Laveran has sought in vain for his plasmodium in the blood of the affected horses, while Pierre found in the blood globules of the Soudan victims refrangent, crescent shaped bodies, thickened and staining deeply in the centre, which in his opinion represented the growing hæmatozoa of Laveran. Gelston found the rounded and crescent shaped forms abundant in the red globules. The disease in the horse is said to be conveyed by direct contact, which would again distinguish it from intermittent fever of man. If the protozoön is the cause, and not a mere sequel or attendant on the disease of the horse, the indications are that it is peculiar to the equine race and distinct from the germ of human malaria.
Causes. Like malarial diseases in man, it is confined to low, damp, undrained or inundated localities, and shows in the hot seasons when the surface dries out. The elevated plains and tablelands which are habitually dry or well drained are exempt. Cadeac alleges that infection is usually inhaled in the floating dust. The mortality of Algerian horses taken to the Soudan is 90 per cent., while but 25 to 35 per cent. of the native horses in the Soudan or in Senegal suffer. This difference is manifestly the result of the survival of a comparatively immune strain of blood, or of immunity resulting from a previous invasion. Subcutaneous inoculation on a soliped failed, while transfusion of blood from the affected horse to a sound mule produced the disease. It is also claimed that it is transmitted from the affected mare to the fœtus in utero, which showed characteristic visceral lesions after birth.
Symptoms. Premonitory symptoms of restlessness, drowsiness, or stiffness, are followed by violent shivering, elevation of temperature (104° or 106° F.), muscular tremors, rapid breathing, hacking cough with expectoration of frothy mucus, tumultuous heart beats, and small irritable pulse. There is complete anorexia, an opaque, infiltrated, petechiated, mahogany colored, conjunctiva, epiphora, and sometimes blood extravasations into the vitreous. The lungs may become intensely congested, with rapid, panting breathing, dyspnœa, a frothy, rusty expectoration, and extended head and limbs. This may prove fatal in a few hours. Otherwise there may be remissions of the fever and dyspnœa at somewhat irregular intervals. Sooner or later are observed urinary changes, the liquid becomes albuminous, yellow, or red, or it shows distinct casts. These indicate the destruction of the red globules and the escape of hæmoglobin. In other cases there are slight colics and constipation alternating with a greenish yellow fœtid diarrhœa. The early nervous prostration and drowsiness may merge into vertigo, or paralysis. Vertigo is a very prominent feature in the Philippine cases (Gelston). The skin which, at first, may often be pricked without response, sometimes becomes tender, itchy and congested, with erection of the hairs and the formation of pustules, or small abscesses like hazelnuts.
Course. Duration. In very acute cases death may take place in a few hours. More commonly illness lasts from three to six days. In certain instances it becomes chronic and may last two or even three months, the early congestion of the mucosæ giving place to pallor and anæmia with advancing emaciation, dropsies and finally marasmus and death.
Lesions. These are mainly in the blood, red globules being distorted, crenated, massed in clusters and greatly diminished in numbers so that the liquid appears thin and watery. The mucosæ, internal organs and serosæ are petechiated and the serous cavities contain a yellowish serum. A yellowish tint pervades the white tissues generally. The liver is congested, virtually gorged with blood, enlarged and yellow or yellowish brown. The spleen is greatly enlarged, blood gorged, and shows irregular, rounded swellings indicating the seats of extravasation of blood. In some instances rupture has taken place. The kidneys are congested, enlarged, softened and of a brownish red or black color, with circumscribed extravasations especially in the cortical area. The lungs are violently congested, with many areas of blood extravasation, and they do not collapse when the chest is opened. The heart is petechiated, with a parboiled aspect and shows areas of commencing necrosis or fatty degeneration.
In the chronic form the watery condition of the blood is remarkable, the serous cavities (peritoneum, pleuræ, pericardium, arachnoid) contain considerable effusion, dropsical conditions of the limbs and dependent parts of the body are common, the lungs show hepatization and minute centres of suppuration, and other viscera may show fibroid degeneration.
Prevention. It is advisable to keep susceptible horses from the low marshy infected lands from June to November and to avoid especially water that is drawn from such lands. It is not needful to take the stock to any very marked elevation provided the land is dry and free from wet or swampy areas. The native horses or those that have been long in the marshy district and have thus secured a partial immunity may profitably replace the more recently imported and susceptible horses during the dangerous summer months.
The habit of the paludal protozoa of securing their transfer from one of the higher animals to another through the intermediation of insects in which they undergo developmental changes essential to their survival, would further suggest the adoption of especial precautions against such invertebrate enemies in the affected district.
Treatment. Pierre employed quinia sulphate or bromide 45 grs. in distilled water 1 oz., intravenously, Gelston, creolin, subcutem. Hot baths, 95° to 100° F. are claimed to lower the temperature and contribute to the arrest of an attack. Other complications are treated according to indications.