LIFE CYCLE

LIFE CYCLE

Vectors

• Hyalomma detritum, Hyalomma anatolicum anatolicum (Hyalomma excavatum), Hyalomma marginatum isaaci (H.savignyi),H. aegyptium, H.dromedarii, H. truncatum and H. sucupense.

Developmental cycle

Cattle are infected from infected ticks by innoculation of large number uninucleated sporozooites from salivary glands.

• Sporozoites reach  the nearest lymph node through lymphatic system to develop initially into macroschizonts known as Koch's blue bodies.

Schizogony

• Sporozoites after entry with saliva of ticks rapidly enter lymphocyte cells.They penetrate in 10 minutes.Parasites ingest host cell cytoplasm by a typical process.
• Nucleus divide repeatedly by binary fission resulting in large number of schizonts containing specific number of nuclei (chromatin granules). They are now known as Koch's blue bodies which is visible in light microscope.
• Schizonts stimulate host cell (lymphocyte do not multiply on its own accord) which undergo cell division during which schizonts also divide and is distributed by action of host cell spindle apparatus to the daughter cell.
• Infected cell displaces uninfected lymph node tissue and in few days produces symptoms identical to those of leucosis.Only a single type of merozoites are formed. Merozoites become free and penetrate actively RBC from 8 days after infection in T.annulata, 13 days in T. parva. Usually 4-7 days after schizogony , main pathological effect in host are found leading to death.

Development in RBC

• Two different forms are seen.1) Slender comma shaped forms measuring 1-1.5µm to 2µm divide by binary fission. These may destroy host cell and may induce erythrocytopaenia.2) Spherical forms which measure 0.5-0.6µm representing probably gamonts from which gamete- like stages are formed in intestine of ticks fed on infected animals. They don't produce pigments as that of Plasmodium sp.

Development in intestine of ticks

• Ray bodies are discovered by Schein (1965) now proved by Mehlhorn et al. under electron microscope and observed by Mehlhorn and Schein (1976).
• Ray bodies seen in 2-4 days after repletion in the gut of ticks and formed from comma shaped bodies. Spherical bodies dont divide, considered as macrogametes and then syngamy observed 12-13 days after feeding.
• Transformation of ovoid or spherical zygotes to club shaped mobile club shaped structures called Kinetes.
• They enter intestinal cells and are seen in haemolymph when tick moults.
• They penetrate cells of salivary glands after moult. Kinete is not observed in any other organ of the tick.

Development in salivary glands

• Kinetes in cytoplasm of host cell i.e. salivary alveoli type 3 acinus which contains 3 glandular cell types, salivary acini which contains secretory granules, cells close to acinar ducts containing spotted granules. These two types of cells are affected by the kinetes. Nucleus of kinetes divides with repeated nuclear division, nucleus becomes small with 1000s of sporozoites being formed.
• Numerous invagination formed cytomere - like compartments on 2nd day of attachment of new adult.
• Infected salivary glands are completely filled with cytomeres with few nuclei.
• Under light microscope, parasites seem to have a compact form as the cytomeres are closely packed together and this development is a continuous process and cytoplasm of host cell is damaged considerably and remnants of cytoplasm are seen scattered between cytomeres.
• Nucleus of host cell increases in size and seen at the periphery of alveolus.
• Cytomere formation ends by 5th day after attachment, formation of infected sporozoits  isthen observed.
• After 5th day following attachment, parasitised alveolus is filled with ovoid sporozoites of 1µm- these infected particles are ready for transmitting number of sporozoites/ salivary gland can hardly be estimated 50,000 sporozoites are there. This amounts to enormous inoculum of tick.