Specific immunity in farm animals to heartwater.

The duration of immunity to heartwater normally varies from 6 months to 4 years. In Angora goats it may be difficult to produce a specific immune response with vaccination. Humoral immunity does not appear to play a role in the development of immunity. It has been suggested that cellular immunity may play a role, but the actual mechanism involved remains obscure. The specific immune response developing in farm animals following infection with Cowdria ruminantium is reviewed.

Treatment and thrombocyte levels in experimentally induced canine ehrlichiosis and canine babesiosis.

Three dogs which were carriers of Babesia canis were infected with Ehrlichia canis. These animals developed clinical signs and haematological evidence of ehrlichiosis and made an uneventful recovery, despite the fact that they were subsequently treated with doxycycline only. Three control dogs which were also carriers of B. canis were clinically normal, despite the fact that they showed a distinct drop in the thrombocyte levels associated with increases in the numbers of parasitized red cells.

The immune response in a dog to Encephalitozoon cuniculi infection.

The immune response to Encephalitozoon cuniculi infection in a dog was investigated by means of the indirect fluorescent antibody test, the leucocyte migration inhibition test and the radial immunodiffusion test for serum IgG and IgM levels. Specific antibodies were detected within 7 days of infection and they persisted for 370 days. A cell-mediated immune response was detected from Day 13 following infection until Day 97. Histopathological examination showed plasma cell infiltration of the kidneys, meninges, lung, bladder, smooth muscle and spleen.

Studies of encephalitozoonosis in vervet monkeys (Cercopithecus pygerythrus) orally inoculated with spores of Encephalitozoon cuniculi isolated from dogs (Canis familiaris).

Encephlitozoonosis was induced in 35 of 38 vervet monkeys (Cercopithecus pygerythrus). They were either directly (orally) inoculated with Encephlitozoon cuniculi or indirectly exposed to this protozoan parasite. Cell-culture-grown spores of E. cuniculi, isolated from the kidneys of dogs with natural, fatal disease, were administered orally to 29 of these monkeys. Another 5 were exposed in utero by orally infecting pregnant females, and 3 were exposed to horizontal infection by nursing infected infants. Only one was given an intravenous inoculation of spores. The disease was induced in non-gravid and late-pregnant adults, immunocompetent infants, and in infants that were immunologically compromised by parenteral steroid administration, as well as in one infant that was immunologically immature because of its premature birth. The effects of age, dosage, post-inoculation (PI) interval, passage level of the parasite in cell culture and immunological status of the host were correlated with macroscopical and microscopical lesions. The experimentally induced infection was confirmed either by reisolation of the parasite in cell culture or by observation of spores in tissue sections. Both confirmatory methods were supported by serological examination. Reisolation of the organism in primary cell culture prepared from kidneys usually resulted in more frequent isolates and larger yields of spores from infants than from adult vervets. Infection with E. cuniculi invariably induced subclinical disease. Based on histology, lesions were minimal to moderately severe, depending on age, PI interval, and immunological status of the host. Alimentary tract infections were seen histologically as early as three days PI. Subsequently, infections resulted in detectable lesions most consistently in the liver, kidneys and brain. Lesions in these organs were generally granulomatous and were similar to those found in canine encephalitozoonosis. In addition, multifocal interstitial pneumonitis and myocarditis as well as vasculitis and perivasculitis were seen in other tissues and organs. Infants had more severe and more widespread lesions than adults. Although lesions and spores were still present in the brain of one immunocompetent infant 36 weeks after initial infection, the disease in immunocompetent infants and adults is thought to be self-limiting. However, infection may persist. Immunological depression favoured increased growth and multiplication of the organism, and resulted in detection of more spores within inflammatory lesions as well as more intracellular colonies of the organism that were free of inflammatory reaction.(ABSTRACT TRUNCATED AT 400 WORDS)

The absence of clinical disease in cattle in communal grazing areas where farmers are changing from an intensive dipping programme to one of endemic stability to tick-borne diseases.

