Long Answer Questions
Q: Describe the life cycle of Plasmodium vivax in mosquito.
A: When female Anopheles mosquito inoculates, and sucks the blood of human host gametocytic stages of malaria parasite enter into the crop of mosquito. Along with gametocytes, other stages of erythrocytic stages reach the crop. Only gametocytic stages show resistance to the digestive juices of the insect and rests of the stages are digested in the gut of mosquito.
Further life cycle of malarial parasite continues in the crop. It is described as Ross cycle after Sir Ronald Ros. It includes following
stages.
i) Gametogony
ii) Fertilization
iii) Formation of ookinete and oocysts
iv) Sporogony.
i) Gametogony: Production of male and female gametes from gametocytes is called gametogony. It occurs in the lumen of crop.
The nucleus of micro/ male gametocytes undergo mitotic divisions and produce eight daughter pronuclei. The cytoplasm of gametocyte is pushed out in the form of flagella like processes. Into each flagella like process a pronucleus enters and transform into micro/
male gametes. The male gametes separate by lashing moments. This
process is called exflagellation. The macro/ female gametocytes do
not divide. They undergo few changes and transform into macro/
female gametes. This is known as maturation. The macrogamete
acquires a conical structure called fertilization cone. The pronucleus of macrogamete moves into the fertilization
cone.
ii) Fertilization: Fertilization takes place in the lumen of crop. Fusion of male and female gametes are called syngamy. In Plasmodium fertilization occurs between two unequal gametes, hence it is called anisogamy. The macro/ female gamete that bears zygotic nucleus (synkaryon) is called zygote which round and non-motile.
iii) Formation of ookinete and oocyst: Within 18-24 hrs the inactive zygote becomes active and transforms into a long, slender, motile, vermiform ookinete or vermicule. Vermicule pierces the wall of
crop wall and settles beneath the basement of membrane of the crop wall. Now, the ookinete undergoes encystment and transforms into oocyst. Oocyst is enveloped by two layers. Outer wall is contributed by the crop and inner layer secreted by ookinete itself. Zygote,
ookinete, vermicule and oocyst are the diploid stages of malarial parasite.
iv) Sporogony: The formation of sporozoites in the oocysts is called sporogony. It occurs on outer surface of the crop wall. According to Bano, the zygotic nucleus of oocyst first undergoes meiotic division
and the following divisions occur in mitotic method. Repeated mitotic divisions in the oocyst result about 1000 daughter nuclei. Each daughter nucleus is surrounded by a small amount of cytoplasm and transform into sickle shaped sporozoites. The cyst with sporozoites is called sporocyst. The sporocysts rupture and
sporozoites released into haemocoel from there they infect the salivary glands of mosquito and ready for infection to the new secondary host.
Very Short Answer Type Questions
Q: Write the route of extra intestinal migration followed by the juveniles of Ascaris lumbricoides.
A: In the small intestine of human 2nd stage juvenile of Ascaris is released. It reaches the liver through hepatic portal system. It reaches the lungs through pulmonary arteries and undergoes 2nd and 3rd moults to become 4th stage juvenile. 4th stage larva reaches the
small intestine through bronchi, trachea, larynx, pharynx, oesophagus and stomach.
Q: What is meant by nocturnal periodicity? Explain with reference to the life history of a nematode parasite you have studied.
A: Microfilaria, larva of Wucheraria bancrofti, migrates into the peripheral blood vessel during the night time between 10 pm and 4.00 am. This behaviour of microfilaria is called nocturnal periodicity.
Q: Distinguish between infectious and noninfectious diseases.
A: The diseases which are easily transmitted from one person to another are called infectious diseases. These are caused by pathogens. e.g.: Amoebiasis, Typhoid. Noninfectious diseases are not transmitted from one person to another. These are not caused by pathogens. e.g.: Genetic disorders, heart problems etc.
Short Answer Type Questions
Q: Write short notes on typhoid fever and its prophylaxis.
A: Typhoid is caused by a gram negative bacterium called Salmonella typhi. It lives in the small intestine of man and infects to various
organs through blood. It spreads through food and water contamination. Humans are infected with fecal-oral route.
The symptoms of typhoid are sustained high fever with 104oF, weakness, stomach pain, constipation, headache and loss of appetite.
Perforations of the intestines, internal bleeding and death may also occur in severe cases.
To diagnosis typhoid Widal test is used. Prophylaxis: Drinking of boiled and filtered water, washing hands, fruits and vegetables
properly, maintaining good sanitary practices prevent the spreading of the disease.