Synonym: South African gall sickness
It is an important rickettsial infectious disease of ruminants characterized by variable degree of pyrexia, progressive anaemia and emaciation.
Distribution
It is widely distributed in tropical and sub-tropical countries. Seroprevalence of the disease has been reported from various states of India by different workers.
Aetiology
The disease is caused by Anaplasma marginale. The Anaplasma are intra-erythrocytic bodies. They remain as inclusion bodies. They lack cytoplasm. The word marginale is attached due to their peripheral location inside the RBC. They multiply by binary fission and form 4-8 inclusion bodies. They can be destroyed by heating at 60° C for 60 minutes.
Susceptible Hosts
Exotic and crossbred cattle are highly susceptible. Subclinical infection is a feature in indigenous cattle. Buffalo and sheep are also affected. The infection has also been recorded in deer, camel, goat and bison. It has been recorded in 15 day old jersey calf.
Mode of Transmission
The infection spreads through ticks. Besides tick, Tabanas spp., Stomoxys spp., and mosquitoes have been found to transmit the disease. Carrier animals like cattle and other wild ruminants play vital roles in the transmission of the disease.
Mechanical transmission through dehorning, castration, vaccination, ear marking has been suggested. Transplacental transmission has been observed.
Pathogenesis
The erythrocytes are parasitized by Anaplasma organisms. The infected erythrocytes are engulfed by the cells of reticuloendothelial system. The process of erythrophagocytosis cause extra vascular haemolysis leading to anaemia.
The spleen is an important organ to limit the establishment of infection. As such splenectomy is done for experimental production of the disease.
Clinical Findings
The infection may appear as pr-acute, chronic and mild form. Acute form is mostly observed in cattle and buffalo and sub-acute form is seen in sheep and goat.
Acute form of the disease is characterized by high rise of temperature, loss of condition, nasal discharge, lacrimation, inappetence, coughing, dry rales, moist rales, rumen atony, dehydration, rough body coat, pale mucous membranes, icteric mucous membrane, dyspnoea, muscle tremors, enlargement of superficial lymph nodes, cardiac dilatation, grinding of teeth, loud heart sound and loss of vision.
Per-acute form is seen in pure and cross bred cattle and characterized by excessive salivation, rapid respiration and death. Nervous manifestation may be present.
Chronic form is characterized by inappetence, variable temperature, anaemia and loss of condition.
Lesion
The lesions are located in the organs of reticulo-endothelial system. All the mucous membranes turn yellow. The spleen is enlarged; liver is enlarged with a yellow brown colour. The gall bladder is distended. There is pericardial and epicardial haemorrhage.
Diagnosis
This based on the following criteria:
1. Clinical findings
2. Examination of blood films: Blood smears should be stained with Giemss or Leishman stain. The organisms will appear in different forms and vary from 0.5 to 1.0 micrometre in size. Organisms are present at the margin of the RBC.
3. Erythrocytometric values: There is severe reduction of total erythrocytic count, packed cell volume and haemoglobin levels. In acute cases, these values get depressed in short period whereas in sub acute ones their levels are maintained for a longer period.
4. Animal sub-inoculation test: The blood from a suspected carrier is to be injected into healthy susceptible splenectomised animals. The infection will be established in the inoculated animal within a week and the presence of Anaplasma organism will be noticed in the blood smear.
5. Serological tests
Complement fixation test: It is a very sensitive test and can detect the antibodies after 20 days of infection. The antigen is prepared from the sonicate of Anaplasma infected bovine red blood cells by a process of differential centrifugation followed by filtration through milli pores filters. The antigen is lipoprotein in nature. The complement fixation antigenicity increases the number of erythrocytes containing Anaplasma bodies.
Capillary tube agglutination test: One third of the known antigen and two third of the suspected serum are taken up by capillary action in the tubes. The results are noted after 24 hours. In positive cases, there is agglutination of bead type.
Curd agglutination test: Amerault and Roby (1968) described this test. This test requires four minutes. In this test, serum or plasma is used as antibodies against A. marginale. On a hard curd one drop each of test serum and bovine serum factor (BSF) are placed separately and mixed together with the help of a wooden stick and shaken for four minutes. Agglutination reaction is noted.
Fluorescent antibody technique: The direct FA test can detect anaplasma bodies even when the parasitaemia is less than .5%. The indirect FA test is useful in detection and quantitation of Anaplasma antibodies in the carrier animals.
Gel preparation test: The soluble antigen is used for this test. This test can detect antibodies after 42 days of initial infection. This test is suitable for carrier cases.
Tube agglutination test: This test is performed by using antigen prepared from spleen. This test can detect 87% of positive cases.
Bentomite flocculation test: This test is similar to indirect haemagglutination test. Bentonite particles are coated with soluble antigen and then the sensitized particles are mixed with equal amount of suspected inactivated serum and the mixture is rotated in mechanical mixer for 10 minutes at 120 RPM for 10 minutes. The presence of flocculation in positive cases is observed under 40X magnification of the microscope.
Immunoperoxidase test: This test has been considered sensitive over examination of blood smear.
Treatment
(i) Tetracycline group of drugs (Oxytetracycline, Tetracycline) are effective @ 10 to 15 mg/kg body weight intramuscularly.
(ii) Imidocarb hydrochloride @ 5 mg/kg body weight IM is effective.
(iii) Berenil @ 20 mg/kg body weight single IM injection produces recovery.
(iv) A combination of berenil and reverin 1:2 proportion have reliable effect.
Supportive treatment with liver extract, haemorrhagic drugs, mineral mixture is to be done to correct anaemia.
Control
- Strict control of insect population should be made by acaricidal spray or dips.
- Carrier animals should be isolated or disposed.
- Serological test of the herd should be made and the positive one should be brought under treatment.
Prophylaxis
Prophylactic immunization against anaplasmosis is done by preimunition, attenuated vaccine of ovine origin and inactivated vaccine of ovine and bovine origins. Killed vaccine has been used with fair success.
