of GIN infection in the four seasons was the highest in spring, followed by in summer, then in autumn, and the lowest in winter. The mean log (FOC) of coccidia infection was the highest in spring, followed by in autumn, and was the lowest in summer and winter. The mean log (FEC) of GIN infection and log (FOC) of coccidia infection of Kazakh sheep was significantly higher than the F1 generation, which was then significantly higher than the F2 generation of summer. A positive correlation was found between the EPG and OPG levels in the sheep. These results showed that the GIN and coccidia infection intensities of the F1 generation sheep of Kazakh ×Texel crosses were significantly lower than that of Kazakh sheep paving the way for marker-based resistance selection.

Quebracho tannins aid in the control of Eimeria spp. and gastrointestinal nematodes in lambs and goat kids

The objective was to examine the effects of supplementary quebracho on control of coccidiosis and gastrointestinal nematodes in lambs and kids. In Exp. 1, naturally infected lambs weaned (87.8 ± 0.4 days of age; day 0) in January (winter) were blocked by sex and randomly assigned (n = 10/treatment) to receive supplement with or without 100 g/lamb of quebracho for 28 days. In Exp. 2, single or twin rearing ewes were randomly assigned into two groups, and naturally infected lambs were fed control (n = 28) or quebracho (100 g/lamb of quebracho tannins in feed; n = 27) between -28 and 21 days (weaning = day 0; 70.8 ± 0.1 days of age). In Exp. 3, weaned doe kids (57.6 ± 2.0 days of age) were randomly assigned to receive alfalfa (Medicago sativa) supplement with (n = 9) or without (n = 8) 50 g/kid quebracho or sericea lespedeza (Lespedeza cuneata) with quebracho (n = 8) for 21 days. Fecal oocyst count (FOC), nematode egg counts (FEC), fecal score, dag score (soiling around rear quarters), and blood packed cell volume (PCV) were determined every 7 days. Data were analyzed as repeated measures using mixed models. In Exp. 1, FOC decreased in quebracho-fed lambs (diet × time, P < 0.001) but FEC was similar between treatments during the feeding period (P = 0.19). Packed cell volume (P = 0.19) and fecal score (P = 0.42) were similar between groups. Quebracho-fed lambs had a greater dag score initially (diet × time, P = 0.02), but were similar by day 42 (P = 0.72). In Exp. 2, FOC remained low (P = 0.02), PCV tended to decrease (P = 0.06), but FEC increased on days 14 and 21 (diet × time; P < 0.001) in quebracho compared with control-fed lambs. Quebracho-fed lambs had lower fecal score (diet × time; P = 0.005) but higher dag score (diet × time; P < 0.001). In Exp. 3, FOC of kids fed quebracho (alfalfa or sericea lespedeza supplement) was lower than control (P < 0.001). Fecal score of kids fed sericea lespedeza compared with alfalfa were lower regardless of quebracho (P = 0.01). There were no differences among treatments for dag, FEC, PCV, or body weight (P> 0.10). Quebracho was effective in reducing FOC but not clinical signs of coccidiosis in both lambs and kids, and may not be highly digestible in lambs as it caused loose stools.

A novel oil-based suspension of a micro-environmental, pH-modifying solid dispersion for parenteral delivery: Formulation and stability evaluation

The objective of this study was to evaluate a novel oil-based suspension as a potential parenteral drug delivery system for drugs with poor water solubility. Most of the new active pharmaceutical ingredients are weak acid or basic drugs with pH-dependent solubility. To limit this dependence, use of micro-environmental pH-modifying solid dispersions (micro pHm SD) has been proved to increase the bioavailability of these drugs. Toltrazuril (TOL), a weakly acidic drug with poor aqueous and pH-dependent solubility, was studied as a model drug. Recently, studies on TOL with focus on the parenteral injection are rarely to find in the literature. A novel parenteral oil-based TOL suspension was prepared containing TOL micro pHm SD (TSD) powders suspended in oil-based vehicles and the optimal formulation was screened. The stability of this formulation was assessed considering particle size distribution, settling volume ratio, redispersibility, thermal stability, and drug content. The optimized white oil-based TOL pHm SD suspension (W-TSDS) showed significant improved stability and shear-thinning behavior. In particular, fumed silica as suspending agent positively influenced the physical stability of the formulation. Furthermore, W-TSDS showed good injectability using 21 G needles and more rapid and sustained drug release compared to TSD powders in vitro. In the in vivo safety evaluation, W-TSDS showed good histocompatibility in rabbits injected subcutaneously or intramuscularly. We believe these findings provide an alternative choice of dosage form for the delivery of new active pharmaceutical ingredients.

Treatment of Toxoplasmosis and Neosporosis in Farm Ruminants: State of Knowledge and Future Trends

Toxoplasmosis and neosporosis are closely related protozoan diseases that lead to important economic impacts in farm ruminants. Toxoplasma gondii infection mainly causes reproductive failure in small ruminants and is a widespread zoonosis, whereas Neospora caninum infection is one of the most important causes of abortion in cattle worldwide. Vaccination has been considered the most economic measure for controlling these diseases. However, despite vaccine development efforts, only a live-attenuated T. gondii vaccine has been licensed for veterinary use, and no promising vaccines against ne-osporosis have been developed; therefore, vaccine development remains a key goal. Additionally, drug therapy could be a valuable strategy for disease control in farm ruminants, as several drugs that limit T. gondii and N. caninum proliferation and dissemination have been evaluated. This approach may also be relevant to performing an initial drug screening for potential human therapy for zoonotic parasites. Treat-ments can be applied against infections in adult ruminants to minimize the outcomes of a primo-infection or the reactivation of a chronic infection during gestation or in newborn ruminants to avoid infection chronification. In this review, the current status of drug development against toxoplasmosis and neosporo-sis in farm ruminants is presented, and in an effort to promote additional treatment options, prospective drugs that have shown efficacy in vitro and in laboratory animal models of toxoplasmosis and neosporosis are examined

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.

