[Forming of gastro-intestinal nematodes fauna of free ranging European bison in Bialowieza Primeval Forest during last 17 years (1984-2001)]

28 European bison of both sexes and in different age shot in Białowieza Primeval Forest in January 1984, (10 animals), January 1992 (10 animals) and in January and the beginning of February 2001 (8 animals) have been necropsied. The examined animals in mentioned years were of similar age. There were examined abomasa and duodena of shot animals. All necropsied bison were infected with gastro-intestinal nematodes. The highest intensity of infection with nematodes of abomasum was found in 1992 year and with nematodes of duodenum in 2001 year. In the examined period were found as many as 21 species of gastro-intestinal nematodes, and 15 of them occurred in 1984, 16 in 1992 and 17 in 2001; 12 species, namely: Trichostrongylus axei, T. capricola, Ostertagia ostertagi, O. lyrata, O. leptospicularis, O. kolchida, Spiculopteragia boehmi, Cooperia oncophora, Nematodirus helventianus, N. roscidus, N. europaeus and Aonchotheca bilobata occurred in all 3 examined years. The highest mean intensity of infection and the percentage index of intensity of these 12 species of nematodes showed O. leptospicularis which was 45% to 47% of all Ostertagiinae. Beyond of these 12 species of nematodes which occurred in all examined years, there were found 9 species more: Ostertagia antipini, Spiculopteragia mathevossiani, S. asymmetrica, Mazamastrongylus dagestanicus, Cooperia surnabada, C. punctata, C. pectinata, Haemonchus placei and Ashworthius sidemi. They occurred sporadically and in low density. During the examined period, bison have adapted 10 species of parasites from Cervides. Mazamastrongylus dagestanicus - parasite primary typical for moose, was for the first time found in bison.

Responses of fertile and sterile screwworm (Diptera: Calliphoridae) flies to bovine blood inoculated with bacteria originating from screwworm-infested animal wounds

ABSTRACT A simple bioassay system was developed to study locomotory and ovipositional responses of screwworm, Cochliomyia hominivorax (Coquerel), flies to bovine blood inoculated with eight species of coliform bacteria that were isolated from screwworm-infested animal wounds. When exposed to odors from bacteria-inoculated blood which was incubated for 72 h at 37 degrees C, approximately 50% of 7- and 10-d-old gravid females landed on the blood by the end of 15 min test exposure. Only 17% of 7-d-old reproductively sterile females (from irradiated pupae) with previtellogenic ovaries and 2% of 4-d-old vitellogenic females responded to the same treatment. Females generally reacted in greatest numbers to bacteria-inoculated blood incubated for 72 h, followed by 48 h, then 24 and 96 h. Males of all ages tested were unresponsive. Although oviposition occurred in tests with gravid females lasting for 1 h, with both inoculated blood and an uninoculated control, the inoculated sample was significantly better than the control at 48, 72, and 96 h incubation duration. Our results are consistent with the conclusion that the inoculated blood, when incubated for 48-72 h, gives off volatile chemicals which attract gravid females and contains an oviposition stimulant that acts following contact and feeding. The volatiles, once isolated and identified, may be useful for sampling gravid females in the field as well as improving the oviposition system in the mass-production facility of the screwworm eradication program.

[The influence of Fasciola hepatica invasion on the assorted milk quality parameters in cows]

The investigations of the influence of Fasciola hepatica invasion on the assorted parameters of milk quality were performed in cows. Mean protein content in the milk from infected animals ammounted 3.60% and was higher than in the milk from uninfected cows (3.30%). Similar tendency was observed in the case of the fat (5.08% and 3.91%) and lactose (4.36% and 4.34%). The count of somatic cells in milk from infected cows was lower than in milk from uninfected animals (356.07 and 1776.92). It can indicate immunosupressive activity of Fasciola hepatica on the host.

