Types of STIs: Bacterial, Viral, Parasitic and Fungal (India Guide)

• STIs fall into four groups — bacterial (chlamydia, gonorrhoea, syphilis), viral (HIV, herpes, HPV, hepatitis B/C), parasitic (trichomoniasis, pubic lice, scabies) and sometimes-sexual (candidiasis, bacterial vaginosis).
• Bacterial and parasitic STIs are curable; viral STIs are usually lifelong but manageable, and many cause no symptoms at all.
• Many STIs are silent — up to 70–80% of chlamydia infections in women cause no symptoms — so screening, not waiting for symptoms, is how they are caught.
• Vaccines exist for HPV and hepatitis B; condoms, PrEP, treatment-as-prevention (U=U) and regular testing cover the rest.
• India offers free or low-cost STI care through NACO Suvidha clinics, ICTCs and ART centres at over 30,000 sites; partner treatment is essential to avoid reinfection.

Sorting STIs by the type of germ that causes them is the simplest way to make sense of a long list, because the germ type largely decides whether the infection can be cured, how it spreads, and how it is prevented.

• Bacterial STIs (chlamydia, gonorrhoea, syphilis, and others) are caused by bacteria and are almost always curable with antibiotics.
• Viral STIs (HIV, herpes, HPV, hepatitis B and C) are caused by viruses. Some clear on their own, some are controlled with daily medicine, and a few stay in the body for life but can be well managed.
• Parasitic STIs (trichomoniasis, pubic lice, scabies) are caused by tiny organisms and are curable with the right anti-parasite treatment.
• Sometimes-sexual infections (vaginal yeast infections, bacterial vaginosis) are linked to sexual activity but are not classic STIs, and are managed differently.

Bacterial STIs are the most common group worldwide and in India, and the good news is consistent: with the correct antibiotic they are curable. The catch is that they are frequently silent, so untreated infections can quietly damage the reproductive system. Partner treatment is essential for all of them to prevent reinfection.

Chlamydia (Chlamydia trachomatis) is the most common bacterial STI. It spreads through vaginal, anal and oral sex and is asymptomatic in around 70–80% of women and half of men. When symptoms appear they include abnormal discharge, pain passing urine, pain during sex, or bleeding between periods. Left untreated it can cause pelvic inflammatory disease (PID), infertility and ectopic pregnancy. Diagnosis is by a NAAT test on urine or a self-collected swab; treatment is doxycycline 100 mg twice daily for 7 days (first-line) or azithromycin 1 g single dose, with cure rates above 95%. For a deeper dive see chlamydia symptoms and treatment in India.

Gonorrhoea (Neisseria gonorrhoeae) also spreads through vaginal, anal and oral sex and can infect the cervix, urethra, rectum and throat. Many women (50–80%) have no symptoms; when present, signs include thick yellow-green discharge, painful urination, abnormal bleeding, or testicular pain in men. Throat infection is usually silent. First-line treatment is ceftriaxone 500 mg as a single injection. Antibiotic resistance in gonorrhoea is rising in India and globally — the WHO lists it as a priority pathogen — which is why a test-of-cure is recommended for throat infections. More in gonorrhoea in Indian women.

Syphilis (Treponema pallidum) unfolds in stages. It begins as a painless sore (chancre) about three weeks after exposure that heals on its own — which is why it is missed. Weeks to months later, secondary syphilis brings a rash (often on the palms and soles), fever and swollen glands. Untreated, it can lie latent for years before affecting the heart, brain and other organs, and can pass to a baby in pregnancy (congenital syphilis). It is diagnosed by blood tests (VDRL/RPR plus a treponemal confirmation) and cured with benzathine penicillin G — a single injection for early syphilis. India screens all pregnant women for syphilis to prevent congenital cases; see syphilis treatment for women in India.

HIV is the most consequential viral STI, but the picture today is very different from the 1990s. With effective antiretroviral therapy (ART), HIV is a manageable long-term condition and people on treatment can expect a near-normal lifespan and have HIV-negative children.

In India, adult HIV prevalence is about 0.2% (roughly 2.4 million people living with HIV), with higher rates in certain states and communities. HIV spreads through vaginal, anal and oral sex, blood-to-blood contact (such as shared needles) and from mother to baby — the last of which is largely preventable with maternal ART. Per-act risk varies widely: receptive anal sex carries the highest risk, oral sex the lowest.

The single most important advance is U=U — Undetectable = Untransmittable: a person on effective ART with a sustained undetectable viral load cannot pass HIV on sexually. This is the basis of treatment-as-prevention.

Testing is free at over 30,000 NACO Integrated Counselling and Testing Centres (ICTCs). A 4th-generation antigen-antibody test detects infection from about 2–6 weeks, with reliable results by 6–12 weeks; HIV RNA PCR can detect it from 10–14 days. Prevention combines condoms, PrEP — pre-exposure prophylaxis that cuts HIV risk by around 99% with consistent use, PEP (a 28-day course started within 72 hours of a high-risk exposure), and U=U. India launched a national PrEP programme in 2022, and treatment at NACO ART centres is free for life.

