Equorum Eggs Research Articles

Anthelmintic efficacy on Parascaris equorum in foals on Swedish studs

BackgroundIn the last few years stud farms have experienced increasing problems with Parascaris equorum infections in foals despite intensive deworming programs. This has led to the question as to whether the anthelmintic drugs used against this parasite are failing. This study aimed to investigate the efficacy of ivermectin, fenbendazole and pyrantel on the faecal output of ascarid eggs of foals.MethodsA Faecal Egg Count Reduction Test (FECRT) was performed on nine large studs in Sweden. Anthelmintic drugs were given orally and faecal samples were examined for ascarid eggs on the day of deworming and 14 days later. Faecal Egg Count Reductions (FECRs) were calculated on arithmetic means of transformed individual FECRs and on arithmetic means of individual FECRs.ResultsSeventy-nine (48%) out of a total of 165 foals sampled were positive for P. equorum eggs before deworming and 66 of these met the criteria for being used in the efficacy assessment. It was shown that there was no, or very low activity of ivermectin on the output of ascarid eggs in the majority of the foals, whereas for fenbendazole and pyrantel it was >90%.ConclusionIvermectin resistance was shown in 5 out of 6 farms. Therefore, ivermectin should not be the drug of choice in the control of P. equorum infections in foals. According to the results of this study, fenbendazole or pyrantel are still effective and should be used against this parasite.

Viability of Rhodococcus equi and Parascaris equorum Eggs Exposed to High Temperatures

There is great concern about the potential pathogen contamination of horse manure compost spread in the same fields horses graze in. To ensure that pathogen destruction occurs, temperatures need to be sufficiently high during composting. Here, we investigated the survival rate of two marker organisms, Rhodococcus equi and Parascaris equorum eggs, exposed to temperatures potentially encountered during horse manure composting. Our results show that the time required to achieve a 1 log10 reduction in R. equi population (D-value) are 17.1 h (+/-1.47) at 45 degrees C, 8.6 h (+/-0.28) at 50 degrees C, 2.9 h (+/-0.04) at 55 degrees C and 0.7 h (+/-0.04) at 60 degrees C. For P. equorum eggs we show that at 45 and 50 degrees C, 2 log10 reduction of viability is reached between 8 and 24 h of incubation and that it takes less than 2 h at 55 and 60 degrees C to achieve a viability reduction of 2 log10. These results are useful for identifying composting conditions that will reduce the risk of environmental contamination by R. equi and P. equorum eggs.

Efficacy of chemical disinfectants on inactivating Parascaris equorum egg development

Efficacy of chemical disinfectants on inactivating Parascaris equorum egg development

Field effectiveness of pyrantel and failure of Parascaris equorum egg count reduction following ivermectin treatment in Italian horse farms

A study was carried out to assess the field efficacy of ivermectin (IVM) and pyrantel pamoate (PYR) against Parascaris equorum. Seventy-three foals (3–18 months old) from 5 stud farms, not treated with anthelmintics in the previous 10 weeks and with individual faecal egg counts (FEC) >200, were included in the study. For each stud farm, 5–7 foals were included in the IVM-treatment group (IVM 0.2%, 200 mcg/kg body weight) or in the PYR-treatment group (PYR 38%, 13.2 mg/kg body weight) and 3 were untreated as controls. For each foal, FECs were carried out before treatment (Day 0) and on Days 7 and 21. An individually based estimation of efficacy was assessed by a bootstrap simulation applied to different previously suggested formulae to evaluate the percent reduction of faecal egg counts (FECR). Two thousand bootstrap resamples were constructed from individual FECRs and the parasite population was considered susceptible for FECs ≥90 and 95% confidence interval (C.I.) ≥95%, suspected resistant for FECRs comprised between 80 and 90% and 95% C.I. <95% and resistant when FECR ≤80 and 95% C.I. ≤90%. IVM treatment was effective in foals from 2 farms, was equivocal at both study times in 1 farm and ineffective in 2 farms, while PYR was fully effective on all farms. This data shows that P. equorum-resistant populations are present also in Italy and the phenomenon is spreading in horses throughout Europe.

