Think of your body as a police station — and pathogens as criminals trying to break in. Some criminals work alone (bacteria), some need a host cell to replicate (viruses), and some are sophisticated organisms in their own right (protozoa, fungi, worms). The job of your immune system — and of vaccines — is to recognise these criminals and neutralise them before they cause damage.
A disease is any condition that disrupts normal body function. A pathogen is the agent that causes it. Not every disease has a pathogen — diabetes or anaemia are non-communicable and have no infectious cause. But for this exam, the focus is almost entirely on communicable diseases: those that spread from person to person or through a vector (carrier).
Here is the key mental model: every communicable disease question tests one of three things —
The vector angle is where most Bihar Police Constable questions are set. Look at past papers — at least two questions every year involve "which disease is NOT spread by mosquitoes" or "which insect spreads which disease." That is the highest-yield sub-topic here.
An analogy: disease transmission vectors are like delivery services. Mosquitoes are one courier company (Flipkart), tsetse flies are another (Amazon), rat fleas are a third (Meesho). If the question asks "which delivery came via Flipkart (mosquito)?" you need to know all the Flipkart-only packages (malaria, dengue, filaria, chikungunya, Japanese encephalitis) and distinguish them from Amazon (tsetse fly — sleeping sickness) and Meesho (rat flea — plague).
Bacteria are single-celled prokaryotes. They produce disease either by directly invading tissue or by releasing toxins. Key fact: antibiotics kill bacteria. They do NOT kill viruses.
| Disease | Causative Bacterium | Transmission | |---|---|---| | Tuberculosis (TB) | Mycobacterium tuberculosis | Airborne droplets | | Cholera | Vibrio cholerae | Contaminated water/food | | Typhoid | Salmonella typhi | Contaminated water/food | | Plague | Yersinia pestis | Rat flea bite | | Leprosy (Kushtha Rog) | Mycobacterium leprae | Prolonged contact | | Tetanus | Clostridium tetani | Wound infection |
Viruses are non-cellular — they are essentially genetic material in a protein coat. They hijack the body's own cells to replicate. Antibiotics are useless against them; antiviral drugs or vaccines are used.
| Disease | Virus | Transmission | |---|---|---| | Polio | Poliovirus | Contaminated food/water (feco-oral) | | Smallpox (Chechak) | Variola virus | Direct contact/droplets | | Chickenpox (Varicella) | Varicella-zoster virus | Contact/airborne | | Dengue | Dengue virus (Flavivirus) | Aedes aegypti mosquito | | Rabies | Rabies lyssavirus | Animal bite | | Hepatitis B | Hepatitis B virus (HBV) | Blood, sexual contact | | Influenza | Influenza A/B virus | Airborne droplets |
Protozoa are single-celled eukaryotes. They are more complex than bacteria and require antiprotozoal drugs (not antibiotics in the standard sense).
| Disease | Protozoan | Vector/Transmission | |---|---|---| | Malaria | Plasmodium spp. | Female Anopheles mosquito | | Kala-azar (Leishmaniasis) | Leishmania donovani | Sandfly (Phlebotomus) | | Sleeping sickness | Trypanosoma brucei | Tsetse fly | | Amoebic dysentery | Entamoeba histolytica | Contaminated water/food |
Helminths (Worms) cause diseases like filariasis and ascariasis.
| Disease | Pathogen | Vector | |---|---|---| | Filariasis (Hathipaon) | Wuchereria bancrofti | Culex mosquito | | Ascariasis | Ascaris lumbricoides | Contaminated soil/food |
This is the single most-tested sub-topic. Memorise it in vector-groups, not disease-groups:
Mosquito-borne diseases (by mosquito species):
Non-mosquito vectors:
Active immunity: Your body makes its own antibodies after exposure to antigen (natural infection or vaccine). It is long-lasting.
Passive immunity: Pre-formed antibodies are introduced into the body (e.g., anti-rabies serum, maternal antibodies through breast milk). It is immediate but short-lived.
Key vaccines to remember:
A recurring trap: questions mix communicable diseases (spread by pathogens) with non-communicable ones. Diabetes, cancer, heart disease, hypertension — these are NOT caused by pathogens. Do not confuse a disease like malaria (communicable, protozoan) with anaemia (often nutritional, non-communicable).
Group all mosquito-borne diseases under the mnemonic MADC-F-J:
Any disease NOT in this list — Sleeping sickness, Plague, Kala-azar, Typhoid — is NOT mosquito-borne. In an elimination question, cross off these five first, and the odd one out is your answer. Standard approach (read each option, recall one by one): ~40 seconds. With MADC-FJ: scan takes ~8 seconds.
Use the split: "BacTeRia = TReatment with antibiotic" and "Virus = Vaccine or wait".
