Bert E. Stromberg

Environmental factors influencing transmission

The free-living stages of gastro-intestinal nematodes on pasture (i.e. eggs, developing and infective larvae) are often overlooked and not considered by producers. The factors that influence the development, survival, distribution, or migratory behavior of the free-living larvae seen on pasture are primarily weather related. The deposition of helminth eggs in feces is the starting point for the contamination of the pasture and the subsequent development of the parasites. The cumulative numbers of eggs can be considerable by the end of the grazing season. Environmental factors will influence both development and survival of the larvae on pasture, as well as their distribution onto the herbage. Eggs deposited on the pasture will hatch and develop to the infective L3 stage. Under optimal conditions of moisture and temperature, larvae of Ostertagia ostertagi will reach the infective stage in approximately 5-6 days. Developmental time varies from one geographic region to another depending on prevailing weather. Eggs hatch and develop more slowly at lower temperatures. The rate of development increases to a maximum at higher temperatures after which development will be adversely affected and death of the larvae occurs. It is difficult to evaluate the effects of temperature without considering moisture. Moisture must be present to prevent desiccation and death of the developing larvae. Moisture has an effect on the movement and motility of the larvae. As the fecal pat dries out the larvae may desiccate and die. If the environment is dry, movement onto surrounding herbage would probably not be possible, thus forcing movement or migration into the soil beneath the fecal pat. Too much moisture (rain) may disrupt the pat, moving the larvae onto the surrounding herbage or carrying them away in the runoff. When moisture is adequate the movement of larvae on pasture may be affected by temperature. Temperature in the optimal range allows for larval activity and thus motility. Moisture provides a medium in which the larvae can move (there is probably little movement on dry surfaces). The effect of rainfall on dispersal of the larvae is important, a drop may transport larvae as far as 90 cm from the dung pat. However, optimal larval recovery is only approximately 5 cm (2-3 inch) from the edge of the fecal pat, with decreasing numbers out to approximately 25 cm. Several authors report larval migration into the soil as deep as 15 cm and as far as 40 cm from the center of the fecal pat. Soil type may have a major effect of the ability of larvae to migrate. The predilication of larvae to remain relatively close to the fecal pat may have substantial impact on transmission, as cattle do not graze close to fecal pats until forage is very limited. Therefore, intensive rotational grazing may enhance transmission by forcing animals to graze the highly contaminated areas. At the same time, intensive rotational grazing causes increased disruption of fecal pats, thus enhancing desiccation. Many investigators have utilized tracer calves grazing a pasture for a prescribed period of time to provide an indication of both species and numbers of worms present. Some investigators have used pasture larval counts, reporting number of larvae per kg of dry herbage and the genera present.

Cooperia punctata: Effect on cattle productivity?

Cooperia spp. have become the most prevalent parasites in United States cow/calf operations as observed in the USDA NAHMS (National Animal Health Monitoring System) Beef Cow/Calf survey in 2008. This is at least in part due to the widespread use of macrocyclic lactones that have recently been shown to have a reduced activity against these parasites. The effects of Cooperia spp. on cattle productivity are largely unknown. This study was conducted to assess their effect upon cattle housed under conditions found in American feedlots. Two hundred yearling calves (average weight 460 lb/209 kg) were acquired from northwestern Arkansas and northeastern Oklahoma and were vaccinated and dewormed upon arrival at the feedlot. Animals were comingled and preconditioned for approximately one month, and were fed a standard growing ration throughout the study. Calves were randomly divided into two groups (n=80, infected and control) and each group was further divided into two replicate pens (n=40). Calves from the two infected pens were orally inoculated with a gavage of 1 × 10(5) and 0.825 × 10(5) infective larvae of a recent isolate of Cooperia punctata on day 0 and 14, respectively, with the two control pens receiving a similar volume of tap water. Data collected included biweekly fecal egg counts, daily individual feed consumption and weight gain over the 60-day test period. The presence of C. punctata (>99% of recovered worms) was confirmed by necropsy and recovery from the small intestine on days 35 and 60 post infection (PI) in a subset of animals. Egg counts were positive by day 14 PI and remained at numbers similar to values seen in field studies. The control group gained weight 7.5% more rapidly (p=0.02) than infected animals (3.24 lb/1.47 kg per day vs. 3.0 lb/1.36 kg per day, respectively). The Cooperia-infected calves also consumed 1.5 lb (0.68 kg) less dry feed per day than the control animals (p=0.02). These data suggest that C. punctata has a deleterious effect on both appetite and nutrient uptake or utilization. At necropsy (days 35 and 60), the draining mesenteric lymph nodes of infected animals were increased in size and the small intestinal mucosa was thickened and covered with a thick layer of mucus in the infected animals. The most prominent histological changes in the Cooperia- infected animals included a moderate increase in the number of intraepithelial lymphocytes and globule leukocytes, as well as aggregates of eosinophils within the lower lamina propria. The only significant difference was an increase in the goblet cell density at day 60. Anthelmintic sensitivity/resistance of the Cooperia isolate used was determined by treatment of one pen of infected calves with a macrocyclic lactone and the other pen with a benzimidazole at the completion of the study. The macrocyclic lactone treatment (n=40) did not remove the parasites (FECRT=8.8%), while treatment with a benzimidazole was very effective (FECRT=98.1%). This study demonstrated that C. punctata has a significant effect on cattle productivity, both reduced weight gain and decreased feed intake compared to controls.

