Applied Biology (Zoology): transplantation, IVF, amniocentesis, transgenic animals, poultry and fish farming, microbial diseases, immunology, applied microbiology

Causative agent: Salmonella typhi (a Gram-negative, rod-shaped bacterium). [1]

Mode of transmission: [2]

• It spreads through the faecal–oral route, i.e. by consuming food or water contaminated with the faeces or urine of an infected person (or a carrier).
• Houseflies, contaminated hands, and poor sanitation help transfer the bacteria from sewage to food and drinking water.
• The bacteria enter the body through the mouth and reach the intestine.

Symptoms: [2]

• High fever (step-ladder pattern, rising gradually over days), often with headache and body ache.
• Weakness, fatigue and loss of appetite.
• Constipation, or diarrhoea in some cases.
• Abdominal pain and discomfort.
• In severe cases, the fever stays high for weeks and may be accompanied by a rash of small red spots on the trunk.

Preventive measures: [2]

• Drink safe, boiled or chlorinated water; eat freshly cooked, covered food.
• Maintain personal hygiene — wash hands with soap before eating and after using the toilet.
• Proper disposal of human excreta and sewage; keep surroundings clean to control flies.
• Avoid eating cut fruits and uncovered street food.
• Isolate and treat patients properly; carriers should not handle food.
• Vaccination (typhoid vaccine) gives protection.

Body organ affected in severe cases: The small intestine (specifically the Peyer's patches of the ileum) — it may ulcerate and even perforate, which is the most serious complication. [1]

Pulmonary tuberculosis (TB) — 8 marks

Causative agent Mycobacterium tuberculosis (a rod-shaped, acid-fast bacterium, discovered by Robert Koch in 1882). The bovine type M. bovis may also cause it.

Mode of transmission

• Airborne droplet infection — the bacilli are expelled as tiny droplets (droplet nuclei) when a patient coughs, sneezes, speaks or spits. These droplets remain suspended in air and are inhaled by a healthy person, reaching the lungs.
• Rarely by ingestion of raw/unboiled milk of an infected cow (M. bovis), or by using articles contaminated with the patient's sputum.

Symptoms

• Persistent cough lasting more than two weeks, at first dry and later with blood-stained sputum (haemoptysis).
• Low-grade evening fever, night sweats, and loss of body weight and appetite.
• Chest pain, breathlessness on exertion, hoarseness of voice.
• General weakness, fatigue and anaemia; in advanced cases, cavitation of the lung tissue.

Strategies for prevention

1. BCG vaccination of infants (at birth) gives protection against severe forms of TB.
2. Early detection and complete treatment — cases are detected by sputum microscopy, chest X-ray and the Mantoux (tuberculin) test, and cured by DOTS (Directly Observed Treatment, Short-course) using drugs such as isoniazid, rifampicin, pyrazinamide and ethambutol for 6–9 months. Completing the full course prevents relapse and drug resistance (MDR-TB).
3. Isolation and disinfection — the patient should cover the mouth while coughing, use a separate handkerchief, and avoid spitting in public places; sputum should be disinfected (e.g. with 5% phenol) and rooms kept well ventilated and sunlit.
4. Protection of contacts — screening and chemoprophylaxis (isoniazid) for family members and close contacts.
5. General measures — pasteurisation/boiling of milk, balanced nutritious diet, good housing with proper ventilation, avoidance of overcrowding, and health education.
6. Public health measures — National TB Control Programme (Nepal: National Tuberculosis Programme under the "End TB" strategy), notification of cases, and raising community awareness.

Why it is called the "disease of poverty" TB is closely linked with poverty and poor living conditions:

• It spreads easily in overcrowded, ill-ventilated slums and poor housing, where droplet infection passes readily from person to person.
• Malnutrition and under-nourishment lower body resistance, so poor people who cannot afford a balanced diet are more susceptible.
• Lack of education and awareness, poor hygiene, and ignorance about completing the long treatment course lead to spread and drug resistance.
• Cost of diagnosis and treatment and loss of wages during the long illness push families further into poverty, and poor people often delay seeking treatment.
• It is thus both a consequence and a cause of poverty, which is why it is called a disease of poverty.

In-vitro fertilization (IVF)

Definition: In-vitro fertilization is an assisted reproductive technique in which an ovum is fertilised by a sperm outside the body, in a laboratory dish (in vitro = "in glass"), and the resulting embryo is then placed in the uterus. The baby is popularly called a test-tube baby (the first was Louise Brown, 1978).