A two-year field study was conducted in four communal grazing areas in South Africa. Sera were collected from young cattle (6-18 months old) in these areas during the winters of 1991 to 1993. The sera were tested for antibodies to Babesia bovis, Babesia bigemina, Anaplasma marginale and Cowdria ruminantium. In two of the four areas, treatment with acaricide was erratic and dependent on the discretion of individual owners. In these areas the drought of 1992 had a major impact on tick burdens and there were changes in the seroprevalence to tick-borne diseases. In the other two areas there was a reduction in the intensity of acaricide application and this was associated with an increase in seropositivity to the tick-borne diseases. Increases in the prevalence of seropositivity and the presence of endemic instability, as calculated from inoculation rates, were not accompanied by outbreaks of clinical disease. Possible reasons for this are discussed.

A comparison of the efficacy of isometamidium, amicarbalide and diminazene against Babesia canis in dogs and the effect on subsequent immunity.

Isometamidium, amicarbalide and diminazene were used to treat experimentally induced canine babesiosis. Relapse parasitaemias developed after treatment in all groups of animals. The relapse interval, however, was shorter and more relapses occurred after treatment with amicarbalide than either of the other 2 drugs. Only half of the dogs treated with either isometamidium or diminazene relapsed to infection. Challenge with homologous parasites 62 days after initial infection resulted in severe babesiosis in all 3 animals which had not developed relapse infections. Of the 9 animals which had relapses after treatment only 1 developed severe babesiosis following homologous challenge.

The pathology of subclinical infection of Encephalitozoon cuniculi in canine dams producing pups with overt encephalitozoonosis.

The macroscopic, microscopic and clinical pathology and the serology of 2 clinically normal Staffordshire Bull Terrier bitches, both of whom produced pups with confirmed encephalitozoonosis, is described. Mild histopathological changes, similar to those seen in the infected pups, were observed. The spores of Encephalitozoon cuniculi were seen in the renal tubules of the kidney of one of the bitches. The serum urea concentrations of one of the bitches was elevated. A positive titre against E. cuniculi was obtained in both of the bitches. A 10-year-old girl who had had close contact with one of the infected litters of pups, seroconverted to E. cuniculi. Her two siblings were serologically negative.

The relationship in dogs between primary renal disease and antibodies to Encephalitozoon cuniculi.

Fifty-two serum samples from dogs with primary renal failure were tested for antibodies to Encephalitozoon cuniculi. Twelve were positive as compared to two positive samples from a control group of 42 dogs. There was a statistically significant difference between these two groups which suggests an association between infection with E. cuniculi and the development of chronic renal disease.

The prevalence of Encephalitozoon antibodies in dogs and an evaluation of the indirect fluorescent antibody test.

Fifteen dogs which were serologically negative to the IFA test against Encephalitozoon developed antibodies in their sera following experimental infection. Six other dogs which were not tested prior to infection had titres to Encephalitozoon after experimental infection. In a sequential study in four dogs, antibodies first appeared between 32 and 39 days after infection. These results show that the IFA test would be suitable for epidemiological studies. Fifty serum samples collected from two kennels in which encephalitozoonosis had been confirmed showed an IFA test positive prevalence rate of 70%. In 220 serum samples submitted for various clinial pathological examinations the prevalence rate of antibodies to Ebcephalitozoon was 18%.

Observations on the pathology of experimental encephalitozoonosis in dogs.

Experimental transmission of canine encephalitozoonosis was effected by oral dosing of urine obtained from naturally diseased animals. Per os, intraperitoneal and intravenous routes were used to induce infection with tissue culture-grown Encephalitozoon spores which were initially isolated from the kidney of a dog with terminal disease. The infection was confirmed by a rise in the indirect immunofluorescent antibody titres, the lesions found in infected dogs and isolation of the parasite in tissue culture from an infected and immunosuppressed dog. The experimentally induced disease was invariably subclinical but the histopathological changes were similar although milder than those found in fatal natural disease. The kidney appears to be the target organ and chronic interstitial nephritis develops regularly.

