Ahmed D (Pathophysiology of STIs) Flashcards
Human Immunodeficiency Virus (HIV)
Retrovirus
- Enveloped, positive sense single-stranded RNA, reverse transcriptase
- Polyhedral capsid
- Spiked envelope
- 80-146nm
2 variants virus
- HIV1 mainly found in Europe
- HIV2 mainly found in West Africa
- 50% sequence homology
Reverse transcriptase
Normally DNA is transcribed to RNA to make proteins. Retroviruses transcribe DNA from RNA using reverse transcriptase. There are 3 steps:
- RNA-DNA hybrid made from +RNA genome using tRNA carried by virion (-ssDNA produced)
- RNA portion degraded by reverse transcriptase
- Reverse transcriptase transcribes a complementary +ssDNA strand to create dsDNA
Replication cycle (HIV)
Attaches to T helper cells
Fuses with cell
Uncoating
Reverse transcriptase
Nuclear import
Integration
Transcription
Nuclear export
Translation
Assembly
Budding
Release
Maturation
Pathogenicity of HIV
Attachment to CD4 cells (T helper cells).
Body fights the virus: HIV and cytotoxic T cells kill 100 million cells (latent phase).
Body cannot make enough CD4 cells so numbers decline over 5-10 years.
HIV virus numbers increase.
Other infections are able to invade easily as immune system is weak of opportunistic pathogens invade.
AIDS- acquired immunodeficiency syndrome.
Symptoms of HIV
From initial infection
- Fever
- Fatigue
- Weight loss
- Diarrhoea
- Body aches
Onset of AIDS indicated by rare infections:
- Kaposi’s sarcoma
- Disseminated herpes
- Toxolpasmosis
- Pneumocytis pneumonia
These infections are not lethal in other patients.
Diagnosis of HIV
From initial symptoms (often mistaken for flu).
Reduction in CD4 cells.
Serology testing for antibodies.
PCR of RNS for definitive test.
Treatment of HIV
Anti-retroviral therapy (ART)
Cocktail of 3-4 different antiviral drugs
- Nucleotide analogs
- Integrase inhibitors
- Protease inhibitors
- Reverse transcriptase inhibitors
Expensive.
Must be taken on a strict schedule.
Stops replication.
Vaccine (HIV)
Development is difficult for a number of reasons.
Vaccine needs to generate IgA and T-lymphocytes.
IgG production can be detrimental
- IgG-virus complex binds to B cells and virus remains infective
HIV is highly mutable so vaccine won’t be effective after a bit.
HIV can spread through syncytia.
HIV infects macrophages, dendritic cells, and helper T cells- cells that normally would be activate by vaccine.
Testing is ethically difficult as only humans are affected
Human Papilloma Virus (HPV) (genital warts)
Non-enveloped.
Double-stranded circular DNA virus.
HPV causes genital warts.
Most common viral STI diagnosed in the UK.
The disease is transmitted mostly through sexual contact.
Genital warts are small, rough lumps that can appear around the vagina, penis or anus.
What is the treatment for Human Papillomavirus? How can it be prevented?
No antibiotic as infection is viral. Most HPV infections do not cause problems and are cleared by the body within 2 years. Genital warts can be treated with prescription medication.
Can be prevented by getting a HPV vaccination, using condoms or avoiding direct contact.
Pubic lice
Parasitic insects found primarily in the pubic or genital hair of humans.
They are usually spread through sexual contact.
Pubic lice symptoms
Itching in the genital area.
Visible nits (lice eggs) or crawling lice
How can you treat pubic lice? How can the infection be prevented?
Main treatments are medicated creams (lotion containing 1% permethrin can be used) or shampoos that kill the lice. The treatment should be left on for a few hours and repeated a week later.
Can be prevented by avoiding sexual contact or sharing bedding/clothing/towels with an infected person.
Scabies
Sarcoptes scabiei
Arthropod- Sarcoptidae
The human itch mite
4 stages in life cycle
Scabies life cycle
Females deposit 2-3 eggs per day.
Eggs hatch in 3-4 days.
Larvae molt in 3-4- days.
Nymphs molt again in 3-4 days.
Adult females are 0.3-0.45nm long.
Males are a little over half size of females.
Once a female has been fertilised, they find their new burrow and continue to burrow for their life span of 1-2 months.