Cases of reduced cyathostomin egg-reappearance period and failure of Parascaris equorum egg count reduction following ivermectin treatment as well as survey on pyrantel efficacy on German horse farms

In 2003 and 2004, on a total of 63 different German horse farms, a survey using the faecal egg count reduction (FECR) test was performed to investigate the efficacy of ivermectin (IVM, Ivomec ®) and pyrantel (PYR, Banminth ®) treatment against gastro-intestinal nematodes in a total of 767 horses. IVM treatment resulted in 100% reduction of the cyathostomin egg production 14 and 21 days post-treatment (d.p.t.) on 37 farms. On the remaining five farms, the mean faecal egg count reduction ranged between 97.7 and 99.9%. The mean cyathostomin FECR following PYR treatment ranged between 92.2 and 100% on the 25 farms tested. Therefore, based on the 90% FECR threshold suggested for detection of anthelmintic resistance in horses, neither IVM nor PYR anthelmintic resistance was detected. However, if the thresholds recommended for the detection of resistance in small ruminants were applied, on one and four farms signs of reduced IVM and PYR efficacy, respectively, were observed. In 2005, to further investigate these findings, the cyathostomin egg-reappearance period (ERP) following IVM treatment was examined on six selected farms, two of which were found to show less than 99.8% FECR in the previous survey. On these two latter farms, the ERP was less than 5 weeks, while on the other four it was at least 8 weeks. Earlier investigations described IVM cyathostomin ERP of at least 9 weeks. The efficacy of IVM to reduce Parascaris equorum egg excretion was also studied. On one farm in 2 consecutive years, IVM treatment did not lead to a significant reduction in P. equorum faecal egg counts in one and five young horses, respectively.

Effects of low and high temperatures on viability of Parascaris equorum eggs suspended in water

Microcentrifuge tubes containing 5000 eggs of Parascaris equorum suspended in water were frozen at −5, −10, −15, −20, and −80 °C for 1–168 h and then thawed at a room temperature. Other samples of P. equorum eggs suspended in water were inserted into wells in the heated metal block of a thermal DNA cycler. Block temperatures were set at 5 °C incremental temperatures from 40 to 100 °C. At each temperature setting microcentrifuge tubes containing P. equorum eggs were removed 1 and 5 min later. Both, frozen and heated egg suspensions as well as untreated control suspensions were then incubated to test of viability based on the development of infective larvae inside viable eggs. We found out that eggs of P. equorum in water can retain viability and infectivity after freezing and that eggs survive longer at higher freezing temperatures. Our results also indicated that when water containing P. equorum eggs reached temperatures of 60 °C or higher within 1 min, the viability of eggs was lost.

Viability of nematode eggs in high rate algal ponds: the effect of physico-chemical conditions

The viability of Parascaris equorum eggs was studied in two experimental pilot-scale high-rate algal ponds (HRAPs) working in parallel with 4 and 10 days hydraulic retention time respectively. Semi-permeable bags of cellulose (15000 daltons pore size) were used to study the effect of physico-chemical conditions on the survival of these helminth eggs. Three thousand eggs were used in each bag. Replicates of these bags were submerged for 4 and 10 days in the HRAPs and egg viability was compared with that in control bags submerged in sterile water. After 4 days exposure, 60% reduction in viability was achieved, reaching 90% after 10 days, much higher than the 16% and 25% found in the control bags for 4 and 10 days respectively. Ionic conditions of the HRAP may have been responsible for up to 50–60% of the egg mortality, suggesting that mortality due to the ionic environment could be more important than physical retention and other potential removal factors.

Clinical trial of moxidectin oral gel in horses

A clinical trial carried out over 98 days was done to evaluate treatment of horses with moxidectin gel for efficacy as measured by (1) reduction in the production of parasite ova post treatment, (2) a comparison of the posttreatment parasite egg count suppression of moxidectin to ivermectin, and (3) assessment of the field safety, animal acceptance of the moxidectin formulation, and the utility of the moxidectin delivery device. One hundred and fifty Standardbred horses with naturally acquired parasite infections were used in the study. Moxidectin had more prolonged and greater suppressive influence than did ivermectin on reappearance and magnitude of strongyle egg counts post treatment. Differences were not observed between the capability of ivermectin or moxidectin to reduce and suppress low Parascaris equorum egg counts. Adverse reactions to treatments were not observed, and the utility of the moxidectin delivery syringe and animal acceptance of moxidectin treatment were satisfactory.

Natural superinfection of Parascaris equorum in a stall-confined orphan horse foal

At 4 days of age, an orphan horse foal born on a pasture was placed in a parasite-free stall. It was euthanized at 205 days of age and examination revealed numerous Parascaris equorum specimens, ranging from 3.0 mm to adult size, indicating reinfections in the stall over an extended period of time. Initial infection of the foal was from stages on pasture. The foal had been observed repeatedly eating its own feces and the question is posed as to whether ‘recycling’ of P. equorum eggs several times by coprophagy allowed time for embryonation and reinfection to occur.