An unidentified Babesia of the domestic cat (Felis domesticus).

An unidentified Babesia was seen in a blood smear from a cat showing signs of anaemia. The cat responded to treatment with diminazene (Berenil). The morphology of the parasite is described and a comparison is made with other Babesia which have been described from the domestic cat and wild felids. This parasite most closely resembled B. herpailuri described from a jaguarundi in South America.

Canine encephalitozoonosis in South Africa.

Clinical, clinicopathological macroscopical and histopathological findings, as well as electron microscopic and cultural confirmation, in twelve natural cases of canine encephalitozoonosis are described, eleven of these under one year of age. Nervous symptoms, including blindness, retarded growth rate and nephritis are prominent clinical signs. The macroscopic findings and histopathology proved of great help in the diagnosis of the disease even in chronic cases. The organism was cultured and some distinguishing electron microscopical features between Encephalitozoon and Nosema are discussed. A transmission experiment confirmed the diagnosis. The results are compared with the reported cases in dogs and Blue Foxes (Alopex lagopus).

The use of a short and a long acting oxytetracycline for the treatment of Anaplasma marginale in splenectomized calves.

Twenty splenectomized Afrikander/Simmentaler cross animals were used. Eight of these were naturally infected with Anaplasma marginale while 12 were infected artificially. When the packed cell volume was reduced to between 24% and 20% during the post splenectomy relapses or primary infections, six animals were treated with a single injection of 20 mg/kg of long acting oxytetracycline (LA) and seven animals were treated on two successive days with 10 mg/kg of short acting oxytetracycline (SA). The remaining seven animals served as untreated controls. Both drugs were effective in controlling A. marginale reactions. No deaths occurred in the group of animals treated with oxytetracycline LA and they showed a longer relapse interval and higher blood levels of oxytetracycline compared to those treated with oxytetracycline SA. A single death occurred in the latter group. Four deaths occurred in the control group which also had the shortest relapse interval.

Canine encephalitozoonosis in kennels and the isolation of Encephalitozoon in tissue culture.

The protozoan Encephalitozoon was isolated in primary kidney cultures from dogs originating from three separate outbreaks of encephalitozoonosis in kennels. The disease was characterized by a fading syndrome in young puppies with nervous signs developing in some cases. It was not possible to reproduce the clinical disease with cultured organisms in either normal dogs or dogs immunosuppressed with methylprednisolone. The organisms were, however, reisolated in primary culture from two immunosuppressed dogs but not from other experimentally infected dogs. The freezing of Encephalitozoon organisms in liquid nitrogen is described.

An investigation into the potential veterinary needs of a semi-rural low-income community.

The diagnostic phase of an interactive veterinary research evaluation model was used in the investigation into the potential veterinary needs of a low-income, semi-rural community. The economic status of households was estimated according to an economic situation score (ESSCORE) and a subjective nutritional score (SNS). Data were gathered by means of structured interviews and direct observations. Sixty-one per cent of the households (n = 190) owned animals. Dogs were the animal most frequently owned. However on the basis of total numbers, chickens were the most numerous and the second most frequent animal kept. The relative frequency of cattle and goats, was also considerably higher than that of dogs. Few sheep were owned by respondents, although they were an animal species that people desired to own. The finding that respondents saw more disadvantages than benefits in their neighbour's animals, indicated that increased animal ownership could lead to friction. Better fencing might decrease the damage caused by goats and donkeys. A considerable excess of consumption over production of animal products, was discovered. Meat and milk were seen as the main benefits by those who did not own animals. This indicated a possible market for animal products if production were increased. It was considered that subsidised veterinary extension might be the most cost-effective solution for those who cannot afford to pay for curative interventions.

An outbreak of babesiosis in imported sable antelope (Hippotragus niger).

