Dyserythropoiesis in animal trypanosomosis

Haemolysis is the most prominent pathogenic cause of the anaemia in trypanosomosis. Haemolytic anaemias are normally accompanied by increased erythropoiesis, reticulocyte response and increase in the mean corpuscular volume of circulating erythrocytes. In trypanosomosis, the anaemia is accompanied by inadequate erythropoiesis. This is suggested by suboptimal reticulocyte response in infected rodents, little or no reticulocyte response in infected ruminants and weak erythrogenic capacity of infected sheep plasma in mice. The mean corpuscular volume increases in the acute phase reaching a peak at 3 to 4 weeks after infection and drops to normal or below normal in the chronic phase; suggesting that erythropoiesis moderately increases in the acute phase but Wanes and becomes completely depressed as the disease progresses into the chronic phase. The causes of the dyserythropoiesis are meanwhile not clear but may be found to be associated with erythroid injury, depressed erythropoietin synthesis and bioactivity or depressed haemoglobin synthesis or their interplay. Extensive studies in these areas are still necessary.     

Trypanosoma evansi experimental infection in the South American coati (Nasua nasua): clinical, parasitological and humoral immune response.

The course of Trypanosoma evansi infection in coatis (Carnivora, Procionidae) was followed for 262 days. Parasites were detected in all infected animals from day 2 post infection until the end of the study. No correlation between temperature and parasitemia was observed. Animals of the infected group demonstrated depression, weakness, lethargy and pale mucous membranes. Indirect fluorescent antibody tests detected anti-T. evansi antibodies within 7 to 14 days post infection and showed high levels until the end of the experimental period. The persistent parasitemia in coati and their relative tolerance to clinical signs suggested that this species develops a chronic disease and plays an important role in the epidemiology of trypanosomosis due to T. evansi in enzootic regions.     

Effect of Trypanosoma vivax infection on semen characteristics of Yankasa rams.

Twelve Yankasa rams aged between 2 1/2 and 3 years with good semen characteristics were used in this 15-week study. Six rams were infected with Trypanosoma vivax, while six served as controls. The infected rams developed chronic trypanosomosis accompanied by fluctuating pyrexia, lethargy, anaemia, scrotal oedema and cachexia. There was a drastic and progressive deterioration in semen quality in all infected rams manifested by a decrease in volume or cessation of semen production, oligozoospermia, a sharp decrease in progressively motile sperm, elevated numbers of dead (eosinophilic) sperm and 100% morphological abnormalities of sperm in most animals. The rams were all deemed unfit for breeding by 3 weeks post-infection. Uninfected rams were healthy and had good semen characteristics throughout the investigation. The results show that rams infected with T. vivax may become infertile within a short interval due to rapid deterioration of semen characteristics and this trypanosome species may be an important causative agent of infertility in endemic areas.     

Toxoplasmosis in rams: possible significance of venereal transmission

Three rams were infected with tick-borne fever eight months after infection with toxoplasma. There was no clinical evidence of reactivation of the latent toxoplasma infection and semen samples from the rams were not infective to mice. Semen samples from 77 apparently normal rams were tested for toxoplasma infection by passage through mice; none of the samples produced patent infections in mice. Two rams with chronic toxoplasma infection were repeatedly mated with seronegative ewes. None of the ewes showed serological evidence of acquired infection and all lambed satisfactorily.     

Antipyrine, erythromycin and oxytetracycline disposition in experimental fasciolosis.

The effects of fasciolosis on drug disposition were studied by administration of antipyrine, erythromycin and oxytetracycline to sheep and cattle. Fasciolosis was produced by administration of 200 or 400 metacercariae (MC) of Fasciola hepatica to sheep and 500 MC to cattle. The disease was subsequently confirmed by determination of plasma glutamate dehydrogenase and gamma-glutamyl transferase and identification and quantitation of mature flukes in the liver at necropsy. Acute or subacute fasciolosis in sheep was accompanied by a significant decrease in the elimination rate constant (beta) and increase in the elimination half-time (t 1/2) for antipyrine and erythromycin when compared with controls or infected sheep which had been treated with the anthelmintic luxabendazole. An increase in apparent volume of distribution (Vd) was seen only for erythromycin in sheep given 400 MC. There were no changes in the disposition of oxytetracycline in sheep with either acute or subacute infection and no effects on disposition of the three test drugs in chronically infected sheep. With early chronic disease in calves, only the disposition of oxytetracycline was affected; not that of antipyrine or erythromycin.     

