Quality control in generic anthelmintics: is it adequate?

We became increasingly concerned about indications of possible substandard efficacy of some generic anthelmintics, particularly after P.C. van Schalkwyk (personal communication, 1990) had found some batches of imported generic products obtained from international brokers to be poorly active, despite apparently normal physical characteristics. Therefore, considering the serious consequences this would have for sheep farming, it was decided to test the efficacy of some of the generic rafoxanide products available on the South African market. One of the three commercial formulations (of highly reputable companies) tested against a known susceptible strain of Haemonchus contortus in sheep was markedly substandard, with an arithmetic mean efficacy of 66.2% (Class B, Reinecke, 1973), compared to Class A efficacy of the other two, which also differed significantly from one another (Mann-Whitney; P = 0.01). Larger differences were found between the three products against a natural infection with a partially resistant strain of H. contortus than against the susceptible strain, with corresponding arithmetic mean efficacies of 28.7% (Class X, or ineffective), 71.3% (Class B) and 87.7% (also Class B). It is concluded that the most likely reason for the observed differences is that international brokers do not disclose the sources of supply of different batches of active ingredient (with the result that the companies buying anthelmintics from them have no way of telling when a source of supply is changed); that the efficacy of such batches differs; and that efficacy testing of individual batches in some cases is inadequate. It is suggested that registering authorities should consider simplified efficacy testing of each new batch of active ingredient before it may be marketed.

Interbreed differences in the efficacy of 1% deltamethrin pour-on to protect small livestock against infestation with Ixodes rubicundus (Acari:Ixodidae).

Synthetic pyrethroid pour-on compounds have been developed for use on cattle but many are now also registered for the control of ectoparasites on small ruminants. The breed of small livestock has been known to influence the efficacy of various pour-ons and we hypothesized that differences in the duration of protection afforded by a synthetic pyrethroid pour-on against ticks on small livestock, would be greatest between hairy and woolly breeds. Angora goats with mohair, Dorper sheep with hairy wool, and Merino sheep with wool were treated with 1% m/v deltamethrin pour-on with an oil base at a dosage rate of 1 ml 5 kg-1 body mass. The duration of effective protection against Ixodes rubicundus, the Karoo paralysis tick, was determined under field conditions. Angora goats proved to be the highest risk group, but were afforded the least protection. Efficacy never reached 100% in this group and within 3 weeks the goats were already at risk of paralysis. Dorper sheep were afforded above 90% protection for 3 weeks and 85% after 4 weeks. In the case of the Merino sheep efficacy of protection remained above 90% up to 7 weeks post-treatment and was still 87% during Week 8. Differences in the amount of sebum and suint in the epidermis of the different breeds may be responsible for differences in the rate of spread and the rate of dilution of the active compound in the epidermis.

The efficacy of Diflubenzuron against the body louse (Damalinia limbata) of Angora goats.

The efficacy of an insect growth regulator, Diflubenzuron, to control biting lice (Damalinia limbata) on Angora goats was investigated. Lice on goats which were dipped in a concentration of 625 g Diflubenzuron to 1,000 1 water and then kept in quarantine was eradicated after a single treatment. Nymphs remained present on these goats up to 4 weeks and adult lice up to 8 weeks post-treatment. A single treatment provided greater than 90% reduction in nymphal stages from Week 6 to Week 16 post-treatment in treated goats continuously exposed to reinfestation. The treatment reduced adult louse infestations on these goats by 78-94% through Weeks 6-16 post-treatment. At the end of the trial (24 weeks post-treatment), these goats had 88% fewer nymphs and 84% fewer adult lice compared with untreated control goats.

A method for the assessment of blackfly (Diptera: Simuliidae) attraction to and engorgement on sheep in South Africa.

A suspended-net technique was used to capture blackflies attracted to and engorging on Dorper and Merino sheep on irrigated pastures. Two bait animals of each breed were restrained individually in wire-mesh enclosures located within four larger pens, each containing nine more animals of the same breed. Nets were suspended partly over the restrained animals and blackflies were collected at the end of 2-hour or longer periods. Mean numbers of blackflies captured in association with Merino (73.3/h) and Dorper sheep (89.1/h) did not differ significantly. Numbers of captured blackflies correlated (rho = 0.8361) with levels of irritation shown by sheep. Engorgement on Merinos was significantly (p = 0.009) higher than on Dorpers. Percentage engorgement was low, mostly below 10% on Merinos and below 5% on Dorpers. When high wind speeds and high saturation deficits (associated with temperatures in the mid-thirties) occurred, the success of capture was impaired. The technique is useful for quantifying the abundance of irritating blackflies in the immediate proximity of smallstock under experimental conditions.

The presence of endotoxin activity in cases of experimentally-induced heartwater in sheep.

