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Human Health and Diseases - Common Pathogenic Diseases in Humans

Grade 12CBSEBiology

Review the key concepts, formulae, and examples before starting your quiz.

🔑Concepts

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Pathogens are organisms such as bacteria, viruses, fungi, protozoans, and helminths that cause diseases in humans.

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Bacterial Diseases: Typhoid is caused by Salmonella typhiSalmonella\ typhi, entering via contaminated food/water and confirmed by the Widal testWidal\ test. Pneumonia is caused by Streptococcus pneumoniaeStreptococcus\ pneumoniae and Haemophilus influenzaeHaemophilus\ influenzae, affecting the lung alveolialveoli.

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Viral Diseases: The Common Cold, caused by Rhino virusesRhino\ viruses, infects the nose and respiratory passage but not the lungs, typically lasting 3−73-7 days.

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Protozoan Diseases: Malaria is caused by PlasmodiumPlasmodium species (P. vivaxP.\ vivax, P. malariaeP.\ malariae, P. falciparumP.\ falciparum). P. falciparumP.\ falciparum causes the most serious, malignant malaria.

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The life cycle of PlasmodiumPlasmodium requires two hosts: Female AnophelesFemale\ Anopheles (vector) and Humans. The infectious stage for humans is the SporozoiteSporozoite.

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Malarial paroxysm (chills and high fever) is caused by the release of a toxic substance called HaemozoinHaemozoin when RBCsRBCs (Red Blood Cells) rupture.

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Amoebiasis (Amoebic dysentery) is caused by Entamoeba histolyticaEntamoeba\ histolytica in the large intestine, with Musca domesticaMusca\ domestica (houseflies) acting as mechanical carriers.

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Helminthic Diseases: Ascariasis is caused by Ascaris lumbricoidesAscaris\ lumbricoides (intestinal parasite), and Elephantiasis (Filariasis) is caused by Wuchereria bancroftiWuchereria\ bancrofti and W. malayiW.\ malayi.

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Fungal Diseases: Ringworms are caused by genera MicrosporumMicrosporum, TrichophytonTrichophyton, and EpidermophytonEpidermophyton. Heat and moisture help these fungi grow in skin folds.

📐Formulae

Diagnostic Marker for Typhoid=Widal Test Positive\text{Diagnostic Marker for Typhoid} = \text{Widal Test Positive}

Malarial Toxin Production: Rupture of RBC→Release of Haemozoin\text{Malarial Toxin Production: } \text{Rupture of RBC} \rightarrow \text{Release of } Haemozoin

Infectious Stage of Plasmodium to Humans=Sporozoites\text{Infectious Stage of Plasmodium to Humans} = Sporozoites

Infectious Stage of Plasmodium to Mosquito=Gametocytes\text{Infectious Stage of Plasmodium to Mosquito} = Gametocytes

💡Examples

Problem 1:

A patient presents with sustained high fever (39∘C39^{\circ}C to 40∘C40^{\circ}C), weakness, stomach pain, constipation, headache, and loss of appetite. Which pathogen is likely responsible and what test confirms it?

Solution:

The pathogen is Salmonella typhiSalmonella\ typhi. The confirming test is the Widal testWidal\ test.

Explanation:

These are classic clinical symptoms of Typhoid fever. The bacteria spread through contaminated food and water and migrate to the small intestine.

Problem 2:

Contrast the site of infection between the Common Cold and Pneumonia.

Solution:

Common Cold: NoseNose and respiratory passagerespiratory\ passage (excluding lungs). Pneumonia: AlveoliAlveoli of the lungs.

Explanation:

In Pneumonia, the alveolialveoli get filled with fluid, leading to severe problems in respiration, whereas the Common Cold only affects the upper respiratory tract.

Problem 3:

Identify the vector and the causative agent for Elephantiasis.

Solution:

Causative agent: Wuchereria bancroftiWuchereria\ bancrofti or W. malayiW.\ malayi. Vector: Female CulexFemale\ Culex mosquito.

Explanation:

The pathogens cause chronic inflammation of the lymphatic vessels of the lower limbs, leading to gross deformities resembling an elephant's leg.

Common Pathogenic Diseases in Humans Revision - Class 12 Biology CBSE