Studies on the epidemiology of bovine parasitic bronchitis.

In the West of Scotland the epidemiology of parasitic bronchitis in grazing calves was studied over a two year period with the aid of tracer calves and herbage examinations for Dictyocaulus viviparus larvae. The observations of both years emphasised the importance of overwintered lungworm larvae as a source of disease. In the first year it was shown that the ingestion and development of these overwintered larvae were, by themselves, directly responsible for severe morbidity, high faecal larval counts and deaths. In the second year it was shown that pasture ungrazed during the winter and spring and from which a hay crop was removed in mid-summer was still capable of producing clinical parasitic bronchitis in susceptible calves within three to four weeks of their introduction in later summer. In both years there was some evidence that the outbreaks appeared to be associated with the sudden availability of infective larvae on the herbage. The possibility that such larvae may have survived for many months in the soil is discussed. Despite the heavy challenge with lungworm larvae experienced by the grazing calves in the first year those vaccinated with lungworm vaccine survived, their clinical signs were mild and of short duration and their faecal larval output was greatly reduced.     

Strongyle infections in ponies. II. Reinfection of treated animals.

Five of seven ponies whose strongyle worm burdens had previously been removed or markedly reduced by repeated thiabendazole treatments were reinfected with doses ranging from 100,000 to 500,000 small strongyle infective larvae. Reinfection of ponies resulted in the development of clinical signs characterized by abnormal feces, marked loss of weight and delayed shedding of winter hair coats. An abrupt increase in circulating eosinophils occurred during the first three weeks following reinfection. Patent infections developed in all ponies with worm eggs appearing in the feces from 12 to 15 weeks after receiving infective larvae. Worm egg outputs followed a cyclic pattern with approximately four to five peaks in egg output per year. There was an abrupt drop in the high worm egg counts in two untreated ponies approximately two and a half years after reinfection. No worms were recovered in the feces of these animals when they were subsequently treated, suggesting that a depletion in the number of inhibited larvae present in these ponies might have occurred.     

Effects of the chitin synthesis inhibitor diflubenzuron on development of Ascaris suum and Haemonchus contortus

The potential of the chitin synthesis inhibitor diflubenzuron (DFB) to alter the development of the parasitic nematodes (Ascaris suum and Haemonchus contortus was investigated. DFB given orally (10 mg kg-1 per day for 30 days) to sheep inoculated with H. contortus infective larvae did not prevent the establishment of adults or affect fecal egg output. However, there was a significant (greater than 90%) decrease in the number of infective larvae recovered from fecal cultures derived from lambs harboring H. contortus adults that were treated with DFB. DFB did not affect egg hatching. Oral administration (10 mg kg-1 per day for 20 days) of DFB to swine harboring adult A. suum adults had no effect on the adult worm burden or on egg morphology, but eggs removed from worms obtained from DFB-treated swine contained less chitin than eggs removed from untreated control swine. DFB also inhibited chitin synthesis in vitro in the isolated reproductive tract of A. suum adults. These results indicate that DFB at high doses can inhibit the subsequent development of H. contortus larvae in the feces. Since H. contortus larvae lack chitin, DFB may act on these larvae by a mechanism independent of a direct effect on chitin synthesis.     

Effects of migrating Gasterophilus intestinalis larvae (Diptera: Gasterophilidae) on the mouth of the horse