The presence of endotoxin was examined in 5 sheep with experimentally-induced heartwater. Two peaks in endotoxin levels were recorded in 4 out of the 5 sheep during the acute stage of the disease. The 1st peak coincided with or occurred shortly after the febrile reaction (over 40 degrees C). The 2nd peak occurred 3-5 days after the 1st, and in 2 sheep this 2nd elevation in endotoxin levels was associated with severe clinical signs (rapid and laboured breathing, cyanosis and recumbency), and 1 of the 2 sheep died on the day of the 2nd elevation. Both endotoxin peaks were of short duration and levels had decreased in the 24-h follow-up samples.

The presence of Cowdria ruminantium antigen in various tissues of Amblyomma hebraeum imagines as detected by an enzyme-linked immunosorbent assay.

Investigation into the presence of C. ruminantium antigen, using an enzyme-linked immunosorbent assay (ELISA) in various tick tissues and haemolymph of adult Amblyomma hebraeum ticks revealed that the organism invades a number of body parts and can be demonstrated in A. hebraeum. In females, the gut, salivary glands, hypodermis and synganglion and in males, the salivary glands and gut showed the highest concentration.

The clinical pathology of heartwater. II. Studies on cardiac and pulmonary function in 4 calves with experimentally-induced heartwater.

Studies to evaluate cardiac and pulmonary function were undertaken in 4 calves suffering from experimentally-induced heartwater. There was a marked variation in the course of the disease. Three of the calves recovered spontaneously after developing clinical signs. These included a rectal temperature in excess of 40 degrees C, anorexia and listlessness but no neurological signs. The remaining calf died 2 days after developing a fever and neurological signs. In the 3 calves that recovered, a mild hypoxemia developed during the acute stage of the disease. Arterial CO2 tension remained within normal limits, but there was a tendency towards an alkalosis. Increases in pulmonary dead space and fluctuations in venous admixture were observed. The calf that died showed similar mild changes in blood gas parameters, despite the presence of a marked reduction in minute volume, and a lung oedema was demonstrated on post-mortem examination. No marked changes in systolic and diastolic blood pressures and in right cardiac intraventricular pressures were observed. Terminally, however, there were marked decreases in stroke volume and cardiac output. These changes were associated with a sharp increase in heart rate. No primary cardiac pathology was observed on clinical and post-mortem examinations.

The clinical pathology of heartwater. I. Haematology and blood chemistry.

Clinical pathological studies were undertaken in 5 calves with experimentally-induced heartwater. The most important findings include a progressive anaemia which may be associated with bone marrow depression and fluctuations in the total and differential white cell count, of which an eosinopenia and a lymphocytosis were the most marked. A severe drop in serum protein, especially in the albumin levels, was observed in all 5 cases. This disease is probably associated with an increased capillary permeability, as the protein content of the pericardial fluid in 1 case that died, approximated that of the serum. The osmolality of the effused fluid was also higher than that of the blood. No significant changes in the serum electrolyte levels occurred, except for total calcium levels which tended to decrease to below normal during the acute stage of the disease. Marked increases in total bilirubin were recorded. This, however, was not associated with liver pathology or haemolysis and may possibly be ascribed to a fasting hyperbilirubinaemia. Darkening of plasma colour was associated with peak rises in total bilirubin. Increases in both blood urea and creatinine levels indicate interference with renal glomerular filtration during the acute stage of the disease.

An ELISA using an SDS extract of Brucella abortus strain 99 as antigen to detect B. abortus antibodies in cattle sera.

An ELISA was developed using an SDS extract of Brucella abortus as antigen to detect antibodies in cattle sera. The antigen was stable at 4 degrees C for at least 4 years and although it gave optimal results at a 1/4,000 dilution it could detect reactors at a 1/32,000 dilution. Based on comparative CF tests on 430 sera from negative herds and 187 sera from positive herds a reading of 0,07 or less using a 492 nm filter could be considered a negative reaction. The ELISA could be a useful test to supplement the CF test but further evaluation is still required.

Heartwater in hosts other than domestic ruminants.

The importance of further research on the susceptibility of wild hosts to Cowdria ruminantium infection is discussed. The literature is surveyed and an attempt is made to divide the various species described into susceptible and refractory hosts. The reasons for the numerous apparently conflicting reports are considered and it is suggested that those making further inquiries in this field of work take these factors into account.

The clinical pathology and pathophysiology of heartwater: a review.

This paper reviews the available literature on the clinical pathology and pathophysiology of heartwater and makes comparisons with unpublished results obtained from a recent study in experimentally-induced heartwater in calves. The pathophysiological changes seem to center on an increased capillary permeability the result of which is reflected most noticeably in cardiac and lung function. There is a marked drop in cardiac output in severe cases and some workers have recorded a severe drop in diastolic blood pressure in the advanced stage of the disease. Changes in lung function are variable, depending on the stage of the disease, and may change from a respiratory alkalosis in the early febrile stage to a respiratory acidosis in more advanced cases. The basic cause for the increased capillary permeability is not known. The main clinical pathological changes measured include a progressive anaemia, fluctuations in total and differential white cell count, of which an eosinopenia and a lymphocytosis are the most marked, increases in total bilirubin which coincide with darkening of plasma colour, and a drop in total serum proteins mostly shown in the albumin levels.