Enrofloxacin and Toltrazuril Are Able to Reduce Toxoplasma gondii Growth in Human BeWo Trophoblastic Cells and Villous Explants from Human Third Trimester Pregnancy

Classical treatment for congenital toxoplasmosis is based on combination of sulfadiazine and pyrimethamine plus folinic acid. Due to teratogenic effects and bone marrow suppression caused by pyrimethamine, the establishment of new therapeutic strategies is indispensable to minimize the side effects and improve the control of infection. Previous studies demonstrated that enrofloxacin and toltrazuril reduced the incidence of Neospora caninum and Toxoplasma gondii infection. The aim of the present study was to evaluate the efficacy of enrofloxacin and toltrazuril in the control of T. gondii infection in human trophoblast cells (BeWo line) and in human villous explants from the third trimester. BeWo cells and villous were treated with several concentrations of enrofloxacin, toltrazuril, sulfadiazine, pyrimethamine, or combination of sulfadiazine+pyrimethamine, and the cellular or tissue viability was verified. Next, BeWo cells were infected by T. gondii (2F1 clone or the ME49 strain), whereas villous samples were only infected by the 2F1 clone. Then, infected cells and villous were treated with all antibiotics and the T. gondii intracellular proliferation as well as the cytokine production were analyzed. Finally, we evaluated the direct effect of enrofloxacin and toltrazuril in tachyzoites to verify possible changes in parasite structure. Enrofloxacin and toltrazuril did not decrease the viability of cells and villous in lower concentrations. Both drugs were able to significantly reduce the parasite intracellular proliferation in BeWo cells and villous explants when compared to untreated conditions. Regardless of the T. gondii strain, BeWo cells infected and treated with enrofloxacin or toltrazuril induced high levels of IL-6 and MIF. In villous explants, enrofloxacin induced high MIF production. Finally, the drugs increased the number of unviable parasites and triggered damage to tachyzoite structure. Taken together, it can be concluded that enrofloxacin and toltrazuril are able to control T. gondii infection in BeWo cells and villous explants, probably by a direct action on the host cells and parasites, which leads to modifications of cytokine release and tachyzoite structure.

The Impact of a Successful Anti-Myxosporean Treatment on the Phagocyte Functions of Juvenile and Adult Sparus Aurata L

The aim of the present study was to investigate the impact of a successful anti-myxosporean medication on the innate immune system of fish intensively cultured in the Mediterranean basin. For this purpose, juvenile and adult gilthead seabream ( S. aurata L.) naturally infected with Polysporoplasma sparis in the kidney were used in a small-scale field trial. The infected fish were treated orally with the combination of salinomycin and amprolium, two drugs well known for their anti-coccidial effect in other animals. Drug efficacy and safety was evaluated in terms of changes observed in histopathology, mortality and P. sparis intensity and prevalence rate. Phagocytic functions of head-kidney leucocytes were also investigated at the end as well as one month post the medication. Salinomycin with amprolium exhibited a significant reduction in intensity and prevalence rate in both juvenile and adult fish, and no histopathological evidence for toxic side effects was observed. In addition, the successful treatment was closely correlated with a complete restoration of the diminished phagocytic ability and capacity as well as NO, and lysozyme secretion in a time dependent manner. This data suggests that salilomycin with amprolium can be an alternative treatment for myxosporean infections in warm-water fish, possibly exhibiting their action through the enhancement of host innate functions.

Expression and identification of the ADF-linker-3-1E gene of Eimeria acervulina of chicken

Coccidiosis is a widely distributed disease with higher mortality and morbidity, which is caused by several species of protozoan parasites belonging to the genus Eimeria and recognized as a serious challenge for the poultry industry. This research was conducted to construct the recombinant plasmid pET32a(+)-ADF-linker-3-1E of Eimeria acervulina (E. acervulina) of the chicken and test the bioactivity of the ADF-linker-3-1E protein. The ADF-linker-3-1E gene of E. acervulina of the chicken was cloned by splicing by overlap extension by the polymerase chain reaction (SOE-PCR) and then inserted into the pET32a(+) to construct the recombinant plasmid pET32a(+)-ADF-linker-3-1E. The recombinant plasmid was transformed into Escherichia coli Rosetta (DE3) competent cells and then induced by IPTG (0.6 mmol/L). The expressed product in the culture medium was identified by the sodium dodecyl sulfate-polyacrylamide gel electrophoresis (SDS-PAGE). The bioactivity of the ADF-linker-3-1E protein was tested by Western blotting. The result showed that the amplified ADF-linker-3-1E gene was about 1346 bp. The PCR amplification with the recombinant plasmid pET-32a(+)-ADF-linker-3-1E as a template resulted in a special band of 1346 bp. The digested products resulted in two fragments of 1346 bp target fragment and 5.9 kb pET-32a(+)-vector fragment. The results indicated that the ADF-linker3-1E gene was successfully inserted into the pET-32a(+)-vector. The expressed products in the culture medium resulted in a single band of approximately 54.8 kDa by SDS-PAGE. Western blotting analysis indicated that the recombinant protein could be reacted specifically with His-Tag(2A8) Mouse mAb. This study indicated that the ADF-linker-3-1E protein with good bioactivity was successfully obtained, which laid a foundation for the exploitation of the nuclear vaccine by using the ADF-linker-3-1E protein.

New Insights into the Understanding of Hepatitis C Virus Entry and Cell-to-Cell Transmission by Using the Ionophore Monensin A

In our study, we characterized the effect of monensin, an ionophore that is known to raise the intracellular pH, on the hepatitis C virus (HCV) life cycle. We showed that monensin inhibits HCV entry in a pangenotypic and dose-dependent manner. Monensin induces an alkalization of intracellular organelles, leading to an inhibition of the fusion step between viral and cellular membranes. Interestingly, we demonstrated that HCV cell-to-cell transmission is dependent on the vesicular pH. Using the selective pressure of monensin, we selected a monensin-resistant virus which has evolved to use a new entry route that is partially pH and clathrin independent. Characterization of this mutant led to the identification of two mutations in envelope proteins, the Y297H mutation in E1 and the I399T mutation in hypervariable region 1 (HVR1) of E2, which confer resistance to monensin and thus allow HCV to use a pH-independent entry route. Interestingly, the I399T mutation introduces an N-glycosylation site within HVR1 and increases the density of virions and their sensitivity to neutralization with anti-apolipoprotein E (anti-ApoE) antibodies, suggesting that this mutation likely induces conformational changes in HVR1 that in turn modulate the association with ApoE. Strikingly, the I399T mutation dramatically reduces HCV cell-to-cell spread. In summary, we identified a mutation in HVR1 that overcomes the vesicular pH dependence, modifies the biophysical properties of particles, and drastically reduces cell-to-cell transmission, indicating that the regulation by HVR1 of particle association with ApoE might control the pH dependence of cell-free and cell-to-cell transmission. Thus, HVR1 and ApoE are critical regulators of HCV propagation.

IMPORTANCE

Although several cell surface proteins have been identified as entry factors for hepatitis C virus (HCV), the precise mechanisms regulating its transmission to hepatic cells are still unclear. In our study, we used monensin A, an ionophore that is known to raise the intracellular pH, and demonstrated that cell-free and cell-to-cell transmission pathways are both pH-dependent processes. We generated monensin-resistant viruses that displayed different entry routes and biophysical properties. Thanks to these mutants, we highlighted the importance of hypervariable region 1 (HVR1) of the E2 envelope protein for the association of particles with apolipoprotein E, which in turn might control the pH dependency of cell-free and cell-to-cell transmission.