Lesions were formed in the mouth of the horse by first- and second-stage Gasterophilus intestinalis larvae. The lesions resulted as larvae burrowed through the top millimeter of the tongue and then became embedded in the interdental gingiva. Appearance of the lesion was dependent on the degree of larval burrowing activity and healing that had taken place. Active tunneling production occurred at the posterior end of the lesion. Extensive change in configuration and color was apparent along the longer lesions with active larvae. Virtually all tissue in the path of the larvae was removed while forming a tunnel. Tissue destroyed included tops of the lamina propria mucosae evaginations and the deeper portions of the lamina epithelialis mucosae. Histopathologic findings showed that the tissue removed included the nerve and blood supply of the proprial evaginations. Hemorrhage and exocytosis into the tunnels included erythrocytes mixed with some macrophages, lymphocytes and scant numbers of eosinophils. Air shafts excavated in the tongue by larvae enabled bacteria to enter into the tunnels. Bacteria became adhered to larvae and initiated microabscesses. Microabscesses were composed of clotted erythrocytes, bacteria, disintegrating epithelial cells, and large numbers of neutrophils. Cells surrounding the tunnel exhibited pyknosis, epithelial hydropic degeneration and became separated from each other. Healing of tongue lesions occurred as epithelial cell growth below raised the tunnel upward and affected tissue desquamated. Interdental gingiva invaded by larvae were hyperemic and denuded of epithelia. Recession and ulceration of the gingiva produced periodontal pockets. Extensive invasion by larvae led to compound periodontal pockets. Larval mouth hooks were embedded in the submucosa of the pockets and tore at engorged capillaries. The cephalic portion of embedded larvae became surrounded by a cellular exudate containing erythrocytes and mononuclear cells. Attachment of second-stage larvae at the root of the tongue did not produce observable damage.     

Recovery of Mycobacterium avium subsp. paratuberculosis from nematode larvae cultured from the faeces of sheep with Johne's disease

A study was conducted to determine whether trichostrongylid nematode larvae become contaminated with Mycobacterium avium subsp. paratuberculosis when they develop in the faeces of sheep with Johne's disease. Nematode larvae were hatched from ova in the faecal samples of affected sheep. Larval sheaths were removed and these as well as exsheathed larvae were subjected to radiometric culture for M. paratuberculosis. The organism was recovered from washing water used to prepare the larvae, third stage larvae and larval sheaths, but not from exsheathed larvae. The recovery of M. paratuberculosis from larvae was associated with the severity of the histological lesions in affected sheep and with the results of culture of the organism from intestinal tissues and faeces. Nematode parasites of sheep might be able to act as mechanical vectors for M. paratuberculosis as the organism associates with infective third stage larvae when these develop in the faeces of sheep with Johne's disease.     

Strongylus vulgaris in the tunica media of arteries of ponies and treatment with ivermectin

A preliminary investigation was made into the effect of fourth-stage Strongylus vulgaris larvae sequestered in the tunica media of ileocolic arteries of pony foals treated with ivermectin. The foals had been reared parasite-free, inoculated with infective larvae and given orally a placebo or ivermectin paste. Two foals received subsequently one or two further inoculations with larvae and treatment with ivermectin. Arteriography was used to identify the lesions in the ileocolic artery following inoculation and their regression following treatment. At necropsy, foals were examined for lesions and larvae grossly and histologically. Ivermectin was highly effective against fourth-stage larvae and those present in the media appeared not to unduly affect the integrity of the ileocolic artery. Increased numbers of larvae were not found in the media of foals receiving repeat inoculations and repeat treatments. Larvae were not found in the media of foals treated with a placebo. The major pathological changes in the arterial wall of all foals were attributed to infection with S. vulgaris and there was no strong tendency for the damaged arteries to return to normal after the S. vulgaris were removed.     

Dracunculus insignis infection in a dog

Painful, fluctuant subcutaneous swellings on the limbs of a dog were attributed to infection with Dracunculus insignis. The diagnosis was obtained by finding larvae in fluid aspirated from the swellings and by identification of the adult female nematodes after they were surgically removed. Six weeks after initial examination, another adult nematode was removed from the subcutaneous tissues of the thorax. Although uncommon, D insignis infection should be considered in the differential diagnosis of subcutaneous swellings.     