The distribution of Parascaris equorum eggs in the soil profile of bare paddocks in some Norwegian studs.

Fifteen bare paddocks, which consisted of soil only and were located on 12 different studs, were examined for their content of Parascaris equorum eggs in the upper 15 cm of the soil profile. The paddocks were classified into three different groups according to the type of soil: clayey soil (A), morainic soil (B) and gravel or gravel-like sand (C). Soil profiles were collected down to a depth of 15 cm and were divided into three layers: 0-5 cm (D1), 5-10 cm (D2) and 10-15 (D3). The eggs in each layer were counted and identified as infective or noninfective eggs. The paddocks in group C, which had good drainage conditions, had significantly lower numbers of eggs in the whole profile and in D1 and D2 than the paddocks in groups A or B. Furthermore, there was a significantly higher proportion of the total egg count present in D3 in the group C paddocks. This may have been due to a higher degree of passive transportation of eggs down in the profile in the gravel or gravel-like sand. Even though there was a significantly higher proportion of infective eggs in the soil from the group C paddocks, the lower total numbers of eggs resulted in a lower total number of infective eggs in those paddocks. The study showed that the soil type was an important factor in determining the content of P. equorum eggs in the upper layer of the soil profile in bare paddocks and consequently for the potential infestation of horses with P. equorum.

Dose titration of moxidectin oral gel against migrating Strongylus vulgaris and Parascaris equorum larvae in pony foals

Moxidectin was tested for efficacy in ponies against experimental infections of 56 day Strongylus vulgaris larvae and 11 day Parascaris equorum larvae. Three dosage of moxidectin were tested: 300 μg per kg live body weight, 400 μg per kg, and 500 μg per kg, and the vehicle served as control. Ponies were first infected with 600 S. vulgaris third-stage larvae (L 3) on Experiment Day 0 and then with 3000 embryonated P. equorum eggs on Day 45. Moxidectin treatments were administered on Day 56 and necropsy examinations were performed on Day 91. Strongylus vulgaris fourth-stage (L 4) and fifth-stage (L 5) larvae were recovered at necropsy from the control ponies, in dissections of the cranial mesenteric artery and its branches (L 4 and L 5), and recovered from nodules in the wall of the cecum and ventral colon (L 5). Parascaris equorum larvae were recovered from the small intestine of control ponies. Moxidectin was highly efficacious against S. vulgaris L 4 and L 5 at all three doses tested (99.6–100%), and appeared to be equally efficacious against P. equorum larvae (100%); however, control ponies had low levels of P. equorum infections compared to previous experimental infections performed using identical methods. This suggests that the prior S. vulgaris infection on Day 0 may have influenced the subsequent experimental P. equorum infection on Day 45 and contributed to the lower recovery.

Comparison of the efficacy of ivermectin, oxibendazole, and pyrantel pamoate against 28-day Parascaris equorum larvae in the intestine of pony foals

Summary Sixteen helminth-free pony foals were inoculated with a mean (±sd) 2,000 (±545.5) infective Parascaris equorum eggs (day 0). Foals were allocated to replicates of 4, and treatments within each replicate were assigned at random. Treatment administered on postinoculation day (pid) 28 included no treatment (control), 0.2 mg of ivermectin/kg of body weight, 10 mg of oxibendazole/kg, or 6.6 mg of pyrantel base (pamoate)/kg. Paste formulations of the anthelmintics were administered orally. The foals were euthanatized 14 days after treatment (pid 42) and examined for P equorum larvae in the small intestine. The mean ± sd (and range) numbers of fourth-stage P equorum larvae recovered from nontreated foals and those treated with ivermectin, pyrantel, or oxibendazole were 1,603.8 ± 1,026.8 (305 to 2,480), 29.3 ± 55.8 (0 to 113), 413.0 ± 568.1 (0 to 1,204), or 889.5 ± 1,123.1 (1 to 2,345), respectively. Compared with the value for control (nontreated) foals, treatment with ivermectin, pyrantel, and oxibendazole was 98.2, 74.2, and 44.5% effective, respectively, when administered 28 days after experimentally induced infection with P equorum. Adverse reactions attributable to treatment were not observed.

