Lungworms of ruminants.

Several species of nematodes parasitize the respiratory tract of ruminants. Disease due to infection with these parasites occurs less frequently in North America than in other parts of the world but can be locally and regionally important. The life cycles, epidemiology, pathology, diagnosis and treatment of Dictyocaulus viviparus, Dictyocaulus filaria, and Muellerius capillaris are summarized in this article.     

Study on small ruminant lungworms in northeastern Ethiopia

A cross-sectional study of lungworm infection was carried out with the aim of determining the prevalence of lungworm infection of small ruminants and identifying the species of the respiratory helminthes circulating in six districts of northeastern Ethiopia: Debresina, Legambo, Habru, Kalu, Chaffa-Dawi and Artumana-Fersejelle. Faecal and postmortem examination were conducted from 1162 and 104 animals, respectively. An overall infection rate of 53.6% and 66.3% was found by faecal and postmortem examinations, respectively. Significant difference (p<0.05) was found between areas of different altitude with an infection rate of 30.4%, 32.5% and 71.3% at low, medium and high altitude areas, respectively. Prevalence on the different months was insignificant (p>0.05). The prevalence of Dictyocaulus filaria and Muellerius capillaris infection showed a significant difference (p<0.05) between young, adult and old age groups. The prevalence of D. filaria decreases and that of M. capillaris increase with increasing age of the animal. Animals under relatively good management system have been found less affected with significant difference (p>0.05) than their counterparts at relatively poor management system. The infection rate between male and female animals showed significant difference (p<0.05) with prevalence rate of 44.4% and 59.3%, respectively. A significant difference between sheep and goats was also noted with infection rate of 24.4% and 50.7%, respectively. Monthly worm burden of D. filaria infection showed significant difference (p>0.05) while it was insignificant in case of M. capillaris. Due to its impact on production, emphasis should be given for the control and prevention of lungworm infection in highland areas.     

Protostrongylid infection in meat sheep from Northwestern Spain: prevalence and risk factors

2093 Faecal samples from 74 commercial meat ovine flocks were collected and examined by the Baermann-Wetzel method for protostrongylid infection. The risk of being infected by lungworms was evaluated with a data mining classification tree (CHAID), and the intensity of infection with a general linear model (GLM). 242 out of 2093 faecal samples examined were positive for protostrongylid infection (11.6%; 95% CI 10.2-12.9). Only two species were found, Muellerius capillaris (97.9%) and Neostrongylus linearis (5.4%). 50 out of 74 farms presented at least one animal shedding protostrongylid larvae in faeces. All of them held animals infected by M. capillaris and seven presented mixed infections with N. linearis. Average larval output in infected sheep was 11.9 (SD 30.91). This study showed that protostrongylid prevalence in sheep for meat production was determined mainly by a positive interaction with Dictyocaulus filaria infection; other factors that have influenced over protostrongylid infection were age, introducing external animals in the flocks, mixed management with goats and animal density in pastures. Treatment effects on prevalence were only observed in flocks that did not introduce ewes. The lowest protostrongylid prevalence has been reported in flocks without D. filaria infection and without contact with goats.     

Efficacy of ivermectin delivered via a controlled-release capsule against small lungworms (Protostrongylidae) in sheep

To evaluate the efficacy of an ivermectin controlled-release capsule (CRC), which delivers 1.6 mg ivermectin per day intraruminally for 100 days to sheep weighing 40-80 kg (IVOMEC Maximizer CR Capsule for adult sheep, Merial), against small lungworms two studies with 48 naturally infected adult female Merino Landrace sheep were conducted. The sheep were allocated by restricted randomization based on bodyweight to untreated controls or received an ivermectin CRC. Eight sheep per group were necropsied 35, 70 or 105 days post-treatment. Lungworms were recovered by dissection or peptic digestion of the lungs. Baermann/Wetzel technique was used for faecal lungworm larval counts at weekly intervals. The efficacy of treatment was 100% against Dictyocaulus filaria and Protostrongylus rufescens (P < 0.05) at each necropsy day. The efficacy against Protostrongylus brevispiculum, Cystocaulus ocreatus and Neostrongylus linearis increased from 35 to 105 days after administration of the CRC and was found to be 100% (P < 0.01), 96.6% (P < 0.01) or 99% (P < 0.01), respectively, at 105 days post-treatment. The reductions of Muellerius capillaris counts varied and were 96.2% (P < 0.05) at 70 days post-treatment and 44.6% (P > 0.1) at 105 days post-treatment. Faecal lungworm larvae disappeared nearly completely from at least 3 weeks after the ivermectin CRC administration for all protostrongylid species including M. capillaris so that pasture infectivity will be subsequently significantly reduced.     

