The diagnostic test that confirms typhoid in humans is (A) ELISA (B) Widal (C) MRI (D) Amniocentesis

Question

Q. The diagnostic test that confirms typhoid in humans is (A) ELISA (B) Widal (C) MRI (D) Amniocentesis

CBSECBSE Class XII Board 2020MCQ· 1mImportance★★★★★

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Concept understanding — Biology Disease Control

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.

Important

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.

Note

Disease control is a continuous process. Even after a disease is eliminated from a region (like polio from India), surveillance must continue. The pathogen can be re-introduced from another country. That's why international travel health regulations exist.

A simple way to remember the levels of disease control

Public health experts talk about three levels:

Primary prevention — stops the disease before it starts (vaccination, sanitation, health education)
Secondary prevention — catches the disease early, when it's easier to treat (screening tests, early diagnosis)
Tertiary prevention — reduces the damage from an established disease (rehabilitation, preventing complications)

For a commerce or humanities student, the most important takeaway is this: disease control is a system, not a single action. It combines biology (how pathogens work), behaviour (what people do), and policy (what governments enforce). Understanding this helps you see why public health campaigns succeed or fail — and why your own choices matter.

A frequent student search pattern for this topic is "Biology Disease Control notes class 12 biology", "NCERT biology syllabus biology disease control", or "Biology Disease Control: Definition, Diagram & Examples". This concept is part of the Human Health and Disease chapter in the NCERT/CBSE Class 12 Biology syllabus, and revising it thoroughly helps with both board exams and general competitive-exam preparation.

Typhoid fever is diagnosed by detecting antibodies against Salmonella typhi in the patient's serum; the Widal test is the classic serological method for this purpose. The answer is (B).

Typhoid fever is caused by the bacterium Salmonella typhi, which enters through contaminated food or water and invades the bloodstream. To confirm an active or recent infection, we need to detect either the pathogen itself or the immune response it triggers—specifically, antibodies the body produces against the bacterial antigens.

The Widal test is a serological assay that detects and measures agglutinating antibodies (IgM and IgG) against two key antigens of Salmonella typhi: the O antigen (somatic) and the H antigen (flagellar). When serum from a suspected typhoid patient is mixed with these antigens, visible clumping (agglutination) occurs if the corresponding antibodies are present. A rising titre over time, or a titre above a certain threshold, supports the diagnosis of typhoid.

Let's see why the other options don't fit:

ELISA (Enzyme-Linked Immunosorbent Assay) — This is a versatile technique used to detect antibodies or antigens for many diseases (HIV, hepatitis, dengue, etc.), but it is not the standard confirmatory test for typhoid. While ELISA-based tests for typhoid exist, they are not the classical diagnostic method taught in most curricula.
MRI (Magnetic Resonance Imaging) — This is an imaging technique that visualizes soft tissues, organs, and the nervous system. It has no role in diagnosing infectious diseases like typhoid; it's used for structural abnormalities, tumors, or neurological conditions.
Amniocentesis — This is a prenatal diagnostic procedure in which amniotic fluid is sampled to detect genetic disorders or chromosomal abnormalities in a fetus (e.g., Down syndrome). It has nothing to do with bacterial infections in adults.

Tip

Remember the mnemonic: "Widal for typhoid"—both have an "i" and relate to bacterial serology. The Widal test specifically targets Salmonella antibodies.

Watch out

The Widal test can give false positives in endemic areas (due to prior exposure or vaccination) and false negatives early in infection (before antibody levels rise). Blood culture remains the gold standard for definitive diagnosis, but Widal is the most widely used serological test in clinical practice and exams.

✓Final answer

The correct option is (B) Widal .

Same / Similar Concept — real previous-year questions on the same or a closely similar concept, not this exact question.

Showing the 12 most recent of 23 on this concept.

CBSE 2026Set ANNUAL1 mark
$Q. Fill in the blank: Virus infected cells secrete proteins are called ______.$
›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 of the virus. Interferons are an important part of the body's innate (non-specific) defence against viruses.

✓Final answer
$Interferons.$
CBSE 2026Set ANNUAL1 markMCQ
$Q. Haemozoin is released as a result of -$
(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 toxic substance called haemozoin.

Haemozoin is responsible for the chill and high recurring fever (every 3–4 days) that is typical of malaria.

✓Final answer
$(B) Rupture of red blood cells.$
CBSE 2026Set ANNUAL1 mark
$Q._________ test is performed to confirm typhoid.$
›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 test, which detects rising antibody (agglutinin) levels against the typhoid bacterium in the patient's serum.

✓Final answer
$Widal test.$
CBSE 2025Set A1 mark
$Q. Write True / False: All microbes are not pathogenic.$
›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), producing antibiotics and other pharmaceuticals, treating sewage, and acting as biocontrol agents and biofertilizers. So the statement that 'all microbes are not pathogenic' is correct.

✓Final answer
$True.$
CBSE 2024Set ANNUAL1 markMCQ
$Q. Bacterial disease is$
(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 ascariasis is caused by the roundworm (nematode) Ascaris lumbricoides. Among the four options, only diphtheria is caused by a bacterium.

✓Final answer
$(a) Diphtheria.$
CBSE 2024Set ANNUAL1 markMCQ
$Q. Choose the pair of viral diseases from the following sets :$
(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 Salmonella typhi and Tuberculosis by the bacterium Mycobacterium tuberculosis — neither pair is purely viral.

✓Final answer
$(b) Common Cold, AIDS — the only pair where both diseases are viral.$
CBSE 2024Set ANNUAL1 markMCQ
$Q. Choose the incorrectly matched pair -$
(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.

Pneumonia – Diplococcus pneumoniae (also called Streptococcus pneumoniae): correct.

✓Final answer
$(iii) Cholera - E. Coli is the incorrectly matched pair.$
CBSE 2023Set ANNUAL1 markMCQ
$Q. The organism which causes disease in plants and animals is called$
(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 infected host to a new host but does not itself cause the disease. 'Insect' and 'worm' are broad taxonomic terms and not synonymous with a disease-causing agent.

✓Final answer
$(b) pathogen$
CBSE 2023Set ANNUAL1 markMCQ
$Q. Which of the following diseases is caused by a DNA Virus?$
(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.

Mumps (c) is caused by the mumps rubulavirus, also an RNA virus.

Chicken pox (d) is caused by Varicella-zoster virus (a herpesvirus), which has a double-stranded DNA genome.

✓Final answer
$(d) Chicken pox.$
CBSE 2023Set ANNUAL1 markMCQ
$Q. Food poisoning is caused by which?$
(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 Lactobacillus is a useful bacterium used in curd formation. Hence Clostridium is the food-poisoning organism among the options.

✓Final answer
$(d) Clostridium.$
CBSE 2022Set ANNUAL1 mark
$Q. Define innate immunity.$
›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) and cytokine barriers (interferons).

✓Final answer
$Innate immunity is the non-specific, inborn (present at birth) defence that provides barriers against the entry of foreign agents into the body.$
CBSE 2022Set ANNUAL1 markMCQ
$Q. Ringworm disease in humans is caused by$
(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 intense itching. They thrive in warm, moist skin folds and spread through contact with infected persons, soil or fomites (towels, clothes).

✓Final answer
$(B) a fungus.$

Q.The diagnostic test that confirms typhoid in humans is (A) ELISA (B) Widal (C) MRI (D) Amniocentesis

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