Study on the use of toltrazuril to eliminate Neospora caninum in congenitally infected lambs born from experimentally infected ewes

To determine if toltrazuril was effective in eliminating Neospora caninum infection from congenitally infected lambs. Twenty-eight ewes were allocated to 3 groups where animals in Groups A and B were inoculated with 1 × 10(7)N. caninum tachyzoites on Day 120 of gestation and Group C was maintained as a negative control group. Lambs born from ewes in Group A were treated with toltrazuril (20mg/kg) on Days 0, 7, 14 and 21 after birth. Lambs in Groups B and C were untreated. All lambs in Groups A and B were seropositive at 12 weeks of age. At 12 weeks of age, no differences between lambs in Group A and Group B were observed in serological results (ELISA and western blot), presence of N. caninum-related brain histopathological lesions or the number of organisms detected by qPCR. Group C remained negative for serology, detection of N. caninum DNA as well as histopathology throughout the study. Results indicate that N. caninum congenitally-infected lambs had a continuing infection with N. caninum despite being treated with toltrazuril.

Great efficacy of sulfachloropyrazine-sodium against acute murine toxoplasmosis

OBJECTIVE

To identify more effective and less toxic drugs to treat animal toxoplasmosis.

METHODS

Efficacy of seven kinds of sulfonamides against Toxoplasma gondii (T. gondii) in an acute murine model was evaluated. The mice used throughout the study were randomly assigned to many groups (10 mice each), which either remained uninfected or were infected intraperitoneally with tachyzoites of T. gondii (strains RH and CN). All groups were then treated with different sulfonamides and the optimal treatment protocol was determined candidates. Sulfadiazine-sodium (SD) was used for comparison.

RESULTS

The optimal therapy involved gavaging mice twice per day with 250 mg/kg bw of sulfachloropyrazine-sodium (SPZ) for five days. Using this protocol, the average survival time and the time-point of 50% fatalities were prolonged significantly compared with SD treatment. Treatment with SPZ protected 40% of mice from death, and the heart and kidney tissue of these animals was parasite-free, as determined by nested-PCR. SPZ showed excellent therapeutic effects in the treatment of T. gondii in an acute murine model and is therefore a promising drug candidate for the treatment and prevention of T. gondii in animals.

CONCLUSIONS

It can be concluded that the effective drug sulfachloropyrazine may be the new therapeutic options against animal toxoplasmosis.

Biosafety of the plasmid pcDNA3-1E of Eimeria acervulina in chicken

To evaluate the biosafety of the plasmid pcDNA3-1E of Eimeria acervulina in chicken, two-week-old chickens were injected intramuscularly with the plasmid pcDNA3-1E at dose of 50 μg/chicken. At the 15 days post-injection, the tissue samples were collected, the total DNA was extracted, and the 3-1E gene was amplified by PCR. Genomic DNA was first purified away from free plasmid using gel electrophoresis, and then assayed for integrated plasmid using PCR amplification of the 3-1E gene. Simultaneously, the environmental dejection samples were collected, the total bacterial DNA was extracted and then transfer of the pcDNA3-1E gene was detected by PCR amplification of the 3-1E gene. Two-week-old chickens were injected intramuscularly with the plasmid pcDNA3-1E with three dosage groups of 100 μg, 500 μg and 2500 μg/chicken for 14 days respectively, and with physiological saline at dose of 2500 μL/chicken as control group for acute toxicity test. A target band of 583 bp was obtained by PCR with chicken genomic DNA as template. If the chicken genomic DNA was purified, no target band could be obtained. It showed that the recombinant plasmid pcDNA3-1E existed in tissues, and no genomic integration of DNA plasmid was detected in the immunized chickens. No target band was found by PCR with environmental dejection bacteria genomic DNA as template. It showed that integration and transfer phenomenon did not exist in environment. The acute toxicity results showed the typical clinical symptoms did not occur in the inoculated chickens, the blood biochemical indices and viscera configuration were not affected significantly in the inoculated group and control group (P>0.05). The results showed that the plasmid pcDNA3-1E was safe and suitable for chicken clinical trials.

In-vivo efficacy of toltrazuril on experimentally induced Toxoplasma gondii tissue cysts in lambs: a novel strategy for prevention of human exposure to meat-borne toxoplasmosis

The aim of the present study was to investigate in vivo efficacy of toltrazuril on Toxoplasma gondii tissue cysts following induction of chronic toxoplasmosis in 4-week-old lambs (n=27) by inoculation of 1×10(5) T. gondii ME 49 strain oocysts (day 0). Beginning at the 15th day after inoculation, lambs in Group T20 and Group T40 were given toltrazuril orally 2 times, once every week (Baycox 5%, Bayer Animal Health) at a dose of 20 mg/kg and 40 mg/kg, respectively. Positive control (PC) lambs were not given any therapy, and 2 clinically healthy non-infected lambs were used as negative controls (Group NC). Two out of 9 lambs in PC group (oocyst inoculated but non-treated) were killed on toltrazuril treatment days (day 15 and 22) to evaluate the tissue cyst presence in their muscles. On day 90, the remaining 25 lambs were necropsied, and samples from the brain and 11 different muscle groups were collected. The tissues were examined for the presence of tissue cysts by histopathology, immunohistochemistry, nested-PCR and percoll gradient centrifugation. Anti-T. gondii antibodies were screened by IFAT throughout the experiment. The increased T. gondii seropositivity beginning from the 15th day of inoculation remained steady at Day 45 and Day 90 in Groups PC while it was significantly lower at Day 90 in toltrazuril receiving groups. In toltrazuril treated groups, histopathological findings included degenerative changes in the cyst wall, complete macrophage invasion to the cysts, and reduction or removal of the cysts in toto. Four out of 9 lambs (44.4%) in both toltrazuril treated group (Group T20 and T40) did not contain tissue cyst in any examined tissues while all positive control animals had T. gondii tissue cysts at least in one muscle group. The toltrazuril treatment efficacy on the cyst presence was determined as 44.4%. The number of the cysts in the musculature was significantly different between non-treated and toltrazuril treated lambs (X(2)=6.613; p=0.037). For the total number of cysts, the positive control lambs had higher number of cysts compared to both toltrazuril treated lambs (T20 and T40) (X(2)=5.629; p=0.018 and X(2)=5.629; p=0.018, respectively) while there were no differences between Group T20 and Group T40 (X(2)=0.000; p=1.000). According to PCR results, the brain and M. semitendinosus were positive in all 7 control lambs while 12 out of 18 lambs were positive in toltrazuril treated lambs. In conclusion, the results are promising as the toltrazuril treated lambs had markedly less parasite counts compared to those of untreated lambs. Further research should be conducted to reveal if toltrazuril treatment in sheep could be used as a strategy to minimize the cyst exposure of humans through consumption of raw or undercooked mutton.

