Demodex gatoi: new species of hair follicle mite (Acari: Demodecidae) from the domestic cat (Carnivora: Felidae).

Demodex gatoi sp. nov. is described in all its life stages from the domestic cat. The host was diagnosed with presumptive feline acquired immunodeficiency syndrome and harbored enormous numbers of both D. gatoi and D. cati Hirst, 1919. Unlike D. cati, which inhabits the hair follicles, D. gatoi resides on the epidermal surface. More than half of the D. gatoi population sampled was made up of ova indicating rapid population growth.

Quantitative determination of coccidian oocysts in beef calves from the coastal plain area of Georgia (U.S.A.).

For two consecutive years, determinations were made of the prevalence and abundance of coccidian oocysts from crossbred beef calves raised on Bahia grass pastures in the coastal plain area of Georgia. Of the 534 fecal samples collected during the survey, 461 (86.3%) contained one or more species of coccidian oocysts. The total mean oocysts per gram of feces (OPG) was significantly different (P less than 0.10) between the two years. Thirteen species of Eimeria were found during both years of the survey. Eimeria bovis was the most prevalent species found in the survey; E. ellipsoidalis, however, had the greatest number of OPG. Eimeria bukidnonensis, E. pellita, and E. brasiliensis were the least prevalent species and also had the lowest numbers of OPG. Only one clinical case of coccidiosis was seen. A nine-month-old calf had E. zuernii coccidiosis; it excreted E. zuernii oocysts in several fecal samples before the clinical disease appeared.

Doramectin efficacy against the kidney worm, Stephanurus dentatus in sows.

Sixteen sows passing Stephanurus dentatus eggs in their urine were bought on the local market and placed in individual pens with solid concrete floors in an open-sided bam. Water was supplied by nipple waterers and sows were fed individually 1.8 kg feed daily. First, urine samples were taken at dawn on days -8 and -7 and weights were taken on day 0. Sows were assigned to one of two groups on the basis of average urine egg counts and weights. Group T1 sows were each injected IM in the neck with sterile saline at the rate of 1.5 ml per 50 kg and group T2 sows were each injected IM with doramectin at the rate of 300 micrograms kg-1 on day 0. Urine samples were again taken on days 56 and 57 and the sows were necropsied on day 57. Urine of all doramectin treated sows were test negative for kidney work eggs on days 56 and 57 as was one control sow, whereas the average count for controls was 3762 eggs ml-1. No worms were found in doramectin treated sows and a total of 499 were found in the controls for an average of 62 per sow. The majority of worms were in the perirenal area and kidneys, a few were scattered in liver, lungs, abdominal muscles and peritoneal cavity. The efficacy of doramectin against Stephanurus dentatus in sows was 100% (P < 0.0001).

Doramectin efficacy against gastrointestinal nematodes in pigs.

Four controlled trials with growing pigs were performed to determine efficacy of doramectin against natural and induced populations of nematodes. In Trial 1 (T1), 20 pigs with natural infections were assigned to one of two like groups on the basis of weight, sex and worm egg counts. In Trial 2 (T2), 20 pigs with negative worm egg counts were assigned to one of two groups on the basis of weight and sex. Each pig was subsequently given (per os) 3000 Trichuris suis embryonated eggs; 2000 Ascaris suum embryonated eggs; 10000 Oesophagostomum spp. infective larvae and 10,000 Strongyloides ransomi infective larvae (SC injection). In Trial 3 (T3), 20 pigs with negative worm egg counts were assigned as in T2, and each pig was subsequently given (per os) 2000 A. suum embryonated eggs, 15000 Oesophagostomum quadrispinulatum infective larvae, and 2891 Hyostrongylus rubidus infective larvae. In Trial 4 (T4), 16 pigs with negative worm egg counts were each assigned to one of two groups as in T2 and were given (per os) 2670 T. suis embryonated eggs. On Day 0 of each trial, each pig of the control group was injected IM in the neck with sterile saline at the rate of 1.5 ml 50 kg-1. Each pig in the treated group of each trial was similarly injected with doramectin at the rate of 300 micrograms kg-1. All pigs were necropsied 14 or 15 days post-treatment and parasites recovered by standard parasitological procedures. Efficacies against natural infections were: A. suum, 100%; Oesophagostomum spp. 100%; H. rubidus, 99.4%; and Strongyloides ransomi, 99.9%. Efficacies against induced infections were: 4th stage A. suum, 100%; 4th stage O.dentatum, 99.9%; 4th stage O.quadrispinulatum, 97.1 and 99.6%; 4th stage H. rubidus, 100%; adult S. ransomi, 100%; adult Trichuris suis in mixed infection, 54.1%; and in pure infection, 95.3%.

