infectious diseases Flashcards
HIV patho
HIV enters cell through binding of viral envelope glycoprotein (GP120) to specific receptors on cell surface (CD4 - present on helper T cells, MP, monocytes, glial cells)
Conformational change in GP120
CD4 cells migrate to lymphoid tissue -> viral replication -> new virions to new T cells
Depletion or impaired function CD4 cells -> decreased immune function
Attachment -> entry -> uncoating -> reverse transcription (reverse transcriptase = error prone) -> genomic integration (integrase) -> transcription viral mRNA -> splicing of mRNA and translation into proteins (GAG) ->new virions -> budding
problems with developing an immune response in HIV
Neutralising antibodies of low magnitude
Envelope glycoprotein is poorly immunogenic
Mutation (reverse transcription = error prone) -> viral escape
reservoirs of HIV replication/sanctuary sites
CNS (glial)
Testes (genital tract)
Macrophage (long lived cell population)
Resting CD4 T cells (latently infected)
what presentations would make you think of HIV
Generalised lymphadenopathy Acute generalised rash Flu like illness/glandular fever like Prolonged herpes simplex Frequent candidiasis Molluscum contagiosum on face Odd looking mouth lesions Unexplained night sweats, weight loss Recurrent bacterial infection
CD4 and viral load aims with HIV mgmt
> 400
viral load 0
stages (pres) of HIV infection
Seroconversion/primary HIV infection: Short illness soon after infection - highest infectivity. Antibody becomes detectable in blood, antigen becomes undetectable Fever lasting >4d Aching limbs Blotchy red rash Headache Diarrhoea Mouth ulcers
Asymptomatic HIV infection:
May last several years
Progressive loss of CD4 cells
30% have generalised lymphadenopathy - nodes >1cm at 2 extra-inguinal sites for >3M
Symptomatic HIV infection:
Opportunistic infections
Certain cancers
Late stage HIV infection +/- diagnosis of AIDS: Further opportunistic infections and cancers AIDS related complex Pyrexia Night sweats Diarrhoea Weight loss +/- Oral hairy leukoplakia Oral candida Herpes zoster Herpes simplex
infections expected in HIV via system
Lung
Bact: s.pneum, h.inf, MAI, TB
Fungi: PCP, candidiasis
GI
Oral: candidiasis (retrosternal discomfort = oesophageal)
Cx diarrhoea: salmonella, shigella, c.diff
Eye
CMV retinitis
CNS
Cerebral toxoplasmosis: CT - ring shaped contrast enhancing lesion
TB meningitis
Psych
Shame, sex etc, HIV dementia
*Cancers Invasive cervical Ca - HPV Kaposi’s sarcoma - HHV8 + molluscum contagiosum Primary CNS lymphoma NHL - EBV
prevention of HIV
Circumcision Microbicidal gel (with tenofovir) Reduce vertical transmission PEP Screen blood products, needle exchange Behavioural - appropriate sex-education, condoms HAART
compliance with HIV meds
Compliance of 95% is important for good response (as about missed doses 2 missed doses make it likely that the virus will mutate significantly to evade host defences)
Barriers to compliance:
SE
Social support
Stigma of HIV
vertical transmission of HIV
risk
prevention
Risk is 25-40%, via delivery or transmission in breast milk
Give antenatal antiretroviral therapy from end of T1: use HAART or zidovudine monotherapy if VL < 6000
Measure VL every 2W from 30W
VL < 50 - consider vaginal delivery, else CS
Postnatal - infant zidovudine monotherapy for 4W + exclusive formula -> risk to <1%
viral haemorrhagic fevers who when suspect causes where from patho pres O/E ix mgmt
who
Extremely rare in the UK, but consider in returning travellers
when suspect
Consider high in DDx if unexplained pyrexia + features suggestive of: bleeding, hypovolaemia, increased vascular permeability, organ failure
Medical and public health emergency
Caused by 5 types of RNA virus
Filovirus - Ebola and Marburg virus
Flavivirus - yellow fever, Zika virus, Japanese encephalitis, tick-borne encephalitis
Etc.