Epidemiology of Haemophilus somnus in young rams

The prevalence of Haemophilus somnus in the prepuce of young rams was examined. Of 473 rams entering Record of Performance (ROP) stations at 50 days of age, 43 (9.1%) were positive. Average daily gain was not affected by Haemophilus status, but was influenced by breed of ram. Suffolks were predicted to gain 0.515 kg daily compared to 0.427 kg for a group combining all other breeds. Using logistic regression to identify risk factors for individual H. somnus infection, rams in 1989 were 0.382 times as likely to be infected as rams in 1988, and Suffolks were 0.314 times as likely to be infected as the other breeds group, but these factors were not significant at the flock level. Of 80 eligible flocks of origin, 22 (27.5%) were classified as infected with H. somnus, based on rams submitted to the ROP station. Infected flocks contributed 133 rams, 43 (32.3%) of which were positive. There was no association between H. somnus status and lambing percent of the percent of abortions and stillbirths, but there was a statistically significant association with the percent of ewes which failed to lamb. In the model developed, 6% of the bred ewes in noninfected flocks failed to lamb, compared to a rate of 12% in infected flocks. These results suggest H. somnus may influence ewe fertility earlier, rather than later in gestation. Purchasing replacement animals and having cattle on the farm were risk factors for Haemophilus infection in the flock. Where replacements had been purchased within the previous year, the risk of flock infection rose 8.5 times, and on farms having cattle as well as sheep, the risk rose 13.2 times.(ABSTRACT TRUNCATED AT 250 WORDS)     

Health and productivity of traditionally managed Djallonke sheep and West African dwarf goats under high and moderate trypanosomosis risk.

Trypanosome infections, packed red cell volume levels (PCV), body weight and nematode faecal egg counts of village-based small ruminants were monitored in two areas in The Gambia with either moderate or high trypanosomosis risk for 24 and 30 months respectively. Outflows from the flock and new-born animals were recorded and data on housing and management were compiled. Reported mortality rates were higher in goats than in sheep, but for both species highest in the moderate risk area. The peak of trypanosome infections lagged the peak of tsetse densities by 1-3 months in both areas. Trypanosoma vivax was the predominant species found in the infected animals, followed by T. congolense. Trypanosome prevalence was, in general, higher in sheep than in goats but only significantly higher during Year 1 in the moderate risk area. Trypanosome infection reduced the PCV level significantly and seasonal effects indicated significantly lower PCV levels during the rains. Trypanosome infection significantly depressed weight gain in both species at periods where infection rates were highest. In both species considerably lower weight gains were observed during the rainy season. Abortion rates were higher in goats than in sheep in both study sites, and highest in the high-risk site. Trypanosome infection in ewes in the high risk area increased lamb mortality significantly but had no effect on birth weights, nor on growth rates up to 4 months. Offspring mortality up to 4 months was generally high at both sites. Trypanosome infection in the dam between 3.5 to 7 months post parturition significantly increased parturition interval in both species. Peak faecal egg output occurred at the end of the rainy season and was highest for both species in the moderate risk site. Poor grazing management was found responsible for a seasonal nutritional constraint. Based on these results, these breeds of sheep and goats can be considered as trypanotolerant since they are able to remain productive under high and moderate levels of trypanosome challenge. Nevertheless, trypanosomosis affected their health and production level as shown by reduced PCV levels, depressed weight gains, longer parturition intervals and higher lamb mortality. In addition, during the rains, helminth infections and poor management leading to nutritional constraints had also a negative impact on health and production and therefore influenced the innate resilience to trypanosomosis in those indigenous breeds. Adaptations in management may have an equal impact as certain disease control measures to improve biological and economical returns from small ruminants in tsetse infested rural areas.     