Process:

1. Ovulation induction: hormones such as FSH and LH (or clomiphene citrate) are given to the woman so that several follicles mature.
2. Collection of ova: mature ova are removed from the follicles by a fine needle guided by ultrasound (follicular aspiration), about 34-36 hours after the final hormone injection.
3. Collection of sperm: semen from the husband (or a donor) is washed and concentrated to get active, motile sperm.
4. Fertilization: ova and sperm are placed together in a nutrient medium in a dish (or one sperm is injected into the ovum in ICSI). Fertilization occurs within hours, forming a zygote.
5. Incubation and cleavage: the zygote is kept at body temperature for 2-5 days. It divides to form a multicellular embryo (about 8-16 cell stage or morula by day 3, blastocyst by day 5).
6. Embryo transfer: one or more healthy embryos are placed into the uterus through the cervix with a thin catheter, where implantation takes place.
7. Pregnancy: if implantation succeeds, pregnancy continues normally and the baby is delivered after the usual gestation period.

IVF helps couples who cannot conceive naturally because of blocked fallopian tubes, low sperm count or other causes of infertility.

(c) Hepatitis B

The hepatitis B vaccine is produced by recombinant DNA technology: the gene for the hepatitis B surface antigen (HBsAg) is inserted into yeast cells, which then produce only that purified antigen. Since it contains no live or whole pathogen, it gives immunity with far fewer adverse reactions.

Advantages of organ transplantation

1. Saves life in end-stage organ failure: For patients with irreversible failure of kidney, liver, heart or lungs, transplantation is the only curative option. A kidney transplant, for example, frees a patient from lifelong dialysis.
2. Restores normal function and quality of life: The recipient can return to work, studies and normal physical activity, with better stamina and a longer, more productive life than on supportive therapy.
3. Cost-effective in the long run: Though the operation is expensive, lifelong dialysis costs more than a one-time transplant with immunosuppressive drugs.
4. Corrects inherited and metabolic defects: Bone marrow transplantation cures conditions like thalassaemia, aplastic anaemia and severe combined immunodeficiency; corneal grafting restores sight in corneal opacity.

Disadvantages of organ transplantation

1. Immune rejection: The recipient's immune system recognises the graft as foreign. This causes hyperacute, acute or chronic rejection, so the graft may fail unless the donor is closely matched (usually a close blood relative) and immunosuppressants are given.
2. Lifelong immunosuppression and its side effects: Continuous use of drugs such as cyclosporin A and steroids makes the patient prone to infections, and may cause kidney damage, hypertension, diabetes and cancers.
3. Shortage of donors and ethical–legal problems: The demand for organs far exceeds supply. This encourages organ trade, commercial dealing and illegal removal of organs, which raises serious ethical and legal issues.
4. Surgical risks and cost: Major surgery carries risks of bleeding, infection and anaesthetic complications, and the high cost of the operation and follow-up treatment is unaffordable for many patients.
5. Graft-versus-host disease: In bone marrow transplants, the donor immune cells may attack the recipient's tissues, which can be fatal.

Candidiasis (Moniliasis)

Causative agent (1 mark) Candida albicans, a dimorphic fungus that is a normal commensal of the mouth, throat, gut and vagina. It becomes pathogenic when host immunity falls or the normal flora is disturbed.

Modes of transmission (2 marks)

• Endogenous (auto-infection): overgrowth of Candida already present in the body, the commonest route.
• Direct contact: sexual contact with an infected person; oral–genital contact.
• Mother to baby: passage through an infected birth canal during delivery, causing oral thrush in the newborn.
• Indirect: sharing towels, undergarments, or contact with contaminated fomites and hospital surfaces.
• Iatrogenic: contaminated catheters, IV lines, dentures and surgical instruments.

Symptoms (2 marks)

• Oral thrush: creamy white, curd-like patches on the tongue, gums and inner cheeks, which bleed when scraped, with soreness and difficulty in swallowing.
• Vaginal candidiasis: thick white discharge, intense itching and burning in the vulva and vagina, pain during urination and intercourse.
• Cutaneous candidiasis: red, itchy, moist patches with satellite lesions in skin folds (armpits, groin, under breasts, diaper area) and around nails (paronychia).
• Systemic/invasive candidiasis: fever, chills, fatigue, muscle pain, low blood pressure and organ dysfunction when the fungus enters the blood, seen in severely immunocompromised patients.

