Infectious Diseases Teaching Flashcards
What is the basic underlying process that leads to infective endocarditis?
Alteration of the valve surface»_space; deposition of platelets and fibrin»_space; colonisation by bacteria»_space; development of vegetation
Can occur on native or prosthetic valves
What are some risk factors for infective endocarditis?
Congenital heart disease
Rheumatic heart disease
IVDU
Mitral valve prolapse
IV devices
What are the key symptoms of infective endocarditis?
Fever
Fatigue
Myalgia
Headache
Nausea + vomiting
Rigors
Malaise
Dyspnosea
Anorexia + weight loss
What is the most common cause of infective endocarditis?
80% are due to strep or staph
What pathogens are responsible for infective endocarditis in specific scenarios?
IVDU = S. aureus
Prosthetic valve = coagulase negative staphylococci
GI/GU source = enterococci
Rare causes = HACEK, fungi
Culture negative causes = coxiella burnettii, Chlamydia sp, bartonelaa, brucella
What specific clinical findings can indicate infective endocarditis?
Roth spots - small white centered hemorrhages in the retina of the eye
Janeway lesions - palms/soles
Osler nodes - fingers/toes
Splinter Haemorrhages (brown/reddish discolouration at the edges of the nail)
What investigations are required in order to diagnose infective endocarditis?
3 sets of blood cultures and an echo
What criteria is used to diagnose infective endocarditis?
Dukes Criteria
Includes pathological elements, minor criteria, surgical criteria, imaging criteria and microbiological criteria.
What factors affect the choice of treatment for infective endocarditis?
Causative organism
Native or prosthetic valve
Patient factors - renal function + allergies.
What is the typical treatment for infective endocarditis?
4-6w IV - start empirical after blood cultures taken
May require therapeutic drug monitoring
May require early valve surgery
Follow up echo to check for complications and establish new baseline function as rarely completely irreversible.
What are the risk factors for infective endocarditis?
Age >60yrs
Male
IV drug use (right sided)
Intravascular lines
Chronic hemodialysis
Immunosuppression
Recent dental or surgical procedure - inc risk of bacteria in mouth getting into blood stream
History of prior IE
Prosthetic heart valve or other cardiac device
Structural heart disease
What is a red flag history for infective endocarditis?
New murmur
Fever
Where in the world is considered a high risk area for malaria?
Tropical areas - subsaharan africa, southern brazil, Philippines etc
30% of all cases are in Nigeria
Particularly dangerous in children under 5yrs
What is meant by premunition in the context of malaria?
In high transmission areas repeated infections lead to immune tolerance.
This is lost very quickly = high rates of serious malaria in visiting friends and relatives abroad then return to UK (65% of UK cases)
How is malaria transmitted?
Bite of infected female anopheles mosquito
Life cycle involves blood ad liver stages - blood stage is responsible for the disease.
What is the life cycle of the malaria parasite?
During a blood meal malaria infected mosquito inoculate sporozoites into human
Sporozoites infect liver cell and mature into schizonts when rupture and release merozoites.
Merozoties can persist in liver causing replases later.
Ruptured parasites invade rbcs, undergo asexual reproduction
These mature inside red blood cells - rbc now a schizonts, which can rupture releasing merozites
Some parasites differentiate into sexual gametocytes
Bitten by another mosquito which takes up gametocytes during blood meal - process repeats.
What are the symptoms of malaria?
Incubation period in most cases 7-30days.
Early symptoms - fever, chills, sweats, headaches, muscle pains, nausea and vomiting
Travel history very important
What is the cause and sign/symptoms of severe malaria?
Primarily caused by plasmodium falciparum
Confusion, coma, neurlogic focal signs, severe anaemia, resp failure
Can lead to rapid deterioration and death
What are some risk factors for severe malaria?
Age under 5yrs
Pregnancy - escp 1st and 2nd pregnancy
Travellers from low endemic areas.
What are the five different species of parasite that can cause malaria in humans?
Plasmodium falciparum - high mortality
Plasmodium ovale - latent liver stage
Plasmodium vivax - latent liver stage
Plasmodium malariae - no latent but can persist for 30yrs
Plasmodium knowlesi - only species with animal reservoir.
How can you differentiate between the different types of malaria based on their symptoms?