Analysis of monensin sensitivity in Toxoplasma gondii reveals autophagy as a mechanism for drug induced death

Understanding the mechanisms by which anti-parasitic drugs alter the physiology and ultimately kill is an important area of investigation. Development of novel parasitic drugs, as well as the continued utilization of existing drugs in the face of resistant parasite populations, requires such knowledge. Here we show that the anti-coccidial drug monensin kills Toxoplasma gondii by inducing autophagy in the parasites, a novel mechanism of cell death in response to an antimicrobial drug. Monensin treatment results autophagy, as shown by translocation of ATG8 to autophagosomes, as well as causing marked morphological changes in the parasites' mitochondria. Use of the autophagy inhibitor 3-methyladenine blocks autophagy and mitochondrial alterations, and enhances parasite survival, in monensin-exposed parasites, although it does not block other monensin-induced effects on the parasites, such as late S-phase cell cycle arrest. Monensin does not induce autophagy in a parasite strain deficient in the mitochondrial DNA repair enzyme TgMSH-1 an enzyme that mediates monensin-induced late S-phase arrest. TgMSH-1 therefore either mediates cell cycle arrest and autophagy independently, or autophagy occurs downstream of cell cycle arrest in a manner analogous to apoptosis of cells arrested in G₂ of the cell cycle. Overall, our results point to autophagy as a potentially important mode of cell death of protozoan parasites in response to antimicrobial drugs and indicate that disruption of the autophagy pathway could result in drug resistance.

Genetic reconstruction of protozoan rRNA decoding sites provides a rationale for paromomycin activity against Leishmania and Trypanosoma

Aminoglycoside antibiotics target the ribosomal decoding A-site and are active against a broad spectrum of bacteria. These compounds bind to a highly conserved stem-loop-stem structure in helix 44 of bacterial 16S rRNA. One particular aminoglycoside, paromomycin, also shows potent antiprotozoal activity and is used for the treatment of parasitic infections, e.g. by Leishmania spp. The precise drug target is, however, unclear; in particular whether aminoglycoside antibiotics target the cytosolic and/or the mitochondrial protozoan ribosome. To establish an experimental model for the study of protozoan decoding-site function, we constructed bacterial chimeric ribosomes where the central part of bacterial 16S rRNA helix 44 has been replaced by the corresponding Leishmania and Trypanosoma rRNA sequences. Relating the results from in-vitro ribosomal assays to that of in-vivo aminoglycoside activity against Trypanosoma brucei, as assessed in cell cultures and in a mouse model of infection, we conclude that aminoglycosides affect cytosolic translation while the mitochondrial ribosome of trypanosomes is not a target for aminoglycoside antibiotics.

Rational design of novel therapeutics relies on the knowledge and understanding of potential drug targets. Historically, the majority of therapeutics have not been rationally designed, but empirically discovered. Paromomycin, an aminoglycoside with antibacterial activity, has been found to show considerable activity against leishmaniasis, a disease caused by the protozoan parasite Leishmania. However, the mechanisms of aminoglycoside action against protozoan parasites have in part remained unclear. In this study we demonstrate that the cytosolic ribosome is the preferred drug target, and that the mitochondrial ribosome does not contribute to the antiprotozoal activity of aminoglycosides. As the cytosolic ribosome of Trypanosoma, the causative agent of sleeping sickness and Chagas disease, resembles that of Leishmania, we tested the efficacy of paromomycin against Trypanosoma. We found that paromomycin not only inhibits the growth of Trypanosoma in culture, but also suppresses trypanosomiasis in a mouse infection model. Our results point to the cytosolic ribosome as a promising drug target for antiprotozoal drug development.

Lower respiratory tract infections in cats: reaching beyond empirical therapy

PRACTICAL RELEVANCE

Lower respiratory tract infections (LRTIs) in cats can be due to bacteria, parasites, fungi and viruses. This review details the practical investigation of these infections and highlights specific therapy where possible. The aim is to avoid the all-too-frequent temptation in practice to treat cats with lower respiratory tract signs empirically for feline bronchial disease (FBD)/asthma. This is potentially hazardous as immunosuppressive therapy for FBD/asthma could exacerbate disease due to a LRTI. Empirical treatment of suspected LRTI is also difficult to recommend given the wide range of potential pathogens.

CLINICAL CHALLENGES

Making a clinical ante-mortem diagnosis of LRTI in a cat can be challenging. Consistent historical, clinical, haematological and radiographic abnormalities are often lacking and findings may be non-specific. Astute clinical acumen, thorough investigation and high quality laboratory analysis are usually required for a diagnosis. Bronchoalveolar lavage, if feasible, and tests for lungworm should be routine in cats with lower respiratory tract signs. Lung fine needle aspiration may be useful in cases of diffuse or nodular pulmonary disease. Histopathology is rarely employed in ante-mortem investigations.

EVIDENCE BASE

The authors have reviewed a substantial body of literature to provide information on many of the reported bacterial, parasitic, fungal and viral pathogens, including some that occur in Asia. Attention has been given to specific therapy for each pathogen, with evidence-based comments when there is a deviation from routine recommendations.

Failure of combination therapy with imidocarb dipropionate and toltrazuril to clear Hepatozoon canis infection in dogs

Current treatments with imidocarb dipropionate for infected dogs with Hepatozoon canis do not always provide parasitological cure. The objective of this study is to determine whether concomitant use of toltrazuril may potentiate the effect of imidocarb dipropionate in the management of H. canis infection (HCI). Twelve dogs were determined to have naturally HCI based on clinical signs, identification of the parasite in blood smears, and serologic assay. The animals were allocated randomly to one of two groups (n = 6 in each group). Dogs in Imi group were given imidocarb dipropionate at a dose of 6 mg/kg body weight subcutaneously in two injections 14 days apart. Imi plus Toltra group was given imidocarb dipropionate as dose mentioned above and toltrazuril at 10 mg/kg/day orally for the first five treatment days. Clinical findings, blood counts and parasitaemia levels in blood before and 14, 28 and 56 days after the initial treatment were performed to evaluate treatment response. The overall clinical efficacy of imidocarb dipropionate with and without toltrazuril was 83.3% and 66.7%, respectively; with a mean recovery time of 21.0 and 25.6 days, respectively. A substantial main effect of time on mean PCV, Hb, WBC, neutrophil and PLT and gradual reduction of parasitaemia were significantly observed in both groups (P < 0.05), whereas no significant difference was noticed between the studied protocols. The parasitologic cure rate at the end of eight weekly observation period was 16.6% and 33.3% in Imi and Imi plus Toltra groups, respectively. Similar clinicopathologic and parasitologic responses were observed in both treated groups; thus, it was concluded that toltrazuril does not reveal additional benefit to imidocarb therapy in dogs with HCI.

