Efficacy of doramectin for treatment of experimentally induced infection with gastrointestinal nematodes in calves.

OBJECTIVE: To determine the efficacy of injectable doramectin against experimentally induced infections with adult and larval (L4) stages of gastrointestinal nematodes in calves. PROCEDURES: In each experiment, between 20 (experiments 1 and 2) and 30 (experiment 3) parasite-free yearling calves were selected and allotted to groups of 10/group. All calves received oral inoculation of the following infective larval stages of these nematode species: Cooperia onchophora, C punctata, C zurnabada, Cooperia spp, Haemonchus placei, Nematodirus helvetianus, Oesophagostomum radiatum, Ostertagia ostertagi, Trichostrongylus axei, and T colubriformis. Infections or treatments were timed so that, by day of treatment, the population of each parasite species had matured to the stage to be tested (adult or L4). On day of treatment, calves received doramectin (200 micrograms/kg of body weight, SC), and infected nonmedicated control calves received saline solution SC at the same time. All calves were slaughtered at least 14 days after treatment. RESULTS: Efficacy against the following adult and L4 species was > or = 99%: C onchophora, C punctata, C zurnabada, Cooperia spp, H placei, Oes radiatum, O ostertagi, and T colubriformis. Doramectin was also 100% efficacious against the L4 stage of T axei. Efficacy against the adult and L4 stages of N helvetianus was 9.6 and 77.4 to 83.3%, respectively. CONCLUSIONS: Doramectin, at a dosage of 200 micrograms/kg, is effective in controlling the prevalent gastrointestinal nematodes (adult and L4 stages) found in naturally infected calves. CLINICAL RELEVANCE: Doramectin, a new anthelmintic, was effective against recent field strains of the most prevalent gastrointestinal parasites found in cattle in the United States, and could provide another alternative for control of these parasites.

Seasonal pattern of inhibition of Ostertagia ostertagi in calves in northeast Mississippi.

The composition of, and seasonal changes in, populations of gastrointestinal parasites of calves in northeast Mississippi were determined for 10 months post-weaning. After weaning on 15 October, 20 mixed breed beef steers were grazed together on a 4 ha fescue/bermudagrass pasture. From November through August of the following year, two of the calves were removed each month for necropsy and counting of gastrointestinal nematodes. Eight species of worms were found: Haemonchus placei, Ostertagia ostertagi, Trichostrongylus axei, Bunostomum phlebotomum, Cooperia spp., Trichostrongylus colubriformis, Oesophagostomum spp., and Trichuris ovis. During all months, Ostertagia ostertagi and Cooperia spp. combined comprised at least 89% of gastrointestinal nematode burdens. Cooperia spp. represented 92.6% of the total worm burden of calves in November but declined to about 56% in January and February. From March through August, Ostertagia ostertagi comprised at least 79% of the worms from calves. Numbers of inhibited Ostertagia ostertagi increased markedly from February to March and remained at high levels prior to resumption of development in August. The proportion of Trichostrongylus axei remained about 4% throughout the year, but the highest numbers were recorded in the summer months. Other species were minor components of the worm population. These data indicate that with respect to Ostertagia ostertagi, northeast Mississippi can be considered a summer inhibition zone.

Epidemiological study of nematode infections in a grazing beef cow-calf herd in Mississippi.

The epidemiology of gastrointestinal nematodes was studied in a spring calving herd in northeast Mississippi. Pregnant, mixed breed beef cows (n = 15) were placed on a 10 ha fescue/bermuda grass pasture from January 1990-February 1992. In both years, calves were born from February-April and were weaned and removed from the pasture in mid-October. Fecal egg counts (EPG) and generic composition of nematodes in fecal cultures were determined monthly for cows and calves. Estimation of numbers of third-stage larvae on herbage also was determined monthly from March 1990-February 1992. Worm-free tracer calves (2-3 per month) were allowed to graze for 1 month periods and slaughtered for counting and identification of gastrointestinal nematodes. The mean monthly EPG of cows was consistently low (0.23-3.41); EPG of calves increased from spring through fall of both years. Five nematode genera were identified from fecal cultures of cows and calves. Ostertagia and Trichostrongylus spp. were the predominant nematodes in cows, while Ostertagia and Cooperia spp. were predominant in calves. Numbers of third-stage larvae on herbage declined from spring through summer and remained at low levels until late fall/winter, when numbers increased markedly. Eleven nematode species were identified from tracers, but O. ostertagi and Cooperia spp. predominated in most months. Seasonal changes in tracer worm counts coincided with similar changes in counts of third-stage larvae on herbage. Inhibition of O. ostertagi occurred in tracer calves during spring, but did not give rise to a marked increase in egg production in cows during fall.