P. falciparium - tertian/subtertian fever - irregular
P. vivax/ovale - tertian fever
P.mamalariea - quartan fever
P. knowlesi - quotidian fever
How is malaria diagnosed?
By demonstration of parasites on blood film - thick is more sensitive, thin to determine the species.
Sent in EDTA bottle - to show conc and type of malaria parasite.
Three negative samples over three consecutive days - required to exclude malaria.
Detection of antigens using immunochromatographic tests - rapid diagnosis test.
What pathogen is the most common cause of malaria?
Plasmodium falciparum - nearly all severe malaria
Most common overall including benign malaria is plasmodium vivax.
What factors affect the potential treatment used in malaria?
Severity of illness
Species of plasmodium
Likelihood of resistance
What treatment should be given in severe malaria?
IV artesunate and notify public health
May also use Quinine dihydrochloride
What treatment options are used in non-severe malaria?
ACT
Quinine
Chloroquine
Doxycycline
P vivax and P ovale - need to treat latent liver stage to prevent relapse - primaquine
Must notify public health
How can we help prevent malaria?
Anti-malaria prophylaxis
Insectivide-treated bed nets
Long clothes and insecticides
Residual indoor spraying
Larvicidal agents
Intermittent preventative therapy
Vaccination.
What bacteria is the most common cause of TB?
Mycobacterium tuberculosis complex
What countries have a high burden of TB?
Aligns with areas of high deprivation
South Africa, nigeria, bangladehs, Indonesia, Philippines etc.
How common is TB?
25% of the worlds population have been infected with TB
5-10% lifetime risk of falling ill with TB
What are the different outcomes after infection with TB?
Clearance by immune system
Latent infection
Reactivation
Active TB
What is the relationship between HIV and TB?
HIV increased the risk of developing active TB infection
TB is the leading killer of people with HIV
How is pulmonary TB spread?
Via inhalation of droplet nuclei
What are some risk factors for TB?
Poverty and overcrowding
Homelessness/prisons
Undernutrition
Alcohol misuse
HIV
Silicosis
CKD
DM
Smoking
Immunosuppression
Mental health - delay seeking, misdiagnosis
Previous lung disease (silicosis)
Occupational (hospitals)
What are the symptoms of a TB infection?
Fever, night sweats, weight loss, malaise
Pulmonary (85%) - productive cough (initial dry prod later, 2-3w), hemoptysis
Extra-pulmonary - back pain, lymphadenopathy, meningitis, genitourinary
What is meant by miliary TB?
Disseminated haematogenous spread of TB
How is active TB diagnosed?
Sputum smear - 3 samples are considered 72% sensitive
Spututm culture - gold standard but slow, required for sensitivity testing
Sputtum PCR - GeneXpert
What two stains are used for identifying TB in sputum?
Traditional Ziehl-Neelson stain - pink rods
Auramine stain - fluorescent stain, typically green or yellow
What is the use of a sputum PCR for TB?
GeneXpert MTB/RIF
100% sensitive on smear positive sputum samples
70% sensitive is smear negative
Detects resistance to rifampicin
Quick an easy to perform
What is the use of a tuberculosis culture?
Can be very slow growing
White, dry, raised irregular cultures
Traditionally use egg based Lowenstein Jensen media
For sensitivity testing and confirmation
Isolates are sent to Birmingham Ref Lab for genotypic +/- phenotypic sensitivity testing and WGS
What is the standard treatment for drug sensitive active TB?
RIPE
Rifampicin and Isoniazid for 6 months (10 months if CNS involvement)
Pyrazinamide and ethambutol for first 2 months
What is the difference between MDR TB and XDR TB?
MDR - resistance to isoniazid and rifampicin
XDR - additional resistance to injectable second line drug and fluoroquinolone.
What signs on examination can indicate malaria?
Pallor due to anaemia
Hepatosplenomegaly
Jaundice
Link the common lifecycle of malaria to its symptoms
Each blood cycle when infected rbcs burst releatins trophozoiet = fever, chills, rigor, sweating - difference in speed of replication influences how often this process occurs
Infected RBCs passing through spleen - anaemia
Infected RBCs express adhesion molecules and cap endo have adhesion molecules = thrombosis and inc vas permeability.
What are some complications from malaria?
Splenomegaly
Hepatomegaly
Liver failure
Jaundice
Cerebral malaria
Seizures
MOF and death
Severe haemolytic anaemia
Disseminated intravascular coagulopathy.