where from
Ebola + Marburg spread from bats, Lassa from rats
patho
Incubation 2-21 days
Initial stage affects vascular system: flushing, conjunctival injection, petechial haemorrhage + fever + myalgia
Viraemia may be overwhelming if delayed host reaction
Central pathological process = increased vascular permeability
Later mucous membrane haemorrhage and hypovolaemia with hypotension, shock and circulatory collapse
pres Febrile illness Foreign travel or contact Exposure to rodents, bats, insects Flu-like symptoms: temperature, sore throat, headache, conjunctival injection, exhaustion, myalgia, cough, sore throat, abdo pain, nausea, vomiting
O/E
High temp, pharyngitis, oedema, maculopapular/petechial rash, hypotension, haemorrhage in mucus membranes, jaundice if hepatic involvement (Marburg/Ebola), oedema secondary to AKI
ix
FBC: leukopenia and thrombocytopenia
LFT: elevated transaminases
Coagulation screen: PTT, INR and clotting times prolonged
Evidence of DIC: D-dimer high and fibrinogen low
Specific antibody tests for viraemia e.g. RT-PCR (reverse transcriptase)
mgmt
Notify public health and proper officer (local communicable disease consultant)
Seek advice on prevention transmission
Barrier nursing and visitor restriction
Supportive management: blood volume, clotting, care of major organs
Antivirals (ribavirin) - no use for Ebola or Marburg
amoebiasis organism spread pres ix mgmt comp
organism
Entamoeba histolytica in the tropics
spread
Ingestion of cysts in faecally contaminated food and water
pres
Diarrhoea, dysentery (blood + mucus) and colitis in infants in low income countries. Abdominal tenderness and weight loss
sweating, pyrexia, pain at R hypochondrium, referred to R shoulder, cough (phrenic nerve irritation)
hepatomegaly, tenderness, pallor, basal lung signs, jaundice
ix stool-antigen PCR for E histolytica DNA serum antibody test stool microscopy x3: - Trophozoites and cysts with 4 nuclei and central karyosome, Motile amoeba Liver USS CXR
mgmt
Nitroimidazole e.g. metronidazole + luminal agent (e.g. paromomycin)
+ aspiration of abscess (unresponsive post 5 days and >5cm)
comp
Amoebic liver abscess - 90% in men 20-40 (via haematogenous dissemination) -> pleural and pericardial effusion
comp pres
Presents with RUQ pain, may not present with diarrhoea
giardiasis orgnism trans pres ix mgmt
organism Giardia lamblia (flagellated protozoan) - tropical
trans
Oral ingestion of cysts via faeco-oral route mainly swallowing water whilst swimming, drinking tap water, eating lettuce
pres Diarrhoea (no mucus/blood) - greasy and foul smelling, frequent belching (sulfurous), abdo bloating and pain
ix
Stool microscopy (x3) - cysts and trophozoites
Stool antigen test (ELISA) - +ve for cell wall
String test (mucus examined for trophozoites)
Baseline FBC
mgmt
Metronidazole/tinidazole (antiprotozoal)
typhoid/enteric fever organism trans where in world patho pres ix mgmt comp
organism
Salmonella typhi, salmonella paratyphi
trans
Faeco-oral route via food and water. N.b. vaccination against typhoid does not prevent paratyphoid
where
Tropical areas particularly India (+ travellers) + Mexico
patho
Adhesion + invasion of gut wall.
Spread through RE system to liver spleen and bone marrow
Bacteria appears in blood and symptomatic bacteraemia ensues
pres high fever - stepwise 5-7 days, 0.5 degrees, height in afternoon dull frontal headache dry cough malaise prostration
ix FBC - mild anaemia LFT - transaminase x2/3 blood cultures - pos stool cult - pos bone marrow culture - pos
mgmt
ABX - ceftriaxone or azithromycin
Fluids
Antipyretics
comp
Chronic biliary carriage
Typhoid hepatitis
Bowel perforation
A 21-year-old man presents with a 3-day history of a continuous high fever. He reports generalised aches and pains that originate in the lower back, a headache that is more severe in the front of the head, and retro-orbital pain that gets worse with eye movement. He has a reduced appetite, but is able to tolerate liquids and reports no other significant symptoms. He lives in a suburb in the US where many cases of dengue fever have been reported recently. On examination, he has a temperature of 38.3°C (101°F), blood pressure of 110/80 mmHg, and a radial pulse rate of 92 bpm. It is noted that he has a generalised skin flush over his body that is more noticeable on his face, ears, and lips, and that blanches with finger pressure. His hands and feet are warm, and capillary refill time is <2 seconds. He is breathing normally and his tongue is a little dry.
dengue fever
