Malaria

Widal test : A classic case in medicine, that of Mary Mallon nicknamedTyphoid Mary, is worth mentioning here. She was a cook by professionand was a typhoid carrier who continued to spread typhoid for severalyears through the food she prepared.Bacteria like Streptococcus pneumoniae and Haemophilus influenzaeare responsible for the disease pneumonia in humans which infects thealveoli (air filled sacs) of the lungs. As a result of the infection, the alveoliget filled with fluid leading to severe problems in respiration. The symptomsof pneumonia include fever, chills, cough and headache. In severe cases,the lips and finger nails may turn gray to bluish in colour. A healthyperson acquires the infection by inhaling the droplets/aerosols releasedby an infected person or even by sharing glasses and utensils with aninfected person. Dysentery, plague, diphtheria, etc., are some of the otherbacterial diseases in man.Many viruses also cause diseases in human beings. Rhino virusesrepresent one such group of viruses which cause one of the most infectioushuman ailments – the common cold. They infect the nose and respiratorypassage but not the lungs. The common cold is characterised by nasalcongestion and discharge, sore throat, hoarseness, cough, headache,tiredness, etc., which usually last for 3-7 days. Droplets resulting fromcough or sneezes of an infected person are either inhaled directly ortransmitted through contaminated objects such as pens, books, cups,doorknobs, computer keyboard or mouse, etc., and cause infection in ahealthy person.Some of the human diseases are caused by protozoans too. You mighthave heard about malaria, a disease man has been fighting since manyyears. Plasmodium, a tiny protozoan is responsible for this disease. Differentspecies of Plasmodium (P. vivax, P. malaria and P. falciparum) areresponsible for different types of malaria. Of these, malignant malaria causedby Plasmodium falciparum is the most serious one and can even be fatal.Let us take a glance at the life cycle of Plasmodium (Figure 8.1).Plasmodium enters the human body as sporozoites (infectious form)through the bite of infected female Anopheles mosquito. The parasitesinitially multiply within the liver cells and then attack the red blood cells(RBCs) resulting in their rupture. The rupture of RBCs is associated withrelease of a toxic substance, haemozoin, which is responsible for the chilland high fever recurring every three to four days. When a female Anophelesmosquito bites an infected person, these parasites enter the mosquito’sbody and undergo further development. The parasites multiply within147them to form sporozoites that are stored in their salivary glands. Whenthese mosquitoes bite a human, the sporozoites are introduced into his/her body, thereby initiating the events mentioned above. It is interestingto note that the malarial parasite requires two hosts – human andmosquitoes – to complete its life cycle (Figure 8.1); the female Anophelesmosquito is the vector (transmitting agent) too.