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This article was published in 1979
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Anthrax - Pathological Fact and Fiction
J.V. Evers, B.V.Sc., Veterinary Inspector, Narrandera
After five years' experience in a District where Anthrax is endemic I have in my own mind a firm concept of the disease and its various manifestations. One thing that has not been modified by this experience is the way in which my observations in the field are constantly at variance with the post-mortem findings described in the literature.
The diagnostic problems associated with Anthrax outbreaks are well known to most of us. A set procedure is clearly outlined for the taking of peripheral blood smears and the subsequent staining and identification of Anthrax bacilli.
So when our naive young V.I. sends in six feet of bowel and several pounds of miscellaneous tissue we all sagely shake our heads when the obvious diagnosis of Anthrax is made. V.R.O.'s chew Ampicillin capsules and the instigator of it all has criticism thrown at him from a great height.
Fortunately, I have not been put in such a position. It is the intention of this talk to give a clearer picture of the diagnostic approach to Anthrax - in particular the post-mortem findings - in the hope that it might help someone recognise an Anthrax cadaver when he is happily diagnosing something else.
1. THE ACCEPTED DIAGNOSTIC APPROACH
All authorities discourage the autopsy of animals suspected of having succumbed to Anthrax. Peripheral blood smears are taken, stained with Polychrome Methylene Blue and examined by microscope. Morphology is characteristic and diagnostic.
This approach has several deficiencies in practice. These are basically:
a. the septicaemic form does not occur in all species - e.g. pig, horse.
b. identification of the organism can occasionally pose problems. e.g. Non-encapsulated forms have been recorded.
c. It is not a good idea to shake your microscope to pieces on the off-chance of confirming an Anthrax outbreak. Additionally the final word rests with the R.V.L. and this only means a delay of a further 24 hours in my district.
d. Anthrax məy be overlooked as the possible cause of mortalities. This is particularly likely in areas where the disease has not been previously reported or inactive for a prolonged period and the losses are not dramatic at the time of investigation.
e. A negative smear is of no value to you or the owner in determining how to prevent further losses. This means a second trip to perform a full post-mortem examination.
2. NON-TECHNICAL AIDS TO THE DIAGNOSIS OF ANTHRAX
On many properties the diagnosis is all but made on the history of the outbreak and sampling is only used to confirm your observations.
On a lesser number of properties you may be faced with a sporadic light mortality which appears to be of little consequence. It is my impression that many Anthrax outbreaks are not reported or investigated for this very reason. The popular concept of the disease is certainly one of a paddock strewn with carcasses, hideously bloated and decomposing, with four sets of digits pointing to the heavens.
The following ante-mortem signs in the various species have been observed* :—
1. Pigs - submandibular swellings and dyspnoea.
2. Horses - submandibular swellings and petechiation of visible mucous membranes.
3. Sheep and Cattle - sudden staggering and collapse with severe dyspnoea and death within about 20 minutes.
*these observations are my collective assessment of impressions gathered by myself, other Veterinarians, and reliable stock-owners.
Pyrexia and respiratory distress appear to be the two main factors contributing to death of the animal.
Appearance of the carcase is not particularly suggestive in my experience. Blood-stained discharges have only rarely been observed and were certainly not copious enough to attract special attention.
Rate of post-mortem decomposition is not nearly as accelerated as most authorities claim. In fact it is quite moderate in comparison to that seen in Clostridial toxaemia/septicaemia. In sheep, the wool does pull out very easily within 24 hours of death in warm conditions.
Blood will continue to ooze from sites of predation by crows, etc.,e.g. eyes, anus.
I cannot detect any characteristic odour as described by some.
3. POST-MORTEM OF THE ANTHRAX CARCASS
There are two basic objections given to this course of action:
a. danger to the operator
b. Stimulation of aerobic spore formation.
To my mind the dangers to the operator are quite exaggerated. Risk of percutaneous infection can be readily minimised and the vegetative form is not so likely to induce pulmonary anthrax. Further reassurance can be obtained by taking a prophylactic course of antibiotics.
Nevertheless, you do exercise far greater care than is normal for the procedure.
There is no doubt that opening up the carcass does generate considerable spore formation. No more in my opinion than the evisceration practised by various predators. However, this problem can be offset by:—
1. a modified post-mortem technique with minimal exposure.
2. immediate burning of the carcass after autopsy.
