Viral infections

The one-sentence rule that a virus must borrow a cell becomes clearer when it is broken into named stages. First is attachment: proteins on the virion’s surface bind specific receptors on the host cell, which is why a virus infects some tissues and not others — influenza binds airway cells, HIV binds CD4 lymphocytes, hepatitis viruses bind liver cells. Second is entry, either by fusion of a fatty envelope with the cell membrane or by the cell engulfing the particle. Third is uncoating, the release of the genome from its coat. Fourth is replication and expression: the viral genome is copied and its genes are translated into viral proteins using the host’s ribosomes. Fifth is assembly, where new genomes and proteins are packaged into particles. Sixth is release, either by budding — taking a piece of the cell membrane as a new envelope, which lets the cell survive for a time — or by lysis, which destroys it. Each round of this cycle takes only hours and produces many particles from one cell, so the number of infected cells grows steeply. This framework explains three clinical facts at once. Symptoms appear after an incubation period because the virus must amplify silently first. Antivirals work best early because they interrupt a cycle that is still running. And a virus that can lie latent inside a cell — herpes viruses in nerve ganglia, HIV integrated into the host genome — can hide from both drugs and antibodies, which is why some viral infections can reactivate years later or cannot yet be cleared.

Antibiotic design exploits a simple fact: bacteria are cells, and many of their essential parts have no equivalent in human cells. A drug that blocks the bacterial cell wall or the bacterial ribosome can therefore be given at a dose that harms the bacterium but not the patient. This principle is called selective toxicity. Viruses break it, because a virus is not a cell and brings very few of its own components into the host. Almost everything it uses to replicate — ribosomes, energy, membranes, many enzymes — belongs to the patient’s own cell, so a drug aimed at those processes would poison the patient too. Antivirals must therefore find the small number of viral-specific targets: reverse transcriptase, protease and integrase in HIV; viral DNA polymerase in herpes; neuraminidase in influenza; the RNA-dependent RNA polymerase of hepatitis C. Even then, the margin between useful and toxic can be narrow, and treatment may need several drugs at once to stop the virus and to prevent resistance emerging. Viruses that integrate into the host genome are the hardest case of all, because destroying every infected cell would mean destroying the patient’s own cells. This is why antiretroviral therapy suppresses HIV but does not cure it, and why most viral illnesses are still managed by supporting the body through a self-limiting course rather than by destroying the virus with drugs. It also explains the nursing teaching point that a prescription for symptom relief is not a failure of care but the appropriate treatment for most viral illness.

The link between viral illness and antibiotic resistance is not a vague warning; it is ordinary natural selection operating inside the patient. Antibiotics kill bacteria that are susceptible and leave alive those that already carry a resistance mechanism, such as an enzyme that destroys the drug or a pump that expels it. With the susceptible competitors gone, the resistant survivors multiply rapidly and can pass their resistance genes to other bacteria — sometimes different species — on small mobile pieces of DNA called plasmids. The patient may then carry resistant organisms in the gut or on the skin without feeling ill, and those organisms can later cause a urinary, wound or bloodstream infection that is much harder to treat. Because this happens at the level of the population as well as the individual, every unnecessary prescription raises the general level of resistance. The consequences are concrete: infections that once responded to a simple antibiotic now require intravenous drugs, longer hospital stays and carry a higher risk of death. Named examples include methicillin-resistant Staphylococcus aureus (MRSA), extended-spectrum beta-lactamase (ESBL) producing gut bacteria, and Clostridioides difficile, whose overgrowth after broad-spectrum antibiotics causes severe diarrhoea. Nursing has direct levers here: never request an antibiotic for a viral illness, explain to patients why it will not help, give antibiotics only when prescribed and on time, complete a prescribed course rather than stopping early, and practise hand hygiene so resistant organisms do not travel between patients. Antimicrobial stewardship — using the right drug, at the right dose, for the right duration, only when a bacterial infection is likely — is the organised form of this discipline, and nurses are central to it.

Not all vaccines work the same way, and the difference matters for how they are stored and given. Live attenuated vaccines, such as measles, mumps, rubella and varicella, contain a weakened virus that multiplies quietly and produces a strong, long-lasting response; they are usually given in two doses and must be kept cold and used within a short time after reconstitution. Inactivated or subunit vaccines, such as the injected influenza vaccine, contain killed virus or a purified piece of it; they cannot cause the infection and are safe in pregnancy and in immunocompromised patients, but they often need repeated doses or boosters. Some vaccines in the childhood schedule are not viral at all: the tetanus vaccine is a toxoid, made from an inactivated bacterial toxin, while the HiB and pertussis vaccines are bacterial components given as conjugates or acellular preparations. They share a schedule with the viral vaccines because the child is immunised against several diseases at the same visit. When enough people in a community are immune, transmission chains break and even unvaccinated people are protected — this is herd immunity. Measles is the most contagious of the vaccine-preventable diseases, with each case able to infect roughly twelve to eighteen susceptible people, so about ninety-five per cent of a population must be immune to stop outbreaks; that is why coverage targets are set so high and why a small fall in uptake can produce a large outbreak. The practical nursing work follows from this: keep the cold chain unbroken, respect the schedule and the minimum intervals, record every dose in the child’s card and register, give the injections safely, watch the patient for fifteen minutes after vaccination, and answer hesitancy with clear explanation rather than pressure. A missed opportunity to vaccinate during any clinic visit is a lost chance at protection.