A complete necropsy performed on 2 sable antelope (Hippotragus niger), revealed lesions concomitant with a massive haemolytic crisis. These included widespread oedema and anaemia of the carcass, severe oedema of the lungs, petechiae and echymoses of the epicardium, a moderate splenomegaly and a severe haemoglobinuria. The histopathological lesions included a moderate alveolar oedema, the presence of haemosiderin in the spleen and lymph nodes, and mild degenerative changes of the renal tubular epithelium. Peripheral blood and brain smears contained numerous parasitised red blood cells. The parasites were round or oval in shape containing a single or double area of purple-staining chromatin along a portion of the margin of the organism. It was identified as Babesia irvinesmithi Martinaglia, 1936, which is unique to sable. Seven sable antelope were subsequently treated with imidocarb diproprionate at a dose of 1.2 mg kg-1. No adverse side-effects have been noted in these animals.

Encephalitozoon infection in a still-born foal.

A stud Clydesdale foal was still-born near full term. Macroscopic examination revealed a normal placenta, pulmonary atelectasis and faint white mottling of the kidneys. Microscopically there was severe lymphoplasmacytic interstitial nephritis. Numerous organisms resembling Encephalitozoon cuniculi were present in the affected kidneys. The organisms occurred in the areas of inflammation as well as in the renal glomeruli and intracellular cysts in the renal tubular epithelial cells and exhibited Gram positive staining. Ultrastructurally the organisms possessed a polar vacuole and a spiral filament typical of Microsporidia. The organisms were not detected in sections of the other organs examined.

Ixodid ticks on indigenous goats owned by small-scale farmers in four communal grazing areas in South Africa.

Indigenous goats belonging to small-scale farmers in 4 communal grazing areas in South Africa were sampled for ixodid ticks during the period September 1991 to May 1993. Three of these areas were in the North West Province (Rietgat, Madinyane and Bethany), and one in Mpumalanga Province (Geluk). No tick control was practised unless requested by the owners. Seven ixodid tick species, of which the majority were immature ticks, were collected from the goats in North West Province. Amblyomma hebraeum was the most numerous of these, followed by Rhipicephalus evertsi evertsi and Rhipicephalus appendiculatus. Substantially more ticks were collected from goats at Rietgat than at the Madinyane and Bethany grazing areas. Five tick species were collected at Geluk and R. evertsi evertsi comprised more than 95 % of the total population. At Rietgat and Geluk A. hebraeum nymphs were present on goats throughout the year, while most R appendiculatus nymphs were collected during September and October 1991 and most adults during January and February 1992. At both Rietgat and Geluk most immature R. evertsi evertsi were collected from spring to late summer, while adults were present throughout the year.

Ixodid ticks on cattle belonging to small-scale farmers at 4 communal grazing areas in South Africa.

Ixodid ticks were collected during the period September 1991 to August 1993 from cattle belonging to small-scale farmers utilising 4 communal grazing areas. Three of these were in North West Province and 1 in Mpumalanga province, South Africa. Ten tick species were collected in North West Province and 7 in Mpumalanga. The adults of Amblyomma hebraeum, Rhipicephalus appendiculatus and Rhipicephalus evertsi evertsi were most numerous in North West Province, while in Mpumalanga Boophilus decoloratus comprised more than 75% of the total population. Amblyomma hebraeum was present on all grazing areas, and heavy infestations of adults occurred during the period October to May on 1 of these. Few B. decoloratus were collected in North West Province, chiefly because the sampling method was inadequate, and most of these were present during early summer (October to December) and late summer and autumn (March to May). The initially low population of B. decoloratus in Mpumalanga increased substantially towards the conclusion of the survey, probably because of the cessation of dipping. Boophilus microplus was present in small numbers on 2 grazing areas in the North West Province. Adult Hyalomma marginatum rufipes reached peak numbers from December to February and Hyalomma truncatum from February to April in the North West Province. Only H. marginatum rufipes was collected in Mpumalanga. Rhipicephalus appendiculatus was present on all the grazing areas, with most adults present from December to April. Most adult Rhipicephalus evertsi evertsi were collected from September to April and Rhipicephalus simus was present during the period October-April.