Heartwater serology: some problems with the interpretation of results.

Antibodies in the sera of domestic ruminants that have been infected with Ehrlichia bovis and other ehrlichial agents cross-react with the Kümm strain of Cowdria ruminantium used in the indirect fluorescent antibody test as antigen. These cross-reactions are also shown by the Elisa test in which the Ball 3 strain of the heartwater agent is used as antigen.

The treatment of heartwater.

This paper reviews the available literature on the treatment of heartwater and draws comparisons with results obtained from recent work on experimentally-induced heartwater in sheep, calves and mice.

The production of heartwater vaccine.

The events leading to the production of an effective vaccine against heartwater are summarized. The production techniques used at Onderstepoort to produce and control the quality of the infected blood and nymph suspension vaccines, and covering their respective advantages and disadvantages, are compared. The many problems of these vaccines and how they may be overcome are discussed.

Further studies of the clinical pathology of sweating sickness in cattle.

Experimentally-induced cases of sweating sickness in calves were used in an effort to correlate the blood chemistry with some of the known pathological changes. Results showed that the "sweating" associated with necrotic dermatitis did not alter blood electrolyte levels. Laboratory evidence of a disseminated intravascular coagulopathy was found which correlated with the microthrombi described in cases of sweating sickness. A high blood cortisol level was found in one of the animals that died from the disease and could possibly be used as a prognostic indicator in clinical cases. Recommendations are made with regard to the supportive treatment based on the clinical pathological findings.

Isolation of a neurotoxin from the salivary glands of female Rhipicephalus evertsi evertsi.

A quantitative study of the changes in the protein pattern of the salivary glands of female Rhipicephalus evertsi evertsi during the entire repletion process was undertaken. These results, in conjunction with the previously determined toxic phase, indicated the presence of a toxic protein. The development of a sensitive in vitro assay using a Xenopus nerve-muscle preparation, made it possible to identify toxic phases during feeding and to assay fractions of salivary gland extracts during toxin isolation. Sufficient amounts of electrophoretically and chromatographically homogeneous toxin could be obtained through the use of chromatofocusing, enabling its characterization with respect to molecular weight (68 kDa; determined by gel permeation chromatography), pI (6.00), and amino acid composition. The toxin was inactivated by pronase digestion as well as by antiserum.

Detection of Cowdria ruminantium antigen and antibody during the course of heartwater disease in sheep by means of an enzyme-linked immunosorbent assay.

An enzyme-linked immunosorbent assay was used to detect Cowdria ruminantium antibodies during the course of heartwater disease. IgM antibodies reached a maximum on the 4th day after infection and disappeared on the 7th day. IgG antibodies first appeared on the 8th day and continued to increase during the remainder of the observation period of 28 days. The presence of C. ruminantium in the blood fractions of diseased animals was demonstrated by an enzyme-linked immunosorbent assay. The earliest day of C. ruminantium antigen detection was in plasma and serum on the 4th day after inoculation. Of all the blood fractions investigated, the red blood cells showed the highest concentration, and this reached a maximum on the 12th day after infection.

Isolation of Cowdria ruminantium by means of Percoll density gradient centrifugation and detection by an enzyme-linked immunosorbent assay.

The isolation of Cowdria ruminantium by means of Percoll density gradient centrifugation permits the recovery of partially purified viable populations of the organism possessing distinctly different densities. These conclusions are based upon results of analyses of density fractions by intravenous inoculation into sheep, protein determination, electron microscopy and enzyme-linked immunosorbent assay. Morphological differences were observed in the density fractions obtained from infected brain tissue and Amblyomma hebraeum nymphae.

The detection of antibodies to Cowdria ruminantium in serum and C. ruminantium antigen in Amblyomma hebraeum by an enzyme-linked immunosorbent assay.

A sensitive and reliable enzyme-linked immunosorbent assay for the detection of antibodies to Cowdria ruminantium in serum and C. ruminantium antigen in Amblyomma hebraeum nymphae is described. For the screening of antibodies, C. ruminantium from A. hebraeum nymphae, partially purified by wheat-germ lectin affinity chromatography, was used as antigen. To screen nymph populations, sera from either Ball 3 strain-infected sheep or Kumm-strain infected mice were used. By using appropriate controls the assays were rendered specific with respect to C. ruminantium.

Isolation of Cowdria ruminantium by cellular affinity chromatography and detection by an enzyme-linked immunosorbent assay.

The isolation of Cowdria ruminantium by means of wheat germ lectin affinity chromatography as described in this paper permits the recovery of partially purified viable organisms under mild conditions in short time. These conclusions are based upon results of analyses of column fractions by intravenous inoculation into sheep, protein determination, electronmicroscopy and enzyme-linked immunosorbent assay. The entire purification procedure could be completed in 4-5 hours using only either infected sheep tissue or nymphae as starting material.