What are some medical options for prophylaxis of malaria?
Taken before and after potential exposure if travelling to a high risk country
Proguanil with atovaquone - 2 pre, 7 post
Doxycycline - Diarrhoea and thrush, skin sensitivity for sunburn, 2d to 4w
Mefloquine - psychiatric side effects weekly, 2wpre to 4w post.
What are the main types of mycobacterium tuberculosis complex that can cause TB in humans?
Mycobacterium tuberculosis (85%)
Mycobcaterium africanum - western and central africa
“” canetti - horn of africa
“” bovis - unpasterusied milk or cattle
“” orygis - from deer, cattle
What is the key public health elements related to TB?
All mycobacterium TB complex organisms are notifiable to PHE under 2010 HPregulations
As highly infectious
Risk of drug resistance means contact tracing should occur.
Patient with active disease should be isolated - norm for 2 weeks as start of treatment.
What are the different outcomes after exposure to TB?
10-30% are infected, of which:
10% active TB
90% develop latent TB of which up to 10% can reactivate
What is the key clinical difference between active and latent TB?
Active - symptomatic, infectious, may die if left untreated
Latent - asymptomatic, non-infectious, no current effect on health. Immune system encapsulates bacteria to stop progression
What are the two main types of TB?
Pulmonary - 85% of cases, infectious - resp symptoms - can spread elsewhere
Non-pulmonary - 15% of cases, typically in immunosuppressed, Potts disease, meningitis, genitourinary, skin, lymphnodes, miliary (disseminated rash)
What is the standard treatment for drug sensitive latent TB?
Isoniazid and rifampicin for 3 months
Isioniazid for 6 months
Total treatment = 6 months.
What drug is important to remember to prescribe alongside the anti_TB medications?
Why?
Pyridoxine or VitB6
Due to isoniazid causes peripheral neuropathy - VB6 helps promote neuronal health.
How might pulmonary TB present on resp examination?
Crackles
Bronchial breath sounds
Maybe normal
What are the first line investigations for TB?
1) Tuberculine skin test - induration diamter of 10mm 48-72hrs - post - may be latent or active or vaccinated
2) IGRAs - measure immune response to TB proteins - not affected by prev vaccination
3) CXR - upper lobe infiltrates, cavitation, military pattern.
What is the gold standard for TB diagnosis?
Sputum culture - however can take up to 6 weeks for results to come in.
Allows detection of mycobacterium tuberculosis, determine drug susceptibility and strain typing.
What investigations should be done for a patient with suspected TB?
Bedside: obs, resp, spututm (3x AM - AFB, ZN and auramine staining)
Bloods: IGRAs, FBC, U&Es, LFTs, HIV test
Imaging: CXR
Other: TB skin prick test
What are some common side effects of TB treatment?
Rifampicin - red/organde discolouration of secretions - urine and tears (Red I’m pissin), COC less effective
Isoniazid - peripheral neuropathy - (I’m so numb azid)
Pyrazinamide - hyperuricemia - gout and kidney stones
Ethambutol - colour blindiess, reduced visual acuity E for eye
Rifampicin, Isoniazid and pyrazinamide are all associated with hepatotoxicity.
How can we prevent TB?
BCG vaccine
Live vaccine - mycobacterium bovis
Offered to health professionals, high risk (babies, young children and travellers to high risk or in high risk areas)
What is meant by a ghon focus, ghon complex and ranked complex in TB?
Ghon focus - granuloma with caesating necrosis centre
Ghon complex - above granuloma and lymph node involvement
Ranke complex - calcified ghon lesion and potentially lymph node.
Describe the basic physiological process underpinning TB
TB bacilli are inhaled in minority of cases an infection is established
TB is engulfed by macrophage triggering an immune response.
If not cleared TB reproduce inside macrophage and in alveolar space
Macrophages and immune cells are attracted to area forming a granuloma.
Necrosis occurs at centre of granuloma - ghon focus
If not contained within granuloma spread to local lymph nodes - ghon complex
May replicate in macro and spread from the lungs via bloodstream to other tissue (Miliary)
Some enter state of latency - where granuloma contains viable bacteria but not actively replicating so are contained = latent TB
In strong immune system, tissue undergoes fibrosis and calcification forming a Ranke complex
If weak immune system does not calcify may never become latent or become latent then reactivate.