Efficacy of fenbendazole and cambendazole against Muellerius capillaris in dairy goats

Two anthelmintics, fenbendazole and cambendazole, were used in an attempt to eliminate Muellerius capillaris infections in a group of 44 goats. During the course of this study (508 days), M capillaris larvae were found in at least one fecal specimen from each of 22 of the 44 goats. All 44 goats were dewormed with fenbendazole (30 mg/kg of body weight) at the onset of this study (day 18). Two additional dewormings with fenbendazole at 4- to 8-week intervals were restricted to the goats that continued to shed M capillaris larvae. On the basis of routine fecal examinations, fenbendazole eliminated M capillaris larvae from the feces of 8 (36%) of these 22 goats. On day 253, cambendazole (60 mg/kg) was given orally to 17 of these 22 goats (2 of the 22 had died and 3 were not available for treatment); 13 of these goats were still shedding M capillaris larvae. Cambendazole eliminated M capillaris larvae from the feces of 10 (77%) of these 13 goats chronically infected with M capillaris.     

Case report: six cases of verminous pneumonia (Muellerius sp.) in goats.

Six cases of verminous pneumonia in goats due to Muellerius sp. were reviewed. In only one case was the pneumonia diagnosed antemortem. The gross necropsy findings and histopathology revealed a widespread interstitial pneumonia in all the cases. There was variability in the local reaction around the parasites from almost none in the mildest cases to larger focal accumulations of macrophages and mononuclear inflammatory cells. Only in the severest cases were eosinophils seen and even then were scattered and few in number. No nodular lesions were seen associated with the parasites. The pathology of the pulmonary lesions in goats appears to be more commonly of the diffuse type and therefore significantly different from the nodular lesion usually observed in sheep.     

Monitoring the health of pigs in New Zealand abattoirs

A survey of the prevalence of pneumonia, ascariasis, mange, oesophagogastric ulcers and porcine intestinal adenomatosis was carried out during 1986-90 on 2792 baconer pigs from 46 herds located in Canterbury, North Otago and the southern part of the North Island of New Zealand. Enzootic pneumonia had an overall prevalence of 45%, ascariasis 13% and clinical mange 13%. Oesophagogastric ulceration was a problem in certain herds only, whilst porcine intestinal adenomatosis and associated ileal lesions had a very low prevalence (7%). Examination of 534 snouts for atrophic rhinitis revealed a prevalence of 31%, but most of the lesions recorded were very mild.     

An Investigation of Ovine Pneumonia in Four Herds from Central Norway: II. Relation Between Pathomorphology and Presence of Micro-Organisms

Sheep lungs obtained at slaughter from 4 herds from Central Norway were subjected to a macroscopical examination. Gross pulmonary findings included normal lungs, fibrous pleurisy, verminous nodules, atelectasis and consolidations of lobular and lobar extensions. A selection of lungs representing the various gross findings was subjected to microbiological and histological examinations. Pleurisy was associated wtih pneumonic consolidations and extension of lesions. Verminous nodules indicative of Muellerius spp. migrations occurred irrespective of gross pulmonary lesions or microbiological findings. A subacute or chronic pneumonia of a mixed proliferative exudative type was demonstrated in consolidated tissue. An association was found between the isolation of Mycoplasma ovipneumoniae and the presence of pneumonic lesions and between the number of organisms and extension of lesions. Histological findings highly indicative of this organism were proliferative changes in the bronchiolar and bronchial epithelium and intrapulmonary lymphoid tissue. The intensity of these changes was correlated to the number of mycoplasma organisms present. Mycoplasma ovipneumoniae is suggested to be of primary etiological significance regarding subacute or chronic pneumonia in lambs at slaughter.     