Prevalence of Toxoplasma gondii antibodies in hunter-killed white-tailed deer (Odocoileus virginianus) in four regions of Minnesota

Sera from 1,367 white-tailed deer (Odocoileus virginianus) from 4 geographic regions in Minnesota collected during 4 hunting seasons (1990-1993) were tested for antibodies to Toxoplasma gondii using the modified direct agglutination test incorporating mercaptoethanol. Sera from 30% of the deer had antibody titers > or = 25; 8.6% were positive at a titer of 25, 11% at a titer of 50, and 10% at a titer > or = 500. There was a significant increase in seropositivity with age (P < 0.0001). Adult deer were twice as likely to be positive as yearlings; yearlings were 2.5 times as likely to be positive as fawns. There was no difference in prevalence by sex when adjusted for age (P = 0.316), nor was there age-sex interaction. Only males showed a slight increase in titer with age (P = 0.049). There were no significant differences in prevalence among the regions of northeast pine/aspen forest, southwest tall-grass prairie, southeast mixed-hardwood forest, and aspen/oak suburban park land. There were no statistically significant differences by year of collection. The prevalence of T. gondii antibodies in white-tailed deer remains high and deer hunters and consumers should ensure that venison is well-cooked or frozen prior to consumption.

Production responses following strategic parasite control in a beef cow/calf herd

Strategic parasite control has been reported to improve performance in a beef cow/calf herd that does not demonstrate clinical parasitism. This study was conducted to determine if strategic anthelmintic treatment at turnout and at midsummer would improve growth and reproduction. Two cow/calf groups of similar composition were grazed on separate, but equivalent pastures in the spring, and at midsummer, they were moved to new pastures. The treated group was given fenbendazole at tumout (cows) and at midsummer (cows and calves). The control group was not treated. The study was repeated in the following year. Across both years of the study, parasite egg counts were substantially reduced in both the treated cows (P < 0.005) and treated calves (P < 0.0001). The calves in the treated group significantly (P < 0.0001) outgained the control calves in both years of the study by 19.3 kg and 13.2 kg, respectively. Average daily gain (ADG) after adjusting for birth weight and birth date for treated calves was 0.13 kg greater than for control calves (0.83 vs 0.70) for the 2-year study (P < 0.0001) There was also a significant (P = 0.0357) increase in the reproductive performance of the cows. The pregnancy rate averaged across years was 94% for the treated cows compared to 82% for the control animals.

Parasites and parasite stages of free-ranging wild lions (Panthera leo) of northern Tanzania.

Abstract Fecal samples from 33 lions (Panthera leo) in Serengeti National Park and Ngorongoro Crater Conservation Area in northern Tanzania contained 19 different parasites, 12 of which, including Aelurostrongylus sp., a species of Acanthocephala, a species of Anoplocephalidae, Capillaria sp., Demodex sp., Eimeria sp., Habronema sp., Isospora felis, Isospora rivolta, one species of Isospora that was previously undescribed from lions, one species of Trematoda that was previously undescribed from lions, and Trichuris sp., were new reports for lions. Seven other species had been previously reported from lions.

Coprological Surveys of Alouatta pigra at Two Sites in Belize

Fecal samples were collected from black howler monkeys (Alouatta pigra) in north central Belize and analyzed for evidence of endoparasite life stages. At least six types of endoparasites were found in Alouatta pigra fecal samples collected in the Lamanai Archaeological Reserve and the Community Baboon Sanctuary in 1999. These include a digenean trematode, an oxyurid nematode, a strongyle-type nematode, an ascarid presumed to be Ascaris sp., Entamoeba coli and Iodamoeba bütschlii. Higher trematode prevalence was found in adult Alouatta pigra compared to juveniles and higher prevalence of nematode larvae in all animals was found in the wet season compared to the dry season.

Epizootiology of Ostertagia ostertagi in cow-calf production systems in the American Midwest

The most common gastrointestinal nematodes found in cattle in the Midwest are Ostertagia ostertagi and Cooperia oncophora. Other parasites include Haemonchus placei, Bunostomum phlebotomum and Nematodirus helvetianus. Parasite numbers are generally low in this region, as indicated by fecal egg counts and tracer calf worm recoveries, and the numbers of parasites decrease as one travels farther north. This decrease in parasite numbers also corresponds to a similar reduction in the prevalence of clinical disease. The dynamics of fecal egg shedding are similar throughout the Midwest. Cow fecal egg counts begin to increase just prior to calving in the spring, continue to rise, reaching a peak in July and August, and return to low numbers (2 or less eggs per gram of feces (epg)) in October. Calves born in the spring (March-May) show increasing numbers of eggs in their feces throughout the grazing season, with peak recoveries in October and November, after which the numbers decline as the calves develop an immunological response. Tracer calf worm recoveries demonstrate pasture contamination for the period grazed. These recoveries show adult O. ostertagi increasing throughout the grazing season then falling to low levels over the winter. Larval inhibition of O. ostertagi, as shown by recovery of inhibited fourth stage larvae (L4) occurs throughout the year, with increasing numbers of larvae recovered in the fall. The production robbing effects of these parasites has been demonstrated by the use of a controlled strategic deworming program. Weaning weight advantages of 14 to more than 20 kg have been reported in this region of the country when compared with an untreated group.2+ !%

