Theileria annulata

Location and host

• These species of parasites are found in blood and lymphatics of cattle and buffalo. Vectot for this parasite is Hyalomma species of tick.

Morphology

• Trophozoites forms in erythrocyte are round to oval; but may also be rod-shaped or comma shaped.
• Division by binary fission may form two or four daughter cells. Four daughter cells appear in shape of cross (Maltese cross).
• Koch bodies are found in lymphocytes of spleen or lymph nodes or even free in these organs. They measure about 8 µm but can be upto 27µm.
• Two types of meronts occur; Macro meronts containing chromatin granules of 0.4-1.9 µm in diameter. They divide further to become micro meronts that contain chromatin granules of 0.3-0.8µm in diameter. They produce merozoites of 0.7-1 µm in diameter.

Lifecycle

• Under natural condition, susceptible animals are infected by tick vector containing number of sporozoites (uninucleate infective particle) during its attachment for engorgement.
• Transmission does not occur immediately on attachment because sporozoites develop in salivary glands during first 2-4 days of engorgement of nymphal and adult stage of ticks.

Note: Synchronously : recurring or operating at exactly the same periods.

Subsequently: After wards

• Sporozoites released then enter lymphocytes. This stimulate lymphoproliferation and parasite or host cell divide synchronously.
• After several days, parasite appear in lymph node and in lymphoid and reticulo endothelial tissues as multi nucleated macro schizonts called ‘Koch’s bodies’. Each macroschizoints contain about 8 nuclei of about 1 µm.
• Portion of macroschizoints develop into micro schizonts by binary fission.
• Micro schizonts occurs as compact bodies in lymphocytes or macrophages or reticuloendothelial cells, initially. These micro schizonts produce 50-120 micro merozoites by budding.
• Micro merozoites then enter erythrocytes while simultaneously morphologically similar protoplasm also occurs. Two types of erythrocytic stage i.e. comma and ovoid forms.
• These merozoites represent micro and macro gamonts. These merozoites when taken up by larval or nymphal stage of tick during feeding on infected animal, develops into macro and microgametes.
• In tick, these gametes unite to form zygote which increase in size by about 12 days. Zygote leaves gut cells and enters haemolymph to become elongate (ookinete) after 14-17 days.
• Ookinete then pass into acinar cells of salivary gland and develop into sporonts. These begin sporogony after development of sporonts.
• Further development occurs after moulting into subsequent stage of tick. This is called stage to stage transmission.
• Sporozoites are produced after one day of feeding in adult tick and two days of feeding in nymph.
• Sporozoites then infects susceptible animal when ticks feed on them.

Transmission

• Transmission is through bite of vector i.e. ticks of genus Hyalomma.
• They can also be transmitted mechanically by inoculation of infective blood and tissue suspension made from spleen, liver of infected animals.

Pathogenesis/ Clinical signs

• Disease may be acute, subacute or chronic
• Incubation period is about 9-25 days.
• Initially or in acute cases, clinical symptoms include:

1. Enlarged superficial lymph nodes
2. High fever (40.5-41.5 ⁰C)
3. Increase in heart and respiratory rates
4. Cessation of rumination
5. Labored breathing
6. Serous nasal discharge and coughing
7. Restlessness
8. Rough hair coat
9. Slight anorexia

• Petechial hemorrhages on conjunctiva and depression may also be found.
• Later, fever starts declining and anemia develops with colored urine. Bilirubinuria and Jaundice seen at this stage. This is followed by extreme weakness, prostration and death.
• IN chronic form, there is intermittent fever, inappetence, emaciation, anemia and jaundice.

PM findings

• Carcass is emaciated, pale mucous membranes.
• Enlargement of superficial lymph node, spleen, liver.
• Distension of gall bladder with thick bile.
• Congestion and petechial hemorrhages, on surface of kidney and lungs.
• Punched necrotic ulcers in abomasum which are characteristics findings.

Diagnosis

• On basis of clinical signs and PM finding, clinical signs can be correlated with hematological

1. Fall of Hb level (2 g/100 ml of blood)
2. Decrease in TEC and PCV (1.5-2 million /mm and 7-9% respectively).
3. Leucopenia in later stages
4. Biochemical changes include low levels of serum calcium and proteins.

• Demonstration of parasite (meronts) in both lymphnode biopsy specimens and blood smears.
• Serological test; CFT, capillary tube agglutination (CA), HI test, agar gel immune diffusion and IFA.

Treatment/ chemoprophylaxis

• Oxytetracycline can be given at time of infection and 15 mg/kg body weight , intramuscular or 5-10 mg/kg body weight, IV, 4-6 times daily.
• Menoctone @ 5-10 mg/kg body weight through intramuscular route.
• Parvaquone is effective. Given @20 mg/kg body weight through IV route as single dose or @10 mg/kg body weight through IV route. Two injections at 48 hours of interval.
• Buparvaquone is highly effective given @ 2.5 mg/kg body weight through intramuscular route. Secon injection is given after 48 hours, if necessary.
• Halofuginone @1-2 mg/kg body weight orally, once. It is schizonticide and produces mild diarrhea.

Immunoprophylaxis

• Tissue culture vaccine has been developed; 3 ml injection is given yearly through sub-cutaneous.
• Another method to immunize animals is infection and treatment method, a round up tick supernate (GUTS) equivalent to a infected acini for infection and simultaneous treatment with buparvaquone @ 2.5 mg/kg body weight can be used safely without any ill effect.

Prevention and control

• Control measures include chemoprophylaxis, immuno prophylaxis and control of ticks.
• Dipping of animals at regular intervals in ectoparasiticidal solution is effective in control of ticks.