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Author: Prof Joop Boomker

Infections of the lungs and trachea

The nematodes Dictyocaulus africana, Dictyocaulus filaria, Dictyocaulus viviparus, and Bronchonema magna occur in the bronchi and trachea of a variety of antelopes. Although the last named species was originally described as Bronchonema by Mönnig,it was placed in the genus Dictyocaulus where it remained for a long time before being transferred back into its original genus, Bronchonema.

The Dictyocaulus species and B. magna in their natural hosts produce lesions similar to, but never as severe as, those seen in domesticated ruminants. Initially, the worms cause alveolitis, followed by bronchiolitis and finally bronchitis as they become mature and move to the bronchi. Cellular infiltrates (neutrophils, eosinophils and macrophages) temporarily plug the bronchioles, causing the collapse of groups of alveoli leading to the clinical signs of coughing, dispnoea and breathing with an extended neck. The patent phase is associated with two main lesions, namely a parasitic bronchitis, characterized by the presence of many adult worms embedded in a white frothy mucus. Secondly, a parasitic pneumonia occurs, characterized by collapsed areas around infected bronchi. The pneumonia is the result of aspirated eggs and L1 which act as foreign bodies and provoke pronounced polymorph, macrophage and multinucleated giant cell infiltrations. Varying degrees of oedema and emphysema may also be seen (Fig. 2). Recovery starts taking place once the adult lungworms have been expelled. The lung tissue organizes and clinical signs abate.

Fig. 2: Varying degrees of emphysema and oedema of the lung can be seen in this picture of a Dictyocaulus infection. Note how thickened the edges of the lung are

Horak et al. (1983) found a few blue wildebeest in the KNP to have fairly extensive pulmonary lesions caused by Dictyocaulus viviparus (Fig. 3). These lesions did not appear to be severe enough to cause death, but may have debilitated the animals sufficiently to make them prone to capture by predators.

Bronchonema magna is considered non-pathogenic for springbok, its natural host. When springbok were introduced into the Bontebok National Park near Swellendam, bontebok became infected and mortalities occurred. As soon as the springbok were removed, the mortalities stopped. The lesions in the bontebok lungs were similar to those caused by the Dictyocaulus species in other antelope.

Fig. 3: Dictyocaulus sp. at the bifurcation of the trachea

As the genus name implies, Pneumostrongylus calcaratus (impalas) and P. cornigerus (bontebok) both occur in the lung where they are so intimately associated with the lung parenchyma that it is virtually impossible to obtain intact worms. Pneumostrongylus calcaratus in impalas is so common that it is considered ‘normal’, and apart from localized discolouration and slight fibrosis the lesions cause no discomfort to both the host species (Fig. 4). Gallivan, Barker, Alves, Culverwell & Girdwood (1989) describe P. calcaratus infection in impalas from Swaziland. Van der Walt & Ortlepp (1960) recorded mortalities in bontebok as a result of P. cornigerus infection.

Protostrongylus capensis (bontebok) and P. etoshai (blue wildebeest and gemsbok, respectively) occur in the lung alveoli where no lesions are produced. Muellerius capillaris is primarily a parasite of the lungs of sheep and goats in the Western Cape Province, and have been recovered from impalas, Grant’s gazelles and okapi’s in Kenya (Round, 1968). No pathogenic effects have been described.

Fig. 4: The lesion caused by Pneumostrongylus calcaratus in the lung of an impala.