Efficacy of netobimin against Muellerius capillaris and resistant strain of digestive tract strongyles in dairy goats

The efficacy of netobimin against digestive tract strongyles and the small lungworm Muellerius capillaris was tested in a dairy goat herd. The drenches were given orally at the rate of 20 mg/kg of body weight once, 10 mg/kg on 2 successive days, or 7.5 mg/kg on 3 successive days. Fecal egg counts and larval counts were done 8 days before and on the day of drenching; further counts were performed on postdrenching days 8 and 18. Two goats were necropsied, 1 on postdrenching day 5 and 1 on day 10 in the group treated on 3 successive days. The fecal egg counts were reduced by 44 to 79% depending on dosage on postdrenching day 18; the remaining worms were Trichostrongylus colubriformis. The larval counts of M capillaris were reduced by 72 to 92%, depending on dose. The reduction was significant in all the treated groups, compared with that in the control group. The use of netobimin at the dosage of 10 mg/kg given on 2 successive days or 7.5 mg/kg given on 3 successive days might be recommended to treat goats infected with Muellerius spp and digestive tract strongyles.     

Immunohistochemical detection of <Emphasis Type="Italic">Mannheimia (Pasteurella) haemolytica</Emphasis> antigens in goats with natural pneumonia

Pneumonia is a leading cause of loss to ruminants throughout the world. Mannheimia (Pasteurella) haemolytica is one of the most important etiological agent of pneumonia in cattle, sheep, and goats. This study was carried out to determine the incidence of M.haemolytica antigens using immunohistochemistry labelling of formalin-fixed, paraffin-embedded tissues in pneumonic lungs of goats slaughtered at abattoir, and then to compare these immunohistochemistry results with the results of bacterial isolation. For these objectives, a total of 1505 goat lungs slaughtered in slaughterhouse were grossly examined and pneumonia was detected in 74 cases (4.91%). Of these, with the exception of verminous pneumonia observed in 32 cases, on 42 pneumonic lungs immunohistochemical examinations were performed. Formalin-fixed and paraffin-embedded lung tissue samples were immunohistochemically stained by the avidin-biotin-peroxidase complex (ABC) procedure using polyclonal antibodies to detect M.haemolytica antigens. Pneumonic lesions were more frequently encountered in cranioventral lobes than caudal lobes, and characterized by irregular lobular foci of atelectasis or lobar pneumonia. The presence of M.haemolytica antigens was detected in 19 (45%) out of 42 pneumonic lungs. Bacterial antigens were found most frequently in the cytoplasm of bronchial and bronchiolar epithelial cells, in the swirling degenerating leukocytes in the alveoli, and in the degenerating leukocytes in the area of coagulation necrosis, less frequently in the epithelial cells of bronchial glands, and lymphoid cells. Conclusionly, immunohistochemical detection of M.haemolytica antigens in pneumonic lungs appear to be more reliable compared to bacterial isolation.     

Cilia-associated respiratory bacillus infection in rats in New Zealand

AIMS: To demonstrate cilia-associated respiratory (CAR) bacillus associated with chronic pneumonia in wild and pet rats in New Zealand. METHODS: A range of tissues from 4 rats were examined grossly and by light microscopy and affected lungs were examined by transmission electron microscopy. RESULTS: All 4 rats had moderate to severe cranioventral bronchopneumonia with bronchiectasis and large numbers of argentophilic bacteria resembling CAR bacillus, intimately associated with the bronchial epithelium. CONCLUSIONS: CAR bacillus infection should be considered as a differential diagnosis for pneumonia in rats in New Zealand.     

Immunohistochemical detection of parainfluenza type 3 virus antigens in paraffin sections of pneumonic caprine lungs

Pneumonia is a leading cause of loss to ruminants throughout the world. Parainfluenza type-3 virus (PI-3) is one of the most important respiratory pathogens of bovine and ovine. In this study, prevalence of PI-3 virus infection as causative agent of pneumonia in goats was investigated. For this purpose, a total of 1505 goat lungs slaughtered in Bitlis and Van slaughterhouses were grossly examined and pneumonia was detected in 74 cases (4.91%). Lesions were more frequently encountered in anteroventral lobes than caudal lobes. With the exception of verminous pneumonia observed in 32 cases, immunohistochemical examinations were performed on 42 pneumonic lungs. Formalin-fixed and paraffin-embedded lung tissue samples were immunohistochemically stained by the avidin-biotin-peroxidase complex procedure using polyclonal antibodies to detect PI-3 viral antigens. The presence of PI-3 viral antigens was detected in 28 (66.6%) of 42 pneumonic lungs. Viral antigens were found most frequently in the cytoplasm of bronchiolar epithelial cells, type II pneumocytes, and less frequently in the epithelial cells of bronchial glands, syncytial cells, alveolar macrophages, and lymphocytes and plasma cells. In conclusion, it was found that there was a close relationship between the pneumonia in goats and the presence of PI-3 viral antigens. Incidence of PI-3 virus in pneumonic lungs of goats was detected to be very high in the present study performed in the region of Bitlis and Van, Turkey.     