Experimental infections with Hyostrongylus rubidus and the effects on performance of growing pigs.

Pigs infected with Hyostrongylus rubidus at the rate of 550 larvae kg-1 body weight followed 15 days later with 220 larvae kg-1 body weight gained less weight (P less than 0.010) than uninfected control pigs. Feed efficiency (feed/gain) was 8% better (P greater than 0.10) in control than in infected pigs. Peak H. rubidus eggs per gram counts (EPG) occurred 22 days after each infection of pigs. H. rubidus EPG at necropsy were correlated with total number of adults recovered and with female/male ratio. High EPG were associated with H. rubidus populations composed of approximately equal numbers of males and females. Digestion trials consisted of pigs infected with 335 larvae kg-1 body weight compared to uninfected controls. Control pigs had higher (P less than 0.05) crude protein digestion coefficients, excreted less (P less than 0.05) N in feces and had a higher (P less than 0.05) N balance than infected pigs.

Performance of pigs with mixed nematode infections before and after ivermectin treatment.

Ninety crossbred parasitized pigs were used in two controlled experiments to compare performance before and after ivermectin treatment. Four groups of 15 pigs were sequentially infected with 2000 Ascaris suum, 10,000 Oesophagostomum spp. and 10,000 Strongyloides ransomi beginning at average pig weights of either 38 kg (Experiment I) or 14 kg (Experiment II). Two infected groups of pigs were treated with ivermectin on Day 34 (Experiment I) or 37 (Experiment II) of the experiments and all pigs were fed to slaughter weights of approximately 100 kg. Average daily gain (ADG) of heavier ivermectin-treated pigs was greater than that of infected non-treated pigs (P less than 0.03) and feed conversion was numerically greater by 5% (P greater than 0.10). ADG was not different between lighter treated or non-treated pigs, but feed conversion was numerically 4% greater in ivermectin-treated compared to non-treated pigs (P greater than 0.10). No differences existed in carcass dressing percentage among the three groups of heavier pigs, but among the lighter groups ivermectin-treated pigs had a higher dressing percentage (P less than 0.03) than infected non-treated or control pigs. Results of the calculation of production costs based on combined data from the two experiments for the post-treatment period, including feed, drug and maintenance costs, indicate that the production cost for ivermectin-treated pigs was $1.53 per pig less than that for infected non-treated pigs when the cost for each group to attain control pig weights is compared with the actual cost for control pigs.

World Association for the Advancement of Veterinary Parasitology (W.A.A.V.P.) guidelines for evaluating the efficacy of anthelmintics in swine.

As a follow-up to a previous guideline publication on efficacy evaluation of anthelmintics in ruminants, an expert group of the World Association for the Advancement of Veterinary Parasitology presents similar guidelines for the testing of anthelmintics in swine. The goal of the guidelines is to develop uniform testing standards and registration requirements. Data obtained from investigations according to the guidelines should be internationally accepted in the registering of drugs. Further, the use of the guidelines may contribute towards reducing costs, labor and the number of experimental animals used for drug testing.

Ascaris suum infection in pigs sensitizes lymphocytes but suppresses their responsiveness to phytomitogens.

The effect of Ascaris suum infection and treatment with fenbendazole on the blastogenic response of peripheral blood lymphocytes to A. suum antigens and to three phytomitogens was assayed by the lymphocyte transformation technique. Repeated infections with A. suum led to the development of sensitized lymphocytes primarily responding to egg hatching fluid antigen. Treatment with fenbendazole decreased the number of specific sensitized lymphocytes, but favorably increased the resistance of pigs to reinfection. Immunity to reinfection did not correlate with the strength of the blastogenic response to A. suum antigens. Repeated infection with A. suum negatively affected the development of the blastogenic response to phytomitogens in the pigs, leading to a partial depression of the responsiveness of lymphocytes and to the partial suppression by serum. Responses to pokeweed mitogen were affected more than the responses to concanavalin A and phytohemagglutinin.