Comparative Parasitological and Haematological Changes in Two Breeds of Sheep Infected with Fasciola gigantica

Twelve each of Red Masai and Dorper sheep, aged between 6 and 9 months, were acquired from a Fasciola-free area of eastern Kenya. Each breed was divided into two groups of 6. The sheep in one group of each breed were experimentally infected with 400 viable metacercariae of Fasciola gigantica. The other group of 6 sheep of each breed remained as uninfected controls. The animals were monitored regularly for any evidence of disease. Blood samples taken weekly revealed a general reduction in red cell counts and packed cell volume, which was much faster in the infected Dorper sheep than in the Red Masai. This reduction started from the tenth week after infection and persisted to the end of the experiment 18 weeks post infection (PI). The absolute eosinophil counts rose in all the infected animals, but the values were higher among the Dorper than among the Red Masai. Patency occurred at weeks 12 and 13 PI in the Red Masai and Dorpers, respectively, with the latter shedding significantly more fluke eggs. The worm recovery rates were higher among the Dorpers than among the Red Masai, though not significantly so. On the basis of egg counts and clinicopathology, the Dorper sheep were considered to be more susceptible to F. gigantica infections.     

Experimental microcyst sarcocystis infection in lambs: serology and immunohistochemistry

Density gradient centrifugation using a performed self generated gradient of colloidal silica enabled the isolation of microscopic sheep sarcocystis cystozoites, free from heart muscle contamination. The efficiency of separation of cystozoites from residual heart muscle after digestion in pepsin and hydrochloric acid was 63 to 92 per cent. Antigens from cystozoites were used on enzyme-linked immunosorbent assays (ELISA) of plasma from six coccidia-free lambs infected once orally with 70,000 microcystic sheep sarcocystis sporocysts and for raising antisera in rabbits. Use of an anti-sheep IgM conjugate in the ELISA showed that anti-sarcocystis IgM production was transitory, appearing five to 10 days after infection, peaking in concentration at 42 days and following the peak of the acute phase of infection (32 and 33 days) in the lambs. In contrast, total anti-sarcocystis immunoglobulins, detected by ELISA, increased from five to 21 days after infection and continued to increase until the lambs were killed (the last at 81 days) and was more useful in diagnosing chronic infection. No cross reactions between microcystic sheep sarcocystis and Toxoplasma gondii or Eimeria species of sheep were observed. A peroxidase anti-peroxidase test, using rabbit anti-sarcocystis sera, detected second generation meronts and sarcocysts in fixed tissues from infected lambs making it useful for the diagnosis of acute or chronic disease post mortem.     

Response of sheep to experimental concurrent infection with tick-borne fever (Cytoecetes phagocytophila) and louping-ill virus

The pathogenesis of concurrent Cytoecetes phagocytophila and louping-ill virus infection was studied in two experiments. In the first experiment 18 four- to seven-year-old rams were used. Ten were infected with C phagocytophila and five days later eight of these animals and the remaining eight sheep were infected with louping-ill virus. The two rams infected with C phagocytophila alone developed no clinical signs apart from a transient pyrexia, while only three of the eight rams infected with louping-ill virus alone showed mild clinical signs. In marked contrast, all eight dually infected sheep developed severe clinical signs with pronounced depression and dysentery and three died and five were killed in extremis. They developed higher titres of viraemia and the antibody response was depressed while necrotising lesions affecting a variety of organs were detected at post mortem examination. Rhizomucor pucillus was recovered from these lesions in seven of the eight sheep. A second experiment using 10 sheep, five aged seven months and five aged two to three years, confirmed the findings of the first experiment indicating that the age of the animal had not significantly influenced the initial result. It was concluded that C phagocytophila infection could enhance the pathogenicity of louping-ill virus and that, operating together, the two pathogens facilitated fungal invasion. It is postulated that sudden deaths in sheep recently transferred to tick-infested pastures may be due to this newly described syndrome.     