Preventive measures (1 mark) Maintain good personal hygiene and keep skin folds dry; treat underlying diabetes and other diseases; avoid unnecessary and prolonged antibiotics, steroids and immunosuppressants; use clean, sterile catheters and dentures; and take antifungal prophylaxis in high-risk immunocompromised patients.

Why candidiasis is common in diabetic patients (2 marks)

• High blood glucose: hyperglycaemia provides abundant glucose for fungal growth and favours the yeast (budding) form of Candida albicans.
• Impaired immunity: diabetes reduces neutrophil chemotaxis and phagocytic activity, so the fungus is not effectively killed.
• Reduced saliva and altered pH: dry mouth and acidic pH in uncontrolled diabetes favour colonization of the oral mucosa.
• Glycosuria: sugar in urine and vaginal secretions promotes growth in the urogenital tract.
• Frequent antibiotic and catheter use: diabetics often receive antibiotics and have urinary catheters, which disturb normal flora and give the fungus a chance to invade.

(a) Cornea transplant

The cornea is an avascular (blood-vessel-free) tissue, so antibodies and lymphocytes of the recipient's immune system cannot reach the grafted tissue easily. Hence corneal transplants usually survive without rejection, unlike kidney, lung or skin grafts which are well vascularised.

(a) Typhoid and cholera

Both are bacterial diseases spread by the faecal–oral route through contaminated food and water (typhoid by Salmonella typhi, cholera by Vibrio cholerae). TB spreads through air, and candidiasis is not water-borne.

Two indigenous fish species: Rohu (Labeo rohita) and Naini (Labeo nandina). Other acceptable indigenous species include Sahar (Tor putitora), Bachuwa (Eutropiichthys vacha), and Mrigal (Cirrhinus mrigala).

Integrated fish farming is the practice of raising fish together with crops and/or livestock (poultry, duck, pig, cattle) on the same farm, so that the wastes of one component become the input of another. It is advantageous over traditional (pond-only) fish farming in the following ways:

1. Higher fish yield per unit area: The pond receives a continuous supply of organic manure from the livestock or crop residues, which promotes the growth of natural fish food (plankton), so more fish can be stocked and harvested from the same pond.
2. Reduced feed cost: Poultry droppings, duck excreta, pig dung, and crop by-products feed the pond directly or through plankton production, so expensive supplementary feed is needed in much smaller amounts.
3. No waste, full recycling of nutrients: Wastes that would otherwise pollute the environment are converted into fish biomass, so energy and nutrients are used efficiently and the farm becomes almost self-sustaining.
4. Additional income and balanced production: The farmer gets fish along with eggs, meat, milk, or vegetables from the same land, giving regular income throughout the year and reducing the risk of loss from a single enterprise.
5. Better use of land, water, and labour: The same pond water is used for irrigation of crops, pond silt is used as fertilizer for fields, and family labour is shared among the enterprises, lowering the overall cost of production.
6. Improved pond environment: Controlled addition of organic manure keeps the pond fertile and productive, and integration with crops helps maintain water quality better than intensive pond-only culture.

Thus, integrated fish farming gives more production, more profit, and less waste from the same resources, and is therefore more sustainable than traditional fish farming.

(a) Sedative – Diazepam

Diazepam (Valium) is a benzodiazepine that acts as a sedative (depressant of the CNS). The other pairs are wrong: caffeine is a stimulant, morphine is a narcotic analgesic (depressant), and barbiturates are synthetic, not natural, drugs.

Sexing in poultry farming is the practice of determining the sex of day-old chicks so that males and females can be separated and reared for different purposes. It is done by examining features such as the shape and size of the vent, feather growth pattern, or by using sex-linked genetic markers.

How poultry farming helps to uplift the economy of a nation:

1. Employment generation: Poultry farming provides direct employment to farmers, farm workers, and hatchery staff, and indirect employment in feed mills, transport, and marketing, thus reducing unemployment.

2. Source of income and poverty reduction: It gives quick and regular income to farmers, including small and marginal farmers and women, because birds mature fast and eggs are produced daily. This raises the living standard of rural people.

3. Nutritious food at low cost: Eggs and chicken meat are cheap sources of high-quality protein. This improves public health and nutrition, reducing malnutrition and the disease burden on the nation.

4. Growth of allied industries: It supports allied agro-industries such as poultry feed production, poultry equipment, vaccines and medicines, and cold storage, which adds to the gross domestic product (GDP).

