Human health is not just the absence of disease; it’s a complete state of physical,
mental, and social well-being. In the journey of understanding biology, especially in
competitive exams like NEET, knowing about various pathogens, their life cycles,
symptoms they cause, and ways to prevent these diseases is vital.
Diseases can arise from genetic disorders, environmental imbalances, or the
invasion of foreign agents like bacteria, viruses, fungi, protozoa, and helminths.
Among these, infectious diseases, which are caused by pathogenic organisms, are
of significant concern due to their rapid spread and potential for outbreaks. This blog
dives deep into various parasites and pathogens that cause common human
diseases like malaria, typhoid, pneumonia, common cold, ascariasis, filariasis,
amoebiasis, ringworm, dengue, and chikungunya — aligning with the NEET syllabus
demands and patterns.
Understanding Pathogens and Parasites
Bacteria, Viruses, Fungi, and Protozoans
Pathogens are disease-causing organisms, and they fall into several categories:
Bacteria: Single-celled microorganisms like Salmonella typhi cause typhoid.
Viruses: Tiny, non-living particles that invade host cells, e.g., Dengue virus.
Fungi: Cause superficial infections like ringworm.
Protozoans: Single-celled eukaryotes like Plasmodium and Entamoeba
histolytica.
Parasites and Their Classification
Parasites are organisms that live on or inside a host and derive nutrients at the
host’s expense. They can be:
Ectoparasites (live on the surface, e.g., lice)
Endoparasites (live inside the body, e.g., Ascaris lumbricoides)
Human parasitic diseases are major public health issues in tropical countries and are
crucial topics in NEET biology.
Malaria
Causative Agent and Vector
Malaria is caused by protozoans of the genus Plasmodium (e.g., P. vivax, P.
falciparum, P. malariae, and P. ovale). The female Anopheles mosquito acts as the
vector.
Life Cycle of Plasmodium
The malaria parasite has a complex life cycle with both asexual and sexual stages:
- Asexual Phase: Occurs in humans. Sporozoites enter the bloodstream
during a mosquito bite, reach the liver, multiply, and then infect RBCs. - Sexual Phase: Occurs in mosquitoes when they ingest gametocytes from
infected blood.
Plasmodium falciparum causes malignant malaria, which is fatal if untreated.
Symptoms and Prevention
Symptoms include chills, fever, sweating, headache, and vomiting. Severe cases
may lead to cerebral malaria.
Prevention includes:
Using mosquito nets
Insect repellents
Draining stagnant water
Antimalarial drugs like chloroquine
Filariasis (Elephantiasis)
Causative Agent and Transmission
Filariasis is caused by Wuchereria bancrofti and Brugia malayi, both of which are
helminth parasites. These parasites are transmitted by female mosquitoes (e.g.,
Culex species).
Symptoms and Control Measures
The disease primarily affects the lymphatic system, leading to chronic swelling,
particularly in the legs (hence the name elephantiasis). The blockage of lymph
vessels causes inflammation and thickening of skin and tissues.
Control and Prevention:
Mass drug administration (MDA) programs
Use of mosquito repellents and bed nets
Improving sanitation
Ascariasis
Etiology and Transmission
Caused by the roundworm Ascaris lumbricoides, ascariasis is one of the most
common helminthic infections globally. It is transmitted through ingestion of eggs
from contaminated food, water, or soil.
Symptoms and Prevention
Once ingested, the eggs hatch in the intestines, and larvae migrate through the
lungs and throat before settling in the small intestine.
Symptoms include:
Abdominal discomfort
Intestinal blockage in severe cases
Nutritional deficiencies
Prevention strategies:
Personal hygiene (handwashing)
Proper disposal of human waste
Thorough washing of fruits and vegetables
Typhoid
Pathogen, Transmission, and Symptoms
Typhoid is a serious bacterial infection caused by Salmonella typhi. It spreads
through contaminated food and water, making it a major public health concern in
areas with poor sanitation. The bacteria enter the small intestine and then travel
through the bloodstream to different organs.