I generally adopt the following approach:—
a. Animal positioned with left side uppermost.
b. Submandibular nodes collected in pigs; peripheral smears from limb extremities taken in sheep and cattle.
c. Incise along costal arch to expose abdominal contents. These are left in situ and the spleen examined and sampled. A cursory examination is also made of the S.I. for any evidence of regional haemorrhagic enteritis - particularly in bovines.
d. The diaphragm is incised and the lungs inspected.
I might add that you stand well back when opening the abdominal and thoracic cavities for visual inspection.
4. POST-MORTEM FINDINGS
I feel many of the findings at post-mortem can be better appreciated by recognising Anthrax for what it is - a toxaemia. It is this preoccupation with the terminal septicaemia which gives rise to so many misconceptions about the anticipated post-mortem findings.
To quote:—
'B. anthracis produces a lethal toxin which causes oedema and tissue damage, death resulting from shock and acute renal failure, and terminal anoxia mediated by the C.N.S.'
(Blood and Henderson, 4th edition, P.318)
Many authors on the subject still seem confused in their own minds:—
'Anthrax has always been regarded as dependent on invasiveness rather than toxigenicity....
Immunity to Anthrax appears to depend on the neutralisation of this toxin. Antibodies against the bacterial cells and capsules are useless.'
(Jubb and Kennedy, 2nd edition, P.376)
1. Pigs. Decomposition is rapid and in fact a 'true' picture of septicaemia may be seen.
Submandibular nodes may vary from being haemorrhagic and enlarged, haemorrhagic with extensive serosanguinous involvement of adjacent tissue [with] a large necrotic cavity with a characteristic grey lining.
Pulmonary involvement is not uncommon, being a sero-fibrinous pleuropneumonia with extensive effusion. At times I feel that has occurred by ventral dissemination from the submandibular nodes, at other times it appears to be the primary site of infection. i.e. inhaled spores.
The intestinal form can be rapidly fulminating where a pig consumes large quantities of an infected carcass - but I have not autopsied such a case.
2. Sheep. Decomposition is not particularly rapid. The musculature has a greyish pallor similar to that seen in Entero-toxaemia, but the organs are in reasonable condition for autopsy examination. Congestion of mucosa and subcutaneous tissue is not pronounced - but occasional serosanguinous effusions may be observed. Blood continues to ooze from cut vessels.
The spleen is generally large and juicy (not gas-filled and collapsible as with Clostridial toxaemia/septicaemia). However, many observe that this is highly variable.
There is generalised congestion of viscera, particularly the kidneys and small intestine.
The lungs are well-inflated (as opposed to Enterotoxaemic congestion) and show scattered ecchymoses on the diaphragmatic lobes. The myocardium is grey and flaccid.
3). Cattle. Decomposition is once again not strikingly advanced. Musculature has a greying pallor, there is moderate congestion of subcutaneous tissues, occasional effusions and blood clots poorly.
Great variation seems to occur in the range of lesions observed. The most constant finding is an enlarged and juicy spleen.
There may be moderate congestion of most organs or at times haemorrhages may be observed in liver, kidney, heart, etc. More often there is not a lot to see but a regional intense haemorrhagic enteritis of the S.I. (duodenum, jejunum) - sometimes only 12" or so in extent, should be regarded with extreme suspicion.
Pulmonary changes are not obvious (as in sheep) and there is a mild congestion.
5. CONFIRMATION OF ANTHRAX
Several sets of peripheral blood smears should be submitted from sheep and cattle. Material for culture - e.g. heart blood, spleen, lymph nodes, haemorrhagic bowel contents, should be collected in small quantities and securely sealed. It is suggested that culture of all negative smear cases should be attempted. Vacutainers seem ideal for collecting small quantities of any liquid/semi-liquid material providing the stoppers are taped down to prevent ejection.
In pigs, submandibular nodes should always be submitted. A vacutainer of intestinal contents may also be of use. Splenic tissue is not likely to be rewarding but lung tissue and pleural effusions most certainly are.
6. CONCLUSIONS
It is hoped that this brief outline might resolve some diagnostic problems for a colleague in doubt. I have been fortunate in my experience with Anthrax to date and hope never to misdiagnose the condition.
Those who ridicule the field Veterinarian for doing so should have a go first. This disease is often manifest in a form quite unlike those so vividly described in the texts.
ACKNOWLEDGEMENT
I wish to a knowledge the informative discussions I have had with other Veterinarians in my area on this topic - Particularly Ian Master, B.V.Sc., Veterinary Officer, Narrandera, and David Harding, B.V.Sc., Private Practitioner, Griffith.