Efficacy of moxidectin 0.5% pour-on against swine nematodes.

Forty pigs with induced infections of Ascaris suum, Trichuris suis, Metastrongylus spp., Oesophagostomum dentatum and O. quadrispinulatum were assigned to five-dose groups of moxidectin 0.5% pour-on with eight pigs per dose group. The doses were: moxidectin, 0 (vehicle control), 0.75, 1.00, 1.25, and 1.50 mg/kg(-1) body weight. Worm egg counts (EPG) were made from fecal samples collected on Day 2 pretreatment and on Day 14 or 15 post-treatment. Animals were ranked according to the descending order of A. suum egg counts made on Day 2 and blocked in groups of five. Pigs in blocked groups were assigned randomly to each of the five dose groups. Treatment doses were calculated on the basis of weights taken on Day 1 and were administered topically from the neck to the base of the tail. Pigs were housed by pairs in individual pens provided with self-feeders and automatic waterers. Necropsies were performed on equal numbers of pigs from each treatment group on days 14 and 15 post-treatment. Adult and larval worms were collected, identified and counted by standard parasitological techniques. All counts were transformed by Y=log10 (count+1) transformation prior to analysis. A two-way analysis of variance was conducted and treatment effect was tested for significance at the 5% level. Efficacies based on geometric means and optimal doses were as follows: Ascaris suum, 98.3% at 1.25; Metastrongylus spp., 100% at 0.75; Oesophagostomum quadrispinulatum, 100% at 1.50; and Trichuris suis, 93.5% at 0.75. Efficacy for O. dentatum was from 81.3% to 100%; however, the average number of O. dentatum (30) was too small for significance. Two species of lungworms were present, Metastrongylus apri and M. pudendotectus but they were not speciated at necropsy. As reported for several anthelmintics, the efficacy of moxidectin was variable for Trichuris. The highest efficacy was in the 0.75 dose group with six pigs harboring a few or no worms. The lowest efficacy was in the 1.25 group with only two pigs harboring a few or no worms.

Immunization of pigs against Ascaris suum by sequential experimental infections terminated with fenbendazole during larval migration.

Three experimental infections of weaning pigs with 2000 embryonated Ascaris suum eggs each, 11 days apart, followed each time by fenbendazole treatment, produced a significant host response when compared with similar infected or uninfected control pigs as assessed by response to a subsequent challenge with 100 embryonated A. suum eggs. The response elicited from pigs treated with fenbendazole on either 2, 3, and 4 days or, 6, 7, and 8 days after each experimental infection was expressed as a reduction in the number of pigs with A. suum, in the number of worms per pig, in the weight of male and female worms, and in the length of male and female worms. No differences in average daily weight gain, feed-conversion efficiency or histology of lungs and liver were noted among the 4 treatment groups.

Bermudagrass management in the Southern Piedmont USA. V: Gastrointestinal parasite control in cattle.