For the exam, remember the 4 common virals with the acronym PPDC — Polio, Pox (small + chicken), Dengue, COVID. Everything else in the standard list (TB, Typhoid, Cholera, Plague, Leprosy, Tetanus) is bacterial. When a question asks "which is caused by virus?" — check your PPDC list plus Rabies, Hepatitis, Influenza. Standard recall attempt: ~30 seconds of uncertainty. With PPDC: ~10 seconds firm answer.
In "which is NOT spread by X" questions, never try to remember all diseases of X. Instead, identify the clearly wrong one first.
Method: Sleeping sickness = always tsetse fly. Plague = always rat flea. Kala-azar = always sandfly. These three are the most commonly tested "NOT mosquito" diseases. If any of these appears in a mosquito-disease list, it is instantly the answer. Reduces 4-option comparison to 1-second recognition. Standard approach: 35 seconds. This method: under 10 seconds.
One fact the exam loves: smallpox is the only human infectious disease declared eradicated (1980, WHO). Polio is nearly eradicated but not fully. If a question asks "which disease has been eradicated?" — the answer is smallpox, full stop. No calculation needed. 2-second retrieval vs 20 seconds of doubt.
Remember vaccine sequence with "BCG First, DPT Next, OPV Along":
If a question asks which vaccine is given at birth, the answer is BCG. If it asks which covers three diseases in one shot, the answer is DPT. Substituting the mnemonic pattern removes all guesswork.
When you see a diseases-and-pathogens question in the exam hall, run this decision tree:
Step 1 — What is the question type?
Step 2 — Eliminate first, confirm second. In a "NOT" question, you only need to identify the correct outlier. Do not verify all four options — that wastes time.
Step 3 — Bihar-context flag. Bihar has specific public health concerns: Kala-azar (sandfly, Bihar-endemic), Japanese Encephalitis (Culex mosquito, UP-Bihar belt), and historically high TB burden. If a current-affairs angle appears, flag these three.
Total time target per question: under 25 seconds.
Why this question: This is the single most repeated question type in Bihar/UP Police GK — identifying the non-mosquito disease from a list. The trap is that all other options are legitimately mosquito-borne, which creates false confidence in the odd one out.
Solving path: Apply the MADC-FJ framework immediately. Malaria (Anopheles — yes), Filariasis (Culex — yes), Dengue (Aedes — yes). Sleeping sickness is tsetse fly — not in the list. Answer locked in under 8 seconds.
Why this question: Plague is the classic distractor because students often confuse "rat-borne" with "mosquito-borne." The rat is the reservoir host, but the rat flea (Xenopsylla cheopis) is the actual vector — and fleas are not mosquitoes.
Solving path: Filaria = Culex mosquito (yes). Dengue = Aedes mosquito (yes). Plague = rat flea (absolutely not a mosquito). "None of the above" is a distractor when a clear correct option exists. Answer: Plague. Time: 10 seconds.
Why this question: Students who memorise only disease names without their pathogen category fall for the bacteria trap here. Both Polio and Chickenpox are viral, not bacterial — this is tested repeatedly because the distinction between virus and bacteria is conceptually foundational.
Solving path: Use the PPDC mnemonic — Polio = P, Pox (small + chicken) = P. Both are in the virus column. Option 4 (विषाणुओं / virus) is correct. Eliminate bacterial option (Option 3) immediately — TB and Typhoid are bacterial, not Polio or Pox. Time: 12 seconds.
Confusing Sleeping Sickness with a mosquito disease. It is the tsetse fly, found in Africa. In every "not mosquito-borne" question it has appeared, students who are unsure pick Dengue or Filaria instead — both of which are genuinely mosquito-borne. Lock this in: tsetse fly = sleeping sickness, every single time.
Treating Plague as a mosquito disease because it is "vector-borne." Plague is vector-borne, yes — but the vector is a rat flea, not a mosquito. The word "vector" does not mean mosquito. Students conflate the two after reading vector-borne disease lists too quickly.
Calling Malaria bacterial. Malaria is caused by Plasmodium, a protozoan, not a bacterium. It cannot be treated with standard antibiotics. The treatment drug (chloroquine, artemisinin-based) is an antiprotozoal.
Assuming all skin diseases are fungal. Leprosy is bacterial (Mycobacterium leprae). Ringworm (Daad) is fungal. Chickenpox is viral. Do not lump all skin-presenting diseases into one category.
Mixing up BCG and DPT targets. BCG targets TB (tuberculosis). DPT is three-in-one for Diphtheria, Pertussis, Tetanus. Polio vaccine is separate (OPV or IPV). A question asking "which vaccine prevents TB" has one answer: BCG.
Claiming Polio is eradicated in India. India was declared polio-free in 2014, but global eradication is not complete. Only smallpox is globally eradicated (1980). If the question says "fully eradicated worldwide," the answer is smallpox — not polio.