Progress towards the eradication of Amblyomma variegatum from the Caribbean

Progress in the Caribbean Amblyomma Program (CAP) is reviewed since its inception in 1995 when regional eradication activities for Amblyomma variegatum ticks were initiated using Bayticol pour-on. Technical achievements in the various islands were slow initially, and showed a wide diversity in attaining eradication targets. St. Kitts, considered as a model program. eliminated the tropical Bont tick (TBT) from most of the island in less than 3 years. However, the elimination of very low numbers of residual adult TBT that persisted in three 'hot-spots' took another 3 years. A similar problem was faced in St. Lucia, although the approach there was to cull the wild cattle in the last remaining hot-spot. Both islands were certified as 'Provisionally free from TBT' in November 2001. In 2002, Anguilla and Montserrat attained the same status, and Barbados and Dominica also qualify for certification. Certification is based on strict, three-monthly, surveillance criteria: essentially, two successive TBT-free surveillance rounds on a statistically acceptable sample of the livestock population. Within the responsibility of the CAP, three islands remain TBT-infested, Antigua, Nevis, and St. Martin/St. Maarten. Nevis is of concern because it has been operational since late 1995, and appears unable to resolve the problem of treating stray small ruminants. Current funding should be adequate to complete eradication on Nevis and in St. Martin/St. Maarten. The major outstanding challenge is Antigua. In comparison to other islands they have the largest number of livestock, and have much larger populations than originally reported: sheep and goats are 4-5-fold higher, and cattle are 1.35-fold higher. The cost for Bayticol is, therefore, almost double and an additional US dollars 1.5 million is required for that commodity alone.

Host responses to Cryptosporidium infection

Cryptosporidium is a clinically and economically important infection whose pathogenic effect begins with colonization of the intestinal epithelium. Despite intensive efforts, a consistently effective therapy for the infection has yet to be identified. Morbidity and mortality results from ongoing loss of absorptive epithelium, which leads to villous atrophy and malabsorption and release of inflammatory mediators that stimulate electrolyte secretion and diarrhea. With further clarification of the mechanisms underlying enterocyte malfunction in Cryptosporidium infection, it should be possible to design rational nutritional and pharmacologic therapies to enhance nutrient and water absorption, promote the clearance of infected enterocytes, and restore normal villus architecture and mucosal barrier function.

Bovine neosporosis: immunoblot improves foetal serology

The purpose of the study is the comparative evaluation of the immunofluorescent antibody test (IFAT) and an immunoblot (IB) test for the examination of foetal fluids for specific antibodies against Neospora caninum. Peritoneal and pleural fluids as well as abomasal contents were analysed. The results of the serological examinations were compared to those obtained by histological, immunohistochemical, and PCR analysis of foetal tissues as well as to the results of maternal serological examinations. Fluids were used undiluted in the IB and reactions against six immunodominant antigens were recorded. When the recognition of at least two immunodominant antigens was regarded as positive, the agreement of the IB with other diagnostic methods was good to moderate as characterised by kappa-values of 0.76 (histology/immunohistochemistry), 0.69 (maternal serology) and 0.54 (PCR on foetal tissues). The IB results agreed better with the results of the other diagnostic methods than those of the IFAT. The higher relative sensitivity of the IB was regarded as the main reason for the better agreement. However, also the specificity of the IB was superior to that of the IFAT in relation to histology/immunohistochemistry, maternal serology and PCR.

Neosporosis in bovine dairy herds from the west of France: detection of Neospora caninum DNA in aborted fetuses, seroepidemiology of N. caninum in cattle and dogs

Neospora caninum is considered one of the major causes of abortion in cattle in most parts of the world. In this study, the role of N. caninum was investigated in groups of aborted cattle and dairy herds from the west of France. Good correlation was found between parasite DNA detection in fetuses and serologic statuses of dams. In groups with documented abortion status and no antibodies to other pathogens, 17-45% of aborted animals were seropositive for N. caninum, and significant relationship between prevalence of Neospora antibodies and frequency of abortions was found. Neospora-associated abortions were observed all the year round, with a peak in summer. Higher ratios of seropositive abortions were found before the 6th month of gestation. In 12 herds studied in the field, serologic prevalence ranged 6-47%. No difference in age was found between seropositive and seronegative cows. Results indicate that N. caninum is an important and stable cause of abortion in cattle in France.