Pneumonic lesions in lambs in New Zealand: patterns of prevalence and effects on production

AIM: To describe temporal and spatial patterns of the prevalence of pneumonia in lambs in three regions of New Zealand, and determine effects on liveweight gain. METHODS: A longitudinal study was conducted in 1999- 2000 on 14 commercial sheep farms, five from the Southland region of the South Island, and five from the King Country and four from the Northland regions of the North Island. Pneumonia was known to be a problem in lambs on all farms selected. On each farm, 400 lambs were randomly selected at weaning and allocated at random to one of two groups (Groups I and II). Lambs in both groups were weighed at 4-weekly intervals. The extent of pneumonic lesions in lungs was scored visually at slaughter in 40 randomly selected lambs after each weighing (Group I). Lambs in Group II were selected for slaughter by the farm manager on a commercial basis of liveweight and body condition, then assessed for pneumonic lesions. RESULTS: Prevalence of extensive pneumonic lesions (>/=10% lung surface area affected) increased from December to March from 1.4 to 10.1% lambs in Southland (n=1,917), 1.2 to 25.7% in the King Country (n=1,831), and 4.7 to 21.4% in Northland (n=1,485). Overall, 42.3% of lambs in both groups had pneumonic lesions (n=5,233) and in 15.1% of these, >/=5% of the lung surface area was affected. Daily weight gain in the month prior to slaughter was reduced in lambs for which >/=20% lung surface area was affected in Group I (p<0.05) but not in Group II. CONCLUSIONS: The association between pneumonic lesions and reduced weight gain was highly significant in lambs from Group I, but not from Group II. Thus, pneumonia had a negative impact on weight gain, and selection by farmers of lambs for slaughter counteracted this association in lambs from Group II. CLINICAL RELEVANCE: Pneumonia occurs commonly as a subclinical disease in lambs in New Zealand. It has no public health significance and is not recorded at slaughter plants nor reported to farmer clients. Effects of the disease on daily weight gain of lambs is considerable and costly for lamb producers.     

Economic effect of pneumonia and pleurisy in lambs in New Zealand

AIM: To estimate the cost of pneumonia and pleurisy in lambs to the sheep industry in New Zealand, in order to provide a reference for future cost-benefit calculations for control programmes to reduce the incidence of pneumonia. METHODS: An estimate of the economic cost of pneumonia and pleurisy in lambs was based on: cohort studies of the association between growth rate and the extent of pneumonic lesions at slaughter (n=14 flocks), the prevalence of moderate to severe (MS) pneumonia (> or =10% lung surface area affected) and pleurisy (n=1,719 flocks), the correlation between the prevalence of MS pneumonia and economic loss at the flock level, and data on annual slaughter statistics and carcass value in New Zealand. A stochastic spreadsheet model was developed and run with 1,000 iterations. Input variables represented by probability distributions were growth rate, average cost of loss according to the prevalence of pneumonia per month, carcass value, prevalence of pleurisy, and carcasses downgraded for pleurisy, and annual national slaughter statistics. The output was a posterior distribution of the annual cost of disease. RESULTS: The cost of pneumonia only included the loss associated with reduced growth rate, while mortality due to pneumonia was assumed to be low and was ignored. The cost of pleurisy included the loss associated with downgraded or condemned carcasses. Thus, the simulated annual average cost of pneumonia was NZ$28.1 (95% CI=NZ$15.0-42.0) million, and that of pleurisy NZ$25.1 (95% CI=NZ$10.2-48.1) million. The combined cost of pneumonia and pleurisy averaged NZ$53.2 (95% CI=NZ$32.4-78.9) million. The parameters with the greatest impact on the combined cost of pneumonia and pleurisy were prevalence of pleurisy between March and May, and cost of reduced growth due to pneumonia for lambs slaughtered in June. CONCLUSIONS: The average cost of pneumonia and pleurisy to the sheep industry in New Zealand due to reduced lamb growth and decreased carcass value is likely to be between NZ$32.4 and $78.9 million. This is a conservative estimate, omitting mortalities, indicating that pneumonia and pleurisy have substantial economic impact on sheep farming in New Zealand. Considering that 23,833,000 lambs were slaughtered in 2003/2004 (average value $65.56/lamb), this cost would equate to NZ$1.36-3.31 per lamb. CLINICAL RELEVANCE: Pneumonia and pleurisy are common diseases in lambs in New Zealand, leading to substantial economic loss to producers.     

