De Kock and Quinlan published the results of their first series of experiments on splenectomised horses, cattle, sheep, and goats in 1926. Since then observations have been continued and extended to other species of domesticated animals as well as to wild antelopes. The results of the later splenectomies have been published mostly as isolated papers in various subsequent Reports of the Director of Veterinary Services. (De Kock and Quinlan, 1927; de Kock, 1929; du Toit, 1931; Neitz and du Toit, 1932.)
HORSES. Of the four horses splenectomised three were immune ''carriers'' of Nuttallia equi and all three showed fatal relapses of Nuttalliosis in from 3 to 8 days after the operation. The fourth animal was a young foal, not a carrier of Nuttalliosis. It was kept under tick-free conditions for four months following the operation when it was killed by injections of haemolytic serum.
CATTLE. Five animals were observed by de Kock and Quinlan (1926 report) and their findings may be summarised briefly as follows: (1) Relapses of Theileriosis (Theileria mutans), anaplasmosis, and piroplasmosis (P. bigeminum) occurred in immune "carriers" of these parasites. Piroplasmosis relapses were in these cases particularly severe.
(2) These diseases in splenectomised animals assumed a chronic course particularly with regard to the blood changes. A total of 23 bovines were splenectomised of which 20 recovered from the operation. One animal died three days afterwards, and on post mortem no apparent cause of death could be established; one died as a result of haemorrhage and one from surgical shock.
Some of the animals were used in East Coast fever transmission experiments and two animals which had recovered from East Coast fever were splenectomised in order to try and break down their immunity (du Toit, 1931). Removal of the spleen was found to have no effect on the course of this disease or on the immunity. Two bovines were splenectomised for further study of the blood changes in anaplasmosis. One animal, No. 4627, infected with the mild A. centrale strain, reacted so severely after splenectomy that it died as the result of the extensive blood changes.
Two calves, Nos. 4658 and 4676, susceptible to anaplasmosis and piroplasmosis, were injected with blood from sheep showing Anaplasma ovis and then splenectomised to see whether the Anaplasma ovis would appear in the calves' blood, or whether the calves could become "carriers" of the disease. After the operation, however, both animals became accidentally infected with bovine piroplasmosis and anaplasmosis and sheep sub-inoculated from them showed no reaction.
SHEEP. Fifty-four sheep have been splenectomised of which seven died as the direct result of the operation. In one of the latter, namely No. 8462, the attachments of the spleen were loosened and the splenic vessels ligated, but the organ itself left in situ. The most striking result of de Rock and Quinlan's observations on sheep was the discovery of the hitherto unsuspected presence of an anaplasma, A. ovis, and a Theileria, T. recondita (called Gonderia ovis by them) present in the blood of some South African sheep.
Anaplasmosis of Sheep. The result of their observations can be briefly summarised as follows:
(1) Non-splenectomised susceptible sheep can be infected by means of blood inoculation. The disease then runs a mild course with distinct anaemic changes and the appearance of parasites in the blood in large numbers, but no mortality.
(2) In splenectomised "carriers" and splenectomised susceptible sheep the course is much more severe and protracted and there is a fairly high mortality.
(3) The disease could not be transmitted to splenectomised or non-splenectomised bovines nor did these animals become carriers of the parasites.
(4) Non-splenectomised goats could not be infected but in splenectomised goats parasites appeared in the blood with very slight anaemic changes, and such animals became carriers of the disease.
Sheep, splenectomised and non-splenectomised, did not react to bovine anaplasmosis nor did they become carriers of the parasites.
Theileriosis of Sheep. De Rock and Quinlan (1927) reported on the occurrence of Theileria (T. recondita, Gonderia ovis) in the blood of some splenectomised sheep. Transmission to non-splenectomised sheep and to bovines failed. The parasites did not produce any symptoms and appeared to be quite harmless.
Histological Changes. De Rock (1929) reported on the appearance of haemo-lymphoid-like nodules in the liver of sheep, bovines and a goat killed three years after splenectomy. The nodules varied in size from ¼ in. to 1½ in. in diameter, were dark red in colour, and circumscribed. In some instances a distinct capsule could be recognised, and in others there was no demarcation between this foreign tissue and the liver substance. Lymphoid nodules could be recognised in some of these structures. The haemo-lymphoid-like nodules were not seen in the animals which died or were killed within the first two years following splenectomy. The first indications being found in a sheep which died 33 months after the spleen was removed. From the microscopic appearances de Kock concludes that this newly formed tissue resembles most closely that of haemolymph glands.
Before splenectomy the two animals were injected with blood from sheep showing anaplasma but no reaction followed nor could anaplasma be demonstrated. Splenectomy failed to produce a relapse as in the case of immune carriers. Subsequent to the operation, however, when reinjected the blood showed the presence of anaplasma with practically no anaemic changes.
The histological changes which were found at autopsy on the one goat which died 8½ years later have been mentioned above.
Seven dogs were successfully splenectomised. One animal showed the presence of microfilaria in the blood three days later and continued to show these parasites until it died from other causes. In no case did piroplasma appear in the blood as the result of removal of the spleen. However, it was only assumed that the animals were carriers of Piroplasma canis as they had been exposed to tick infestation, but there can be no certainty with regard to this. Subsequently three of these dogs were injected with blood from a known carrier of the disease. One of them died from piroplasmosis and two recovered after treatment, but continued to show parasites for several weeks afterwards.
Owing to the uncertainty with regard to the previous immunity it is not possible to draw definite conclusions on the effect of the removal of the spleen on canine piroplasmosis. The disease, however, appeared to affect the splenectomised dogs more severely than is experienced in clinical cases of the disease in normal dogs. One of the animals showed a severe haemoglobinuria. Miessner (1931) reports on a few cases of relapses of piroplasmosis following splenectomy in dogs. The experiment will be repeated with known carriers of Piroplasma canis.
Four dogs were injected with the virus of African horsesickness after splenectomy but did not show any reaction to the disease.
Four pigs were splenectomised and all made uneventful recoveries.
No parasites appeared in the blood following the operation. Attempts were made to infect the splenectomised pigs with African horsesickness (two cases) and with ovine blue tongue (two cases) without success.
Neitz and du Toit (1932) reported on a method of obtaining pure strains of Anaplasma marginale and centrale by transmission through antelopes. The antelopes were injected with blood from bovine carriers of Piroplasma bigeminum, Theileria mutans, and either Anaplasma marginale or A. centrale. In each case only the anaplasma appeared in the blood. These antelopes were then splenectomised in order to exclude the possibility of the other parasites from the donor's blood being present in a latent form. In the cases of the two that survived the operation only the anaplasma reappeared in the blood after splenectomy. Three blesbuck (Damaliscus albifrons) and one grey duiker (Sylvicapra grimmi grimmi L.) were operated on.
One blesbuck died soon after the operation and the other two recovered. The duiker seemed to recover completely but interfered with the wound on the eighth day and died as a result. One of the blesbuck, No. 33606, was later injected with the virus of ovine blue tongue and although it showed no reaction it was found to be a carrier on subinoculation of susceptible sheep.
Spirochaeta theileri could also be transmitted to the blesbuck.
Heartwater. Finally the animal was injected with heartwater from a sheep and died 23 days later of this disease. Rickettsia could be demonstrated and susceptible sheep were infected from it.
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