The DPI NSW Primefact on lungworm in sheep, goats, and cattle is just over a page long, with the section on cattle afforded three lines. In those lines it states that lungworms "occasionally cause[s] disease in Australia in young cattle, mainly dairy cattle". In addition to this statement, the introduction states that "lungworms in cattle, sheep and goats are generally not economically important [and] usually [occurs] in host animals debilitated by other parasitic diseases and sub-optimal nutrition". This paper outlines a case of lungworm in adult beef cattle on a fodder crop that caused death and was of economic concern to the producers.
Following three years of dry conditions from Jan 2017 to Jan 2020, this property restocked with Angus cows on agistment, originally from the Julia Creek region, but had been grazing on country in the Guyra/Ebor region of the Northern Tablelands, before being agisted at this property. They had been resident for two months. This property was on mostly heavy black basalt soils and was within the slopes region to the west of Warialda and north of Gravesend. Rainfall had been excellent and the cows were placed onto an oat crop that was 1 metre high and green. The June and July average rainfall for Warialda is 50.1 and 43.6mm respectively. In 2021, they received 118mm for June and 120mm for July. Conditions were wet and there was significant run-off in paddocks.
The producers called me to examine a cow that appeared unwell after another cow had died within the herd of 120 cows.
I examined the cow in the crush. It had a temperature of 40.7 degrees and was dyspnoeic with an increased respiratory rate. When applying the stethoscope to the chest it was evident from the significant palpable crepitus that there was subcutaneous emphysema that extended from ventrally near the brisket to dorsally near the withers and caudally to the extent of the rib cage. Auscultation of the lungs was made difficult by the audible crepitus. The cow was treated with antibiotics by a private veterinarian but was given a poor prognosis. The cow died two days later and was necropsied.
The abdominal cavity was unremarkable. Within the chest cavity there was significant mediastinal emphysema and lung emphysema most obvious caudally and dorsally. The mediastinal area was ballooned. Within the airways there were abundant worms and bloody froth with erythema of the airway lining. Worms were evident within the airways from around the area of the first bifurcation of the trachea. A sample of parasites was taken for identification by the laboratory.
The lung parasites were identified as Dictyocaulus sp. by the State Veterinary Diagnostic Laboratory at EMAI. A fixed sample of lung tissue revealed eosinophilic fluid within alveoli and a diffuse histiocytic pneumonia with congestion, oedema, and emphysema. Interestingly the pneumonia was classified as mild.
As there is no known resistance of lungworm to cattle drenches, all available commercial drench products for cattle ought to be effective against lungworm. The producer applied an abamectin backline drench to all at-risk animals on the property. There were no subsequent cases.
Disease caused by cattle lungworm is categorised as verminous pneumonia. It is described as "most commonly seen in calves during their first summer grazing pastures that are repeatedly used from year to year" and also that it occurs mostly in "a moist cool climate". The animals affected in this instance were adult cows, with no disease reported in calves. It would be rare for anyone to describe the Warialda climate as moist and cool. However, the winter of 2021 was indeed moist, with plentiful rainfall in the district, and the previous habitation of these animals, in the Ebor region of NSW (East of Guyra on the Northern Tablelands), would be as close to a European climate as could be found in NSW.
A Google search of "subcutaneous emphysema + lungworm" revealed no hits, and yet it was this clinical presentation that led to a more thorough investigation and ultimately to the diagnosis. Pneumonia, as a bacterial disease often secondary to stress, co-mingling of foreign herds, and/or viral insult in cattle, is a very common diagnosis in this region, mostly in young cattle, but not uncommonly in adults. Without the emphysema, the case may not have been investigated more thoroughly with a necropsy but rather presumed to be a standard pneumonia with a later onset or more chronic from previous stress of transport.
Interstitial emphysema is, however, a commonly noted finding of verminous pneumonia, due to pressure build-up during exhalation with partially blocked bronchioles. It may be possible for this lung damage to extend to the mediastinum and then through to the subcutaneous region with time. Or, it may be that this case was an anomaly or at least a very unusual presentation for verminous pneumonia.
The lungworm lifecycle is largely similar to other roundworms with some notable differences. The Wormboss website contains the following excellent summary:
Adult females in the lungs lay eggs containing a first stage larvae. Some of these eggs hatch in the lungs but most are mixed with the mucous exudate, are coughed up, swallowed, and then hatch during transit through the digestive system. First stage larvae (not eggs) are passed in the dung pat. Further development into the infective third stage takes about 4-5 days.
Infective larvae are very sluggish and do not actively migrate out of the dung pat. They may be carried by heavy rains, or when the crust of the pat is broken up by farm equipment or hoofs. Larval lungworms also gain access to clean grass using the spore structure of the fungusPilobolus, which grows on cattle faeces. Larvae congregate on the sporangium (reproductive capsule) of the fungus and when it explodes, they can be propelled as far as three metres.
When eaten by grazing cattle, infective larvae move to the small intestine, penetrate the walls, moult to the pre-adult stage in the mesenteric lymph nodes, and travel via the mesenteric lymph system to the thoracic duct and blood system into the lungs.
This case was an unusual outbreak of cattle lungworm in an area that would not be the preferred environment of the parasite. With the value of hindsight there are three main factors that contributed to this outbreak:
It is worth mentioning that quarantine drenching is not routinely practiced by cattle producers as there is presumed to be less drench resistance in cattle worms. In this case any drench ought to have been effective in treating the lungworm infected cattle and the disease outbreak likely would have been prevented.