Respiratory system

Introduction

Pulmonary oedema and emphysema are non-specific changes associated with many infectious, parasitological and toxicological conditions in livestock. However, in most diseases these changes are usually mild, develop terminally, are generally not associated with overt and prolonged signs of respiratory distress, and, apart from oedema and emphysema, no other significant changes are usually discernible macro- or microscopically in the lungs.

On the other hand, respiratory distress associated with marked oedema and/or emphysema, coupled with noteworthy microscopical changes in the lungs, rarely occurs in stock in South Africa and has been associated with poisoning by only a few plants, such as Crotalaria spp. and Hertia pallens; also with a variety of lush green pastures containing L-tryptophan, which is responsible for acute bovine pulmonary oedema and emphysema or fog fever; or with an ephemeral fever virus.


Crotalaria spp. (Fabaceae)


C. dura Wood & Evans
Wild lucerne, wilde lusern, jaagsiektebossie
C. globifera E. Mey.
Wild lucerne, wilde lusern, jaagsiektebossie
C. juncea L.
Sunn-hemp, Sunn-hennep
C. spartioides DC.
Dune bush, duinebos, besembossie

Crotalaria spp., such as C. dura,19, 47, 49, 50, 55, 58 C. globifera31, 49, 53 and C. juncea,53, 58 have been associated in South Africa with a chronic respiratory disease called jaagsiekte (Crotalariosis equorum) in horses and mules. The disease is characterized by fever, polypnoea, dyspnoea, subcutaneous and pulmonary emphysema, interstitial pneumonia and sometimes also fibrosis or cirrhosis of the liver.19, 31, 47, 49, 50, 53, 55, 58

Crotalaria dura (Figures 1 and 2) is a low, spreading bush with trifoliate leaves and typical yellow pea-flowers that are borne in terminal racemes, 28 mm long. The fruits are subglobose, densely hairy pods, 10 mm long and 8 mm in diameter.36 The leaves of C. globifera differ from those of C. dura in that the former are minutely hairy. The yellow pea-flowers are arranged in terminal racemes 60–80 mm long and the plant bears pods c.6 mm in diameter with a dense covering of fine hairs.36

Figure 1 Crotalaria dura

Figure 2 Crotalaria dura in the veld (Courtesy R. Last, Pietermaritzburg)

Crotalaria dura and C. globifera occur in certain parts of KwaZulu-Natal, where the disease was first noticed55 and still occurs today,27 and the former Transvaal (Figures 3 and 4).19 In the original elucidation of the aetiology of jaagsiekte, Theiler55 described a number of feeding experiments on horses using C. dura at the Allerton Laboratory and at Onderstepoort. During November 1915, a farmer from Singletree in KwaZulu-Natal submitted hay contaminated with C. dura to the Allerton Laboratory for toxicity trials. A horse was fed with 126 kg of this hay in 16 days, namely an average of 7,8 kg/day. The animal died 109 days after the commencement of the trial or 93 days after feeding had ceased. Another horse, at Onderstepoort, consumed 20,9 kg of C. dura (collected at Singletree) mixed in food over a period of 23 days. Ten days after feeding had started the horse developed a fever which lasted about 12 days. On the seventy-fifth day, the horse was again feverish and died six days later of jaagsiekte. Theiler55 conducted many feeding trials with C. dura and found the minimal quantity of plant material required to induce jaagsiekte to be c.21 kg of C. dura consumed over 23 days. When larger quantities were fed for shorter periods the disease likewise made its appearance. The disease developed after a period of apparent normality which varied among individual horses and in different experiments. Taking into account only those experiments that gave positive results after the shortest feeding trials, Theiler55 found that this period might be fixed at c.50 days. The disease lasted for 6–29 days and fever was in some instances present before the signs of jaagsiekte were evident.

Figure 3 Distribution of Crotalaria dura (Courtesy of the NBI, Pretoria)

Figure 4 Distribution of Crotalaria globifera (Courtesy of the NBI, Pretoria)

Some years later Steyn47 found evidence to support Theiler’s findings that C. dura is the cause of jaagsiekte. He induced the disease in a horse by feeding it with dry C. dura plants that had been collected in the late seeding stage, and had been stored for five years. According to Steyn49 and Marais,30 fresh C. globifera in the flowering and seeding stages, fed at a level of 90–180 g daily over 116 days, caused the death of a horse from jaagsiekte on Day 128 (Allerton Laboratory, Experiment 141, 27/1127). Though no South African experimental data could be traced on the toxicity of C. juncea, Steyn and Van der Walt53 and Vahrmeijer58 referred to it as an additional cause of jaagsiekte in horses58 and the condition has been induced experimentally with the plant abroad. Loss of wool has been reported in sheep after consuming large quantities of C. juncea53 (see The skin and adnexa). The toxic principle of both C. dura and C. globifera has been shown to be a pyrrolizidine alkaloid, dicrotaline (Figure 5).30

Figure 5 (a) Monocrotaline and (b) and dicrotaline

Figure 6 Fibrotic and emphysematous lung of a horse poisoned with Crotalaria juncea

Jaagsiekte was at first thought to be an infectious disease, mainly on account of the lung lesions and the fever. However, the fever that was noticed during the period the horses...

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