Q.Can a disease be detected before its symptoms appear? Explain the principle involved.
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Biology Disease Control — A First Look
Think of your body as a city. Every day, germs (bacteria, viruses, fungi, parasites) try to enter — through the air you breathe, the food you eat, a cut on your skin. Most of the time, your body's defence systems stop them before you even notice. That's immunity, your natural security force.
But sometimes the invaders break through. You get a fever, a cough, an infection. Now you need disease control — the set of actions that stop the illness from spreading and help you recover.
What exactly is disease control?
In biology, disease control means reducing the incidence (new cases), prevalence (total cases), or transmission of a disease. It's not about wiping out every germ — that's impossible. It's about keeping the disease at a level where it no longer threatens public health.
The NCERT textbook divides disease control into two broad approaches:
1. Preventive measures — stopping the disease before it starts
These are actions taken by individuals, communities, and governments to block the entry of pathogens.
- Vaccination — training your immune system to recognise a germ before it attacks. This is the single most powerful tool in disease control.
- Sanitation and hygiene — clean drinking water, proper sewage disposal, handwashing. Many diseases (cholera, typhoid, hepatitis A) spread through contaminated water or food.
- Vector control — killing or avoiding the organisms that carry disease. Mosquito nets, insect repellents, draining stagnant water — these control malaria, dengue, chikungunya.
- Quarantine and isolation — separating sick people from healthy ones during outbreaks. You saw this during COVID-19.
Prevention is always better than cure. Once a disease spreads in a population, controlling it becomes exponentially harder and more expensive. That's why governments invest heavily in vaccination drives and public sanitation.
2. Curative measures — treating the disease once it occurs
Even with the best prevention, some people will fall ill. Curative measures aim to:
- Reduce the severity of the illness (e.g., antibiotics for bacterial infections, antiviral drugs for flu)
- Shorten the duration of the illness
- Prevent complications and death
- Stop the patient from infecting others
The key point: treatment alone cannot control a disease in a population. If you only treat sick people without preventing new infections, the disease keeps circulating.
Why does disease control matter for society?
A single outbreak can paralyse a city. Schools close, hospitals overflow, businesses shut down. The economic cost is enormous. That's why disease control is not just a medical issue — it's a public health issue.
The NCERT textbook emphasises that disease control requires community participation. No matter how good the doctors or vaccines are, if people refuse to vaccinate their children or ignore hygiene, the disease will keep spreading. …
Modern molecular diagnostics can pick up the presence of a pathogen from a tiny amount of its nucleic acid, long before the body shows any illness.
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Yes — a disease can be detected before symptoms appear using PCR, which amplifies the trace amount of a pathogen's nucleic acid so it can be detected even when present in very low numbers.
Answer: Yes, a disease can be detected before symptoms appear, because at the early stage the pathogen is present in very low numbers and conventional methods fail. This topic is from the TS Intermediate biotechnology-applications unit, which follows the NCERT/CBSE curriculum.
Principle involved (PCR):
- PCR (Polymerase Chain Reaction) can amplify even a very small amount of the pathogen's nucleic acid (DNA/RNA) into millions of copies.
- Once amplified, the pathogen's nucleic acid becomes detectable, so the infection is diagnosed early, before the disease has manifested symptoms. …
Showing the 12 most recent of 23 on this concept.
- CBSE 2026Set ANNUAL1 markQ.Fill in the blank: Virus infected cells secrete proteins are called ______.
›Reveal solutionSolution
Proteins secreted by virus-infected cells are called interferons.
When a cell is infected by a virus, it secretes a group of protective proteins called interferons. These interferons diffuse to the surrounding, still-healthy cells and make them resistant to viral infection, thereby limiting the spread o …
- CBSE 2026Set ANNUAL1 markMCQQ.Haemozoin is released as a result of –(a) Rupture of liver cells(b) Rupture of red blood cells(c) Multiplication of sporozoites(d) Replication in macrophages
›Reveal solutionSolution
Haemozoin, the toxic malarial pigment, is liberated when parasitised red blood cells rupture, causing the characteristic recurring chills and fever.
When a female Anopheles mosquito bites, Plasmodium sporozoites enter the human liver, multiply, and then invade red blood cells. Inside the RBCs the parasite digests haemoglobin and multiplies. When the infected RBCs burst to release the next generation of parasites, they also release a to …
- CBSE 2026Set ANNUAL1 markQ._________ test is performed to confirm typhoid.
›Reveal solutionSolution
The blank is the Widal test — the diagnostic test that detects antibodies against Salmonella typhi to confirm typhoid fever.
In the CBSE/NCERT Human Health and Disease chapter, typhoid is caused by Salmonella typhi, spread through contaminated food and water. It is confirmed by the **Widal te …
- CBSE 2025Set A1 markQ.Write True / False: All microbes are not pathogenic.
›Reveal solutionSolution
The statement is True: most microbes are non-pathogenic and many are beneficial to humans.
