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This article was published in 1944
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INSTITUTE OF INSPECTORS OF STOCK OF N.S.W. YEAR BOOK.
Post-mortem appearances in some swine septicaemias
K. V. BYRNE, B.V.Sc., Inspector of Stock, Narrandera.
The following notes on the above subject are in the case of Anthrax, based on field experiences in the Central Rivertna, and in the other diseases on observations made whilst employed in the 1942-43 Swine Fever eradication campaign in the County of Cumberland. They are also a resume of a talk given on the subject during the 1944 Conference of Inspectors of Stock.
Anthrax. During nine years in the Central Riverina three outbreaks of Anthrax in pigs have been encountered; two of these, not in any way connected with one another, taking place in February 1944. The other, in June, 1940, occurred on a property which had no previous history of Anthrax, and in a locality where this disease had not been recorded for more than 20 years. The pigs were born and bred on the holding, and there had been no recent introductions. Deaths were taking place after about 48 hours sickness, some of the animals showing a submaxillary swelling. The general history was not one suggestive of the presence of an acutely infectious disease, the losses over several weeks amounting to four, and because of this, the season of the year (all previous losses in this district taking place in the summer), the absence of mortality in any other class of stock and the odds were against the disease being present. A post-mortem was conducted, therefore, on the one animal found dead on the day of the visit, this eventually turning out to be the last fatality. The throat swelling in this animal was only slight, and on incision was found to contain a small quantity of a clear oedematous fluid. The other changes noted were:—pharyngitis, marked congestion of stomach mucosa and injection of vessels of small intestine. No haemorrhages were seen at all. Smears from this pig were positive for Anthrax. These animals were grain fed and no possible source of infection was ever discovered. However, they had had free range, and as the mortality ceased without inoculation after they were confined to their sties, their access to the carcase of an animal dead of the disease is the obvious possibility.
Of the two outbreaks encountered this year the first took place in pigs being maintained at a slaughteryard, and fed on offal from the slaughterhouse. No progress was made in locating the source of infection here also, as there was no history of any sick animal passing through the yards, nor of any carcase being condemned by the local meat inspectors. These particular slaughteryards are attached to one of the few towns in this part of the State where the local civic body maintains qualified meat inspectors. This outbreak caused considerable excitement because of the fact that both the butcher and his slaughterman also developed Anthrax, apparently obtaining their infection not from the pigs, but from the same source as the latter. The butcher, who devoted most of his time to attending to his shop, assisted in the dressing of only one carcase just before he became infected, but Ascoli tests carried out on portions of the hide obtained from this animal gave negative results. Throat swellings were a prominent feature in this mortality, and some of the animals (according to the owner) took as long as four days to die from the time the swelling was first noted. Deaths ceased without inoculation. No post-mortem examinations were conducted.
Anthrax in Humans. A digression is made here to comment on this most important aspect of this disease.
Of the various forms of Anthrax in humans the cutaneous is the one most likely to be encountered in this country, pulmonary and gastro-intestinal infections, it is understood, being extremely rare. The typical cutaneous lesion is stated to be a purplish-black central area, usually raised, surrounded by a more or less complete ring of vesicles upon a background of inflamed skin. The writer has had the opportunity of examining the skin lesions of four persons suffering from Anthrax and all conformed to this general picture, although in each the ring of vesicles appeared as a continuous circle of greyish necrotic skin. However, it is to be remembered that medical text books state that variations are not uncommon, and that streptococcal infections may produce a picture very similar to the above. Diagnosis by macroscopic appearances alone, therefore, is not very reliable, and any person developing a skin lesion which might possibly be due to Anthrax would be well advised not to accept any opinion based on a naked eye inspection, but to secure an immediate microscopical examination of the material from it. The wisdom of this is made more clear by the recollection that the condition is something of a rarity, and one which would be seen by the majority of medical practitioners on infrequent occasions only. For the information of any reader who might find it expedient to carry out such an examination the following points are emphasised. The use of a capsular stain is not so imperative as in the case of a smear taken from a carcase, as the need for differentiation between B. anthracis and putrefactive bacilli does not exist, and the appearance of any organism morphologically similar to the former can be regarded as an almost certain indication of the presence of Anthrax. In addition, it must be kept in mind that the bacilli may not be numerous in material obtained from a human lesion, and that prolonged searching may be necessary to locate them in such cases. Treatment of all recent cases in the writer's locality has been confined, so far as is known, to the use of hyperimmune serum; and except in one instance, when the patient delayed too long in seeking medical attention, all recovered. (It is desired here to acknowledge the assistance of Dr. H. 0. Lethbridge, of Narrandera, who has had a wide experience with cutaneous Anthrax in humans, and to whom the writer is indebted for much of his own knowledge of the subject).
