380 MAL DE CADERAS 
Geographical distribution. Mal de caderas is a disease of tropical 
South America. 
Etiology. Elmassian differentiated the trypanosoma of this affec- 
tion in 1901. Voges pointed out its pathogenic action and named it 
Tr. equinum. In length it is 3 or 4 times the diameter of the red blood 
corpuscles. Its width is one-third to one-half the diameter of a red 
blood cell. Its free flagellum is about 5y, in length. 
Its motion resembles that of an eel, but its actual motility is not 
great, the whole body taking part in an excessively active wriggling 
motion with the flagellum and beak ends moving in opposite direc- 
tions. The nucleus is toward the anterior end, a very small centro- 
some near the posterior end, and there is a granular protoplasm. 
It is found in the blood of horses, mules, asses, hogs and water hogs 
suffering from mal de caderas. It is transmissible to white and gray 
rats and mice, rabbits, dogs, goats, sheep, and certain monkeys found 
in South America. Cattle are said to be more immune. They 
acquire infections but do not suffer from the disease. 
The parasites are most numerous in the circulating blood during 
the rise of temperature. Upon its reaching 40-41° C. they gradually 
disappear, but reappear with the next rise of temperature. 
Mode of infection. Unlike dourine, the virus of mal de caderas is 
not transmitted by copulation. It has been proven that animals are 
infected with it by means of certain insects. Stomozys calcitrans, 
Tabanidae and several other insects are under suspicion. It is also 
stated that acommon rodent of Paraguary (Hydrocherus Capybara) 
suffers naturally from this disease and that when it dies with it in 
pastures the horses are attacked. 
Symptoms. The first symptom is an elevation of temperature 
which rises irregularly but suddenly falls to normal. Emaciation is 
rapid. The urine is dark colored and usually contains albumin, and 
perhaps blood. The blood changes so that it gives the picture, on 
microscopic examination, of pernicious anemia. There is an increase 
in the lymphocytes and in the eosinophiles. The most obvious symp- 
tom is said to be a symmetrical or asymmetrical paresis of the hind 
legs. Defecation and urination are difficult (coinciding with paralysis 
of the sphincters). The paralysis gradually extends to other parts 
of the body. Edema is often present. The appetite remains good 
until near the end when there is extreme thirst. 