Herpes simplex virus (HSV) comes in two types — HSV-1 (classically cold sores, but increasingly genital through oral sex) and HSV-2 (classically genital). Both cause a lifelong infection with periodic outbreaks and quiet phases. HSV-2 affects an estimated 5–15% of the general Indian population; HSV-1 is far more common, usually acquired in childhood.

Herpes spreads through skin-to-skin contact, including during symptom-free shedding, which is why it is so common. The first outbreak is usually the worst — painful blisters and ulcers, swollen glands, fever — while later outbreaks are milder and many people have very few. There is no cure, but antivirals (acyclovir, valacyclovir, famciclovir) shorten outbreaks, and daily suppressive therapy for frequent outbreaks cuts both their frequency and the chance of passing herpes to a partner. In pregnancy, acyclovir from 36 weeks and a caesarean for active lesions protect the baby. More in genital herpes in India.

Human papillomavirus (HPV) is the most common STI of all — around 80% of sexually active people acquire some type during their lives, and most clear it within one to two years. The concern is persistent infection with high-risk types (16, 18 and others), which can cause cervical, anal, throat and other cancers; low-risk types (6, 11) cause genital warts. Cervical cancer is the second-most-common cancer in Indian women, with roughly 125,000 new cases a year — almost all preventable.

There is no medicine that cures the virus itself; instead, HPV is managed by preventing and treating the disease it causes. Vaccination is the most effective tool — Cervavac (India's own vaccine, around Rs 2,000 per dose) and Gardasil 9 protect against the cancer-causing types when given before exposure, ideally at ages 9–14. India began rolling out HPV vaccination for adolescent girls in 2024; see the HPV vaccine in India — Cervavac vs Gardasil. Alongside vaccination, regular cervical cancer screening finds and treats pre-cancer before it becomes cancer. For the full picture, see HPV types, symptoms and treatment.

Three hepatitis viruses can spread through sex, and they behave very differently.

Hepatitis B (HBV) infects the liver and is highly infectious through sex — far more so than HIV. India sits at intermediate endemicity, with an estimated 40–50 million people living with chronic HBV. Acute infection causes jaundice, fatigue and nausea; most adults recover, but about 5–10% develop chronic infection that can silently progress to cirrhosis or liver cancer over decades. The key fact is that HBV is vaccine-preventable — India has given the vaccine to all infants since 2002, and adults at risk (healthcare workers, partners of HBV-positive people, others) can have a low-cost three-dose series. Diagnosis is by HBsAg and a full hepatitis B panel; chronic cases are treated with antivirals such as tenofovir or entecavir.

Hepatitis C (HCV) also infects the liver and usually becomes chronic. It spreads mainly through blood (shared needles, unsafe medical practices), with sexual transmission less efficient than hepatitis B. Most people have no symptoms for years. There is no vaccine, but HCV is now curable — direct-acting antivirals (DAAs) clear over 95% of cases in an 8–12 week course, and India's affordable generic DAAs have made elimination a realistic national goal.

Hepatitis A (HAV) is usually a short-lived illness that does not become chronic. It spreads mainly through contaminated food and water — common in India — but also through oral-anal sexual contact. A two-dose vaccine gives lasting protection and is worth considering for those at higher risk.

Parasitic STIs are caused by tiny organisms living on or in the body, and all are curable with the right treatment.

Trichomoniasis (Trichomonas vaginalis) is one of the most common curable STIs. In women it can cause a frothy yellow-green discharge with an odour, itching, and discomfort passing urine or during sex — though it is often silent. In men it usually causes no symptoms, which is why partners keep reinfecting each other. It is diagnosed by NAAT (most accurate) or wet-mount microscopy and cured with metronidazole — a single 2 g dose or 500 mg twice daily for seven days. Avoid alcohol during and just after treatment, and treat partners together. In pregnancy it is linked to preterm birth, so it should be treated. More in trichomoniasis in Indian women.

Pubic lice ("crabs") are tiny insects that live in pubic and other coarse body hair, spread by close intimate contact. The main symptom is intense itching, worse at night, with visible lice or eggs. Treatment is permethrin 1% cream (repeated after 7–10 days), with oral ivermectin for stubborn cases; bedding and towels should be hot-washed and partners treated. See what pubic lice feel like and how to treat them.

Scabies (Sarcoptes scabiei) are microscopic mites that burrow into the skin, causing intense night-time itching and a rash with tiny burrows — often in finger webs, wrists, waistline and the genital area. It spreads through prolonged skin contact, sexual or not. Treatment is permethrin 5% cream applied head-to-toe overnight and repeated after a week, or oral ivermectin; all household contacts and partners must be treated at the same time. Itching can linger for two to four weeks after the mites are gone — that is an allergic reaction, not failed treatment.

Some common conditions are linked to sex but are not classic STIs — and treating them as STIs causes needless worry. Understanding the difference helps you respond correctly.