Evidence for arrested development of abomasal nematodes in white-tailed deer.

White-tailed deer (Odocoileus virginianus) obtained from Noxubee National Wildlife Refuge, Noxubee County, Mississippi (USA) during April (n = 3), June (n = 5), September (n = 5), and November (n = 5) 1989, were necropsied for counting and identification of adult and larval stages of abomasal nematodes. Fourth-stage larvae (L4) (n < or = 25) from each deer were randomly selected for measurement of total worm length and width. Adults of four worm species were found: Mazamastrongylus odocoilei, M. pursglovei, Ostertagia mossi, and O. dikmansi. There were no differences between months in adult male worm burdens for all species except O. dikmansi for which the April worm burden was greatest (P < or = 0.05). Overall, the length of L4 ranged from 929 to 4,361 microns. There were no significant differences (P > 0.05) between months in the mean length (1,334 to 1,532 microns) of L4. Except for low numbers of developing fourth-stage larvae (length > 1,650 microns) in April (2.6%), June (7.4%), September (11.3%), and November (3.7%), worms were early fourth-stage larvae (EL4) or fully developed adults. Overall, the proportion of EL4 in individual deer ranged from 19 to 97%; in male (n = 3) and female (n = 15) deer the proportions of EL4 were 22.5% and 67%, respectively. The mean proportions of EL4 in female deer were 51.4% (April), 63.2% (June), 78.1% (September), and 74.7% (November), but there was no difference (P > 0.05) among the 4 months.(ABSTRACT TRUNCATED AT 250 WORDS)

Estimation of the numbers of trichostrongylid larvae on pastures.

Estimates of the density of larvae on herbage are used in epidemiologic studies to determine seasonal or monthly variations in contamination of pastures with third-stage larvae of the trichostrongyles, and to provide an index of the risk of exposure of grazing animals. Estimates of density are affected by many variables, including laboratory techniques, climate, forage types, and farm and animal management methods. Thus, a comparison of results given by different workers is not desirable. In obtaining and interpreting larval density estimates, it is important to standardize the technique over the period of observation. Because techniques for estimation of larvae are cumbersome and time-consuming, statistical design is often compromised. Herbage samples should be taken randomly and with sufficient replication to overcome the variability of the herbage sampling technique. Studies to determine an appropriate sampling design to obtain the best estimate for pastures of all sizes have not as yet been carried out.

Dose-titration to confirm the level of fenbendazole for control of Raillietina cesticillus in broiler chickens.

A total of 452 broiler chickens, naturally infected with Raillietina cesticillus, were allotted into six treatment groups. One group was fed unmedicated broiler ration (Group 1), and the other five groups were fed broiler ration containing fenbendazole at 180 ppm for 3 days (38.5 mg/kg body weight [BW]), 240 ppm for 3 days (50.9 mg/kg BW), 120 ppm for 6 days (52.2 mg/kg BW), 180 ppm for 6 days (79.9 mg/kg BW), or 240 ppm for 6 days (104.3 mg/kg BW). Fenbendazole was 100.0% efficacious against R. cesticillus when administered in the diet at 240 ppm for 6 days; 99.9% at 240 ppm for 3 days and at 180 ppm for 6 days; 99.5% at 120 ppm for 6 days; and 96.9% at 180 ppm for 3 days. Fenbendazole treatment had no adverse effect on weight gain or feed intake.

Diseases diagnosed in gray foxes (Urocyon cinereoargenteus) from the southeastern United States.

