Equine Piroplasmosis |
Babesiosis is an acute or chronic disease transmitted by a tick and it is produced by the parasitizing of the tick's erythrocyte. It is characterized by temperature, hemolytic anaemia and icterus. This disease usually occurs in tropical and subtropical areas, such as: our province of Salta which is located in this kind of climate, the Mesopotamian region, Chaco and Formosa. All the cases of animals testing positive in our region were tested by serology without symptomatology. It also occurs in warm and cold areas if there are adequate conditions (plains with shrubs and trees, boggy areas),i.e. when the transmitting ticks find an environment that lets them survive. Particularly, I attended a patient with acute symptomatology in the Cavalry School (Province of Buenos Aires). |
In Western Europe babesiosis is not very important; however, some regions as France and Italy seem to be significantly affected. This disease was well-known when the U.S.A only allowed into the country those horses which were serologically negative to babesiosis. In that country the disease is not widely spread so its importance is not significant. It is only significant in Florida and Texas where some cases have been registered. There are two different babesias that affect the horse: Babesia equi and Babesia caballi. There are simultaneous mixed infestations. Babesia equi reaches a size of 1,5 4 m. This organism is round, ovoid and has a pear-like shape. It is usually found only one babesia every one erythrocyte. Some other times four of these organisms are found in a Malta cross-like shape. The parasitemia is usually intense. 80% of the erythrocytes can be affected. The length of the parasites is generally smaller than the radius of the erythrocyte. They are checked by means of a 40 or 100x magnifying glass optic microscope and coloring must be done with Giemsa. Babesia caballi is up to 6 m long so it is bigger than the radius of the erythrocytes. A parasitemia of 4-5% of the erythrocytes can be considered intense. Babesiosis is only transmitted by ticks and Dermatocentor nitens is the most important. The cycle in the tick has not been completely investigated yet. Horses seem to be more sensitive than donkeys. From the clinic point of view, the immunological condition of the equine population is important. In those regions where the babesia appears enzootically, the only horses that get acutely ill are the ones which have been recently introduced. Horses and wild solipedes acquire a good resistance in endemic areas where re-infestations seem necessary. Immunity is only kept if the presence of the antigen stimulates the humoral and cellular reaction. The invasion of erythrocytes and the multiplying of parasites produces a massive destruction of the red blood cells. The hematocrit may fall to 5 vol% and the number of erythrocytes may be lower than 2 x106 l. Consequently there is hemiglobinemia and icterus but this is worse if there is hemoglobinuria B. Equi. The blood count usually shows a characteristic monositosis. Symptomatology varies slightly according to the agent involved. Generally, the disease appears after a 6 to 21-day incubation period with a high temperature of up to 41.5°C. At the beginning most of the patients show good appetite conditions and in spite of the temperature they look lively, but after some days of having temperature they feel weak and wander unsteadily. It seems that when there is B. caballi a continuous temperature is observed; whereas, a remitting fever is observed when there is B. equi. Icterus is always noticeable and to some extent, it shows petechias in the visible mucous membranes. Horses develop edemas in the body and limbs and most of the times there is cardiac insufficiency and in some cases there are cutaneous symptoms (urticaria). Animals can suffer from polyuria (in severe cases from anuria) combined with hemoglobinuria and hematuria but it is worse in those cases of parasitosis with B. Equi. Íf the animal survives to the initial acute disease, the disease becomes chronic most of the times and it is worse with B. equi in a carrier state. Sometimes the horses affected in a latent way lose weight progressively. They are always a little anemic and have a slight temperature; these symptoms are stronger after work. Evidently the infestation with B.caballi shows a better tendency to cure spontaneously. There are also some hyperacute forms and animals die within 2-3 days. Central nervous disorders are observed more frequently in the affection with B. equi. Clinically, it is difficult to diagnose in the first stages of the disease. It is very important to test the agent in the erythrocytes. It is easier to test it between the 2nd and 7th day of the disease. In B. equi the test is easier than in B.caballi , i.e although it is not observed in a blood extended test it could be piroplasmosis. The serologic tests (Complement Fixation agar-gel immunodifussion test) indicate the diagnosis although direct checking of babiesa were not possible. The following differential diagnoses must be reminded: Equine Infectious Anemia, Leptospirosis, Hemorrhagic Purpura, equine viral Arteritis (it is exotic in our country), equine granulolitic Ehrlichiosis, and other diseases that produce vasculitis and hemolysis. In case a mare is pregnant, the disease is not transmitted to the foal and the foal acquires immunity through the colostrum. For this reason, the tests carried out on foals of positive mares will also be positive although there are no factors indicating so and they are in an area free of ticks. Then, they will become negative after 4-5 months of being weaned. This fact must be considered so as not to make mistakes when interpreting the results of the tests. The other possible ways of contagium are all the insects (mosquitoes, horseflies, etc) and the use of non-sterile syringes. The indicated treatment for this disease is intramuscular, iminocarbamida, Dipropionate (2,2 mg/Kg. If it is B. caballi one dose is enough, but if it is B. equi the treatment must be carried out for two days. Sometimes a four-dose treatment will be necessary to cure it. This drug may cause in horse: excessive salivation, colics and gastric and intestinal hypermotility. This drug is contraindicated for donkeys because it produces anaphylatic shocks that lead them to death. Once the babesias are eliminated from the body the seropositive titles can be present for more than 8 (eight) months. Stress, long trips, diseases may often help the appearing of positive titles again. (Case: it happened with some Polo horses which were exported from Buenos Aires to Miami. All of them were serologically negative in Argentina) Concluding, I would say that this disease is not usually taken into account by veterinarians because most of the cases observed are asymptomatic with positive results from the laboratory. An annual test should be done to those horses that have the opportunity to travel abroad, especially, to the U.S.A because to get into that country horses must be serologically negative. As a comment, in the Atlanta Olympic Games several horses from Argentina, France and Germany could not participate because they were asymptomatically positive to the disease. In Europe animals which are positive can be exported. Owners and horse keepers must be warned about this disease and it must be motivated the use of discardable syringes and needles, good horse hygiene, the use of disinfectant in the brakes, fumigation during summer time to lower the number of mosquitoes and horseflies, improve the drainage of the stables or pasture ground to avoid hematophagous insect spread. |
By Fernando Ribotta (Salta, Argentina) |