5. Foreign exchange earning: Export of eggs, broilers, and processed poultry products earns foreign currency, which strengthens the national economy.

6. Efficient use of resources: Poultry birds convert agricultural by-products and kitchen wastes into valuable protein, and require less land and capital than large livestock, so even landless and small farmers can take it up.

In this way, poultry farming creates jobs, supplies cheap protein, supports related industries, and earns foreign exchange, all of which contribute to the economic development of the nation.

Candidiasis (Candidosis / Moniliasis)

Causative agent [1] Candida albicans, a dimorphic fungus that exists as both yeast and pseudohyphae. It is a normal commensal of the mouth, throat, gut and vagina, and becomes pathogenic when the host's immunity or normal flora is disturbed.

Mode of infection [2]

• Endogenous infection: Overgrowth of Candida already present in the body, which is the usual route. It occurs when normal bacterial flora are destroyed (prolonged broad-spectrum antibiotics), immunity is lowered (AIDS, diabetes, cancer, corticosteroid or immunosuppressive therapy), or the mucosa is damaged (dentures, catheters, pregnancy, oral contraceptives).
• Exogenous infection: Direct contact with infected persons or articles, e.g. oral thrush in infants from an infected birth canal or feeding bottles; sexual contact in adults.
• Nosocomial spread: Through contaminated catheters, IV lines and hospital instruments in immunocompromised patients.

Symptoms [3]

• Oral thrush: Creamy white, curd-like patches on the tongue, gums and inner cheeks that leave a red, bleeding surface when scraped; soreness, difficulty in eating and a cottony feeling in the mouth.
• Vaginal candidiasis: Thick white vaginal discharge, intense itching and burning, painful urination and pain during intercourse.
• Cutaneous candidiasis: Red, itchy, moist rashes in skin folds (groin, armpits, under breasts, between fingers), often with satellite pustules.
• Systemic (invasive) candidiasis: Fever, chills, fatigue and infection of the blood (candidemia), heart valves, kidneys or brain; this is serious and may be fatal in immunocompromised patients.

Control measures [2]

• Maintain personal and oral hygiene; clean and disinfect feeding bottles and dentures.
• Avoid unnecessary and prolonged use of broad-spectrum antibiotics, corticosteroids and immunosuppressive drugs.
• Control underlying diseases such as diabetes and HIV/AIDS.
• Keep skin folds clean and dry; change catheters and IV lines regularly.
• Treat with antifungal drugs — nystatin or clotrimazole (local), fluconazole or amphotericin B (systemic).
• Avoid sexual contact with an infected partner until cured.

Pullets are young female chickens (hens) that have not yet started laying eggs. They are usually reared from about the time they leave the brooder stage until they reach sexual maturity and begin egg production, generally around 18–20 weeks of age. Pullets are reared separately from cockerels and laying hens so that they can be given proper nutrition and management for healthy growth before entering the laying flock.

Scope of poultry in Nepal:

1. Source of protein and nutrition: Poultry provides cheap, high-quality animal protein through eggs and chicken meat. It helps meet the protein deficiency in the average Nepali diet and is acceptable to almost all communities, as there is no major religious restriction on poultry consumption.

2. Employment and income generation: Poultry farming is a source of self-employment and cash income, especially for small and marginal farmers, women, and youth. It requires low initial investment and can be started on a small scale, so it is suitable for rural households as a supplementary income source.

3. Poverty alleviation and women's empowerment: Backyard and commercial poultry raising is promoted by the government and NGOs as a tool for poverty reduction. Women can manage small flocks at home, which gives them income and decision-making power.

4. Availability of local resources and suitable climate: Nepal has local breeds such as Sakini, Ghanti Khuile, and Pwankh Ulte, and agro-byproducts like maize, rice bran, and mustard cake can be used as feed. The climate in many hill and Terai areas is suitable for poultry rearing.

5. Growing market demand: With rising urbanization and population, the demand for eggs and chicken meat is increasing every year. This creates a ready market for poultry products and encourages commercial poultry enterprises.

6. Government and organizational support: The Ministry of Agriculture and Livestock Development, Nepal Agricultural Research Council (NARC), and various projects provide improved breeds, vaccines, training, credit, and extension services to poultry farmers.

