References UK clinical guidance from the NHS, the British HIV Association (BHIVA), and the British Association for Sexual Health and HIV (BASHH). Last updated: April 2026.
A few STIs are caused by parasites — organisms that live on or inside the body. The main parasitic STIs are trichomoniasis, pubic lice (crabs) and scabies. They’re all treatable and curable. Understanding the difference from bacterial and viral STIs helps you recognise symptoms and get the right treatment.
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Main Parasitic STIs
| Parasite | Condition | Treatment |
|---|---|---|
| Trichomonas vaginalis | Trichomoniasis | Metronidazole |
| Phthirus pubis | Pubic lice (crabs) | Insecticidal lotion or cream |
| Sarcoptes scabiei | Scabies | Permethrin cream |
Trichomoniasis
- Most common curable STI globally
- Frothy yellow-green discharge, itching, burning
- Up to 50% asymptomatic
- Diagnosed by NAAT or microscopy
- Cured with metronidazole
Pubic Lice
- Tiny insects that live in coarse body hair
- Intense itching, visible lice or eggs (nits)
- Spread by close body contact
- Treated with insecticidal lotions
- Less common now due to grooming trends
Scabies
- Tiny mites that burrow into the skin
- Intensely itchy rash, especially at night
- Affects wrists, fingers, genitals, buttocks
- Spread by prolonged skin contact (not just sexual)
- Treated with permethrin cream
How They Differ From Bacterial and Viral STIs
- Parasites are organisms, not just bacteria or viruses
- All parasitic STIs are curable
- Some spread through close contact as well as sex
- Treatment targets the parasite specifically
Read more: What is trichomoniasis? | Bacterial STIs | Viral STIs
Frequently Asked Questions
Are parasitic STIs serious?
Usually not life-threatening, but uncomfortable and treatable.
Can I catch pubic lice from a toilet seat?
Extremely unlikely — they need body warmth to survive.
Is scabies only sexually transmitted?
No — any prolonged close skin contact can spread it.
Related reading
- A to Z of Sex: Sexual Health Terms Explained
- Alcohol and HIV: What You Need to Know
- Anxiety and HIV: Coping and Getting Support
- Are All STIs Curable?
- Blood Problems and HIV: Anaemia, Low Platelets and More
Sources
- NHS — Sexual health conditions
- BASHH — UK clinical guidelines for STI management
- British HIV Association (BHIVA) — HIV treatment guidelines
- Terrence Higgins Trust — sexual health information
- UK Health Security Agency — STI surveillance data
Steve Page is a recognised expert on Sexually Transmitted Diseases (STDs) and STD treatments, having published numerous articles in peer-reviewed journals and presented his research at conferences around the world. He has an in-depth understanding of the latest medical research on STDs, and is an advocate for the development of new treatments and protocols to improve the health of those affected. In addition to his research, he has dedicated his career to understanding the causes and symptoms of STDs, as well as how to best treat those impacted.