Parasite-free pastures would improve cattle health and performance, resulting in possible economic return to producers. Our objective was to determine the effect of a single series of anthelmintic treatment of steers prior to stocking on Coastal bermudagrass pastures, during five consecutive summers, on the parasite burden in cattle. The site for this experiment had been conventionally cropped for several decades, with no exposure to cattle, and would be expected to be relatively free of nematode larvae. The experimental design was a randomized complete block (landscape features) with a split plot arrangement of treatments where main plots were pasture fertilization treatments (mineral, clover plus mineral, and broiler litter) and split plots were low and high forage mass. Anthelmintic treatment included pour-on ivermectin on day -21, albendazole on day -7, and injectable ivermectin 48 h prior to stocking of pastures, with the cattle remaining in drylot during the 48-h period prior to being placed on the experimental paddocks. All steers received only one series of treatments during any given year. Yearling Angus steers (Bos taurus) were managed in a put-and-take grazing system with three "tester" steers assigned to each paddock and "grazer" steers added or removed at 28-day intervals. From 1994 to 1998, steers grazed the paddocks for a 140-day period from mid May until early October each year. Fecal samples for worm egg counts were obtained on day 0 and at 28-day intervals, thereafter. On all sampling days after day 0, samples were obtained only from tester animals. Over the 5-year period, the mean eggs per gram of feces (epg) gradually increased from 0 (following treatment) to a mean of 2.2 (range from 0.7 to 3.0) by the end of the grazing season (the last sampling date) in October. Although the epg were not zero, they were below threshold levels that would allow development of a parasite burden in cattle. In traditional management systems, cattle graze parasite-contaminated pastures; therefore, parasites negatively impact growth and productivity throughout the entire grazing period. Periodic anthelmintic treatments simply give a temporary reprieve from those parasitic infections. Conceptually, using the current grazing system, it should be possible to maintain these pastures in a parasite-free status indefinitely; however, from a drug resistance perspective, it would be most applicable in sod-based rotation systems where cattle graze from two to five years before land is returned to row-crops. By removing the effect of parasites, cattle can grow without the physiological constraints that gastrointestinal parasites place on appetite, digestion, nutrient utilization, and general well being.

Verminous encephalitis apparently caused by the filarioid nematode Chandlerella quiscali in emus (Dromaius novaehollandiae).

Verminous encephalitis attributed to Chandlerella quiscali was diagnosed in a flock of emus (Dromaius novaehollandiae). Clinically affected birds showed torticollis and progressive ataxia. Filarioid parasites with morphological characteristics resembling C. quiscali were identified in one case. Histologic lesions in the brain and spinal cord consisted of mild to moderate perivascular cuffing and scattered areas of variable mild necrosis. Parasites observed within the parenchyma of the brain and spinal cord often were not associated with either necrosis or an inflammatory reaction. Ivermectin administered subcutaneously at 4-week intervals at a dose rate of 200 micrograms/kg body weight appeared to prevent clinical signs in flocks in the presumed endemic area.

Performance and tissue copper concentrations of control and Ascaris suum-infected pigs fed excess dietary copper.

Ninety-eight crossbred growing-finishing swine were used in 2 experiments to investigate the interaction between naturally occurring Ascaris suum infections and excess copper ingestion. In both experiments, pigs were fed a 14% crude protein basal diet or the basal diet + 250 ppm copper. These 2 dietary groups were subsequently divided into 2 additional treatment groups (A. suum-infected or uninfected) based on worm recovery from the intestine or from fecal egg counts. Excess dietary copper improved pig performance slightly, but it dramatically increased liver, kidney and lung copper levels. The A. suum infection did not affect pig performance, but it tended (not significantly) to reduce tissue copper levels. Serum copper was not affected by dietary copper or by A. suum infection.

Comparative efficacy of fenbendazole, dichlorvos, and levamisole HCI against gastrointestinal nematodes of pigs.

Forty-two weanling pigs raised under similar management conditions were used to compare the effectiveness of fenbendazole, dichlorvos, and levamisole HCl against Oesophagostomum dentatum, O. quadrispinulatum, Ascaris suum, Trichuris suis, Hyostrongylus rubidus, and Strongyloides ransomi. All three drugs were given in the feed. Eleven pigs served as unmedicated controls; 11 pigs received fenbendazole (3 mg/kg) on days 1, 2, and 3; 10 pigs received dichlorvos (17 mg/kg) on day 3; and 10 pigs received levamisole HCl (8 mg/kg) on day 3. Fecal specimens from all 11 pigs were collected before and after anthelmintic treatment and examined for nematode eggs. All pigs were killed on day 7, and residual nematodes were counted. The calculated efficacies against the above species, respectively, were: fenbendazole, 99.9, 100, 92.4, 66.0, 99.9, and 0%; dichlorvos, 99.4, 99.9, 100, 99.9, 99.9, and 86.9%; levamisole HCl, 97.1, 99.7, 97.9, 26.1, 94.4, and 99.9%.