The antibiotic monensin causes cell cycle disruption of Toxoplasma gondii mediated through the DNA repair enzyme TgMSH-1

Monensin is a polyether ionophore antibiotic that is widely used in the control of coccidia in animals. Despite its significance in veterinary medicine, little is known about its mode of action and potential mechanisms of resistance in coccidian parasites. Here we show that monensin causes accumulation of the coccidian Toxoplasma gondii at an apparent late-S-phase cell cycle checkpoint. In addition, experiments utilizing a monensin-resistant T. gondii mutant show that this effect of monensin is dependent on the function of a mitochondrial homologue of the MutS DNA damage repair enzyme (TgMSH-1). Furthermore, the same TgMSH-1-dependent cell cycle disruption is observed with the antiparasitic ionophore salinomycin and the DNA alkylating agent methyl nitrosourea. Our results suggest a novel mechanism for the mode of action of monensin and salinomycin on coccidial parasites, in which the drug activates an MSH-1-dependent cell cycle checkpoint by an unknown mechanism, ultimately leading to the death of the parasite. This model would indicate that cell cycle disruption is an important mediator of drug susceptibility and resistance to ionophoric antibiotics in coccidian parasites.

Importance of nonenteric protozoan infections in immunocompromised people

There are many neglected nonenteric protozoa able to cause serious morbidity and mortality in humans, particularly in the developing world. Diseases caused by certain protozoa are often more severe in the presence of HIV. While information regarding neglected tropical diseases caused by trypanosomatids and Plasmodium is abundant, these protozoa are often not a first consideration in Western countries where they are not endemic. As such, diagnostics may not be available in these regions. Due to global travel and immigration, this has become an increasing problem. Inversely, in certain parts of the world (particularly sub-Saharan Africa), the HIV problem is so severe that diseases like microsporidiosis and toxoplasmosis are common. In Western countries, due to the availability of highly active antiretroviral therapy (HAART), these diseases are infrequently encountered. While free-living amoebae are rarely encountered in a clinical setting, when infections do occur, they are often fatal. Rapid diagnosis and treatment are essential to the survival of patients infected with these organisms. This paper reviews information on the diagnosis and treatment of nonenteric protozoal diseases in immunocompromised people, with a focus on patients infected with HIV. The nonenteric microsporidia, some trypanosomatids, Toxoplasma spp., Neospora spp., some free-living amoebae, Plasmodium spp., and Babesia spp. are discussed.

Inhibition of Plasmodium sporozoites infection by targeting the host cell

There is a great need of new drugs against malaria because of the increasing spread of parasite resistance against the most commonly used drugs in the field. We found that monensin, a common veterinary antibiotic, has a strong inhibitory effect in Plasmodium berghei and Plasmodium yoelii sporozoites hepatocyte infection in vitro. Infection of host cells by another apicomplexan parasite with a similar mechanism of host cell invasion, Toxoplasma tachyzoites, was also inhibited. Treatment of mice with monensin abrogates liver infection with P. berghei sporozoites in vivo. We also found that at low concentrations monensin inhibits the infection of Plasmodium sporozoites by rendering host cells resistant to infection, rather than having a direct effect on sporozoites. Monensin effect is targeted to the initial stages of parasite invasion of the host cell with little or no effect on development, suggesting that this antibiotic affects an essential host cell component that is required for Plasmodium sporozoite invasion.

Disruption of a mitochondrial MutS DNA repair enzyme homologue confers drug resistance in the parasite Toxoplasma gondii

MutS homologues (MSHs) are critical components of the eukaryotic mismatch repair machinery. In addition to repairing mismatched DNA, mismatch repair enzymes are known in higher eukaryotes to directly signal cell cycle arrest and apoptosis in response to DNA-damaging agents. Accordingly, mammalian cells lacking certain MSHs are resistant to chemotherapeutic drugs. Interestingly, we have discovered that the disruption of TgMSH-1, an MSH in the pathogenic parasite, Toxoplasma gondii, confers drug resistance. Through a genetic selection for T. gondii mutants resistant to the antiparasitic drug monensin, we have isolated a strain that is resistant not only to monensin but also to salinomycin and the alkylating agent, methylnitrosourea. We have shown that this phenotype is due to the disruption of TgMSH-1 as the multidrug-resistance phenotype is complemented by a wild-type copy of TgMSH-1 and is recapitulated by a directed disruption of this gene in a wild-type strain. We have also shown that, unlike previously described MSHs involved in signalling, TgMSH-1 localizes to the parasite mitochondrion. These results provide the first example of a mitochondrial MSH that is involved in drug sensitivity and implicate the induction of mitochondrial stress as a mode of action of the widely used drug, monensin.

NcGRA2as a molecular target to assess the parasiticidal activity of toltrazuril againstNeospora caninum

The treatment ofNeospora caninuminfection in the bovine host is still at an experimental stage. In contrast to thein vivosituation, a wide range of compounds have been intensively investigated in cell-culture-based assays. Tools to demonstrate efficacy of treatment have remained conventional including morphological and cell biological criteria. In this work, we present a molecular assay that allows the distinction between live and dead parasites. Live parasites can be detected by measuring the mRNA level of specific genes, making use of the specific mRNA available in live cells. TheNcGra2gene ofN. caninum, which is known to be expressed in both tachyzoites and bradyzoites, was used to establish a quantitative real-time RT-PCR, for monitoring parasite viability. Validation of the systemin vitrowas achieved usingNeospora-infected cells that had been treated for 2–20 days with 30 μg/ml toltrazuril.NcGRA2-RT-real time PCR demonstrated that a 10-day toltrazuril-treatment exerted parasitostatic activity, as assessed by the presence ofNcGRA2-transcripts, whereas after a 14-day treatment period noNcGRA2-transcripts were detected, showing that the parasites were no longer viable. Concurrently, extended culture for a period of 4 weeks in the absence of the drug following the 14-day toltrazuril treatment did not lead to further parasite proliferation, confirming the parasiticidal effect of the treatment. This assay has the potential to be widely used in the development of novel drugs againstN. caninum, with a view to distinguishing between parasiticidal and parasitostatic efficacy of given compounds.