Bluetongue disease in Swiss sheep breeds: clinical signs after experimental infection with bluetongue virus serotype 8

Clinical disease of bluetongue (BT) in sheep may differ depending on breed, age and immunity of infected sheep and may also vary between serotype and strain of BT virus (BTV). Since there are no data available on the susceptibility of Swiss sheep breeds for BT, we performed experimental infection of the 4 most common Swiss sheep breeds and the highly susceptible Poll Dorset sheep with the BTV serotype 8 (BTV-8) circulating in Northern Europe since 2006. Clinical signs were assessed regarding severity, localisation, progression and time point of their appearance. The results clearly show that the Swiss sheep breeds investigated were susceptible to BTV-8 infection. They developed moderate, BT-characteristic symptoms, which were similar to those observed in Poll Dorset sheep. Regardless of breed, the majority of infected animals showed fever, swelling of the head as well as erosions of the mouth and subcutaneous haemorrhages.     

Comparative histopathology of the lymph nodes, spleen, liver and kidney in experimental ovine trypanosomosis

The infection of Yankassa rams with three important trypanosome species affecting livestock, namely, Trypanosoma congolense, T. vivax and T. bruceiproduced both acute and chronic fatal conditions. Chronic infections were induced in the three infections by the application of subcurative doses of diaminazene aceturate (Berenil). Pathological changes in the infected animals included splenomegaly and hepatomegaly which were more pronounced in acute than in chronic T. congolense infection. However, these changes were more severe in chronic than in acute T. vivax infection. While splenomegaly was more pronounced in chronic T. bruceiinfection than in acute, hepatomegaly and lymphadenopathy were more severe in acute than in the chronic condition. The increases in size of the spleen, lymph nodes and liver were associated with congestion, increases in cell density related to increased immunological reactions in the spleen and lymph nodes as well as increase in numbers, size and activity of the phagocytic cells in these organs.     

Studies of infectivity and pathogenicity of an isolate of Trypanosoma evansi in Yankasa sheep.

The course of experimental infection and pathogenicity of an isolate of Trypanosoma evansi were investigated using eight infected and six uninfected control Yankasa sheep. The sheep were each infected intravenously via the jugular vein with approximately 2.0 x 10(6) T. evansi parasites. The effects of the parasite on body temperature, packed cell volume (PCV), haemoglobin, erythrocytes, total protein, were monitored three times a week for approximately 9 weeks. Body weights were determined once every week for the duration of the experiment. The results showed that all the infected sheep were positive for the parasite. The prepatent period varied between 3 and 6 days. T. evansi produced parasitaemic waves at an average of 8.3 days interval. Two distinct forms of the disease were produced namely, acute (4-14 days postinfection), and chronic (43-59 days postinfection). Anaemia was a distinct feature of the disease. While the mean rectal temperatures were significantly elevated (P < 0.05), the mean values of the haematological parameters of the infected sheep dropped significantly (P < 0.05) compared to the preinfection levels. Observed clinical signs included pale mucous membrane, epiphora, loss of appetite, emaciation, dullness and rough hair coat together with fluctuating pyrexia which in most cases coincided with rise in parasitaemia. It is suggested that the isolate of T. evansi is pathogenic for Yankasa sheep.     

Epidemiological Observations in a Corriedale Flock affected by Brucella ovis

Brucellosis in sheep, caused by Brucella ovis, is primarily a chronic infectious disease of rams with epididymitis as its most characteristic lesion. Six hundred rams from an infected farm were clinically and serologically examined once a year, over a 3-year period. An increase from 2.1% to 6.3% in the prevalence of animals serologically positive to B. ovis occurred over the 3 years. However, the prevalence of rams with lesions in the reproductive tract declined from 14.2% to 6.5% in the third year following one year of strict culling of clinically affected and rams that were serologically positive for B. ovis. Clinical lesions found in the 179 affected rams fell into two main categories: rams with epididymitis and rams with affected lymph nodes. These results suggest that the prevalence of the disease relates mainly to the sexual activity of the animal and not to age in itself. A single cull based on the results of clinical examination and serological test results was unable to decrease the prevalence of B. ovis in an extensive Corriedale sheep flock.     