Symptoms of typhoid include:
High fever (up to 104°F)
Weakness and fatigue
Abdominal pain
Rash (rose-coloured spots)
Headache and constipation
Typhoid carriers: Some individuals, even after recovery, continue to harbour
bacteria in their gall bladder and shed them through faeces. They are called chronic
carriers (e.g., Typhoid Mary).
Widal Test and Preventive Measures
The Widal test is commonly used to detect typhoid. It checks for antibodies against
Salmonella antigens (O and H).
Preventive measures:
Drinking boiled or purified water
Avoiding street food
Vaccination (Vi polysaccharide vaccine)
Practicing good sanitation
Pneumonia
Causes and Symptoms
Pneumonia is an acute infection of the alveoli of the lungs caused by Streptococcus
pneumoniae and Haemophilus influenzae. It spreads via droplets from coughs or
sneezes of infected individuals.
Key symptoms:
Difficulty breathing
Chest pain
Cough with sputum
High fever and chills
Bluish coloration of lips and nails (due to lack of oxygen)
In severe cases, pneumonia can lead to respiratory failure, especially in the elderly
and immunocompromised individuals.
Prevention and Treatment
Prevention:
Vaccination (Pneumococcal vaccine)
Good hygiene practices
Avoiding crowded places during outbreaks
Treatment:
Antibiotics (penicillin, amoxicillin)
Rest and hydration
Oxygen therapy in severe cases
Common Cold
Causes and Symptoms
The common cold is a viral infection caused by rhinoviruses, among others. It is one
of the most widespread infections and spreads quickly via airborne droplets, hand-to-
hand contact, or contaminated surfaces.
Symptoms include:
Runny nose
Sneezing
Sore throat
Mild fever
Nasal congestion
The cold is self-limiting and usually resolves within a week without complications.
Differences from Flu
While both are respiratory illnesses, the flu (caused by influenza virus) is generally
more severe. The flu is accompanied by high fever, body aches, and fatigue, which
are uncommon in a regular cold.
Common cold does not usually result in complications, unlike pneumonia or
influenza.
Amoebiasis
Pathogen and Life Cycle
Amoebiasis is caused by the protozoan parasite Entamoeba histolytica, which
resides in the large intestine. Infection occurs through ingestion of mature cysts in
contaminated food or water.
Life cycle stages:
Cyst: Infective form ingested by host
Trophozoite: Active, motile form that invades intestinal wall
Cyst formation: Passed in faeces to infect another host
Symptoms and Hygiene Practices
Symptoms:
Bloody diarrhoea
Abdominal cramps
Fever and fatigue
Weight loss in chronic cases
Preventive hygiene measures:
Safe drinking water
Washing hands thoroughly
Proper sanitation facilities
Avoiding uncooked foods in endemic areas
Ringworm (Dermatophytosis)
Fungal Agents and Transmission
Ringworm is not caused by a worm but by a group of fungi known as dermatophytes
(e.g., Trichophyton, Microsporum, Epidermophyton). It is highly contagious and
spreads through skin contact or sharing personal items.
Common sites of infection:
Scalp (Tinea capitis)
Body (Tinea corporis)
Feet (Tinea pedis or athlete’s foot)
Symptoms and Prevention
Symptoms include:
Itchy, red, ring-shaped rashes
Scaling and cracking skin
Blisters in severe cases
Prevention strategies:
Keeping skin dry and clean
Avoiding sharing towels or combs
Antifungal powders or creams
Wearing breathable clothing
Ringworm is a superficial fungal infection affecting only keratinized tissues (skin,
hair, nails).
Dengue
Virus and Vector
Dengue fever is caused by the Dengue virus, which belongs to the Flavivirus genus.
It is transmitted to humans through the bite of an infected female Aedes aegypti
mosquito, which is a day-biting mosquito often found near human dwellings.
There are four serotypes of the dengue virus (DEN-1 to DEN-4), and infection with
one serotype provides lifelong immunity to that type but only short-term protection
against others.