7. Limitations to be addressed: Despite good scope, poultry in Nepal faces problems such as disease outbreaks (e.g., Newcastle disease, avian influenza), high feed cost, lack of quality chicks, weak marketing and cold storage, and inadequate veterinary services. Addressing these would further expand the scope of poultry in Nepal.

(d) Isograft

An isograft is a graft between two genetically identical individuals (e.g. identical twins or members of the same inbred strain). An autograft is from one part of the body to another in the same individual, an allograft is between genetically different members of the same species, and a heterograft (xenograft) is between different species.

Cholera as an acute diarrhoeal disease

Cholera is an acute diarrhoeal disease of the small intestine caused by the bacterium Vibrio cholerae. It is characterised by profuse, painless, watery diarrhoea ("rice-water stool"), rapid dehydration and collapse, and can kill within hours if untreated. It is endemic in many developing countries including Nepal, and occurs in epidemic form where water supply and sanitation are poor.

Causative agent
Vibrio cholerae, a Gram-negative, comma-shaped (curved), motile bacterium with a single polar flagellum. The serogroups O1 (classical and El Tor biotypes) and O139 cause epidemic cholera. The bacterium produces a powerful enterotoxin (cholera toxin) that acts on the intestinal mucosa.

Mode of transmission
It is transmitted by the faecal–oral route, mainly through:

• Drinking water contaminated with human faeces or vomitus containing the bacteria (most common).
• Eating food contaminated by flies, dirty hands or infected food handlers.
• Raw or partly cooked seafood, and vegetables irrigated with sewage water.
• Direct contact with the vomitus or stool of a patient (carriers also spread infection).

Symptoms

• Incubation period: a few hours to 5 days (usually 1–2 days).
• Sudden, profuse, painless, watery diarrhoea with a fishy odour; stool resembles rice-water (colourless, flecked with mucus).
• Repeated vomiting, often after diarrhoea.
• Rapid dehydration: sunken eyes, dry wrinkled skin, dry mouth and tongue, intense thirst, scanty or no urine.
• Muscle cramps due to loss of salts, weak pulse, low blood pressure, cold clammy skin, and finally circulatory collapse and death if untreated.

Control measures

• Purification of drinking water: boiling, chlorination, filtration; use of safe tube-well water.
• Proper sewage disposal and use of sanitary latrines; protection of water sources from contamination.
• Personal hygiene: hand washing with soap before eating and after defecation.
• Washing and cooking food properly; protecting food from flies; avoiding raw seafood.
• Isolation of patients and disinfection of their stool, vomitus and soiled articles.
• Oral rehydration therapy (ORS) and intravenous fluids to correct dehydration; antibiotics (doxycycline, tetracycline) to shorten the illness.
• Vaccination in outbreak areas and health education about hygiene and early treatment.

Fish farming (pisciculture) — steps involved

Fish farming is the controlled rearing of fish in ponds, tanks or cages for food and profit. The main steps are:

1. Selection of site and pond construction: A site with a reliable water supply, suitable soil (clay or loam that holds water) and easy market access is chosen. Ponds are dug with a proper inlet and outlet, and the bottom is made slightly sloping so that water can be drained completely when needed.

2. Preparation of the pond: The pond is drained, dried and treated with lime (to kill pathogens and pests and to correct soil pH) and then manured with organic manure (cow dung, poultry droppings) or chemical fertilizers to encourage the growth of natural fish food such as plankton.

3. Selection of fish species: Fast-growing, disease-resistant species are selected. In composite fish culture, three or six species with different feeding habits are stocked together so that food at all levels of the pond is used — for example, catla (surface feeder), rohu (column feeder) and mrigal (bottom feeder). Exotic species such as silver carp, grass carp and common carp are also used.

4. Stocking of fingerlings: Healthy fingerlings (young fish) of the right size are released into the pond at the correct density (stocking rate) so that they do not compete for food and space. The pond is stocked at the beginning of the monsoon or a suitable season.

5. Feeding and fertilization: Supplementary feed such as rice bran, oil cake, fish meal and kitchen waste is given regularly. The pond is manured from time to time to maintain the growth of natural food.

6. Water and health management: Water level, temperature, pH, oxygen and turbidity are checked regularly. Fresh water is added when needed. Ponds are inspected for diseases, predators and weed growth, and appropriate treatment is given.

7. Harvesting: When the fish reach marketable size, they are harvested by netting or by draining the pond. Partial harvesting may be done earlier so that the remaining fish grow faster.

8. Marketing and restocking: The harvested fish are graded, packed in ice and sold. The pond is then prepared again for the next crop.

