Infectious disease 2 Flashcards

Question

what are enterotoxins?

Answer 1

Enterotoxins act on the gastrointestinal tract causing one of two patterns of illness: diarrhoeal illness vomiting illness ('food poisoning')

Answer 2

Neurotoxins act on the nerves (tetanus) or the neuromuscular junction (botulism) causing paralysis.

Answer 3

ADP ribosylates elogation factor (EF-2), resulting in inhibition, causing a 'diphtheric membrane' on tonsils caused by necrotic mucosal cells. Systemic distribution may produce necrosis of myocardial, neural and renal tissue

Answer 4

Factors which reduce vertical transmission (from 25-30% to 2%) maternal antiretroviral therapy mode of delivery (caesarean section) neonatal antiretroviral therapy infant feeding (bottle feeding)

Answer 5

vaginal delivery is recommended if viral load is less than 50 copies/ml at 36 weeks, otherwise caesarian section is recommended a zidovudine infusion should be started four hours before beginning the caesarean section

Answer 6

zidovudine is usually administered orally to the neonate if maternal viral load is <50 copies/ml. Otherwise triple ART should be used. Therapy should be continued for 4-6 weeks.

Answer 7

in the UK all women should be advised not to breast feed

Answer 8

chloroquine can be taken proguanil: folate supplementation (5mg od) should be given Malarone (atovaquone + proguanil): the BNF advises to avoid these drugs unless essential. If taken then folate supplementation should be given mefloquine: caution advised doxycycline is contraindicated

Answer 9

The most common cause is E.coli Giardiasis Cholera Shigella S.aureus campylobacter Bacillus cereus Amobiasis ## Footnote Incubation period 1-6 hrs: Staphylococcus aureus, Bacillus cereus* 12-48 hrs: Salmonella, Escherichia coli 48-72 hrs: Shigella, Campylobacter > 7 days: Giardiasis, Amoebiasis

Answer 10

Gram-positive cocci facultative anaerobes produce catalase

Answer 11

S.Aureus * Coagulase-positive * Causes skin infections (e.g. cellulitis), abscesses, osteomyelitis, toxic shock syndrome S.epidermidis * Coagulase-negative * Cause of central line infections and infective endocarditis

Answer 12

Rickettsiae are Gram-negative obligate intracellular parasites. Types of rickettsiae cause a variety of diseases that are typically characterised by fever, headache and rash. A notable exception is Q fever (cause by Coxiella burnetti which causes pneumonia but no rash. The Weil-Felix reaction is positive except in Q fever. Rickettsial diseases are all treated with tetracyclines.

Answer 13

Rickettsia ricketsii Ticks carru the disease ## Footnote Headache and fever are common Rash starts on the peripheries (wrist, ankles) before spreading centrally. It is initially maculopapular before becoming vasculitic Endemic to east coast of US

Answer 14

Coxiella burnetti ## Footnote No rash but causes pneumonia

Answer 15

Rickettsia typhi -Carried by Flaes ## Footnote Rash starts centrally then spreads to the peripheries

Answer 16

Rickettsia prowazekii - caused by human body louce

Answer 17

Diphtheria is caused by the Gram positive bacterium Corynebacterium diphtheriae Pathophysiology releases an exotoxin encoded by a β-prophage exotoxin inhibits protein synthesis by catalyzing ADP-ribosylation of elongation factor EF-2 ## Footnote Diphtheria toxin commonly causes a 'diphtheric membrane' on tonsils caused by necrotic mucosal cells. Systemic distribution may produce necrosis of myocardial, neural and renal tissue

Answer 18

Possible presentations recent visitors to Eastern Europe/Russia/Asia sore throat with a 'diphtheric membrane' - grey, pseudomembrane on the posterior pharyngeal wall bulky cervical lymphadenopathy may result in a 'bull neck' appearanace neuritis e.g. cranial nerves heart block

Answer 19

Investigations culture of throat swab: uses tellurite agar or Loeffler's media

Answer 20

intramuscular penicillin diphtheria antitoxin

Answer 21

Gram-positive bacteria will turn purple/blue following the gram staining. Microscopy will then reveal the shape, either cocci or rods.