Differential responses of Duroc, Hampshire, and crossbred pigs to a superimposed experimental infection with the intestinal threadworm, Strongyloides ransomi.

In both spring and fall, 12 Duroc, 12 Hampshire, and 12 Duroc times Hampshire F1 weanling pigs all reared under the same management were fed in pens of 3 to slaughter weights. Three Duroc and 4 Hampshire boars, essentially unrelated within breed, were used in sampling the breeds. Swine herd management allowed pig infection with Strongyloides ransomi and Ascaris suum, but neither clinical nor subclinical parasitism was evident in the herd. Pigs were percutaneously exposed by pens within breed and season, half to none (control) and half to 3,000,000 (exposed) S. ransomi infective larvae, Breed, treatment, and seasons were prominent sources of variation in pig response. Breeds failed to respond alike to parasitism in respect to experimental periods and exposure levels. This interaction response (P smaller than 0.01) showed that S. ransomi egg production increased rapidly for all breed groups but decreased quicker and greater in Durocs, slowest and least in Hampshires, with cross breds intermediate in these respects. The 2.0830 for mean of log A. suum EPG from exposed Durocs was near double that of control Durocs but the mean for exposed Hampshires was less than half that for controls; crossbreds tended to be intermediate in this respect. Daily gains of 0.70 and 0.73 for Durocs and crossbreds were similar (P greater than 0.10) but averaged 11.7% more (P smaller than 0.05) than the 0.64 kg for Hampshires and gains by control pigs were 20.6% above (P greater than 0.01) that of exposed pigs. Exposed pigs required more feed per kg of gain (P greater than 0.05) than control pigs (3.60 vs. 3.33 kg). Comparison of relative gains and feed efficiences of control and exposed pigs among and within breed groups supported the position that a superimposed exposure of 3,000,000 S. ransomi larvae was more severe for Hampshires, intermediate for crossbreds, and least severe for Durocs.

Parastrongylus (=Angiostrongylus) cantonensis now endemic in Louisiana wildlife.

Parastrongylus (=Angiostrongylus) cantonensis, a lung worm of rats, was first reported in the United States in 1987, with a probable introduction by infected rats from ships docking in New Orleans, Louisiana, during the mid-1980s. Since then, it has been reported in nonhuman primates and a boy from New Orleans, and in a horse from Picayune, Mississippi, a distance of 87 km from New Orleans. Parastrongylus cantonensis infection is herein reported in a lemur (Varencia variegata rubra) from New Iberia, Louisiana, a distance of 222 km from New Orleans, and in a wood rat (Neotomafloridanus) and in 4 opossums (Didelphis virginiana) from Baton Rouge, Louisiana, a distance of 124 km from New Orleans. The potential of a great variety of gastropods serving as intermediate hosts in Louisiana may pose a threat to wildlife as well as to domesticated animals in the areas where infected Norway rats (Rattus norvegicus) are present.

Losses to internal parasites in swine production.

Experimental infections of pigs with Strongyloides ransomi, Stephanurus dentatus, Ascaris suum, Oesophagostomum spp. or Trichuris suis at increasing levels generally decrease daily gain and increase feed to gain ratio linearly. At lower, subclinical levels of infection, the feed to gain ratio typically is increased 3% to 6% by an infection. Based on low-level experimental infections with A. suum, the economic loss to producers in the U.S. from increased feed to gain ratio is estimated at $155 million annually.

Influence of an experimental infection of Ascaris suum on performance of pigs.

Thirty-two pigs (average 26.6 kg live weight) were individually housed and fed to study the effect of an infection of Ascaris suum (either 0, 600, 6,000 or 60,000 A. suum eggs/pig) on performance of growing-finishing pigs. Increasing the level of A. suum infection produced linear (P less than .07) and quadratic (P less than .09) effects on final weight, weight gain and average daily gain. Feed to gain ratio and number of A. suum worms recovered from the intestines of pigs at slaughter increased linearly (P less than .01) with increasing doses of A. suum eggs. Pigs receiving 60,000 A. suum eggs were 13% less (P less than .01) efficient than the noninfected controls. In each of two trials, eight crossbred barrows (15.7 kg in trial 1 and 16.1 kg body weight in trial 2) were examined for the effects of two levels of A. suum infection (0 and 20,000 eggs/pig) on digestibility coefficients for dry matter, crude protein and gross energy. The infection did not affect (P greater than .05) digestibility coefficients during the first two collection periods (d 6 through 10 and 19 through 23). However, digestion coefficients for dry matter, crude protein and gross energy obtained from the total collection period on d 33 through 37 postinfection were greater (P less than .01) for control pigs than for pigs given 20,000 A. suum eggs each. Also, N retention was greater (P less than .05) for control pigs than for infected pigs.