Hematology and clinical pathology of experimental Fascioloides magna infection in cattle and guinea pigs

The hematologic and clinico-pathologic response to Fascioloides magna infection in cattle and guinea pigs was investigated. Twelve calves (six infected and six controls) were monitored for 26 weeks after inoculation with 1000 metacercariae. All calves remained healthy and there were no significant differences in weight gains between infected and control groups. Flukes (mean = 9.2, range 1-32) were recovered from the liver and abdominal cavity of all infected calves. The only significant response observed in the complete blood counts was an eosinophilia present in the infected calves extending from Weeks 2 to 26 post-infection. There were no significant differences in serum levels of aspartate aminotransferase and only minor increases in the levels of gamma-glutamyl transferase and sorbitol dehydrogenase. A total of 48 infected and 48 control guinea pigs from three separate experiments were monitored for 16 weeks after inoculation with 20 metacercariae of Fascioloides magna. Infected guinea pigs died between 7 and 114 days after infection, and flukes (mean = 2.5, range 0-13) were recovered from the liver, abdominal cavity, lungs, thoracic cavity, skeletal muscle and subcutaneous tissue. There were no differences in weight gains between infected and control guinea pigs. Complete blood counts showed increases in white blood cells, monocyte and neutrophil counts from between the third and fourteenth weeks post-infection; however, the differences were not consistently significant. Infected guinea pigs developed a significant eosinophilia and basophilia from 2 to 16 weeks post-infection. There were no significant changes in the serum levels of alanine aminotransferase or gamma-glutamyl transferase. There was an increase in the serum levels of aspartate aminotransferase beginning at 5 weeks post-infection. The response observed in the guinea pigs was similar to that reported in sheep, suggesting the suitability of the guinea pig as a model for Fascioloides magna infection in the sheep.

ENZYME-LINKED IMMUNOSORBENT ASSAY AND INDIRECT HAEMAGGLUTINATION TECHNIQUES FOR MEASUREMENT OF ANTIBODY RESPONSES TO EIMERIA TENELLA IN EXPERIMENTALLY INFECTED CHICKENS

An indirect haemagglutination test (IHA) and ELISA technique were developed to detect antibodies against Eimeria tenella. The ELISA technique was relatively easy to perform, more sensitive than the IHA test, and needed only a fraction of the antigen required for IHA. The highest titers using ELISA were 1:16,384 compared to the IHA titers of 1:64 for the same sera. The ELISA titers depended upon the age of the birds when they were infected, the number of oocysts inoculated and the number of inoculations. Immunodeficient birds (cyclophosphamide-treated), when inoculated with several doses of oocysts of E. tenella (350, 3,000, 30,000) showed no IHA or ELISA antibody titers. The immuno-competent chickens of the same age, which received identical doses of oocysts responded with readily detectable antibody levels. Chickens inoculated with E. maxima or E. necatrix had sera titers of 1:50 or 1:400, respectively, when reacted with E. tenella antigen. The E. tenella inoculated birds had titers as high as 1:3,200 with the same antigen.

Outbreak of Trichinella spiralis Infections Associated With a Wild Boar Hunted at a Game Farm in Iowa

BACKGROUNDnRates of trichinellosis have declined significantly in the United States due to improved pork production practices and public awareness of the danger of eating raw or undercooked pork. In April 2011, the Minnesota Department of Health received a report of presumptive trichinellosis in a 50-year-old man with a history of wild boar consumption. A public health investigation was initiated.nnnMETHODSnMedical record reviews and patient and family interviews were conducted. Trichinella species serology was performed on patient and family serum samples, and larval identification was attempted on clinical specimens and meat samples.nnnRESULTSnThe index patient harvested a wild boar from an Iowa game farm; he processed the meat after returning home and developed gastrointestinal symptoms 2 days later. Four days after his illness onset, all 5 family members consumed a roast from the boar. The index patient sought healthcare 4 times after illness onset before being definitively diagnosed with trichinellosis. Following initiation of albendazole therapy, the index patient developed atrial fibrillation. One additional family member who processed the raw meat was diagnosed with trichinellosis. Trichinella spiralis larvae were identified in wild boar meat samples.nnnCONCLUSIONSnTrichinellosis has long been recognized as a potential hazard of consuming undercooked wild carnivore meat, and historically has been associated with consumption of pork from domestic swine, but may be unfamiliar to practicing clinicians in the United States. Education of hunters and the broader population on the potential for trichinellosis and the importance of proper handling and cooking meat from wild or free-range animals needs to be reinforced.