Persistent efficacy of doramectin topical solution against induced infestations of Bovicola bovis and Solenopotes capillatus

A study was conducted in two locations, Wyoming and Wisconsin, USA, to evaluate the persistent efficacy of doramectin topical solution at a dose rate of 500 microg/kg body weight against artificially induced infestations of Bovicola bovis and Solenopotes capillatus on cattle. At each location, lice-free beef calves were individually housed and randomly allocated to treatment. Both B. bovis and S. capillatus were transferred from untreated donor animals to doramectin-treated cattle at the end of 35, 63, 91 or 126 day post-treatment periods. Cattle treated with a saline pour-on served as the control. Based on the geometric means of lice counts 2 weeks following transfer, the persistent efficacy of a single treatment with doramectin topical solution against induced infestations of B. bovis was 100.0, 100.0, 99.5, and 100.0% at post-treatment days of 35, 63, 91, and 126, respectively. Persistent efficacy against induced infestations of S. capillatus, for the same intervals, were 100.0, 94.9, 86.3, and 74.9%.

Epidemiology of Cryptosporidium spp. and Giardia duodenalis on a dairy farm

Prevalences of Cryptosporidium spp. and Giardia duodenalis in relation to age and season were investigated on a dairy farm in The Netherlands over the course of 1year. The whole herd was sampled five times, whereas calves younger than about 2 months were sampled every 2-3 weeks. Associations between diarrhoea and presence of one or more pathogens (Cryptosporidium spp., G. duodenalis, rotavirus) were investigated. Potential transmission routes of Cryptosporidium spp. were evaluated and positive samples of Cryptosporidium spp. and G. duodenalis were identified to genotype level by PCR microsatellite identification and fingerprinting. Shedding of Cryptosporidium spp. was found in all age categories but peaked in calves 1-3 weeks old (39.1%). Herd prevalence of shedding for Cryptosporidium spp. varied from 2.4% in June to 22.2% in December. Shedding of G. duodenalis was found in all age categories but peaked in animals 4-5 months old (54.5%). Herd prevalence of shedding for G. duodenalis varied from 0.8% in June to 15.5% in February. Cryptosporidium spp. and rotavirus appeared to be significantly associated with diarrhoea in calves. Microsatellite analysis showed two different subtypes (C3 and C1) of Cryptosporidium parvum calf strains. Two genotypes of G. duodenalis were found, one positive by A lineage specific PCR and thus closely related to human genotypes and one genotype, which was negative by A and B lineage specific PCR. The results indicate that cow-to-calf and indirect calf-to-calf transmission both are important routes for acquiring infection with Cryptosporidium spp.

A Swiss case-control study to assess Neospora caninum-associated bovine abortions by PCR, histopathology and serology

Neospora caninum is one of the most frequent infectious organisms causing abortion in cattle worldwide. The present case-control study was designed to assess the importance of bovine neosporosis for causing abortion in Swiss cattle and to identify selected risk factors. Infection was primarily diagnosed by a N. caninum-specific PCR and serology, complemented with histopathology and immunohistochemistry. A total of 113 case and 113 corresponding control-farms were studied for 1.5 year. During this time period, 242 abortions were reported and referred for bacteriological, virological, parasitological and pathohistological examinations. N. caninum was detected by PCR in the brains of 21% of all aborted fetuses. Microscopic lesions indicative for cerebral protozoa infection were detected in 84% of PCR-positive fetal brains. Bovine viral diarrhea virus (BVDV) was demonstrated in 7% of the cases, and bacterial infections were detected in 4% of the abortions. One or more N. caninum-abortions occurred in 20% of the herds (41 case-farms and 3 control-farms). Serological examination of aborting mother cows revealed a significantly higher percentage of N. caninum-seropositive animals (44%) in comparison to the prevalence in a randomly selected population (12%). However, in eight cases (4% of all investigated abortions) seronegative cows aborted N. caninum PCR-positive fetuses, and in 50 cases the fetus remained negative although the respective mother cow was N. caninum-seropositive. Repetitive serological investigations (at a 3-12 months interval) of 3551 cows from case- and control-farms showed a decrease of the overall N. caninum-seroprevalence from 17 to 12%. Ninety out of 3008 seronegative animals were converted to N. caninum-seropositivity. Conversely, 212 out of 543 initially seropositive animals became seronegative for their second serum sample. The obtained data underlined the importance of N. caninum as a causative agent for abortion in Swiss cattle. Furthermore, PCR was confirmed to be a valuable diagnostic tool for the primary diagnosis of N. caninum in aborted fetuses. On the other hand, the value of serology appears to be hampered by the temporal instability of N. caninum antibody concentrations in adult cattle, including especially seronegativity of some individual animals. Thus, seronegativity in a mother cow or heifer does not exclude N. caninum-associated abortions.

