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Paralysis. Dragging of the hind legs, difficulty in getting up off the ground, and great prostration, denote a severe form of the disease, which is soon likely to end fatally. Pallor of the visible mucous membranes and conjunctivæ is one of the characteristic symptoms. Sometimes, however, in addition to the pallor, petechiæ (dark red or purple spots varying in size from a pin's head to a pea) may be seen on the membranes. There may be a watery discharge from the eyes, and in very chronic cases the cornea (the front coat of the eye) becomes cloudy, and may even be ulcerated.
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Two of the cases I saw had aborted in the early stages of the disease, and to this the illness had been attributed by their owners, but a microscopic examination of the blood left no doubt as to the nature of the disease. One mare donkey, which had a chronic form of the disease, although repeatedly covered by the horse, failed to hold with foal.
Prognosis. When an animal the property of a native is sick, little or no attempt is made to keep it in the shade, and provide it with the delicacies sick animals require. It is turned out and left to its own resources, so that it is not surprising that such a large number die. If some attempt was made at nursing them, more recoveries would probably take place. An improvement in condition with increasing strength and brightness point to favourable progress; progressive emaciation, weakness, and loss of appetite are indicative of a fatal termination.
Symptoms in cattle.-The symptoms observed in cattle were emaciation, weak- ness, and a slight rise in temperature. In those giving milk there was a falling off in the quantity given. Cattle bred and reared near the river do not suffer so severely as those brought from non-infected districts. The percentage of recoveries is greater than in horses and donkeys.
Diagnosis. To make a positive diagnosis the parasite should either be seen in the blood when examined microscopically, or the disease should be produced in susceptible animals when suspected blood is inoculated into them. For practical purposes, however, a fairly accurate diagnosis can be made from the symptoms already described.
The discovery of the parasite is not always made at the first or second attempt, and it may easily be found one day and disappear the next, although the clinical symptoms have become more pronounced.
A drop of blood placed on a cover glass, and pressed face downwards on a slide, when placed under the microscope will show the parasite wriggling about like an eel among the red blood cells.
Staining. The materials ordinarily used in laboratories for staining these para- sites deteriorate very quickly in the tropics, where one's baggage is often unavoid- ably exposed to the sun. The best results are obtained by having monthly supplies of stains sent out from England. Wrights' and Giemha's stains were used for stain- ing the parasite, and gave excellent results.
Treatment. The treatment of tsetse fly disease is disappointing. There is no known drug which can be said to have a distinctly curative action on the disease, although arsenic was thought at one time to be a specific. Horses treated with arsenic have undoubtedly recovered, but many that have not been so treated have also recovered, so it is difficult to say how much the arsenic had to do with the recoveries. Various drugs are now being tried, but no satisfactory practical results have been published. The administration of atoxyl is reputed by Koch and others to have a curative action on human beings suffering from trypanosomiasis (sleeping sickness) but sufficient time has not elapsed to prove whether the effect will be permanent. It might be tried on horses in the Gambia where reliable observations could be made.
Prevention. The disease is transmitted to animals by the tsetse fly (Glossina palpalis), which is found from one end of Gambia to the other. The flies suck the' blood of animals that have trypanosomes in their blood, and then transfer their attentions to other animals. Recent observations point to the inoculation by the fly not being direct; the parasite probably remains one or two days in the fly's digestive canal before it is transmitted by a bite to other animals. Some animals appear to be naturally immune, whilst others acquire immunity by recovering from an attack of the disease, when they are known as "salted." It is not known to what extent wild animals suffer, but it is probable that many have the parasite in their blood, and are not the least affected by it. There was proof of this in the Transvaal,
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where tsetse fly disease used to be prevalent till rinderpest made its appearance, and destroyed nearly all the wild ruminants which kept up the parasites in their blood. Since then horses and cattle graze with perfect safety on belts of land which at one time were notoriously fatal. The fly is still there, but there are no animals with parasites in their blood to act as centres of infection. During the months of April, May, and June I never saw the tsetse fly once away from the river, even on cattle returning from the marshes to the villages, where they are tethered up for the night. Whether this is the case during and after the rains I could not ascertain. Every case of the disease I saw in horse, donkey, or ox had, during the previous three or four months, been to the river. It would appear from this that the fly prefers shade and an exposed stretch of water, a combination of which is rarely seen away from the river, or in the native villages.
From what has been said, it will be clear that the prevention of the disease is no easy matter. It is not practical either to attempt to destroy all centres of infection, or to do away with the mangrove and other shady trees along the banks of a river like the Gambia. All that can be done for the present is to advise natives to keep affected animals isolated, and a considerable distance away from the river. The cutting down of bushes and mangrove trees near places of business should be encouraged.
All attempts at protective inoculation up to the present have failed. Experi- ments are being made by scientists in various parts of the world. Some are very hopeful of success, but there is nothing yet known which can be safely recommended.
SHEEP DISEASES.
In Sandu and Baddibu a disease of sheep was described by natives which has a strong resemblance to parasitic gastritis. I saw no sick sheep during my visit; this was because the disease is only prevalent in August and September, when the rains are well established.
In examining the stomachs and intestines of a sheep in Sandu which had been killed for food, I found parasitic nodular disease of the intestines, and large numbers of worms (Strongylus contortus) in the fourth stomach. It was an old sheep, and the parasites had had no appreciable effect on its condition, nor on the quality of the flesh. As it is more than likely that it is one of these diseases which is responsible for the sickness referred to, I propose giving a short description of both in the hope that it will lead to its recognition, and so reduce the numbers of outbreaks and deaths. I have not forwarded the parasite which causes the nodular disease, as it is very small, and hardly visible when preserved in spirit, but the disease will easily be recognised from its description and the worm more easily seen when fresh nodules are incised. Specimens of the Strongylus contortus are sent which will help the Commissioners to describe the disease to natives where it is prevalent.
Parasitic gastritis of sheep is caused by the presence of worms in the fourth stomach. They belong to the genus Strongylus, and there are three varieties. The one found in the Gambia is the Strongylus contortus. It is a small, thin, round worm, from 1 to 11 inches in length, with a peculiar twisted appearance, like a piece of worsted made with two strands, one white and the other dark red or brown. The latter is the body of the worm, and the former represents the oviducts which wind round inside the body. The worm lives by sucking blood from the wall of the stomach, to which the brown colour is due. They live out of the body in an immature state in foul stagnant water, and in damp wet soils; they reach maturity in the stomach of the sheep. The disease is seen in animals of all ages, but it is most severe in lambs and young sheep.
Symptoms.-There is nothing very characteristic about the symptoms: dulness, loss of appetite, thirst, emaciation, and a dirty foul diarrhoea. When such symptoms appear the disease usually ends in death.
Post-mortem examination reveals hundreds, or even thousands, of worms fastened on to the lining membrane of the fourth stomach, which is paler than normal, and may be ulcerated.
Treatment-Move the animals to higher and drier land, and give them extra food, a little koos, and some ground-nut hay.
Dose them daily with one teaspoonful of turpentine and half a teaspoonful of salt in a wineglassful of milk.
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