Which one of the following term characterizes the interaction between herpes simplex virus and a human?

Question

UnlockIAS · Accepted Answer

Correct — D, Endoparasitism. Begin with what this question is not: option (a), Parasitism, is not wrong. Herpes simplex virus is unquestionably a parasite — it gains, the human is harmed, and the interaction is the textbook plus-minus. Endoparasitism is a kind of parasitism, so the two options stand as a general term and a specific one, both true. The key takes the specific, and the Commission's own record shows it deciding exactly that: the provisional key marked (a) Parasitism, and the final revised key of 31 October 2025 changed the answer to (d), publishing its reason — all viruses, herpes simplex included, are obligate intracellular parasites that use the host cell's resources and cellular functions for their replication and survival, so this is one of the best examples of endoparasitism. The precision is earned. An ectoparasite lives on the host's surface — a head louse, a tick, a leech. An endoparasite lives inside the host — a roundworm in the gut, Plasmodium in the blood and liver. HSV goes further than either: it lives inside the host's individual cells. The virion is a relatively large, linear, double-stranded DNA genome sealed in an icosahedral capsid, joined by a protein tegument to a lipid envelope, and carrying at least 74 genes. It has no ribosomes, no metabolism and no way of making a single protein for itself, so replication is only possible within a living cell — its virion host shutoff protein, VHS or UL41, degrades the host's own messenger RNA and shuts down host protein synthesis so that the cell's machinery is turned over to making virus. That is precisely why bacteria and fungi grow happily on artificial media and viruses cannot be cultured on any medium at all. And the tenancy does not end with the illness. After the lytic episode the viral genome retreats into neurons and persists as circular DNA held in the nucleus as an episome — HSV-1 characteristically in the trigeminal ganglion, HSV-2 in the sacral ganglia — expressing latency-associated transcript RNA that interferes with the cell's own death programme and so preserves the reservoir for later reactivation. A lifelong residence inside the host's own nerve cells is endoparasitism in its strongest possible form.

Why the other options are wrong — (a) True, and deliberately so — this is the trap, not an error. Parasitism is the genus and endoparasitism the species, and HSV satisfies both descriptions: the virus benefits, the human is harmed. BPSC's own provisional key marked this option before the revised key moved to (d). It is not the answer because it omits the one feature that defines this particular relationship — that the parasite lives and replicates INSIDE the host's cells. The general rule to take away: where two options are both true and one is strictly more specific, mark the specific one.  (b) In the sense Indian textbooks use, symbiosis means mutualism — both partners gain. Rhizobium fixes nitrogen and the legume feeds it; zooxanthellae photosynthesise and the coral shelters them; in a lichen the fungus supplies structure and the alga supplies food. The human gains nothing whatever from herpes simplex. One honest caveat: Anton de Bary, who coined the word in 1879, defined symbiosis broadly as the living together of unlike organisms, which would technically embrace parasitism — but Indian prelims papers use the narrow mutualistic sense throughout.  (c) The most seductive distractor, because it supplies the right location and the wrong sign. Endosymbiosis means one organism living inside another to MUTUAL benefit: Rhizobium inside root nodules, zooxanthellae inside coral polyps, cellulose-digesting flagellates inside the termite gut, and above all Lynn Margulis's 1967 endosymbiotic theory that mitochondria and chloroplasts descend from bacteria engulfed and retained to the host's advantage. HSV is indeed inside the cell, but the human derives no benefit at all, so the 'symbiosis' half of the word fails.

Concept: Ecology labels every interaction between two species by the sign of its effect on each partner. Mutualism is plus-plus, commensalism plus-zero, amensalism minus-zero, competition minus-minus, and both predation and parasitism are plus-minus. Predation and parasitism are separated by what happens next: a predator kills its prey immediately and lives outside it, while a parasite feeds on a living host over time and usually does not kill it, because a dead host is a lost habitat — a parasitoid, which does eventually kill, sits between the two. Parasites are then sorted by location — ectoparasites on the surface, endoparasites within — and by dependence, obligate parasites being unable to complete their life cycle without a host while facultative ones can live free. Viruses are the extreme case on every axis. They are acellular, have no ribosomes and no metabolism of their own, and are inert outside a host, which is why they sit on the boundary of the living and the non-living. Indian textbooks trace that discovery through D. J. Ivanowsky, who in 1892 showed that the agent of tobacco mosaic disease passed through filters that stopped bacteria; M. W. Beijerinck, who in 1898 called the infectious sap contagium vivum fluidum; and W. M. Stanley, who in 1935 crystallised the tobacco mosaic virus. Every virus is therefore an obligate intracellular parasite by definition, and herpes simplex is simply the version of that fact the examiner chose to name.

State PCS 2025 Q140 — Science & Technology PYQ with Answer

State PCS 2025 Q140 — Science & Technology PYQ with Answer