Relationships between host species and morphometric patterns in Fasciola hepatica adults and eggs from the northern Bolivian Altiplano hyperendemic region

The highest prevalences and intensities of human fasciolosis by Fasciola hepatica are found in the northern Bolivian Altiplano, where sheep and cattle are the main reservoir host species and pigs and donkeys the secondary ones. Morphometric comparisons of many linear measurements, areas and ratios of F. hepatica adults (from sheep, cattle and pigs) and eggs (from sheep, cattle, pigs and donkeys) in natural liver fluke populations of the Bolivian Altiplano, as well as of F. hepatica adults and eggs experimentally obtained in Wistar rats infected with Altiplanic sheep, cattle and pig isolates, were made using computer image analysis and an allometric model. Although morphometric values of adult flukes from natural populations of sheep, cattle, and pigs showed great overlap, there were clear differences in allometric growth. The allometries analyzed were: body area (BA) versus body length (BL), BA versus body width (BW), BA versus perimeter (Pe), BA versus distance between posterior end of body and ventral sucker (P-VS), BL versus BW, BL versus Pe, and BL versus P-VS. These allometries show a good fit in the seven pairs of variables in all the populations examined. Comparative statistical analysis of the allometries shows that fluke adult populations from sheep, cattle and pigs significantly differ in BL versus BW and BL versus P-VS functions. Statistical analysis of F. hepatica egg size shows characteristic morphometric traits in each definitive host species. In experimentally infected rats, fluke adult allometry and egg morphometry do not vary depending on the Altiplanic definitive host species isolate. Our study reveals that the definitive host species decisively influences the size of F. hepatica adults and eggs, and these influences do not persist in a rodent definitive host model.

Acquired methemoglobinemia in anemic cattle infected with Theileria sergenti

To investigate the mechanism of anemia accompanying Japanese bovine theileriosis, we examined whether production of methemoglobin (MetHB), an indicator of erythrocyte oxidation, was associated with anemia in cattle experimentally infected with Theileria sergenti. The percentage of MetHB, which is an oxidized form of hemoglobin, increased according to the onset of anemia. During severe anemia, high levels of acquired methemoglobinemia were observed in all infected cattle. A significant correlation (r=-0.649; P<0.01) between an increase in MetHB concentration and a decrease in packed cell volume (PCV) was observed. It was considered that hemoglobin oxidation may be one of the aggravating factors of anemia in T. sergenti infection.

Immunity in calves against Dictyocaulus viviparus following a low primary infection

Thirty Holstein Friesian heifer calves, 3 months of age, were used to evaluate whether a low primary infection with Dictyocaulus viviparus would result in immunity against challenge infection 5 or 12 weeks later. Fifteen calves were experimentally infected with 30 larvae at day 0, while the other calves remained as uninfected controls. On day thirty-five 6 primary infected (G1) and 6 non-infected calves (G2) were challenged with 2000 larvae. These groups were necropsied on day 70. On day 84 the remaining 9 primary infected (G3) and 9 non-infected (G4) calves were similarly challenged and necropsied on day 119. Respiratory signs developed in most calves from approximately 2 weeks after challenge, but signs were more severe in G2 and G4 than in G1 and G3. The low primary infection resulted in significantly reduced faecal larval excretion (> 80%) and worm burdens (> 70%). In the primary infected groups the proportion of female worms in the worm burden was increased, suggesting that part of the developed immunity affected survival of the worms after their establishment in the host. Worm lengths and worm fecundity were also significantly reduced. All observed effects were stronger following challenge on day 84 than on day 35, but the effect of the duration of a primary infection (contrast between G1 and G3) was only statistically significant in the case of mean faecal larval excretion on the day of necropsy (P < 0.05) and fecundity (P < 0.05).