Immune response in rams experimentally infected with Brucella ovis

Cellular as well as humoral immune responses were detected in six rams experimentally infected with Brucella ovis. Specific antibodies were detectable by enzyme-linked immunosorbent assay by day 11 after infection in all the rams. The levels of IgM antibodies and total antibodies in the serum rose until 33 and 41 days after infection respectively, then levelled off. Antigen-induced blastogenic responses by lymphocytes developed as early as five days after infection in all rams but had decreased to low levels by day 63 in most. Blastogenesis induced by phytohaemagglutinin and concanavalin A varied among infected rams and did not differ significantly (P greater than 0.05) from control rams. All rams had developed delayed-type skin hypersensitivity by day 63 after infection. One ram which did not become infected as a result of exposure had low levels of B ovis serum antibodies and a detectable antigen-induced lymphocyte blastogenic response before infection, suggesting the involvement of cell-mediated immunity in protection against B ovis.     

Immunosuppression in toxoplasmosis: studies in sheep with vaccines for chlamydial abortion and louping-ill virus

Toxoplasma gondii infection was established in sheep seven days (acute infection) or 28 days (chronic infection) before they were given enzootic abortion (EAE) vaccine alone or simultaneously with louping-ill (LI) vaccine. Uninfected controls received the same vaccination schedule. The serological response of acute toxoplasma-infected sheep to initial LI vaccination was significantly depressed but after revaccination four weeks later these sheep demonstrated a response equal to that of the revaccinated controls. Infected sheep also gave a significantly poorer response to EAE vaccine than control animals, the effect being more marked in those with chronic infection. Revaccination evoked no clear response in any group but on three of five sampling days antibody titres of controls were significantly higher than those of infected sheep.     

Comparison of the effects of infection with Trichostrongylus colubriformis, T. vitrinus and T. rugatus in merino lambs

Groups of six worm-free merino lambs were infected with 100,000 larvae of T. colubriformis, T. vitrinus, T. rugatus or a mixture of the three species and were slaughtered 21 days later. Nematodes were distributed predominantly in the first 3 m of the small intestine where they caused subtotal villus atrophy. T. vitrinus caused severe erosion of the epithelium; erosion was less severe with T. colubriformis infections and mild with T. rugatus infections. Plasma concentrations of albumin declined during the experiment and were most marked in sheep infected with T. vitrinus. Plasma phosphate concentrations declined during infection with all three species, while plasma concentrations of globulin and calcium declined only in sheep infected with T. vitrinus. Food intake was reduced in all groups, but was most marked with sheep infected with T. vitrinus. T. vitrinus appeared to be more pathogenic than the other species.     

Experimental infection of camels with bluetongue virus

Three camels aged 4–5 years were experimentally infected with Bluetongue virus serotype 1 (BTV-1) and were observed for 75 days. No clinical signs of disease were observed throughout the experiment, however all three animals seroconverted and developed BTV-1 specific neutralising antibodies after challenge. All three camels developed a viraemia from 7 days post infection albeit at a lower level than that usually observed in experimental infections of sheep and cattle. Virus was isolated from the blood of all three animals suggesting that camels may act as a reservoir for BTV and play an important role in its transmission.     

Assessing the efficacy of a ram-genotyping programme to reduce susceptibility to scrapie in Great Britain

Susceptibility to clinical scrapie is associated with polymorphisms in the PrP gene. The 'ARR' allele of this gene reduces susceptibility to clinical disease caused by all known strains of the transmissible spongiform encephalopathy (TSE) agent. The British government proposes to use a ram-genotyping scheme to breed genetic resistance to clinical scrapie into the national sheep population. We considered how best to target limited genotyping resources to achieve the maximum rate of genotype evolution. We created a metapopulation model of the British sheep industry, which includes the major pure-breeds of sheep and the cross-breeds produced by crossing these pure-bred animals. The main criterion for assessing the efficacy of different strategies was the time taken to increase the prevalence of the ARR allele in the slaughter-lamb population. Our model predicted that the most-effective strategy would be to target genotyping to those rams used for pure-breeding (i.e. mated with the same breed of ewe). This strategy was compared to two further strategies, in which the proportion of rams genotyped in each breed depended on the prevalence of the ARR/ARR genotype in that breed. A policy in which the proportion of animals genotyped is reduced as the ARR prevalence in that breed increases is efficient. The most-effective policy was targeting the hill sector in the early years and gradually switching to genotyping more terminal-sire and longwool rams as the resistance of the hill sector increases.