Symptoms and Preventive Strategies
Classic symptoms of dengue include:
High fever
Severe headaches
Pain behind the eyes
Joint and muscle pain (“breakbone fever”)
Skin rashes
Nausea and vomiting
In severe cases, dengue haemorrhagic fever or dengue shock syndrome can
occur, leading to bleeding, low platelet count, and even death if untreated.
Prevention:
Eliminate mosquito breeding grounds (e.g., stagnant water)
Use mosquito nets and repellents
Wear long-sleeved clothing
Governmental fogging and awareness campaigns
Dengue does not have a specific antiviral treatment; supportive care is the mainstay.
Chikungunya
Transmission and Symptoms
Chikungunya is caused by the Chikungunya virus, also transmitted by Aedes
mosquitoes (both Aedes aegypti and Aedes albopictus). Like dengue, it spreads via
mosquito bites, especially in urban and semi-urban areas.
Key symptoms include:
Sudden onset of high fever
Severe joint pain (most distinctive)
Rash
Headache and fatigue
Joint pain may persist for weeks or even months, making it a debilitating disease.
Prevention and Control
There is no vaccine for chikungunya, so prevention focuses on mosquito control:
Avoiding mosquito bites
Wearing protective clothing
Using insecticide-treated nets
Keeping surroundings clean
Chikungunya and dengue have overlapping symptoms, but persistent joint pain is a
distinctive feature of chikungunya.
Prevention and Control of Infectious Diseases
The best way to manage infectious diseases is by breaking the chain of infection:
- Personal Hygiene
Washing hands regularly
Using sanitizers
Avoiding close contact with infected individuals - Environmental Sanitation
Proper waste disposal
Safe drinking water
Avoiding water stagnation - Vaccination
A powerful tool to build immunity
E.g., Typhoid, Pneumococcal, and Hepatitis B vaccines - Public Health Measures
Mass drug administration for diseases like filariasis
Vector control programs
Community health education
- Medical Interventions
Use of antibiotics, antivirals, and antifungal agents
Early diagnosis through tests like Widal, blood smear, etc.
Monitoring and quarantine during outbreaks
NEET Previous Year Questions (PYQs) with Answers
Here’s a list of relevant NEET questions (up to 2024):
Q1 (NEET 2022): The pathogen Microsporum responsible for ringworm in
humans belongs to which group?
A: Fungi
Q2 (NEET 2021): Which of the following diseases is not transmitted by mosquitoes?
a. Dengue
b. Filariasis
c. Typhoid
d. Malaria
A: c. Typhoid
Q3 (NEET 2020): The drug chloroquine is used to treat which disease?
A: Malaria
Q4 (NEET 2019): Which disease is caused by Entamoeba histolytica?
A: Amoebiasis
Q5 (NEET 2018): What is the vector for transmission of dengue virus?
A: Aedes aegypti mosquito
Q6 (NEET 2023): Which of the following shows a liver stage in its life cycle?
A: Plasmodium (Malaria)
Q7 (NEET 2024): The diagnostic test used for Typhoid is:
A: Widal Test
These questions emphasize the importance of knowing the life cycle, transmission,
prevention, and treatment of parasitic and infectious diseases for NEET.
FAQs
Q1: What is the difference between typhoid and common cold in terms of
transmission?
A: Typhoid spreads through contaminated food and water, while the common cold
spreads via airborne droplets or surface contact.
Q2: How is malaria diagnosed in the laboratory?
A: Malaria is diagnosed using a peripheral blood smear to identify Plasmodium
species.
Q3: What is the primary prevention method for filariasis?
A: Avoiding mosquito bites and participating in mass drug administration programs.
Q4: Can dengue and chikungunya occur at the same time?
A: Yes, co-infections are possible as they share the same vector (Aedes mosquito).
Q5: What is the most important hygiene habit to prevent ascariasis?
A: Washing hands thoroughly before eating and after defecation.
