What is pathogenicity in biology?

Aug 09, 2022, 16:45 IST

PATHOGENICITY

Pathogenicity can be explained as the absolute ability of an infectious agent to cause disease in a host an infectious agent is either pathogenic or not.

Of all the communicable diseases caused by protozoans, malaria is the most destructive to humans. It is widespread in tropics, subtropics and certain areas in the temperate zone.

Plasmodium vivax causes benign tertian or vivax malaria. It is characterized by the recurrence of fever every third day i.e. after every 48 hours (the period of erythrocytic schizogony in P. vivax). Its incidence (chance of occurrence) is worldwide especially in the temperate regions.

Malarial symptoms appear several days after the infection of man by the sporozoite. This time interval or the incubation period is utilized by the parasite to increase its progeny or daughter population. It is a must, for the malarial symptoms to appear, that a large number of organisms continue erythrocytic cycle simultaneously. Each episode of pyrexia or fever exhibits 3 successive stages.

a) Cold state

It is occurs at the onset of malaria fever and is characterized by the chills and rigors. It lasts for about 20 minutes to 1 hour.

b) Hot or febrile stage

As the cold stage subsides, the body temperature rises as high as . The patient feels very hot with severe headache. Its duration is one to four hours.

c) Sweating stage

As the temperature subsides, the patient sweats profusely. Eventually, the fever disappears and the patient is comfortable until the next episode which occurs at regular intervals of 48 hours in a case of P. vivax malaria. Depending on the Plasmodium spp. the total duration of paroxysm varies from 6 to 10 hours.

Malaria fever appears due to the release of haemozoin (malaria pigment) in the blood plasma, simultaneous to the liberation of merozoites owing to the rupture of schizonts within the erythrocytes. The rupture of schizonts tends to be synchronous i.e. they all burst at the same point of time. Haemozoin is toxic as it induces high fever and shivering.For More Biology Doubts check out Physics Wallah Biology Doubts sections.

Anaemia is unavoidable in cases of infection with Plasmodium spp. In chronic or long standing cases, hepatosplenomegaly (abnormal enlargement of liver & spleen) is observed. The bone marrow turns blue.

P.falciparum infection is also known as ‘black water fever’ as it is characterized by the massive destruction of erythrocytes followed by the excretion of liberated haemoglobin in the patient’s urine.