Diagnostic findings were reviewed on 157 sick or dead gray foxes (Urocyon cinereoargenteus) from the southeastern United States examined during the period 1972 through 1989. Most foxes (n = 118) originated from Georgia; fewer animals were from Florida, Kentucky, Maryland, Mississippi, North Carolina, South Carolina, Tennessee, Virginia and West Virginia. Etiologic diagnoses included canine distemper (n = 125), congenital absence of guard hairs (n = 7), traumatic injuries (n = 7), rabies (n = 3), suspected toxicoses (n = 3), verminous pneumonia due to Paragonimus kellicotti (n = 1), bacterial septicemia secondary to Dracunculus insignis (n = 1), and tick paralysis (n = 1). Concurrent toxoplasmosis or toxoplasmosis or cryptosporidiosis was noted in six and three foxes with canine distemper, respectively. Only lesion diagnoses were attainable for three foxes, and six cases were classified as undetermined. Canine distemper was diagnosed in 78% of the foxes, was geographically widespread, was detected in 16 of 18 yr, and exhibited a seasonal pattern of occurrence. These facts indicate that canine distemper is more significant as a mortality factor for gray foxes than all other infectious and noninfectious diseases combined.

Potential natural exposure of Mississippi sandhill cranes to aflatoxin B1.

A survey was conducted to determine if carcinogenic mycotoxins were present in foods consumed by Mississippi sandhill cranes (Grus canadensis pulla). Samples of field corn (Zea mays) (n = 111) and chufa (Cyperus esculentus) (n = 20), obtained in 1987, 1988 and 1989 on the Mississippi Sandhill Crane National Wildlife Refuge (MSCNWR) and nearby private lands were analyzed for aflatoxin B1(AB1), ochratoxin A and sterigmatocystin using thin layer chromatography. Chufa samples were negative for all three mycotoxins. Aflatoxin B1 was found in corn at concentrations from 5 to 5,000 ppb; the other mycotoxins were not found in corn. Contaminated corn was found in 72% of all corn fields, but the proportion of contaminated fields was 57 to 100% for the 3-yr period. Contamination with AB1 was greatest in corn obtained from the ground post-harvest. Overall, 32% of corn samples from the ground had levels greater than or equal to 200 ppb with a mean of 427 ppb (range = 5 to 5,000 ppb) in contaminated fields. In 1989, mean AB1 concentration in corn on the ground was 5 to 1138 ppb for individual fields. The concentration of AB1 was less than or equal to 200 ppb in all corn samples from upright stalks. The study demonstrated that AB1 is available to sandhill cranes and at levels that may pose a serious health threat.

Absence of avian pox in wild turkeys in central Mississippi.

Eastern wild turkeys (Meleagris gallopavo silvestris) (n = 1,023), obtained during winter, spring, and summer from 1983 to 1988 on Tallahala Wildlife Management Area (TWMA) (Jasper County, Mississippi, USA) were examined for avian pox lesions. Domestic turkey poults (n = 152) maintained on the area for 1 to 2 wk periods from 1987 to 1989 also were examined. Neither wild nor domestic birds showed gross evidence of pox virus infection. This study indicated that avian pox was not endemic in wild turkeys at TWMA.

Occurrence and seasonal transmission of hematozoa in wild turkeys.

The occurrence and seasonal patterns of transmission of the blood protozoa of wild turkeys (Meleagris gallopavo silvestris) were studied at Tallahala Wildlife Management Area (TWMA) (Jasper County, Mississippi, USA). Blood smears obtained from wild turkeys in winter, spring and summer, and from sentinel domestic turkeys throughout the year were examined for Haemoproteus meleagridis and Leucocytozoon smithi. Whole blood from wild turkeys captured in summer was subinoculated into malaria-free domestic turkey poults and recipient birds were examined for Plasmodium spp. The prevalence of H. meleagridis and L. smithi were not different (P greater than 0.05) between adults and juveniles or between male and female turkeys in any season. Leucocytozoon smithi was not detected in poults in summer or in juveniles examined in winter. Sentinel studies and information from wild birds revealed that transmission of H. meleagridis and L. smithi did not overlap. Haemoproteus meleagridis was transmitted from May through November, while L. smithi was transmitted only from January through April. The onset of transmission of H. meleagridis coincided with peak hatching (mid-May) and brood-rearing (May-November) of turkey poults. Plasmodium spp. were not found in turkeys from TWMA (n = 27) nor in birds from three widely separated counties (n = 28) in Mississippi.

Epidemiologic features of an intracranial abscessation/suppurative meningoencephalitis complex in white-tailed deer.