Epidemiology of parasitic protozoan infections in Soay sheep (Ovis aries L.) on St Kilda

The feral Soay sheep (Ovis aries L.) population on Hirta, St Kilda, is host to a diverse component parasite community, but previous parasitological studies of the population have only focussed on the metazoan species. This paper reports the first epidemiological study of the protozoan species comprising Cryptosporidium parvum, Giardia duodenalis and 11 species of Eimeria in Soay sheep across 3 years of varying host population density. Prevalence and intensity of almost all species of protozoa significantly decreased with host age, with the exception of E. granulosa, which increased in prevalence with host age. The prevalence of C. parvum appeared to vary positively with host population density but that of G. duodenalis did not vary significantly with density. Most species of Eimeria showed a distinct lag in infection level following the host population crash of 2002, taking up to 2 years to decrease. Mixed Eimeria species intensity and diversity were highest in 2002, a year of low host density. Parasite diversity decreased with host age and was higher in males. There were 5 positive pair-wise associations between protozoa species in terms of prevalence. The results of this study highlight the potential for protozoal infection to shape the evolution of parasite resistance in wild host populations harbouring diverse parasite species.

MEDICAL MANAGEMENT OF TOXOPLASMA MENINGITIS IN A WHITE-THROATED CAPUCHIN (CEBUS CAPUCINUS)

A 32-yr-old white-throated capuchin monkey (Cebus capucinus) was presented for paraparesis. A diagnosis of protozoal meningitis was made on the basis of a lymphocytic pleocytosis with elevated protein in cerebrospinal fluid and a positive serum titer to Toxoplasma gondii of 131,072 using an indirect hemagglutination test. Treatment with clindamycin and trimethaprim-sulfamethoxazole resulted in improvement within 3 days and complete clinical resolution within 2 wk.

Biochemical characterization of recombinant dihydroorotate dehydrogenase from the opportunistic pathogenic yeast Candida albicans

Candida albicans is the most prevalent yeast pathogen in humans, and recently it has become increasingly resistant to the current antifungal agents. In this study we investigated C. albicans dihydroorotate dehydrogenase (DHODH, EC 1.3.99.11), which catalyzes the fourth step of de novo pyrimidine synthesis, as a new target for controlling infection. We propose that the enzyme is a member of the DHODH family 2, which comprises mitochondrially bound enzymes, with quinone as the direct electron acceptor and oxygen as the final electron acceptor. Full-length DHODH and N-terminally truncated DHODH, which lacks the targeting sequence and the transmembrane domain, were subcloned from C. albicans, recombinantly expressed in Escherichia coli, purified, and characterized for their kinetics and substrate specificity. An inhibitor screening with 28 selected compounds was performed. Only the dianisidine derivative, redoxal, and the biphenyl quinoline-carboxylic acid derivative, brequinar sodium, which are known to be potent inhibitors of mammalian DHODH, markedly reduced C. albicans DHODH activity. This study provides a background for the development of antipyrimidines with high efficacy for decreasing in situ pyrimidine nucleotide pools in C. albicans.

A newborn mouse Cryptosporidium parvum infection model: its application to the study of therapeutic and prophylactic measures for controlling cryptosporidiosis in ruminants

In this study, a newborn mouse model of Cryptosporidium parvum infection is presented so as to evaluate therapeutic and prophylactic measures for controlling cryptosporidiosis in ruminants. Ninety-six suckling mice from ten litters were used. The mice in group I were infected with C. parvum oocysts, and the mice in group II served as non-infected controls. In both groups, intensity of infection and serum IgG, IgA and IgM responses were measured at 6, 9, 12 and 16 days post-infection (pi). Experimentally induced infection in mice proved to be similar to natural infections in lambs, kids and calves. Thus, the intensity of infection peaked at 9 days pi then decreased slightly, showing its lowest value at 16 days pi. This decline in the number of oocysts coincided with peaks in IgM and IgA. Finally, non-infected mice had no oocysts and did not show any increase in their anti-C. parvum antibody levels.

Obtaining hyperimmune anti-Cryptosporidium parvum ovine colostrum. A study of the humoral immune response in immunized sheep

Three ewes were immunized five times over a 2-month period prior to giving birth by intramuscular injection, oral administration and intramammary infusion of antigen and viable or freeze-dried Cryptosporidium parvum oocyst solution emulsified with Freund's complete and incomplete adjuvant. Two animals served as controls and another two as adjuvant controls. Serum was collected at first immunization and thereafter every 2 to 4 weeks. Colostrum and milk were collected as well. All samples were assayed for C. parvum-specific antibodies using an enzyme-linked immunosorbent assay methodology, and Western blotting was used to recognize the C. parvum antigens. Hyperimmunization resulted in a progressive and significant increase in specific anti-C. parvum serum IgG, IgA and IgM titres, with the highest values noted at the point of lambing. Titres decreased slightly in milk, although they were in all cases higher than those in the control animals. Moreover, some 30 bands of C. parvum were recognized.

Antiparasitic and immunomodulatory effect of innovative treatments against Myxobolus sp. infection in Diplodus puntazzo

The potential antiparasitic and immunomodulatory effect of three treatments against myxosporean parasites on the innate immune system of sharpsnout sea bream (Diplodus puntazzo) was investigated. Fish naturally infected with Myxobolus sp. (Bivalvulida/Platysporina), a histozoic parasite mainly affecting the renal interstitial tissue, were treated by oral administration of a combination of salinomycin with amprolium, Origanum essential oil or fumagillin in a small-scale field trial. Various leucocyte functions influenced by myxosporean infection were examined in order to determine treatment effects on leucocyte immunocompetence of treated fish. One month post treatment all drugs caused a significant decrease in prevalence and intensity of infection in comparison to untreated, infected fish. The effect was most prominent in salinomycin with amprolium treated fish, which 1-month post treatment contained either no cysts at all or a few spores free in melanomacrophage centres revealing almost total elimination of the parasite and the antiparasitic action of the treatment. There was no histopathological evidence of drug toxicity. Antiparasitic action was accompanied by a significant enhancement of phagocytic activity demonstrated by ingestion of large numbers of latex beads and the secretion of high levels of reactive nitrogen intermediates by phagocytes in vitro. Complete restoration of the diminished mitogenic responses and serum lysozyme secretion was also detected in salinomycin with amprolium-treated fish compared to untreated, infected fish. These data suggest that salilomycin with amprolium may be a promising treatment for myxosporean infections in intensively cultured warm-water fish, exhibiting action partially via the enhancement of host, innate immune functions and leading to parasite elimination.