Answer 22

Rods (bacilli) Actinomyces Bacillus antracis Clostridium Corynebacterium diphtheriae Listeria monocytogenes

Answer 23

Cocci makes catalase: Staphylococci does not make catalase: Streptococci Staphylococci makes coagulase: S. aureus does not make coagulase: S. epidermidis (novobiocin sensitive), S. saprophyticus (novobiocin resistant) Streptococci partial haemolysis (green colour on blood agar): α-haemolytic complete haemolysis (clear): β-haemolytic no haemolysis: γ-haemolytic α-haemolytic streptococci optochin sensitive: S. pneumoniae optochin resistant: Viridans streptococci β-haemolytic streptococci bacitracin sensitive: Group A: S. pyogenes bacitracin resistant: Group B: S. agalactiae

Answer 24

The most common causes of viral meningitis in adults are enteroviruses non-polio enteroviruses e.g. coxsackie virus, echovirus mumps herpes simplex virus (HSV), cytomegalovirus (CMV), herpes zoster viruses HIV measles

Answer 25

patients at the extremes of age (< 5 years and the elderly) immunocompromised, e.g. patients with renal failure, with diabetes intravenous drug users

Answer 26

common features headache evidence of neck stiffness photophobia (often milder than the photophobia experienced by a patient with bacterial meningitis) confusion fevers less common features focal neurological deficits on examination seizures: suggests a meningoencephalitis

Answer 27

whilst awaiting the results of the lumbar puncture, treatment should be supportive and if there is any question of bacterial meningitis or of encephalitis, the patient should be commenced on broad-spectrum antibiotics with CNS penetration e.g. ceftriaxone and aciclovir intravenously. This is particularly the case if the patient has risk factors e.g. elderly, immunocompromised generally speaking, viral meningitis is self-limiting, with symptoms improving over the course of 7 - 14 days and complications are rare in immunocompetent patients aciclovir may be used if the patient is suspected of having meningitis secondary to HSV

Answer 28

caused by HHV-8 (human herpes virus 8)

Answer 29

presents as purple papules or plaques on the skin or mucosa (e.g. gastrointestinal and respiratory tract) skin lesions may later ulcerate respiratory involvement may cause massive haemoptysis and pleural effusion

Answer 30

Radiotherapy and resection

Answer 31

pregnancy SLE, anti-phospholipid syndrome tuberculosis leprosy malaria HIV

Answer 32

Human Normal Immunoglobulin (HNIG) or hepatitis A vaccine may be used depending on the clinical situation

Answer 33

HBsAg positive source if the person exposed is a known responder to the HBV vaccine then a booster dose should be given if they are a non-responder (anti-HBs < 10mIU/ml 1-2 months post-immunisation) they need to have hepatitis B immune globulin (HBIG) and a booster vaccine unknown source for known responders the HBV vaccine the Green Book advises considering a booster dose of HBV vaccine for known non-responders HBIG + vaccine should be given whilst those in the process of being vaccinated should have an accelerated course of HBV vaccine

Answer 34

monthly PCR - if seroconversion then interferon +/- ribavirin

Answer 35

a combination of oral antiretrovirals (e.g. Tenofovir, emtricitabine, lopinavir and ritonavir) as soon as possible (i.e. Within 1-2 hours, but may be started up to 72 hours following exposure) for 4 weeks serological testing at 12 weeks following completion of post-exposure prophylaxis reduces risk of transmission by 80%

Answer 36

VZIG for IgG negative pregnant women/immunosuppressed

Answer 37

flu-like symptoms including fever (present in > 95% of patients) dry cough relative bradycardia confusion lymphopaenia hyponatraemia deranged liver function tests pleural effusion: seen in around 30% of patients

Answer 38

diagnositic test of choice:urinary antigen chest x-ray findings are non-specific but may include: a mid-to-lower zone predominance of patchy consolidation pleural effusions in around 30%

Answer 39

treat with erythromycin/clarithromycin

Answer 40

It typically affects alcohol-dependent individuals and those with diabetes mellitus, presenting with red currant jelly sputum and upper lobe consolidation on chest radiographs.

Answer 41

characterised by dry cough and flu-like symptoms, it predominantly affects younger patients. Further although it typically also causes consolidation that would appear bilaterally on a chest X-ray, it often involves only involves the lower zones. Some patients may also experience complications such as erythema multiforme, pericarditis or myocarditis, gastrointestinal symptoms, or bullous myringitis.