Strongyloides papillosus: prenatal and transmammary infection in ewes

The absence of larvae in lambs of six infected and controlled ewes immediately killed at birth without suckling may indicate the absence of prenatal infection. The ewes had larvae in their milk immediately prior to lambing and several hours afterwards. The persistence of infection, even after intestinal infection was removed with thiabendazole at 50 mg/kg body weigh, may be due to the pool of inhibited larvae. All the suckling lambs had patent infections within 4 to 5 days. Infection of suckling lambs with Strongyloides papillosus via milk from their ewes demonstrates the transmammary route of infection of this nematode.     

Critical tests with oxibendazole against gastrointestinal parasites of ponies.

Twenty ponies were allotted to 4 groups of 5 ponies each, and oxibendazole was orally administered at dose levels of 5, 10, 15, and 20 mg/kg. In the 3 groups of ponies given the largest doses, efficacy against 3 species of Strongylus was between 92 and 100% and that against small strongylids of the genera Cyathostomum, Cylicocyclus, Cylicodontophorus, and Cylicostephanus was more than 99%. All adults and 95 to 100% of larvae of the pinworm Oxyuris equi were removed. In the group of ponies given 5 mg/kg, 86 to 100% of the large strongylids and 84 to 100% of the small strongylids were removed, as were all larval and adult pinworms. Trichostrongylus axei was found only in 4 of the 5 ponies given 5 mg/kg; results were encouraging, but not consistent. Almost all of the Parascaris equorum were found in this group of ponies; no anthelmintic activity was detected at this dose level. Oxibendazole removed approximately 99% of small strongylid 4th-stage larvae. No efficacy against the larval stages of Gasterophilus intestinalis and against Habronema spp and Setaria equina was observed.     

Overwintering of larvae of the cattle lungworm (Dictyocaulus viviparus) on pasture in Kentucky

Seventeen dairy calves, raised lungworm-free, were used in an experiment to determine whether lungworm (Dictyocaulus viviparus) larvae survived on a pasture in central Kentucky during the winter of 1979/1980. On Apr 22, 1980, the calves were placed on pasture. Three calves were put on pasture A, on which no cattle had grazed for over 20 years. Fourteen calves were put on pasture B, which had been vacant since Dec 12, 1979 (132 days before beginning of experiment), when several lungworm-infected calves had been removed from the pasture. Fecal samples from the 17 calves were examined for lungworm larvae at weekly intervals for about 6 weeks; lungworm larvae were not found in any of the 3 calves on pasture A, but were found in 12 of 14 (86%) calves on pasture B. One calf from pasture A and 3 calves from pasture B were euthanatized 37 days after being placed on pasture; lungworms were recovered from 1 calf from pasture B.     

中意蜂混合群工蜂清理异种蜂卵和幼虫行为的比较

通过比较中蜂和意蜂混合群内工蜂对异种蜂卵和幼虫的清理行为,研究中蜂工蜂和意蜂工蜂的亲属辨识能力。混合蜂群稳定一周后开始第一次实验,再隔一周进行第二次实验。每次实验连续进行5天。结果表明:混合群刚稳定时,中蜂工蜂和意蜂工蜂对异种蜂卵和幼虫均有较强的亲属辨识能力,意蜂工蜂对中蜂幼虫的清理率明显高于中蜂工蜂对意蜂幼虫的清理率。随着混合群稳定3周后,中蜂工蜂和意蜂工蜂对异种蜂的卵和幼虫的清理积极性明显降低。     

Efficacy of ivermectin against inhibited larvae of Ostertagia ostertagi

The efficacy of ivermectin against inhibited early 4th-stage larvae of ostertagia ostertagi and other nematodes of the abomasum and intestinal tract was determined in naturally infected yearling beef cattle. The time when large numbers of inhibited larvae were acquired was determined by monthly slaughter of monitor cattle, beginning in January. In April, 12 animals were removed from pasture and maintained free of further helminth exposure until slaughter (21 days). At 9 days after the cattle were removed from pasture, ivermectin was administered to the principals by subcutaneous injection (200 micrograms/kg); the other 6 animals were given subcutaneous injections of the ivermectin vehicle. both groups were klled and necropsied at 12 days after treatment. Mean numbers of O ostertagi in the 6 controls were: adults, 41,906; developing 4th stage, 73,813; and early 4th stage, 334,965. The mean proportion of early 4th-stage larvae was 73.7%. In the 6 principals (treated with ivermectin), the following reductions were observed: O ostertagi adults, 100%; developing 4th stage, 99.8%; and early 4th stage, 99,9%. Small numbers of dead and degenerated O ostertagi of all developmental stages were recovered from abomasal washings before fixation; few viable worms were recovered.     