Influence of an experimental infection of nodular worms (Oesophagostomum spp.) on performance of pigs.

Four trials were conducted to determine the effect of different levels of nodular worm (Oesophagostomum spp.) infection on the performance of growing-finishing swine and on digestion and absorption of nutrients by the growing pig. In each of two growing-finishing trials, 48 crossbred pigs (average body weight 26.6 kg in trial 1 and 24.4 kg in trial 2) were individually housed and given a single infection of nodular worms (0, 550, 1,100 or 1,650 infective larvae/kg body weight in trial 1 and 0, 1,500, 3,000 or 4,500 infective larvae/kg body weight in trial 2). At 21 days postinfection, pigs given either 1,100 or 1,650 nodular worm larvae/kg body weight required more feed (P less than .05) per unit gain than pigs not infected, but for the 77-day test period, as a whole, nodular worms did not significantly affect performance. in trial 2, pigs given either 3,000 or 4,500 nodular worm larvae/kg body weight were lighter (P less than .05) and gained weight slower (P less than .05) for the first 21 days postinfection than pigs not infected, while pigs given 4,500 larvae gained slower (P less than .05) than pigs on the other three treatments. During the first 21 days after infection, pigs given 4,500 larvae/kg body weight consumed less feed (P less than .05 than pigs given either 0 or 1,500 larvae. Even at the higher levels of infection, nodular worms did not significantly affect performance over the entire 77-day test period. In each of the two other trials, eight crossbred barrows (average body weight 28.8 kg in trial 1 and 28.4 kg body weight in trials 2) were examined for the effects of two levels of nodular worm infection (0 and 4,950 larvae/kg body weight) on digestion and absorption of nutrients and on N balance. Pigs experimentally infected had a lower digestion coefficient for dry matter (P less than .01), ash (P less than .05), crude fiber (P less than .01), N free extract (P less than .05) and N (P less than .05) than noninfected pigs. Pigs not infected with nodular worms had a higher (P less than .05) N balance.

Excess crude protein for nongravid gilts.

Twenty-five nongravid crossbred gilts (avg initial wt, 126 kg) were placed on either a high (38%) or a low (13%) crude protein (CP) diet and fed either at the rate of 1.82 kg/d or had ad libitum access to feed. In addition, a fifth group was pair-fed the 13% CP diet to the average intake of the gilts fed high CP ad libitum. The experimental period lasted 30 d. Corn-soybean meal diets were used and CP levels were varied by altering the corn:soybean meal ratio. Gain and gain/feed were reduced (P less than .01) in gilts fed 1.82 kg/d compared with the gilts fed ad libitum or pair-fed gilts. Gain (P less than .03) and feed intake (P less than .01) of gilts with ad libitum access to the 13% CP diet were higher than those of gilts with ad libitum access to the 38% CP diet. Gain/feed was not different (P greater than .10) between the two groups, however. Rate of gain and feed efficiency of gilts pair-fed the 13% CP diet were similar (P greater than .10) to those of gilts with ad libitum access to the 38% CP diet. Plasma total free amino acids, NH3 and total protein were not (P greater than .10) affected by treatment. Plasma urea-N and urinary total N, urea-N and orotic acid were increased (P less than .01) in gilts fed the high CP diet regardless of feed intake level. However, urinary NH3 was higher (P less than .01) in gilts fed the low-protein diet. These results indicate that excess dietary CP for nongravid gilts decreases gain and feed intake and has no effect on efficiency of feed utilization, but it increases plasma urea-N and urinary total N, urea-N and orotic acid.