Gastro-Intestinal Anthrax in pigs. The third mortality referred to was of this nature. It occurred in Anthrax country, but in pigs which were not offal-fed and which had not had access to any area on which a carcase dead of the disease might have existed. Further, there was a complete absence of throat swellings. On these grounds it was considered safe to carry out post-mortem examinations, and two carcases were examined. The changes seen were:— Congested stomach mucosa, congestion of small intestine with some haemorrhagic areas, congestion and some ulceration of the mucous membrane of the caecum and colon, kidney petechiae, haemorrhagic mesenteric lymph glands, sub-epicardial petechiae, extensive sub-endocardial haemorrhages and splenic petechiae. In neither animal was the spleen enlarged, although there was some breaking down of the pulp in one case. Both pigs showed all the above changes, but in one the general severity of the haemorrtiagic picture was less than that usually seen in the other diseases referred to later in this article; whilst in the other it was somewhat greater. In the former case, for example, apart from the absence of obvious damage to the spleen pulp the haemorrhages in that organ, as well as in the kidneys and heart, were neither numerous nor extensive. The impression formed, therefore, from these two post-mortem examinations was that gastro-intestinal Anthrax was not to be distinguished with certainty on post-mortem appearances from other septicaemias in pigs. In this mortality it seemed certain that the pigs had obtained the infection by ingestion of spores from the ground, and not in the more usual manner with these animals by ingestion of bacilli from an Anthrax carcase. For this reason the case varied from the other two in history, symptoms (notably absence of throat swellings and greater rapidity of death), post-mortem appearances and in the fact that recourse had to be had to inoculation to terminate the losses.
Swine Fever. After the main burst of losses in the 1942-43 summer two further outbreaks occurred during 1943 at intervals of several months. The infections in these latter cases were obtained from the feeding of improperly sterilised garbage containing pig meats, and the main effort in the final stages of the eradication campaign was directed at endeavouring to induce pig keepers to carry out effective sterilisation. Apart from the to-be-expected cussedness of a minority, the effectiveness of this effort was jeopardised also by the fact that a number of piggeries had for sterilisation purposes a small horizontal type of steam boiler, which worked at a low pressure, and of which the efficiency in treating the large quantities of garbage with which it had to deal was very much suspect.
Of the actual outbreaks the last six were seen by the writer, and the following observations are based on approximately 30 post-mortem examinations of pigs which had died from, or had been killed in the last stages of acute Swine Fever. The changes seen in these examinations were:—Severe congestion of stomach mucosa, congestion of mucosa of small intestine (occasionally with numerous petechiated haemorrhages), splenic haemorrhages and infarcts, kidney haemorrhages (usually petechiated but in two cases ecchymotic), congestion and petechiatlon of mesenteric lymph glands, necrosis diptheresis and ulceration of the caecum and colon, pneumonia (usually lobar), lung haemorrhages, subepicardial and subendocardial haemorrhages. It is emphasised that not all these lesions were present in every pig; some animals showing only a few of them and then not in a very marked degree. The most constant abnormalities seen were the cardiac haemorrhages, usually consisting of numerous petechiae congregated in the vicinity of the coronary groove and extensive haemorrhages (subendocardial) in the ventricles, and kidney petechiae. Splenic infarcts were not seen in any septicaemia other than Swine Fever, but they were not present always in the latter. Large bowel lesions were very variable. Changes in the mesenteric lymph glands sometimes gave them a uniformly purplish red appearance. Severely congested stomach mucosa was not by itself of any significance, and was seen frequently in pigs dying of non-infectious conditions.
Acute Salmonellosis. From time to time losses from this cause were encountered, and because of the close similarity of lesions to those of Swine Fever, considerable suspense was occasioned whilst the final verdict of a transmission trial was awaited. Usually, however, the course of the mortality gave an answer before the trial; Swine Fever cases usually commencing with a slow death rate but going on to a high one, whilst Salmonellosis outbreaks usually were characterised by an initial high death rate for a few days with a rapid decline to a low one and final cessation. All the above post-mortem changes given for Swine Fever, with the exception of kidney infarcts were seen in acute Salmonellosis, and the greater one's experience with the two diseases the clearer became the realisation that it was inadvisable to be dogmatic in the matter of their differentiation by macroscopic appearances. An incident illustrating the force of this is cited. A post-mortem examination of a pig dying during a sudden and heavy mortality showed, in association with a collection of haemorrhages in most of the usual places, a large number of typical button ulcers in the caecum. Some textbooks call these "Swine Fever ulcers," and write in a vein suggesting that they are diagnostic. On showing these lesions to a veterinarian with a very considerable experience of Swine Fever he stated that he could not recollect ever having seen such ulcers before in any disease other than Swine Fever, and was inclined, therefore, to the opinion that the latter was the cause of this death. Fortunately for the eradication campaign (it was late in l943) his fears were unfounded, as it turned out to be acute Salmonellosis.
Acute Swine Erysipelas. Comments on this condition are included with diffidence as only one mortality was encountered. The losses were small, and opportunity was had to carry out post-mortem examinations on only two pigs. In these the changes seen were:—Some congestion of mucous membrane of stomach and small intestine, few and small kidney petechiae, numerous subepicardial petechiae, some subendocardial haemorrhages. There were no lung, spleen nor large intestine lesions. Neither pig showed the diamond skin marking, although each animal had a reddish purple discolouration along the ventral surface. However, somewhat similar appearances were seen not only in Swine Fever, but also in pigs dying from non-infectious conditions, and in this particular mortality such skin discolouration did not appear very helpful from a diagnostic standpoint. The haemorrhagic picture seen in these pigs was less severe on the average than those encountered in the other septicaemias, but this apparently has not been the case in other mortalities from this disease in New South Wales, where the reverse has been the rule. The difference is exemplified, particularly in the kidney haemorrhages, which in this case were few petechiated, but in others have been numerous and ecchymotic. However, as mentioned above ecchymoses were seen in Swine Fever kidneys also.
Conclusion, Gastro-intestinal Anthrax in pigs and the acute stages of Swine Fever, Swine Erysipelas and Swine Salmonellosis are not distinguishable with certainty from one another by post-mortem appearances.