Sporozoite

Sporozoite is a motile, infective form of few sporozoans that is an outcome of sporogony initiating an asexual cycle in the new host. It is a cell form which infects the new hosts. For instance, the sporozoites in Plasmodium are cells that evolve in the salivary gland of mosquito, leave the mosquito whilst a blood meal and proceed towards the liver cells wherein they reproduce. These cells which are infected by the sporozoites burst out eventually and release merozoites into the bloodstream. The sporozoites are motile and their movement is brought about by the gliding motion. These sporozoites multiply and grow in the liver to turn into merozoites.

Sporozoites are carried by the blood into the liver. Here they turn into schizonts, mature forms. In a course of 1-2 weeks, each of this schizont multiplies into hundreds and thousands of other forms referred to as merozoites. These merozoites burst open into the liver and consequently are reintroduced into the bloodstream. Here they invade the red blood cells, divide and grow, later destroy the blood cells in this process. The period between invasion of blood cells and rupturing of such a cell by the subsequent generation of merozoites is nearly 2 days and varies for different species. As a result, the parasites tear up every day from the infected blood cells.

The Plasmodium parasite leads to malaria in mammals with RBCs, including humans. Their main vector for transmitting diseases is the female Anopheles mosquito however, there are some mites which can carry parasites. Reproduction in these parasites takes place both sexually in a vector and asexually, in the host. The parasite in this process experiences three life stages – sporozoites, gametocytes and merozoites which take place at various phases of the reproductive cycle and in various parts of the host.

  • Sporozoites – in this stage, the parasites are spore-like and are motile. It is in this very stage that the parasites are transferred from the vector to the host. Sporozoites then mature into the schizonts once they enter the host.
  • Gametocytes – These are the precursor cells of the plasmodium parasites and are the outcome of sexual reproduction of merozoites present in the host as well as the vector.
  • Merozoites – in the infected hosts when the schizonts rupture, merozoites are liberated which are capable of asexual and sexual reproduction.

Parasites take the form of gametocytes initially which later develop into the sporozoites in the vector mosquito. Whenever a mosquito bites a host, these sporozoites are then passed into the bloodstream of the host through the saliva of the mosquito. The parasite thereby enters into the parenchyma cells of the liver and eventually matures into the schizonts, which reproduce by dividing asexually and rupturing to release the merozoites.

These merozoites attack the red blood cells of the host. Now they multiply asexually to grow in number infecting more and more cells. Few of the merozoites go on to grow into the gametocytes for sexual reproduction. These are ingested by a mosquito that feeds on the host, thereby initiating the cycle all over again.

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