Development and survival ofhaemonchus contortus larvae on pasture in iraq

The survival of Haemonchus contortus infective larvae on pasture and soil was studied over a period of 12 months in the Baghdad area. Infective larvae were found on herbage and soil at all times except in the summer months. During autumn and winter infective larvae in pasture survived for periods of up to 32 weeks. Little larval migration into soil was observed during this study and larvae did not survive for long in the faecal pellets during the summer.     

The occurrence, cost and control of sawfly larval (Lophyrotoma interrupta) poisoning of cattle in Queensland 1972–81

A postal survey of cattle producers in the Maranoa, Warrego and Leichhardt districts of Queensland where poisoning of cattle by larvae of the sawfly (Lophyrotoma interrupta) occurs was carried out in 1982 with 179 replies (64% of those contacted). During 1972-81, 50 farms with 84,300 cattle experienced deaths (5254 on 37 farms) during July to September. The worst years were 1975 (955 deaths) and 1979 (1895 deaths). Heavy losses occurred on 9% of farms. These were where the silver-leaved iron bark (Eucalyptus melanophloia) was most common. To prevent the disease, 37 graziers moved cattle from dangerous areas and 52 partly removed E. melanophloia from their farms. 31 fed supplements to try to prevent the pica thought to cause cattle to eat larvae. 53 who had suffered sporadic or no deaths took no action. The survey results indicated that cattle should not be returned to dangerous areas until early October. The estimated total yearly cost from reduced carrying capacity, control measures and deaths was $1,100,000 (1981 values). Improved control by advice on property management and a better knowledge of the population dynamics of the sawfly was suggested. The use of antidotes or toxoids was thought inappropriate.     

The response of sheep vaccinated with irradiated Trichostrongylus colubriformis larvae to impulse and sequential challenge with normal larvae

Sheep aged 9–10 months were vaccinated with three doses of 20 000 irradiated Trichostrongylus colubriformis larvae at fortnightly intervals. This gave 97–99% protection against subsequent “impulse” challenge with 40 000 normal larvae or “sequential” challenge with 2 000 larvae/week-day for 4 weeks.The sheep were protected against both types of challenge when worms from the immunizing infections were present at the time of challenge, and when these worms were first removed by anthelmintic treatment.     

Effects of grazing undrenched weaner deer on chicory or perennial ryegrass/white clover pasture on the viability of gastrointestinal nematodes and lungworms

This study determined the in vitro effects on the viability of internal parasites of grazing undrenched weaner deer on either chicory (Cichorium intybus) or perennial ryegrass (Lolium perenne)/white clover (Trifolium repens) pasture. One experiment investigated the hatching and development of gastrointestinal nematode eggs and larvae, and the development and motility of L1 lungworm (Dictyocaulus eckerti) larvae, and a second experiment used larval migration inhibition assays to test the viability of L1 lungworm larvae extracted from the faeces of weaner deer grazed on either chicory or pasture when they were incubated with rumen and abomasal fluids from fistulated deer also grazing on chicory or pasture. The incubations were undertaken with and without added condensed tannins purified from chicory and with or without polyethylene glycol (PEG) to bind the tannins. Chicory had no effect on the hatching and development of gastrointestinal nematode eggs and larvae. Grazing chicory reduced the number of lungworm larvae developing to the L3 stage, and L1 lungworm larvae from the faeces of chicory-grazed deer were less viable in rumen and abomasal fluid than larvae from pasture-grazed animals. Abomasal fluid was significantly (P < 0.001) less inhibitory to the migration of L1 lungworms than rumen fluid. When the larvae were incubated in rumen and abomasal fluids from chicory-grazed deer, their passage through sieves was significantly (P < 0.001) reduced in comparison with when they were incubated in the fluids from pasture-grazed deer Adding condensed tannins to rumen fluid increased the inhibition of the migration of L1 lungworm larvae but PEG removed this inhibition; this effect was not observed with abomasal fluid.     