Study of Theileria annulata population structure during bovine infection and following transmission to ticks

Tams1 is the polymorphic immunodominant merozoite-piroplasm surface protein of Theileria annulata. Evidence for selection of divergent forms of Tams1 has been obtained recently. This study was performed to address whether selection takes place during persistent infection of the bovine host or during passage through the Hyalomma tick vector. Four calves were infected with a T. annulata isolate representing multiple parasite genotypes. The development of the parasite population was analysed by denaturing gradient gel electrophoresis (DGGE) using the Tams1 gene as a marker. In addition, the parasitaemia was measured by a semi-quantitative reverse line blot hybridization assay in order to correlate Tams1 variation to changes in parasitaemia. It was found that both parasitaemia and parasite population displayed limited variation during persistent infection. Ticks were allowed to acquire T. annulata during 2 periods of the bovine infection. Tams1 alleles detected in ticks fed during acute infection were identical to the population in the bovine host. However, ticks fed during the carrier status acquired parasites showing a single Tams1 isotype that represented, in several cases, a minor population in the bovine host at the time of infestation. Although only a limited number of ticks were studied, these preliminary data suggest that specific parasite genotypes may be selected during tick transmission from a carrier animal.

Titration of subcutaneously administered eprinomectin against mature and immature nematodes in cattle

Eprinomectin has been approved for use as a topically applied endectocide for beef and dairy cattle. To determine if eprinomectin has utility as an injectable anthelmintic, it was titrated at 0.05, 0.1, and 0.2 mg/kg s.c. against adult (Trial 1) and at 0.05, 0.1, 0.14, and 0.2 mg/kg s.c. against immature (Trial 2) stages of lung and gastrointestinal nematodes in cattle. In Trial 1, every dose of subcutaneously delivered eprinomectin showed maximal or near-maximal (> or = 99%) efficacy against Haemonchus placei, Ostertagia ostertagi, Trichostrongylus axei, T colubriformis, Cooperia punctata, Nematodirus helvetianus, Oesophagostomum radiatum, and Dictyocaulus viviparus. Adult C. oncophora was the only exception. However, even against this species, the lowest dose of 0.05 mg/kg showed 93% efficacy, and the efficacious dose necessary to kill 95% (ED95) of adults was 0.056 mg/kg. In Trial 2, every dose of subcutaneously delivered eprinomectin showed maximal or near-maximal (> or = 99%) efficacy against the immature stages of all of the above species of endoparasites. As a result, ED95 values could not be calculated. Consequently, the exquisite potency against endoparasites through parenteral administration suggests that eprinomectin may also have potential utility as an injectable product for cattle.

Epidemiological understanding of Taenia tapeworm infections with special reference to Taenia asiatica in Korea

In endemic areas of Taenia tapeworms in Korea, most of the reports showed that T. saginata was dominant over T. solium, but eating pigs is the dominant habit over eating cattle. Why do they have more T. saginata despite lower consumption of beef? This problem actually has long been recognized but until recently there has been no intensive trial to give a scientific explanation on this epidemiological enigma. By summing up the data published between the years 1963 and 1999, the ratio of armed versus unarmed tapeworms in humans was estimated at approximately 1:5. The ratio of pig-eaters versus cattle-eaters, however, was approximately 5:1. This inconsistency could be explained with the recently described T. asiatica, which infects humans through the eating of pig's viscera. We re-evaluate the importance of the consumption of visceral organ of pigs. leading us to an improved epidemiological understanding of the T. asiatica infection together with co-existing T. saginata and T. solium in Korea.