The prevalence and microbiology of pneumonia in a flock of lambs

A flock of New Zealand Romney lambs on a property in Hawkes Bay was examined from August 1978 to June 1979. In November, the lambs in the flock were allocated to groups as follows: 600 lambs from which groups were selected for slaughter by commercial criteria each month (selected groups); 700 lambs which were subdivided into 8 groups (random groups), one of which was sent for slaughter each month; and 25 lambs to monitor serological responses to viral infections (surveillance group). At slaughter, lesions in the anterior lobes of the lungs were classified into small, large or mottled lesions while those in the posterior regions of the diaphragmatic lobes comprised a separate group. The prevalence of the pneumonic and pleural lesions was recorded in all groups of lambs. Pneumonic lesions in lambs from the random groups were further classified after microscopic examination. The prevalence of infections with parainfluenza virus type 3, adenoviruses, Mycoplasma spp., and Pasteurella haemolytica was also recorded in the random groups. Average carcase weights of all groups of lambs were also recorded. The prevalence of large lesions in the anterior lobes, pleural lesions and devaluation of carcases due to pleural lesions was significantly lower in the selected than in the random groups. In the random groups, the prevalence of small lesions in the anterior lobes of the lungs was high and was not always associated with infections with the viruses, P. haemolytica or Mycoplasma spp. Microscopically, these lesions could he divided into four types as previously described. The prevalence of large lesions in the anterior lobes was low in November but increased to peak levels in February and March and then declined to intermediate levels. The prevalence of large lesions was associated with that of infections with the micro-organisms and significantly more large lesions contained P. haemolytica and Mycoplasma spp. than did small lesions or normal lungs. The prevalence of large lesions also appeared to be inversely related to the average carcase weights of the lambs. Most large lesions were similar on microscopy to those of "enzootic" or "atypical" pneumonia but were divided into four types on the basis of exudative and proliferative features. The prevalence of mottled lesions in the anterior lobes was low throughout the period of observation but peaks were observed in January and May. The peaks were associated with adenovirus infection and elevated prevalence of infection with P. haemolytica and Mycoplasma spp. Significantly more mottled lesions contained P. haemolytica than did small lesions or normal lungs. Microscopically, most mottled lesions were similar to exudative large lesions. Lesions in the posterior diaphragmatic lobes were most numerous in November and from April to June. Their prevalence appeared to be related to anthelminthic treatment and environmental conditions. Microscopically, these lesions were typical of those following infection with Dictyocaulus filaria.     

Field efficacy of eprinomectin against a natural Muellerius capillaris infection in dairy goats

The field efficacy of eprinomectin against a natural infection with Muellerius capillaris was evaluated in adult dairy goats. A total of 13 animals were included in a crossover treatment study. Animals were treated with eprinomectin (0.5 mg/kg) in the spring and again in the autumn of 2006, and monitored by enumeration of the lungworm larvae per gram of faeces (LPG). The reduction in LPG on days 7, 21 and 42 after treatment was used to evaluate the anthelmintic efficacy. Both in the spring and in the autumn a 100% reduction (P<0.01) in LPG was observed on days 21 and 42. These results illustrate that eprinomectin applied as a topical pour-on is a practical alternative to benzimidazole treatment of lungworms in dairy goats. No adverse reactions to the eprinomectin treatment were observed.     

Experimental respiratory infection of goats with caprine herpesvirus and Pasteurella haemolytica