The efficacy of in-feed medication with fenbendazole against gastrointestinal nematodes of sheep, with particular reference to inhibited larvae.

Anthelmintic activity of fenbendazole in a feed formulation was tested against nematode parasites of sheep. Dose rates ranging from 1.4 mg per kg for four days to 0.4 mg per kg for 14 days removed 98 to 100 per cent of the total gastrointestinal worm burden, including large numbers of inhibited fourth stage larvae of Ostertagia circumcincta. One hundred per cent effectiveness against adult Dictyocaulus filaria was also recorded.     

Identification and distribution of swine serum immunoglobins that react with Trichinella spiralis antigens and may interfere with the enzyme-labeled antibody test for trichinosis.

Sera from Trichinella spiralis digestion-negative swine contained variable amounts of two immunoglobins that reacted with T spiralis antigen in the indirect enzyme-labeled antibody test for trichinosis. One of these immunoglobins, detected by heavy chain-specific anti-swine immunoglobulin G (IgG) conjugate, was removed by absorption with T spiralis larvae. A second immunoglobin, detected by heavy chain-specific anti-swine IgM, was not removed by absorption with T spiralis larvae and increased in amount with the age of the animal. These two immunoglobins varied independently in individual animals and showed some specificity for the antigen; ie, they did not merely reflect changes in total serum IgG or IgM. In contrast to IgG anti-T spiralis antibody from experimentally infected animals, neither of these immunoglobins could be detected in double-diffusion tests against the antigen or by counter immunoelectrophoresis. Either of these immunoglobins could interfere with the indirect test for T spiralis antibodies, depending upon whether anti-swine IgG or IgM conjugate is used. The factors which initiate synthesis and control serum concentrations of these immunoglobins are not known.     

Comparison of two control systems for cyathostome infections in the horse and further aspects of the epidemiology of these infections

The small strongylid infections of two groups of three yearling female Shetland ponies and one yearling Shetland tracer pony were studied. One group was set stocked from April to November and was treated monthly with 5 mg kg-1 albendazole from two days before turnout until July. The other group grazed similar pasture until July, was treated with 5 mg kg-1 albendazole and subsequently removed to pasture grazed by sheep from April to July. The tracer ponies were added to both groups in September. The efficacy of both methods was not completely satisfactory probably because of low efficacy of anthelmintic treatment. There were no significant differences between the cyathostome burdens of the two groups. A high proportion of the cyathostome populations of all ponies consisted of inhibited early third stage larvae (L3). The finding of low numbers of immature fifth-stage worms in the tracer ponies indicated that the considerable adult burdens in the permanent ponies originated from infection picked up before the tracer ponies were added. In the group which was removed to sheep pasture after treatment in July it was likely that the majority of the adult worm burden had been ingested as infective larvae before treatment.     

UPPER AIRWAY OBSTRUCTION IN A LLAMA CAUSED BY ABERRANT NASOPHARYNGEAL BOTS (CEPHENEMYIA SP.)

A 9 month old female llama was presented with inspiratory dyspnea. Radiographically, there was a large soft tissue mass nearly occluding the nasopharynx. During endoscopic examination three nasopharyngeal bots were identified embedded in the mass. The larvae were removed and the patient treated with ivermectin. The patient was discharged one week later free of clinical respiratory disease. In follow-up radiographs made 6 weeks later, only residual radiopacity in the area of the mass remained.