Answer 42

Dengue fever is a viral infection that can progress to viral haemorrhagic fever (other examples include yellow fever, Lassa fever, Ebola). Aetiology dengue virus is a RNA virus of the genus Flavivirus transmitted by the Aedes aegypti mosquito incubation period of 7 days

Answer 43

dengue fever: without warning signs with warning signs severe dengue (dengue haemorrhagic fever)

Answer 44

fever headache (often retro-orbital) myalgia, bone pain and arthralgia ('break-bone fever') pleuritic pain facial flushing (dengue) maculopapular rash haemorrhagic manifestations e.g. positive tourniquet test, petechiae, purpura/ecchymosis, epistaxis 'warning signs' include: abdominal pain hepatomegaly persistent vomiting clinical fluid accumulation (ascites, pleural effusion)

Answer 45

this is a form of disseminated intravascular coagulation (DIC) resulting in: thrombocytopenia spontaneous bleeding around 20-30% of these patients go on to develop dengue shock syndrome (DSS)

Answer 46

typically blood results leukopenia, thrombocytopenia, raised aminotransferases diagnostic tests serology nucleic acid amplification tests for viral RNA NS1 antigen test

Answer 47

entirely symptomatic e.g. fluid resuscitation, blood transfusion etc no antivirals are currently available

Answer 48

Prominent symptoms are severe joint pain and abrupt onset of high fever. Other symptoms include general flu-like illness of muscle ache, headache, and fatigue. The disease shares its symptoms with dengue but tends to have more joint pain which can be debilitating. A rash may develop as with other viral illness and swelling of the joints in not uncommon. Treatment: Relief of symptoms. No specific treatment. ## Footnote Alphavirus disease caused by infected mosquitoes

Answer 49

doxycycline or a macrolide (e.g. erythromycin/clarithromycin)

Answer 50

The majority of bites seen in everyday practice involve dogs and cats. These are generally polymicrobial but the most common isolated organism is **Pasteurella multocida**.

Answer 51

cleanse wound. Puncture wounds should not be sutured closed unless cosmesis is at risk current BNF recommendation is co-amoxiclav if penicillin-allergic then doxycycline + metronidazole is recommended

Answer 52

Human bites commonly cause multimicrobial infection, including both aerobic and anaerobic bacteria. Common organisms include: Streptococci spp. Staphylococcus aureus Eikenella Fusobacterium Prevotella Co-amoxiclav is recommended, as for animal bites.

Answer 53

Parvovirus B19 is a DNA virus which causes a variety of clinical presentations. It was identified in the 1980's as the cause of erythema infectiosum Erythema infectiosum (also known as fifth disease or 'slapped-cheek syndrome') ## Footnote The illness may consist of a mild feverish illness which is hardly noticeable. However, in others there is a noticeable rash which appears after a few days. The rose-red rash makes the cheeks appear bright red, hence the name 'slapped cheek syndrome'. The rash may spread to the rest of the body but unlike many other rashes, it only rarely involves the palms and soles. The child begins to feel better as the rash appears and the rash usually peaks after a week and then fades. The rash is unusual in that for some months afterwards, a warm bath, sunlight, heat or fever will trigger a recurrence of the bright red cheeks and the rash itself. Most children recover and need no specific treatment. School exclusion is unnecessary as the child is not infectious once the rash emerges. In adults, the virus may cause acute arthritis.

Answer 54

It is spread by the respiratory route and a person is infectious 3 to 5 days before the appearance of the rash. Children are no longer infectious once the rash appears and there is no specific treatment. The child need not be excluded from school as they are no longer infectious by the time the rash occurs.