Treatment of mice with the anticoccidial drug Toltrazuril does not interfere with the development of a specific cellular intestinal immune response to Eimeria falciformis

Immunity against Eimeria-infections is highly specific and it depends on cell-mediated effector mechanisms. Infections of BALB/c mice with 1,000 sporulated oocysts of Eimeria falciformis led to protection against challenge infections. Treatment with the anti-coccidium Toltrazuril, during primary infection, terminated the ongoing disease and did not interfere with the establishment of protective immunity against challenge infections. Mesenteric lymph node cells of infected, treated as well as non-treated and challenged BALB/c mice, showed a similar proliferation upon stimulation with parasite antigen. In contrast, neither cells of the Peyer's patches, intraepithelial lymphocytes, nor spleen cells responded to stimulation with parasite antigens. Cells from all compartments and of all investigated groups proliferated and released the cytokines IFN-gamma and IL-4 in response to the mitogen Concanavalin A. The number of cells releasing IFN-gamma or IL-4 was not dependent on the status of infection or previous treatment with Toltrazuril. The serum IgG response against total sporozoite antigens of individual mice showed that in addition, a systemic humoral response developed in infected mice, independent of a previous drug treatment, although the specific IgG antibody concentration was higher in non-treated mice. Thus, Toltrazuril does not impair the parasite specific intestinal cellular and systemic antibody response and does not prevent the development of protection against challenge infection.

ORAL ADMINISTRATION OF HYPERIMMUNE ANTI–CRYPTOSPORIDIUM PARVUM OVINE COLOSTRAL WHEY CONFERS A HIGH LEVEL OF PROTECTION AGAINST CRYPTOSPORIDIOSIS IN NEWBORN NMRI MICE

Hyperimmune anti-Cryptosporidium parvum ovine colostral whey (HOCW) was tested to determine whether it conferred passive immunity to newborn NMRI mice. Three HOCWs (groups IV-VI), 2 nonimmune colostral wheys (groups II and III), and PBS (group I) were administered once (experiment A) and 3 times (experiment B) daily from -1 to 15 days postinfection (PI). Mice in groups I-VI were inoculated with 5 x 10(5) oocysts (day 0 PI), and group VII mice acted as controls. The percentage and intensity of infection were measured at 6, 9, 12, and 16 days PI. In experiment A, HOCW did not reduce significantly the percentage and intensity of infection except for mice in group VI treated with HOCW with the highest titers of anti-C. parvum antibodies. In contrast, no infection was detected in between 18.7 and 62.5% of the mice in groups IV-VI in experiment B. Furthermore, in these groups, the intensity of the infection decreased significantly, ranging from 83.5 to 97.4%. Thus, HOCW did not completely avoid infection, but a high level of protection was observed, being proportional to the titer of specific antibodies and the amount of whey administered orally. Finally, group VII showed no presence of oocysts.

Immunization protocols against Cryptosporidium parvum in ovines: protection in suckling lambs

Ovine colostrum and milk from immunized ewes were tested for their ability to prevent cryptosporidiosis in the lambs experimentally infected with 10(6) oocysts of Cryptosporidium parvum at 36-48 h of age (day 0 post-infection). All lambs became infected and developed clinical cryptosporidiosis. However, lambs fed by immunized dams have shown shedding involved, significantly, fewer oocysts and lasted for a shorter period than in control lambs. In addition, diarrhoea was less severe. The best results emerged in lambs of ewes immunized by intramuscular injection of an emulsion of 2 ml of Freund's complete adjuvant and 2 ml of C. parvum antigen in sterile phosphate buffered saline solution, administrated four weeks before parturition, together with an intramammary infusion of 25 microg of antigen in 2 ml of sterile PBS emulsified in 2 ml of Freund's incomplete adjuvant, which showed the highest anti-C. parvum titres in lacteal secretions. In their case, the onset of output of oocysts was delayed by two days, the patent period was shortened by three days, their diarrhoea continued for only three days, and the quantity of oocysts shed decreased by 77%. The outcome was that at the end of the study they had a live weight gain of 2 kg more than the lambs in the control group. These results indicate that lactogenic immunoprophylaxis should help mitigate the financial losses caused by cryptosporidiosis in small ruminants, as well as reducing the risk of infection of humans through the decreased contamination of the environment with oocysts.

Ponazuril inhibits the development of Eimeria vermiformis in experimentally infected outbred Swiss mice

We evaluated a 15% paste formulation of ponazuril in outbred Swiss mice that were experimentally infected with Eimeria vermiformis. Thirty, 8-week-old female mice (approximately 20 g) were placed in one group of 10 mice and one group of 20 mice. Mice in both groups were gavaged with approximately 5,000 sporulated oocysts of E. vermiformis on day 0. Mice in group 2 (n=10) were treated orally on days 3 and 4 with ponazuril (suspended in 30% propylene glycol) at the rate of 20 mg/kg. Mice in group 1 (n=20) were gavaged with a similar volume of 30% propylene glycol. Rates of oocyst passage (oocysts/g feces) were determined on day 10 (peak patency) for treated and nontreated mice using a fecal aliquot oocyst counting technique. Oocysts were not observed in the feces of treated mice using the aliquot technique. Control mice passaged oocysts at a geometric mean rate of >104,000 oocysts/g feces. Control mice also produced significantly less feces on day 10. These results indicate that ponazuril is effective against E. vermiformis under the conditions utilized in this study, and that the E. vermiformis mouse model could be useful in predicting the efficacy of new anticoccidial drugs.

Two different dihydroorotate dehydrogenases from yeast Saccharomyces kluyveri

Genes for two structurally and functionally different dihydroorotate dehydrogenases (DHODHs, EC 1.3.99.11), catalyzing the fourth step of pyrimidine biosynthesis, have been previously found in yeast Saccharomyces kluyveri. One is closely related to the Schizosaccharomyces pombe mitochondrial family 2 enzymes, which use quinones as direct and oxygen as the final electron acceptor. The other one resembles the Saccharomyces cerevisiae cytosolic family 1A fumarate-utilizing DHODH. The DHODHs from S. kluyveri, Sch. pombe and S. cerevisiae, were expressed in Escherichia coli and compared for their biochemical properties and interaction with inhibitors. Benzoates as pyrimidine ring analogs were shown to be selective inhibitors of cytosolic DHODs. This unique property of Saccharomyces DHODHs could appoint DHODH as a species-specific target for novel anti-fungal therapeutics.