Controlled trials of fenbendazole and febantel in ponies with parascaris equorum infections

The activity of fenbendazole and febantel was evaluated in 12 pony foals whichwere inoculated with 2600 P. equorum eggs. The foals were not maintained free of parasites before or after inoculation. Once patent for P. equorum, the foals were randomly assigned to groups and treated one time intraorally with either 0.5 ml corn syrup/kg of body weight (controls; n=4), 10 mg fenbendazole/kg (n=4), or 6 mg febantel/kg (n=4). Foals were necropsied and examined for parasites 10 days after treatment. Fenbendazole and febantel were highly effective against adult and immature P. equorum. Grosslesions attributed to P. equorum were evident in all foals. P. equorum were not foundin any of the fenbendazole-or febantel-treated foals. The mean number of adult and immature P. equorum found in the controls was 66.8 (15–166) and 65.0 (21–147), respectively. Strongyle infections were insufficient for efficacy evaluations to be done. Neither anthelmintic was effective against mature Drasehia megastoma, mature Habronema majus, immature H. muscae, Gasterophilus intestinalis or late 4th-stage larvae of Strongylus vulgaris. Adverse side effects due to treatment were not observed.

The migration and development of Parascaris equorum in the horse

Eight worm-free pony foals, aged 2–4 weeks received a single infection of 8000 Parascaris equorum eggs. The foals were killed at intervals to investigate the migration and subsequent development of P. equorum. Signs of larval invasion were found in the liver within 48 h after infection. Larvae migrated from the liver to the lungs from 7 to 14 days after infection and the majority had returned to the small intestine via the tracheooesophageal route by day 23. After completion of their tissue migration, the parasites grew rapidly in size in the lumen of the small intestine, but after day 37 the total number of worms present in this site decreased. Patent infections developed on days 101–104.

The development of immunity to Parascaris equorum infection in the foal

Following infection with 8000 Parascaris equorum eggs in two- to four-week-old foals reared under worm-free conditions a high percentage of the infective dose completed its tissue migration and returned to the small intestine. Patent infections were establisehd between 81 and 104 days after infection and high faecal egg counts were recorded. A group of six- to 12-month-old foals, which had been either reared under worm-free conditions or exposed to natural ascarid and strongyle infections on pasture, received a similar infection of 8000 P equorum eggs. Compared with the younger foals there was a marked reduction in the number of larvae reaching the small intestine. Also, patent infections were established less frequently (50 per cent of cases) and, when present, the faecal egg counts remained low.

Hepatic pathology of experimental Parascaris equorum infection in worm-free foals

The pathological changes associated with the migration through the liver of P. equorum larvae were investigated. Twenty pony foals were killed at intervals of 2 to 185 days after a single infection with 160 or 8000 P. equorum eggs and 4 pony foals were killed at intervals of 94 to 144 days after twice weekly infections of 50 eggs from birth. At post-mortem examination the macroscopic changes included the development of focal haemorrhages and small, white diffuse or nodular lesions. Microscopic lesions were found mainly around the portal triads and consisted of infiltration by cells, including eosinophils and lymphocytes, and fibrosis. Other lesions, occurring in older animals infected with 8000 eggs, included thrombosis and the development of lymphoreticular nodules and granulomata.

A pathological study of the lungs of foals infected experimentally with Parascaris equorum

Eight pony foals 2 to 4 weeks old were infected with a single dose of 8000 P. equorum eggs. The animals were killed at intervals to investigate the pulmonary lesions produced. Two distinct lesions were found in the lungs. The migrating P. equorum larvae provoked a transitory eosinophilic bronchitis and bronchiolitis which was later replaced by a lymphocytic response. Large numbers of subpleural lymphocytic nodules were also present for a short period. In addition, there was a cranial lobe pneumonia with a mainly polymorphonuclear leucocytic response. It is suggested that this second lesion may be a form of enzootic pneumonia and that its pathogenesis is enhanced by the migrating P. equorum larvae.

Clinical signs associated with parascaris equorum infection in worm-free pony foals and yearlings

The clinical signs associated with a single infection of 8 000 Parascasis equorum eggs in eight worm-free foals and two yearling ponies are described. Foals had mild respiratory disease 2–4 weeks after infection whilst the yearlings showed a more severe respiratory syndrome with systemic illness. The foals became progressively lethargic and emaciated from the third month onwards, but they yearlings maintained good condition. Infections became patent on days 101–104 post inoculation.

Experimental Parascaris equorum infection of foals

Six worm-free pony foals, two to four months old, were infected with parascaris equorum eggs using three different dosage regimes and killed at either 40 or 95-100 days after infection. Coughing and a circulating eosinophilia were features of large infections from which only a small number of worms developed to maturity. In small infections a high percentage of the parasites matured in the small intestine and this was associated with unthriftiness. Pre-patent periods of 80 and 83 days were recorded.