Common human diseases · Part 3

Mosquito vector Aedes aegypti Severe flu like illness with a sudden onset of fever and painful headache, muscle and joint pain Chikungunya Alpha virus (Toga virus) Nervous system Mosquito vector Aedes aegypti Fever and joint pain, headache and joint swelling Table: . Viral diseases in human beings XII Std Zoology Chapter XII Std Zoology Chapter Human Health and Diseases Amoebiasis also called amoebic dysentery or amoebic colitis is caused by Entamoeba histolytica, which lives in the human large intestine and feeds on mucus and bacteria (Fig. . ) . Infective stage of this parasite is the trophozoite , which penetrates the walls of the host intestine (colon) and secretes histolytic enzymes causing ulceration, bleeding, abdominal pain and stools with excess mucus. Symptoms of amoebiasis can range from diarrhoea to dysentery with blood and mucus in the stool. House flies ( Musca domestica ) acts as a carrier for transmitting the parasite from contaminated faeces and water. Food vacuole Plasmalemma Ectoplasm Endoplasm Endosome Nucleus Fig. . Entamoeba histolytica African sleeping sickness is caused by Trypanosoma species . Trypanosoma is generally transmitted by the blood sucking Tsetse flies. Three species of Trypanosoma cause sleeping sickness in man. . T. gambiense is transmitted by Glossina palpalis (Tsetse fly) and causes Gambian or Central African sleeping sickness (Fig. . ). . T. rhodesiense is transmitted by Glossina morsitans causing Rhodesian or East African sleeping sickness. . T. cruzi is transmitted by a bug called Triatoma megista and causes Chagas disease or American trypanosomiasis. Kala – azar or visceral leishmaniasis is caused by Leishmania donovani, which is transmitted by the vector Phlebotomus (sand fly) . Infection may occur in the endothelial cells, bone marrow, liver, lymph glands and i. Pneumotropic diseases (respiratory tract infected by influenza) ii. Dermotropic diseases (skin and subcutaneous tissues affected by chicken pox and measles) iii. Viscerotropic diseases (blood and visceral organs affected by yellow fever and dengue fever) iv. Neurotropic diseases (central nervous system affected by rabies and polio). Some common viral diseases of human beings are given in table