Long-term study of Haematobia irritans (Diptera: Muscidae) seasonal distribution in central Argentina with focus on winter fly abundance

The seasonal distribution of Haematobia irritans (Linnaeus, 1758) was evaluated at 31 degrees 12' S-61 degrees 29' W, Santa Fe, Argentina from November 1992 to August 2000 by weekly fly counts on 20 Holstein cows not treated against ectoparasites. The analysis was mainly focused on winter fly abundance. Two peaks of abundance were found from spring to autumn. Adults of H. irritans were consistently found on cattle during winter, with increasing numbers from the end of July to late August. The only climatic parameter soundly correlated with the four week period, before each winter fly count, was the mean air temperature with the exception of year 1998. No significant relationship was found between level of cow infestation and relative humidity, saturation deficit and rainfall. Horn fly infestation on cows was lower than 20% from end of June to end of August only in 1995, when mean air temperature was consistently lower than 11 degrees C during the four week period previous to most fly counts. Conversely, the mean temperature was higher than 12 degrees C previous to fly counts in 1998, when most cows remained infested. The results indicate that a proportion (unknown) of immature stages of H. irritans were insensitive to diapause inducing factors and developed through winter.

Free amino acid concentration in hydatid cyst fluids from fertile and infertile human and animal Echinococcus granulosus

The aim of this study was to search and compare free amino acid composition of fertile and infertile cyst fluids obtained from humans and animals infected naturally with Echinococcus granulosus, by using automated analysis based on cation-exchange chromatography with post-column ninhydrin derivatization system. 11 free amino acids from fertile (sheep origin), nine from infertile (cattle origin), 13 from infertile (human origin) hydatid cyst fluids and 19 amino acids from sera of patients with hydatid infection were detected. The levels of glycine, alanine, valine and lyrosine in fertile and infertile hydatid cysts fluids were significantly higher than in sera from patients with hydatid cysts. Glycine level in the fertile hydatid cyst fluids (sheep origin) was significantly higher than those of infertile cysts fluids (cattle and human origin) and sera with hydatid patients. Glycine level in fertile hydatid cyst fluids was about two times more concentrated in infertile cattle cyst fluids, 10 times more concentrated in infertile human hydatid cyst fluids and 13 times more concentrated in sera with hydatid patients. On the other hand, alanine and valine concentration in the fertile and infertile cyst fluids were at similar level with the exception that valine level in fertile cyst fluids was 12 times more concentrated in infertile human cyst fluids. The levels of tyrosine, citrulline, leucine, isoleucine and lysine amino acids in fertile and infertile hydatid cyst fluids were similar. Our findings with respect to fertile and infertile cysts fluids showed that free amino acids concentrations in cyst fluids were significantly, higher in sera from patients with hydatid cyst. Total amount of free amino acids content in fertile and infertile cyst fluids was three to eight times higher from that of human sera with hydatid patients.

Characterization of host responder types after a single Cooperia oncophora infection: kinetics of the systemic immune response

After primary infection with 100,000 third stage larvae of the intestinal nematode Cooperia oncophora in 3-month-old calves, a high variability in egg output and worm counts is observed. Based on this variability, infected animals can be divided in different responder types. The three major phenotypes can be classified as high, intermediate and low responder animals. We investigated whether calves classified into different responder types show different immune responses during infection. Peripheral blood eosinophil counts and flow cytometric analysis of different lymphocyte subsets of the blood did not reveal major differences between infected and control animals, nor between responder types. However, the levels of Cooperia-specific immunoglobulin (Ig)G1 and IgA during primary infection were significantly higher in intermediate responders than in low responders. In the intermediate responders, isotype specific responses were negatively correlated with parasitological parameters expressing worm expulsion and influence on worm fecundity. Total serum IgE levels were elevated in most of the infected animals. A quantitative positive relationship between worm counts and total serum IgE levels was observed. Based on the observed correlations, we propose a role for the humoral response against the maintenance of the infection in the gut.