Answer 55

asymptomatic pancytopaenia in immunosuppressed patients aplastic crises e.g. in sickle-cell disease parvovirus B19 suppresses erythropoiesis for about a week so aplastic anaemia is rare unless there is a chronic haemolytic anaemia hydrops fetalis

Answer 56

parvovirus B19 in pregnant women can cross the placenta in pregnant women this causes severe anaemia due to viral suppression of fetal erythropoiesis → heart failure secondary to severe anaemia → the accumulation of fluid in fetal serous cavities (e.g. ascites, pleural and pericardial effusions) **treated with intrauterine blood transfusions **

Answer 57

prodrome fever, lethargy, headache trismus (lockjaw) risus sardonicus: facial spasms opisthotonus (arched back, hyperextended neck) spasms (e.g. dysphagia)

Answer 58

Management supportive therapy including ventilatory support and muscle relaxants intramuscular human tetanus immunoglobulin for high-risk wounds (e.g. compound fractures, delayed surgical intervention, significant degree of devitalised tissue) metronidazole is now preferred to benzylpenicillin as the antibiotic of choice

Answer 59

Amoebiasis should be considered The history of abdominal pain, gradual onset bloody diarrhoea, and a long incubation period in a returning traveller is highly suggestive of amoebiasis dysentery. The causative organism for amoebiasis is Entamoeba histolytica.

Answer 60

Escherichia coli is a facultative anaerobic, lactose-fermenting, Gram negative rod which is a normal gut commensal.

Answer 61

E. coli O157:H7 is a particular strain associated with severe, haemorrhagic, watery diarrhoea. It has a high mortality rate and can be complicated by haemolytic uraemic syndrome. It is often spread by contaminated ground beef.

Answer 62

diarrhoeal illnesses UTIs neonatal meningitis

Answer 63

Live vaccines given by injection may be either given concomitantly or a minimum interval of 4 weeks apart to prevent risk of immunological interference To prevent the risk of immunological interference

Answer 64

Clostridia are gram-positive, obligate anaerobic bacilli.

Answer 65

typically seen in canned foods and honey prevents acetylcholine (ACh) release leading to flaccid paralysis

Answer 66

produces α-toxin, a lecithinase, which causes gas gangrene (myonecrosis) and haemolysis features include tender, oedematous skin with haemorrhagic blebs and bullae. Crepitus may present on palpation

Answer 67

produces an exotoxin (tetanospasmin) that prevents the release of glycine from Renshaw cells in the spinal cord causing a spastic paralysis

Answer 68

Mycobacterium marinum is one of many mycobacteria that can cause disease in humans. Fish tank granuloma typically presents in patients who have had an exposure to, or frequently work with fish.

Answer 69

It has an incubation period of 3-4 weeks and lesions can be painful or painless. A cut or break in the skin can be enough for the organism to enter the blood stream and track up the lymphatic system (sporotrichoid spread).

Answer 70

Treatment options include tetracyclines, fluoroquinolones, sulfonamides and macrolides.

Answer 71

Type of viral haemorrhagic fever (also dengue fever, Lassa fever, Ebola). Basics zoonotic infection: spread by Aedes mosquitos incubation period = 2 - 14 days

Answer 72

Features may cause mild flu-like illness lasting less than one week classic description involves sudden onset of high fever, rigors, nausea & vomiting. Bradycardia may develop. A brief remission is followed by jaundice, haematemesis, oliguria if severe jaundice, haematemesis may occur Councilman bodies (inclusion bodies) may be seen in the hepatocytes

Answer 73

Lymphogranuloma venereum (LGV) is caused by Chlamydia trachomatis serovars L1, L2 and L3*.

Answer 74

men who have sex with men the majority of patients who present in developed countries have HIV historically was seen more in the tropics

Answer 75

Typically infection comprises of three stages: stage 1: small painless pustule which later forms an ulcer stage 2: painful inguinal lymphadenopathy may occasionally form fistulating buboes stage 3: proctocolitis

Answer 76

Doxycycline

Answer 77

HIV seroconversion is symptomatic in 60-80% of patients and typically presents as a glandular fever-type illness. Increased symptomatic severity is associated with poorer long-term prognosis. It typically occurs 3-12 weeks after infection Features sore throat lymphadenopathy malaise, myalgia, arthralgia diarrhoea maculopapular rash mouth ulcers rarely meningoencephalitis

Answer 78

Plasmodium vivax, with Plasmodium ovale and Plasmodium malariae accounting for the other cases. Plasmodium vivax is often found in Central America and the Indian Subcontinent whilst Plasmodium ovale typically comes from Africa. ## Footnote Plasmodium knowlesi is another non-falciparum species which causes clinical pathology, found predominantly in South East Asia.

