Further investigations into anaplasmosis of South African cattle

Abstract

(1) The transmission of Anaplasma marginale is only possible with blood containing red corpuscles. Filtrated blood failed to produce the disease when inoculated, the injected animals not showing any lesions at all and proving susceptible to subsequent blood inoculation (heifer 1211).

(2) The incubation period after the injection of blood containing anaplasms varies in length and depends on the quantity of blood injected, being shorter after an injection of a large quantity of blood and after the anaplasms have passed through a number of animals.

(3) Distinction has to be made between varieties of anaplasms. In this article one variety has been distinguished as Anaplasma marginale and the other as Anaplasma marginale (variety centrale ).

(4) The distinction is based (1) on the different position the two parasites take up within the red corpuscle; (2) on the difference in size, there being slightly smaller individuals in the centrale variety; (3) on the different virulency, the centrale variety having caused neither death nor any serious lesions; (4) on the fact that a recovery from an infection from Anaplasma centrale does not cause complete immunity.

(5) Anaplasmosis was transmitted in four instances by means of Boophilus decoloratus larvae, and once by Rhipicephalus simus larvae, the mothers of which ticks were collected off immune animals.

(6) The incubation times after tick infection varied from between a few days under two months to a few days over three months.

(7) It has been noticed in one case (heifer 935) that when a very heavy infestation of ticks is made, an animal may die as a result of loss of blood due to the repletion of the engorged females.

(8) The Anaplasma centrale infection transmitted either by ticks or by inoculation, in no instance caused the death of any of the thirty-nine English heifers. Accordingly an inoculation with Anaplasma marginale (variety centrale ) can be made use of as a practical method of inoculation against anaplasmosis.

(9) Recovery from Anaplasma centrale infection gives so much protection that a subsequent inoculation of Anaplasma marginale no longer causes death or any serious lesions.

(10) Animals which were immune to Babesia bigemina could easily be infected with anaplasmosis, either by means of ticks or by injection of blood.

(11) Animals which were immune to the anaplasma infection could easily be infected with Babesia bigemina , either by means of ticks or by blood inoculation.

(12) Injected animals can be exposed to natural infection before the Anaplasma centrale reaction has run its course. The anaplasmosis infection due to ticks having a long incubation time (55 to 100 days) will not develop severely in the inoculated animal, in which the disease runs with a shorter incubation time (16 to 40 days).

(13) All animals which have passed through an attack of anaplasmosis and redwater conveyed by inoculation and exposed to natural infection for over a year are still alive.

(14) The anaplasmosis transmitted by ticks was that of the type centrale and marginale .

(15) To judge by the blood smears obtained from the cattle exposed in the veld, a double infection is frequently met with.

(16) Animals immune to Anaplasma and Babesia bigemina infections could easily be infected with Babesia mutans .

(17) As an accidental occurrence in some instances the larval ticks of Boophilus , collected off immune cattle, transmitted an infection of Spirochaeta theileri in typical time. In one instance the inoculation with blood of a horse in which the spirochaetes were noted, the pure infection was transmitted to a susceptible animal.

(18) For the requirements of the conditions of South Africa, it is necessary to combine the immunization against anaplasmosis with an inoculation against redwater.

(19) The redwater inoculation can be done before or after the anaplasmosis inoculation, but it is practical to do both at the same time.

(20) The redwater, having a shorter incubation time, will develop first, and a recovery will usually be effected before the anaplasmosis reaction sets in.

(21) In applying this method to the practice, it is necessary to keep the animal during the redwater reaction (about fifteen days) under close observation and to check any unusual reaction by means of a trypan blue injection, and whilst the animal is undergoing the anaplasmosis reaction it will have to be well fed.