Licking behaviour and environmental contamination arising from pour-on ivermectin for cattle

Pour-on formulations of endectocides are extensively used to treat and control systemic parasitic diseases in cattle, worldwide. The purpose of the present study was to investigate the influence of the natural licking behaviour of cattle on the plasma and faecal disposition of topically administered ivermectin. Twelve Holstein cattle were given one single intravenous (i.v.) (200 microg/kg) and topical (500 microg/kg) administration of ivermectin at a 5-month interval. For the pour-on administration, the animals were allocated into two groups (n=6): one control group (lickers) and one group where licking was prevented (non-lickers). Ivermectin plasma (total) clearance (270+/-57.4 ml/kg/day) was very homogeneous among the 12 cattle. In contrast, major differences between lickers and non-lickers were observed following pour-on administration. Prevention of licking resulted in an extended terminal plasma half-life (363+/-16.2 vs. 154+/-7.4 h in lickers) and in a lower and less variable systemic availability of ivermectin (19+/-4.9 vs. 33+/-18.5% in lickers). More importantly, nearly 70% of the pour-on dose was recovered as parent drug in the faeces of lickers vs. only 6.6% in non-lickers. Altogether, these results are consistent with an oral rather than percutaneous absorption of topical ivermectin in control animals, the non-systemically available fraction of ingested ivermectin providing a major contribution (80%) to the drug faecal output. The consequences of licking on the disposition of pour-on ivermectin are discussed in terms of environment, given the known ecotoxicity of this drug, and of cross-contamination. Animals licking themselves and each other could result in unexpected residues in edible tissues of untreated animals and in possible subtherapeutic drug concentrations, a factor in drug resistance. According to the Precautionary Principle, these considerations elicit concern over the use of topical drug formulations in cattle.

First confirmed case of Neospora caninum-associated abortion outbreak in Portugal

In a dairy herd experiencing an abortion outbreak, 49% of the 119 cows were positive for Neospora caninum antibodies and the remaining 51% were seronegative. Using immunohistochemical analysis of foetal brain tissue, Neospora cysts and bradyzoite clusters were identified in two of the 15 aborted foetuses submitted for testing. Other agents that commonly cause abortions were not found. These results, coupled with neurological clinical symptoms in new-born calves, implicated N. caninum as the major cause of abortions in this dairy herd. This is the first report that associates N. caninum infection with bovine abortions in Portugal.

The Ivomec SR Bolus for control of Boophilus annulatus (Acari: Ixodidae) on cattle in South Texas

When Hereford heifers infested with Boophilus annulatus (Say) were treated with a single Ivomec SR Bolus, the concentration of ivermectin in the serum of the treated cattle reached a maximum of 8.8 +/- 0.9 ppb at 2 wk posttreatment. The single bolus treatment resulted in 84.4% control of standard engorging B. annulatus females on treated cattle over the 20-wk trial. Although fewer engorged ticks were collected from the sentinel heifers exposed in the treated pasture than those in the control pasture at weeks 4, 10, and 16 posttreatment, none of the differences was statistically significant. Each exposure of sentinel cattle found free-living ticks in both the treated and control pastures, indicating the infestation was not eliminated by the treatment. When the trial was repeated using two Ivomec SR Boluses/heifer, the concentration of ivermectin in the serum of the treated cattle reached a maximum level of 31.2 +/- 3.9 ppb at week 13 posttreatment. The use of two boluses/heifer resulted in 99.6% control of standard engorging B. annulatus females over the 20-wk trial. No ticks were found on sentinels placed in the treated pasture after week 9 posttreatment, an indication that the treatment had eliminated the free-living population in the treated pasture. From these studies, we conclude that a single Ivomec SR Bolus is incapable of sufficient control of B. annulatus to meet the rigid requirements of the Cattle Fever Tick Eradication Program in South Texas. Although two boluses per animal did eliminate the ticks from treated heifers and the pasture they were in, the treatment would not be sufficiently efficacious for mature cattle (>400 kg) for it to be useful in the program.