Case records of 683 white-tailed deer (Odocoileus virginianus) submitted to the Southeastern Cooperative Wildlife Disease Study (Georgia, USA) for diagnostic purposes from 1971 to 1989 were reviewed for the occurrence of pyogenic infections of the central nervous system, specifically intracranial abscessation or suppurative meningoencephalitis. These conditions, either alone or in combination, were diagnosed in 24 of 683 (4%) deer. Thirteen genera of bacteria were isolated; the most frequent species was Actinomyces pyogenes. The disease was strongly sex biased (P less than 0.01); 88% of the cases occurred in males. Cases were more prevalent (P less than 0.05) in older bucks; the median age of infected bucks was 3.2 yr, and 71% of these were greater than or equal to 2.5-yr-old. Intracranial abscessation/suppurative meningoencephalitis cases accounted for 20% of the diagnoses among 56 bucks greater than or equal to 3-yr-old. Cases were seasonal, occurring only from October to April. Characteristic necrosis, erosion, and pitting of skull bones were common, and this bone damage may be useful in determining cause of death when only skeletal remains are found. Males, especially older bucks, apparently are predisposed to intracranial abscessation/suppurative meningoencephalitis because of the cycle of antler development and behavioral traits associated with reproduction. The strong bias toward prime age bucks suggests that these infections could specifically hinder management strategies designed to produce populations with older buck age structures.

Multiple feather follicle cysts in a wild turkey.

A hunter-killed wild turkey (Meleagris gallopavo silvestris) was submitted for examination because of numerous 2 to 30 mm diameter, yellowish, hard nodules in the skin. The nodules were confined to the skin and did not involve subcutaneous tissues. Nodules consisted of dilated feather follicles packed with a caseous tan to pale yellow material. Histologically, affected feather follicles were markedly dilated and filled with laminated keratin debris. The lesions were determined to be multiple feather follicle cysts of unknown etiology.

Efficacy of oxfendazole against inhibited larvae of Ostertagia ostertagi in naturally infected calves in the southern USA.

Forty yearling calves were assigned to four equal groups; three of the groups were treated with oxfendazole at dose rates of 6.75 mg/kg, 4.50 mg/kg, or 2.25 mg/kg bodyweight while the fourth group served as an untreated control. The calves were native to north-east Mississippi, USA, and harboured natural infections of gastrointestinal nematodes. The study was conducted during July when inhibited early fourth-stage larvae may be found in large numbers after their acquisition in the spring. The calves were maintained in separate groups on concrete-floored pens for 17 days before the intraruminal administration of oxfendazole. Seven days after treatment, the calves were slaughtered and the gastrointestinal parasites counted. At all the dose rates examined oxfendazole exhibited an efficacy of at least 99.4 per cent against adults of Haemonchus placei, Trichostrongylus axei, Bunostomum phlebotomum, Cooperia species, T colubriformis, Oesophagostomum radiatum, and Trichuris ovis. The efficacy against adult Ostertagia ostertagi was at least 99.4 per cent at dose rates of 6.75 and 4.50 mg/kg bodyweight, but decreased to 93.7 per cent at 2.25 mg/kg. The efficacy of oxfendazole against inhibited larvae of O ostertagi decreased with dose rate from 78.8 per cent at 6.75 mg/kg, to 58.9 per cent at 4.50 mg/kg and 20.3 per cent at 2.25 mg/kg bodyweight.

Efficacy of a morantel sustained-release bolus for control of gastrointestinal parasites in winter-grazed steers in Mississippi.