Characterization of Stage-Specific and Cross-Reactive Antigens from Eimeria acervulina by Chicken Monoclonal Antibodies

The characterization of five chicken monoclonal antibodies (mAbs) that were developed against apical complex antigens of Eimeria acervulina sporozoites is realized and the mAbs reactivity to merozoites belonging to this species is tested. Using immuno-fluorescence assay (IFA), one mAb (HE-4) that recognized apical antigens common to sporozoites of E. acervulina and E. brunetti bound antigens localized on the apical tip of merozoites from all stages of development examined. The mAb 8E-1, reactive with antigens found on the apical tip of all chicken Eimeria sporozoites, also showed binding to antigens common to merozoites from all generations. Another mAb, 8C-3, which identified an antigen shared by sporozoites apical tip and sporocysts wall of E. acervulina reacted very weak and inconstantly with the merozoites from all generations whereas the mAbs 5D-11 and 8D-2 that recognized antigens shared by the sporozoites of E. acervulina and E. maxima (mAb 5D-11) and E. acervulina and E. brunetti (mAb 8D-2) did not react with the merozoites from any generation. Collectively, these results showed that the invasive stages of chicken Eimeria share cross reactive apical complex antigens which are inter-species and inter-generation-specific that might be components of a potential recombinant vaccine.

Plant dihydroorotate dehydrogenase differs significantly in substrate specificity and inhibition from the animal enzymes

The mitochondrial membrane bound dihydroorotate dehydrogenase (DHODH; EC 1.3.99.11) catalyzes the fourth step of pyrimidine biosynthesis. By the present correction of a known cDNA sequence for Arabidopsis thaliana DHODH we revealed the importance of the very C-terminal part for its catalytic activity and the reason why--in contrast to mammalian and insect species--the recombinant plant flavoenzyme was unaccessible to date for in vitro characterization. Structure-activity relationship studies explained that potent inhibitors of animal DHODH do not significantly affect the plant enzyme. These difference could be exploited for a novel approach to herb or pest growth control by limitation of pyrimidine nucleotide pools.

Drosophila melanogaster dihydroorotate dehydrogenase: the N-terminus is important for biological function in vivo but not for catalytic properties in vitro

Dihydroorotate dehydrogenase (DHODH, EC 1.3.99.11), the fourth enzyme of pyrimidine de novo synthesis, is an integral flavoprotein of the inner mitchondrial membrane and is functionally connected to the respiratory chain. Here, experiments have been directed toward determining the roles of the N-terminal sequence motifs both in enzymatic properties of insect DHODH produced in vitro and the in vivo function of the protein. Full-length and three N-terminal truncated derivatives of the Drosophila melanogaster enzyme were expressed in Escherichia coli and purified. For identification on Western blots of recombinant DHODH as well as the native enzyme from flies polyclonal anti-DHODH immunoglobulins were generated and affinity-purified. The enzymatic characteristics of the four versions of DHODH were very similar, indicating that the N-terminus of the enzyme does not influence its catalytic function or its susceptibility to prominent DHODH inhibitors: A77-1726, brequinar, dichloroallyl-lawsone and redoxal. Whereas the efficacy of A77-1726 and dichloroallyl-lawsone were similar with Drosophila and human DHODH, that of brequinar and redoxal differed significantly. The differences in responses of insect DHODH and the enzyme from other species may allow the design of new agents that will selectively control insect growth, due to pyrimidine nucleotide limitation. In vivo expression of the full-length and N-truncated DHODHs from engineered transgenes revealed that the truncated proteins could not support normal de novo pyrimidine biosynthesis during development of the fly (i.e., failure to complement dhod-null mutations), apparently due to instability of the truncated proteins. It is concluded that the proper intracellular localization, directed by the N-terminal targeting and transmembrane motifs, is required for stability and subsequent proper biological function in vivo.

Recent advances in the search for new anti-coccidial drugs

Coccidia provide a rich hunting ground for drug-designers, as there are significant biochemical differences between the parasites and their hosts. Recent years have brought the discovery of the plastid and its possible metabolic machinery, characterisation of acidocalcisomes, reports on the apparent absence from some coccidia of a typical mitochondrion, and the discovery of the mannitol cycle and shikimate pathway in the parasites. Moreover, modern technologies such as genomics and proteomics are bringing new insights into the biochemistry of coccidia and highlighting possible drug targets in abundance. A major issue for would-be drug discoverers is to decide upon the targets to prioritise. This review provides an update on recent findings on how coccidia differ biochemically from vertebrates. It includes discoveries within coccidian parasites themselves but also uses findings in Plasmodium to provide an overview of biochemical features that may be characteristics of many apicomplexan parasites and so potential targets for broad-spectrum drugs.

Rheumatic manifestations of parasitic diseases

OBJECTIVES

To consolidate the spectrum and frequency of parasite-related rheumatic syndromes, which have largely been regarded as exceedingly rare by the general medicine, infectious disease, and rheumatology literature.

METHODS

A MEDLINE search was performed for articles on rheumatic syndromes related to parasitic infections published from 1966 through December 2000. Identified articles included clinical and epidemiologic studies describing cases of rheumatic syndromes associated with verified parasitic infection.

RESULTS

Rheumatologic syndromes, including inflammatory arthritis, inflammatory myositis, and vasculitis, have been described among multiple different parasite infections of all parasitic divisions, including Protozoa, Nematoda, and Platyhelminthes. Individual parasitic divisions are often associated with particular rheumatic syndromes, such as reactive arthritis and spondyloarthropathy, inflammatory or infectious myositis, and reactive or parainfectious vasculitis.

CONCLUSIONS AND RELEVANCE

Parasitic infection may underlie the clinical presentation of some rheumatic conditions. Given the continued and growing number of patients at risk for parasitosis by virtue of their country of origin, travel habits, and an immunocompromised state, potential parasitosis must be considered in patients undergoing evaluation for rheumatic complaints.

A plastid segregation defect in the protozoan parasite Toxoplasma gondii

Apicomplexan parasites--including the causative agents of malaria (Plasmodium sp.) and toxoplasmosis (Toxoplasma gondii)--harbor a secondary endosymbiotic plastid, acquired by lateral genetic transfer from a eukaryotic alga. The apicoplast has attracted considerable attention, both as an evolutionary novelty and as a potential target for chemotherapy. We report a recombinant fusion (between a nuclear-encoded apicoplast protein, the green fluorescent protein and a rhoptry protein) that targets to the apicoplast but grossly alters its morphology, preventing organellar segregation during parasite division. Apicoplast-deficient parasites replicate normally in the first infectious cycle and can be isolated by fluorescence-activated cell sorting, but die in the subsequent host cell, confirming the 'delayed death' phenotype previously described pharmacologically, and validating the apicoplast as essential for parasite viability.