Groups of six male goats were inoculated intratracheally and intranasally with either caprine herpesvirus followed 6 days later by Pasteurella haemolytica, canine herpesvirus alone or P. haemolytica alone. Pneumonic lesions were observed in five of the six goats inoculated with caprine herpesvirus followed by P. haemolytica and in three of the six goats inoculated with P. haemolytica alone, but were not observed in goats inoculated with caprine herpesvirus alone or in non-infected controls. Pasteurella haemolytica was isolated from seven of eight lungs with pneumonia, but only from one of sixteen lungs without pneumonia. The lesions ranged from fatal acute exudative necrotising pneumonia to predominantly proliferative pneumonia. Half of the caprine herpesvirus-inoculated goats developed a clinical catarrhal rhinitis five days post-inoculation and the only virus-specific histopathological lesion was a mild tracheitis. Canine herpesvirus was recovered from the nasal swabs of all caprine herpesvirus- inoculated goats developed a clinical catarrhal rhinitis five days post-inoculation and the only virus-specific histopathological lesion was a mild tracheitis. Canine herpesvirus was recovered from the nasal swabs of all canine herpesvirus-inoculated goats and from the lungs of three goats inoculated with caprine herpesvirus alone. The experimental inoculations demonstrated that P. haemolytica alone can produce pneumonia in goats. In addition, the study showed that caprine herpesvirus readily proliferates in the upper respiratory tract and lungs of goats but the role of caprine herpesvirus in the aetiology of pneumonia remains uncertain.     

Efficacy trial of an irradiated cattle lungworm vaccine in red deer (Cervus elaphus)

Lungworm (Dictyocaulus sp.) is the parasite of most concern to the New Zealand deer industry. Although lungworm can be controlled by anthelmintics there is an increasing concern over excessive drenching programmes and reliance on chemicals for parasite control. A live irradiated larval vaccine developed for cattle has been available in Europe for the past 40 years but has never been evaluated in red deer in New Zealand. Four groups of red deer and two of cattle were hand reared from birth in parasite-free conditions. The cattle acted as a control group to ensure that the vaccine was still efficacious on arrival in New Zealand. Two groups of deer were vaccinated, and all four groups were challenged with either D. viviparus or deer origin Dictyocaulus, tentatively identified as D. eckerti. The vaccine provided excellent protection to cattle under New Zealand conditions, there was no larval output in the vaccinated cattle and no adults were found in their lungs at necropsy. In red deer, patency was delayed in the vaccinated groups regardless of challenge species and larval output was lower but was not prevented. Adult lungworms were found in the lungs of all deer at necropsy but fewer were recorded in the vaccinated deer. Although Huskvac provided a degree of protection for red deer it was not effective enough to recommend its use.     

Parasites in sheep grazing on Kikuyu (Pennisetum clandestinum) pastures in the winter rainfall region

Regular worm counts were done post-mortem on sheep that had grazed on Kikuyu pastures at the Elsenburg Research Station near Stellenbosch, a winter rainfall region. Major species were Trichostrongylus colubriformis, Trichostrongylus axei, while Ostertagia circumcincta was usually present in large numbers. Minor species were Haemonchus contortus, Nematodirus spathiger, Dictyocaulus filaria, Oesophagostomum venulosum, Trichuris spp., Chabertia ovina and larvae of the arthropod Oestrus ovis. Muellerius capillaris caused the formation of nodules in the lungs but were not counted. The trial started in April 1982 and was concluded in March 1984. One hundred and four sheep died or were slaughtered and 99 were examined post-mortem during this period. Total worm burdens rose to a peak of 88,763 (range 67,281-124,735) worms in March 1983, i.e. sheep mortality was such that the flock had to be treated with an anthelmintic in April 1983 to prevent further losses. Kikuyu pastures provide shade, form an excellent mat, the humus layer under the grass retains moisture and is an excellent incubator for preinfective larvae and a protector for infective larvae. If these qualities are combined with more than 100 mm of rain in spring and summer, Kikuyu pastures are a paradise for the free-living stages.     

The pathology and aetiology of lung lesions in goats infected with caprine arthritis-encephalitis virus

Fifty dairy goats, of various ages, sexes and breeds were selected for examination on the basis of positive serological reactions to caprine arthritis-encephalitis virus (CAEV). Thirty-one had lung lesions including chronic interstitial pneumonia of caudal or cranioventral lobes, bronchopneumonia, verminous pneumonia, pulmonary cryptococcosis or combinations of these. The only infective agent recovered from all the chronic interstitial pneumonia cases examined was CAEV, which was also recovered from lung tissue of 3 goats with arthritis but no lung lesions. The presence of CAEV in lavaged alveolar macrophages from normal lung tissue and from lungs affected with chronic interstitial pneumonia and verminous pneumonia, and the demonstration of a marked increase in nonspecific esterase staining macrophages in areas of chronic interstitial pneumonia, are discussed in relation to the aetiology of the pneumonia.