Microbes (bacteria, fungi, protozoa, viruses, archaea) are extremely diverse, and only a small proportion of them are pathogens capable of causing disease in humans, plants or animals. The overwhelming majority of microbes play beneficial or neutral roles — decomposing organic matter, fixing nitrogen, fermenting food and beverages (curd, bread, alcoholic drinks), pro …
- CBSE 2024Set ANNUAL1 markMCQQ.Bacterial disease is(a) Diphtheria(b) Malaria(c) Amoebiasis(d) Ascariasis
›Reveal solutionSolution
Diphtheria is bacterial; malaria and amoebiasis are protozoan diseases and ascariasis is a helminth (roundworm) disease.
Diphtheria is caused by the bacterium Corynebacterium diphtheriae. In contrast, malaria is caused by the protozoan Plasmodium (transmitted by female Anopheles mosquito), amoebiasis is caused by the protozoan Entamoeba histolytica, and **asc …
- CBSE 2024Set ANNUAL1 markMCQQ.Choose the pair of viral diseases from the following sets :(a) Ringworm, AIDS(b) Common Cold, AIDS(c) Dysentery, Common Cold(d) Typhoid, Tuberculosis
›Reveal solutionSolution
Both Common Cold and AIDS are caused by viruses.
Common Cold is caused by Rhinoviruses (a group of viruses), and AIDS (Acquired Immuno Deficiency Syndrome) is caused by the Human Immunodeficiency Virus (HIV), a retrovirus. Checking the other pairs: Ringworm is fungal (not viral); Dysentery is caused by bacteria/protozoa (Entamoeba histolytica for amoebiasis, or bacteria); Typhoid is caused by the bacterium Salmonel …
- CBSE 2024Set ANNUAL1 markMCQQ.Choose the incorrectly matched pair -(i) Mumps - Paramyxovirus(ii) Typhoid - Salmonella typhi(iii) Cholera - E. Coli(iv) Pneumonia - Diplococcus pneumoniae
›Reveal solutionSolution
Cholera is caused by the bacterium Vibrio cholerae, so pairing it with E. coli is incorrect.
Checking each pair against the actual causative organism:
- Mumps – Paramyxovirus: correct.
- Typhoid – Salmonella typhi: correct.
- Cholera – E. Coli: incorrect — cholera is caused by Vibrio cholerae, a comma-shaped bacterium, not by Escherichia coli. …
- CBSE 2023Set ANNUAL1 markMCQQ.The organism which causes disease in plants and animals is called(a) vector(b) pathogen(c) insect(d) worm
›Reveal solutionSolution
A pathogen is any disease-causing organism, whereas a vector is merely the carrier that transmits the pathogen from one host to another.
A pathogen is any organism (bacterium, virus, fungus, protozoan, or helminth) capable of causing disease in a host organism, whether plant or animal. A vector (a), such as the female Anopheles mosquito for malaria, is an intermediate organism that transmits the pathogen from an inf …
- CBSE 2023Set ANNUAL1 markMCQQ.Which of the following diseases is caused by a DNA Virus?(a) AIDS(b) Measles(c) Mumps(d) Chicken pox
›Reveal solutionSolution
Chicken pox is caused by Varicella-zoster virus, a double-stranded DNA virus; the other three listed diseases are all caused by RNA viruses.
Let's classify each disease by its causative virus's genome:
- AIDS (a) is caused by HIV, a retrovirus with an RNA genome (reverse-transcribed into DNA inside the host cell).
- Measles (b) is caused by the measles morbillivirus, an RNA virus. …
- CBSE 2023Set ANNUAL1 markMCQQ.Food poisoning is caused by which?(a) Rhizobium(b) Azotobacter(c) Lactobacillus(d) Clostridium
›Reveal solutionSolution
Clostridium causes food poisoning.
Food poisoning is caused by consuming food contaminated with bacteria or their toxins. Clostridium species produce powerful toxins — Clostridium botulinum causes botulism and Clostridium perfringens causes food-borne illness. In contrast, Rhizobium and Azotobacter are beneficial nitrogen-fixing soil bacteria, and Lac …
- CBSE 2022Set ANNUAL1 markQ.Define innate immunity.
›Reveal solutionSolution
Innate immunity is the inborn, non-specific defence we are born with.
Innate (non-specific) immunity is present from the time of birth and is inherited from the parents. It is non-specific - it acts against a wide range of foreign agents in the same general way, without needing prior exposure. It works through four types of barriers: physical (skin, mucus), physiological (acid in stomach, saliva, tears), cellular (phagocytes, NK cells) a …
- CBSE 2022Set ANNUAL1 markMCQQ.Ringworm disease in humans is caused by(a) a bacterium(b) a fungus(c) a virus(d) a worm
›Reveal solutionSolution
Ringworm is caused by fungi (dermatophytes), so the answer is (B).
Despite its name, ringworm is not caused by a worm. It is one of the most common fungal (dermatophyte) diseases of humans, caused by genera such as Microsporum, Trichophyton and Epidermophyton. These fungi infect the skin, nails and scalp, producing the characteristic dry, scaly, ring-shaped lesions with in …
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