Thus fish farming involves proper site selection, pond preparation, choice of suitable species, scientific stocking, feeding, health care and timely harvesting to get a good yield.

(b) Amniotic fluid

In amniocentesis, a needle is inserted through the abdominal wall of the pregnant woman into the amniotic sac under ultrasound guidance, and a small sample of amniotic fluid containing foetal cells is withdrawn. It is tested for chromosomal and genetic disorders such as Down syndrome.

Causative agent: Human Immunodeficiency Virus (HIV), a retrovirus with RNA as genetic material that attacks the helper T cells (CD4 cells).

Mode of transmission

• Unprotected sexual contact with an infected person.
• Transfusion of infected blood or blood products.
• Sharing of contaminated needles and syringes.
• From an infected mother to the child during pregnancy, birth or breastfeeding.

Symptoms

Prolonged fever, rapid weight loss, persistent diarrhoea, swollen lymph glands, night sweats, extreme tiredness, and repeated infections such as tuberculosis and pneumonia because immunity falls.

Preventive measures

• Safe sex with condoms and mutual fidelity.
• Use of tested blood and sterilised or disposable needles.
• Antiretroviral treatment for infected pregnant women.
• Education and awareness about the disease.

Why prevalent among intravenous drug users

They often share the same needles and syringes, so infected blood from one person is directly injected into the bloodstream of the next. Also, drugs reduce judgement, which leads to risky sexual behaviour.

(d) Amniocentesis

In amniocentesis, a sample of amniotic fluid containing fetal cells is withdrawn and tested for chromosomal and genetic disorders (e.g. Down syndrome). Test-tube baby and IVF are methods of assisted conception, and organ transplantation is unrelated.

(b) It may cause fetal injury and lethality

Early amniocentesis (done before 15 weeks) carries a higher risk of fetal injury, miscarriage and complications such as club foot than the standard test done at 15-20 weeks. Option (a) describes the standard (mid-trimester) amniocentesis and (c) holds for both, so (b) is the statement specific to the early test.

Poultry farming is the rearing of birds such as hens for eggs (layers) and meat (broilers). The main steps are:

1. Selection of breed: choose a high-yielding, disease-resistant breed suited to the climate, e.g. White Leghorn or Rhode Island Red for eggs and Cobb or Hubbard for meat.
2. Housing: build a well-ventilated, dry, clean shed with proper light, space per bird, nest boxes and perches. Litter such as rice husk is spread on the floor. Temperature is kept warm for chicks using brooders.
3. Feeding: supply balanced feed with proteins, carbohydrates, vitamins and minerals (starter, grower, layer or finisher ration) and clean drinking water.
4. Breeding and hatching: eggs from healthy parents are hatched by a broody hen or by incubators at about 37.5 °C for 21 days.
5. Brooding and rearing: day-old chicks are kept warm under a brooder for the first weeks and then moved to grower or layer houses.
6. Disease control: vaccinate on schedule (e.g. Ranikhet, Gumboro, fowl pox), keep sheds clean and disinfected, separate sick birds and use biosecurity.
7. Management and marketing: collect and grade eggs, cull unproductive birds, keep records and sell eggs and meat while fresh. Waste litter can be used as manure.

(c) Tuberculosis, typhoid, cholera

Tuberculosis (Mycobacterium tuberculosis), typhoid (Salmonella typhi) and cholera (Vibrio cholerae) are all bacterial. The other sets are wrong because hepatitis and influenza are viral, and candidiasis is a fungal disease.

Immunity is the ability of the body to resist or fight pathogens and their toxins and so prevent disease.

Types of immunity

• Innate (natural) immunity: present from birth and non-specific, it acts the same way against all pathogens. It includes physical barriers (skin, mucus), physiological barriers (stomach acid, saliva lysozyme, fever), cellular barriers (neutrophils, macrophages, NK cells) and cytokine barriers such as interferons.
• Acquired (adaptive) immunity: developed during life after exposure to a particular pathogen. It is specific, has memory and is carried out by B and T lymphocytes. It is of two kinds.
  • Active immunity: the body makes its own antibodies, either after infection (natural) or after vaccination (artificial). It develops slowly but lasts long.
  • Passive immunity: ready-made antibodies are given, either from mother to baby through the placenta and colostrum (natural) or by injecting antiserum such as antitetanus or antisnake venom (artificial). It acts quickly but is short-lived.