Answer 79

Features general features of malaria: fever, headache, splenomegaly Plasmodium vivax/ovale: cyclical fever every 48 hours. Plasmodium malariae: cyclical fever every 72 hours Plasmodium malariae: is associated with nephrotic syndrome. Ovale and vivax malaria have a hypnozoite stage and may therefore relapse following treatment.

Answer 80

in areas which are known to be chloroquine-sensitive then WHO recommend either an artemisinin-based combination therapy (ACT) or chloroquine in areas which are known to be chloroquine-resistant an ACT should be used ACTs should be avoided in pregnant women patients with ovale or vivax malaria should be given primaquine following acute treatment with chloroquine to destroy liver hypnozoites and prevent relapse

Answer 81

Cryptosporidiosis is the commonest protozoal cause of diarrhoea in the UK. Two species, Cryptosporidium hominis and Cryptosporidium parvum account for the majority cases. Cryptosporidiosis is more common in immunocompromised patients (e.g. HIV) and young children.

Answer 82

watery diarrhoea abdominal cramps fever in immunocompromised patients, the entire gastrointestinal tract may be affected resulting in complications such as sclerosing cholangitis and pancreatitis

Answer 83

stool: modified Ziehl-Neelsen stain (acid-fast stain) of the stool may reveal the characteristic red cysts of Cryptosporidium

Answer 84

is largely supportive for immunocompetent patients if the patient has HIV and is not on antiretroviral therapy then this should be started and often will be enough to resolve the infection nitazoxanide may be used for immunocompromised patients rifaximin is also sometimes used for immunocompromised patients/patients with severe disease

Answer 85

HIV antibody - enzyme-linked immunosorbent assays (ELISAs) are often used for screening HIB antibody and HIV antigen p24 antigen can be detected as early as 2-3 weeks after exposure the sensitivity of these fourth-generation tests approaches 100% for patients with chronic HIV infection now the first-line test for HIV screening of asymptomatic individuals or patients with signs and symptoms of chronic infection HIV RNA (qualitative or quantitative) - may be useful for diagnosis of neonatal HIV infection and screening blood donors ## Footnote most people develop antibodies to HIV at 4-6 weeks but 99% do by 3 months

Answer 86

Schistosomiasis, or bilharzia, is a parasitic flatworm infection. The three main species of schistosome are S. mansoni, S. japonicum and S. haematobium.

Answer 87

Acute manifestations may include: swimmers' itch acute schistosomiasis syndrome (Katayama fever) fever urticaria/angioedema arthralgia/myalgia cough diarrhoea eosinophilia

Answer 88

These worms deposit egg clusters (pseudopapillomas) in the bladder, causing inflammation. The calcification seen on x-ray is actually calcification of the egg clusters, not the bladder itself. Depending on the site of these pseudopapillomas in the bladder, they can cause an obstructive uropathy and kidney damage. This typically presents as a 'swimmer's itch' in patients who have recently returned from Africa.

Answer 89

squamous cell bladder cancer.

Answer 90

frequency haematuria bladder calcification

Answer 91

Investigation for asymptomatic patients serum schistosome antibodies are generally preferred for symptomatic patients the gold standard for diagnosis is urine or stool microscopy looking for eggs Management single oral dose of **praziquantel**

Answer 92

These worms mature in the liver and then travel through the portal system to inhabit the distal colon. Their presence in the portal system can lead to progressive hepatomegaly and splenomegaly due to portal vein congestion. These species can also lead to complications of liver cirrhosis, variceal disease and cor pulmonale.

Answer 93

Vancomycin is a glycopeptide antibiotic used in the treatment of Gram-positive infections, particularly methicillin-resistant Staphylococcus aureus (MRSA). Mechanism of action inhibits cell wall formation by binding to D-Ala-D-Ala moieties, preventing polymerization of peptidoglycans Mechanism of resistance alteration to the terminal amino acid residues of the NAM/NAG-peptide subunits (normally D-alanyl-D-alanine) to which the antibiotic binds Adverse effects nephrotoxicity ototoxicity thrombophlebitis red man syndrome; occurs on rapid infusion of vancomycin3

Answer 94

t refers to the number of distinct antigenic components or serotypes a vaccine can protect against.