Vaginal yeast infections (candidiasis) affect about 75% of women at least once. They usually result from an overgrowth of yeast that normally lives in the body — triggered by antibiotics, diabetes, pregnancy or a weakened immune system — rather than from a partner. Signs are thick white "cottage-cheese" discharge with intense itching. Treatment is a topical antifungal or a single oral fluconazole 150 mg dose. If you get four or more a year, it counts as recurrent and needs a tailored plan.

Bacterial vaginosis (BV) is an imbalance of the vaginal microbiome, with a thin grey-white discharge and a fishy odour. It is associated with sexual activity, especially new or multiple partners, but is not strictly transmitted. It is treated with metronidazole or clindamycin, and recurrent BV needs a longer-term approach. Because BV and yeast infections look different from each other and from STIs, it helps to know what normal versus abnormal discharge looks like before assuming the worst.

A few other organisms sit at the edges: molluscum contagiosum (small dome-shaped skin lesions), cytomegalovirus (CMV) and certain intestinal parasites can spread sexually but are usually mild or managed outside standard STI care. The practical point is that not every genital symptom is an STI — testing tells you which is which.

India uses two broad approaches to STI care, and knowing the difference helps you ask for what you need.

Syndromic management treats based on the symptom pattern rather than a specific lab result — for example, treating "vaginal discharge" or "genital ulcer" with a standard medicine kit. NACO has used this for decades because it delivers care quickly at small clinics without advanced labs. Its limitation is that silent infections (much of chlamydia and gonorrhoea in women) are missed entirely, and newer germs like Mycoplasma genitalium aren't covered.

Etiologic (lab-based) management uses tests like NAAT to identify the exact germ, then targets treatment. It is more precise, catches silent infections and supports antibiotic stewardship, but costs more and takes longer. NACO is steadily expanding lab-based testing at Suvidha clinics, and major private labs offer comprehensive panels.

What this means for you: you can ask for lab testing rather than empirical treatment, especially if you want to know exactly what you have, have a complex history, or simply want to confirm your status. Free testing is available at NACO sites; private comprehensive STI panels typically run a few thousand rupees. A practical caution — many Indian pharmacies dispense STI antibiotics without a prescription, but this risks the wrong drug, missed co-infections, no partner notification and growing antibiotic resistance. A proper consultation is safer.

Finally, test-of-cure matters most for gonorrhoea (because of resistance) and syphilis (tracked by falling VDRL/RPR titres), while for chlamydia a re-test at 3 months mainly checks for reinfection.

No single method prevents every STI, so prevention works best as overlapping layers matched to your situation.

Vaccines are the closest thing to one-time protection: the HPV vaccine prevents most cervical and other HPV cancers and genital warts, the hepatitis B vaccine prevents HBV, and the hepatitis A vaccine prevents HAV.

Barriers reduce transmission of nearly everything. External and internal (female) condoms cut the risk of HIV, gonorrhoea, chlamydia and trichomoniasis substantially, and herpes and HPV partially. For oral sex, dental dams and condom-based barriers lower throat and genital exposure.

HIV-specific tools — PrEP for those at ongoing risk, PEP within 72 hours of a high-risk exposure, and treatment-as-prevention (U=U) — round out protection where condoms alone aren't enough.

Regular screening is the layer most people skip. Annual testing is sensible for sexually active adults under 25 or anyone with new or multiple partners, and more often for higher-risk activity. People who have oral or anal sex should specifically ask for throat and rectal testing, which standard panels often leave out. Screening catches the silent infections — which is most of them — before complications set in.

STIs don't affect everyone the same way, and a few situations deserve specific attention.

Pregnancy. Untreated STIs can cause premature birth, stillbirth and newborn infection, so India screens all pregnant women for HIV, syphilis and hepatitis B through the PPTCT programme. Some treatments change in pregnancy (for example, azithromycin instead of doxycycline for chlamydia). See STIs during pregnancy and antenatal screening in India.

Adolescents and young adults carry the highest rates of chlamydia and gonorrhoea; India's RKSK programme and Adolescent Friendly Health Clinics provide confidential services.

LGBTQ+ communities. Men who have sex with men have higher rates of HIV, throat and rectal gonorrhoea and chlamydia, and HPV-related disease, and benefit from PrEP, site-specific testing and hepatitis A/B vaccination. Women who have sex with women have lower but real risk — herpes, HPV and bacterial vaginosis can still spread.

After sexual assault, immediate care matters — HIV PEP if appropriate, emergency contraception, hepatitis B prophylaxis and preventive STI treatment, plus baseline testing and emotional support, available at One Stop (Sakhi) Centres. See what to do after non-consensual contact.

Older adults are not immune — STI rates are rising in this group, and post-menopausal changes can even raise susceptibility, so standard screening still applies to new relationships at any age.

Because so many STIs are silent, the most important rule is to test on schedule rather than wait for symptoms. That said, see a clinician promptly if any of the following apply.

• WHO — Sexually transmitted infections (STIs) fact sheet)
• National AIDS Control Organisation (NACO), India — STI/RTI services and guidelines
• WHO — HIV and AIDS fact sheet
• CDC — Sexually Transmitted Infections Treatment Guidelines
• WHO — Human papillomavirus and cervical cancer
• NHS — Sexually transmitted infections (STIs)