From Nov 22, 1983 through May 15, 1984, 36 crossbred steers were allotted into 3 treatment groups (12/group) and were grazed on separate 3.4-hectare pastures. On Nov 22, 1983, the steers were administered a single morantel sustained-release bolus (MSRB), orally (group 1), or a single dose of thiabendazole (TBZ; 66 mg/kg of body weight, orally; group 2), or were left untreated (group 3; controls). Animal weights, nematode egg counts in fecal specimens, and plasma pepsinogen concentrations were monitored monthly. At the termination of the study, 4 steers from each treatment group were slaughtered and necropsied and worm counts were determined. A set of parasite-free tracer calves (3/treatment group) were grazed with each treatment group for 1 month, beginning on Nov 22, 1983; a second set of tracer calves (3/group) were grazed with each treatment group for 1 month, beginning Apr 3, 1984. At the end of their respective grazing periods, tracer calves were held for 3 weeks and then were slaughtered and necropsied and their worm counts were determined. Mean nematode egg counts in fecal specimens of group 1 (MSRB treated) were significantly lower (P less than 0.05) than that of the TBZ-treated or nontreated steers. Differences in worm counts were not found between treatment groups. Differences in worm counts of tracer calves were not found among the 3 groups for November 1983 nor for April 1984. Steers treated with the MSRB had a higher mean weight gain (P less than 0.06) than did the control or TBZ-treated steers.

Failure to demonstrate viscerotropic velogenic Newcastle disease in psittacine birds in the Republic of the Philippines.

Birds on the islands of Luzon, Mindanao, and Palawan in the Republic of the Philippines were surveyed for viscerotropic velogenic Newcastle disease (VVND). Virus isolation was attempted on 728 cloacal samples from native and exotic psittacine birds, non-psittacine birds, and domestic chickens and ducks. A VVND virus isolate was obtained from a single domestic chicken that had exhibited ocular discharge and diarrhea 3 days before sampling. All other birds were negative for VVND.

Temporal occurrence of third-stage larvae of Elaeophora schneideri in Tabanus lineola hinellus on South Island, South Carolina.

The occurrence of third-stage larvae of the arterial worm (Elaeophora schneideri) in populations of the horse fly, Tabanus lineola hinellus, was studied on South Island, Georgetown County, South Carolina. Over the period from mid-April to mid-October 1982, horse flies had a bimodal pattern of abundance with peak populations in June and September. During individual bimonthly horse fly collections, the prevalence of infection of T. l. hinellus ranged from 0 to 1.23%. Prevalence of infected horse flies was biphasic with peaks in mid-May (1.23%) and mid-August (1.22%), 2 to 4 wk prior to peaks in horse fly populations. The intensity of infection of T. l. hinellus increased as time progressed and was highest in late summer. This increase resulted in greater recovery of infective larvae during August-September (mean intensity = 25) than in May-June (mean intensity = 4). Both prevalence and intensity of infection of T. l. hinellus were low compared to primary intermediate hosts of E. schneideri in the western U.S.

Elaeophorosis in white-tailed deer: pathology of the natural disease and its relation to oral food impactions.

The lesions of naturally occurring elaeophorosis in white-tailed deer (Odocoileus virginianus) were studied. Arterial changes caused by adult Elaeophora schneideri occurred mainly in cephalic arteries and were characterized by circumferential intimal thickening, disruption of the internal elastic lamina, and verminous thrombosis. Microfilariae caused focal necrosis and fibrosis in the myocardium, but produced only minor changes in other tissues. Radiographic studies indicated that E. schneideri can cause impairment of the cephalic arterial circulation in white-tailed deer. Eleven of 14 (78%) infected deer had oral food impactions, with sublingual impactions being most common. Seven deer with impactions had other oral pathologic conditions, such as gingivitis, loose or absent premolar and/or molar teeth, and remodeling and/or lysis of mandibular bone. The evidence indicates a relation between food impactions and infection by E. schneideri in white-tailed deer, but no definitive connection was established.

Diseases diagnosed in wild turkeys (Meleagris gallopavo) of the southeastern United States.

Diagnostic findings are presented on 139 sick or dead wild turkeys examined during the period 1972 through 1984. Turkeys originated from eight southeastern states (Alabama, Arkansas, Florida, Georgia, South Carolina, Tennessee, Virginia, West Virginia) and included 31 turkeys categorized as capture-related mortalities and 108 turkeys categorized as natural mortalities. Frequent diagnoses (greater than or equal to 10% of case accessions) in the natural mortality group were trauma, avian pox, and histomoniasis. Less frequent diagnoses (less than or equal to 4% of case accessions) included malnutrition/environmental stress syndrome, coligranuloma-like condition, crop impaction, bumblefoot, organophosphate toxicosis, infectious sinusitis, a lympho-proliferative disease, salmonellosis, aspergillosis, toxoplasmosis, crop trichomoniasis, and melorheostosis.