Actinomycosis

- indolent, slowly progressive infection caused by anaerobic or microaerophilic bacteria
- most commonly caused by A.israelii
- in vivo growth of actinomycetes usually results in the formation of characteristic clumps called grains or sulfur granules
- occurs most frequently at an oral, cervical or facial site as soft tissue swelling, abscess or mass lesion that is often mistaken for a neoplasm
- abdominal and pelvic actinomycosis usually follows introduction of organism through surgery or IUCD
- thoracic actinomycosis usually follows an indolent progressive course with involvement of pulmonary parenchyma and/or pleural space
- treatment: high dose IV benzylpenicillin and surgical resection/drainage

Babesiosis

- tick-borne malaria-like illness caused by parasite of genus Babesia
- Babesia microti is the cause of babesiosis in northeastern United States
- intraerythrocytic Babesia destroy the red blood cells causing hemolytic anemia and hemoglobinuria
- mild illness presents with malaise, fatigue, weakness, fever, chills, sweat, headache, myalgia, anorexia, dry cough, arthralgia and nausea
- post-splenectomy, HIV, malignancy and immunosuppression are at risk of severe illness
- symptoms are greater with higher percentage of parasitism
- diagnosed by microscopic examination of Giemsa-stained thin blood smears - round or pear-shaped organism
- asymptomatic need not be treated
- mild illness: oral atovaquone + azithromycin for 7 - 10 days
- severe illness: IV clindamycin + oral quinine for 7 - 10 days

Echinococcosis

- infection caused by larval stage of Echinococcus granulosus complex (dog tapeworm), which produce unilocular cystic lesion
- slowly enlarging echinococcal cyst generally remain asymptomatic until their expanding size or their space occupying effect in an involved organ (commonly liver and lungs) elicits symptomss
- hydatid liver disease presents with right upper quadrant pain, palpable mass in right upper quadrant or bile duct compression resulting in jaundice
- calcification is often seen on abdominal X ray and ultrasound is excellent means of demonstrating the cyst
- the most pathognomonic finding if demonstrable is that of daughter cysts within the larger cyst
- diagnostic aspiration is not usually recommended because of risk of fluid leakage resulting in either dissemination or infection or anaphylactic reaction
- treatment: Albendazole or PAIR (percutaneous aspiration, infusion of scolicidal agent and reaspiration), or pericystectomy for complicated cyst

Yersiniosis

- zoonotic infection with an enteropathogenic Yersinia species (Yersinia enterocolitica or Yersinia pseudotuberculosis)
- presents with abdominal pain and diarrhea
- can present with pseudoappendicitis (mesenteric adenitis)
- initial replication in small intestine is followed by invasion of Peyer's patches of distal ileum via M cells with onward spread to mesenteric lymph nodes
- gold standard for diagnosis is serology
- most cases of diarrhea are self limiting
- fluoroquinolone therapy is effective for bacteremia in adults

Histoplasmosis

- caused by Histoplasma capsulatum, a thermal dimorphic soil fungus
- a.k.a Darling's disease (Histoplasma discovered in 1905 by Darling)
- infection follows inhalation of microconidia. Once they reach the alveolar space, microconidia are rapidly recognised and engulfed by alveolar macrophages
- clinical spectrum of histoplasmosis ranges from asymptomatic infection (immunocompetent individuals with low level of exposure) to life threatening illness (immunocompromised - progressive disseminated histoplasmosis)
- it causes TB-like illness
- fungal culture remains the gold standard diagnostic test for histoplasmosis (Groccott stain)
- treatment is indicated for progressive disseminated histoplasmosis, chronic pulmonary histoplasmosis or symptomatic patients with acute pulmonary histoplasmosis
- drug: liposomal amphotericin B or itraconazole

Loiasis

- filarial infection caused by Loa loa (African eye worm)
- transmitted by Chrysops fly
- adult parasites live in subcutaneous tissue
- microfilariae circulate in blood with a diurnal periodocity
- subconjunctival migration of an adult worm
- Calabar swelling (localised area of angioedema and erythema developing on extremities) is thought to result from a hypersensitivity reaction to adult worm antigens
- definitive diagnosis requires the detection of microfilariae in peripheral blood or isolation of adult worm from the eye or subcutaneous biopsy
- eosinophilia suggest the diagnosis
- diethylcarbamazine (DEC) for 3 weeks

Leptospirosis

- zoonotic disease caused by spirochetes of genus Leptospira
- most important source of transmission to humans are rats, dogs, cattle and pigs
- flooding is a major risk for epidemic severe disease. Military training, outdoor athletic activities and adventure travel have led to recognised outbreaks and spradic cases of leptospirosis
- Leptospires infect humans through the mucosa or macerated, punctured or abraded skin
- incubation period averages 5-14 days
- leptospirosis is classically described as biphasic
 ~ leptospiremic phase: acute fever lasts for 3-10 days (blood culture postive up to day 4 of illness)
 ~ immune phase : fever not responsive to antibiotic but leptospires can be isolated from urine
- conjunctival suffusion, pharyngeal edema without exudate, muscle tenderness (esp calves), rash, jaundice or signs of meningism
- Weil's disease is characterised by jaundice, acute renal failure, hypotension and hemorrhage (usually pulmonary), aseptic meningitis, cholecystitis, acute abdomen and pancreatitis
- diagnosis is by serologic assay
- treatment: oral doxycycline 100mg bd for mild infection, IV penicillin G 1.5 mega unit QID for severe infection
- chemoprophylaxis: oral doxycycline 200mg once a week

West Nile Virus infection

- transmitted by Culex mosquitoes
- associated with maculopapular rash, headache, ocular pain, sore throat, nausea, vomiting and arthralgia
- occasionally causes aseptic meningitis and severe encephalitis (incidence of neurological involvement ~ 1%)
- diagnosis is initially clinical and subsequent serological confirmation
- real time PCR of CSF may identify the viral RNA
- treatment is supportive
- interferon alpha has been the only treatment which may affect the outcome in West Nile encephalitis

Aspergillosis

- caused by A.fumigatus (most common), A.flavus and A.niger
- these fungi are ubiquitous in environment and commonly found on decaying leaves and trees
- human infected by inhalation of spores
- 3 major forms

i) Allergic bronchopulmonary aspergillosis (ABPA)
- commoner among asthmatics with variable airflow obstruction
- Aspergillus grows in the wall of bronchi
- presents with wheeze, cough, fever and malaise, eventually produce proximal bronchiectasis
- type III hypersensitivity reaction
- suspect if asthma is refractory and is associated with fever, cough and grey/black sputum
- eosinophilia and IgE levels extremely high
- serum precipitins and skin prick test both positive
- abnormal chest X ray (transient pulmonary shadow)
- treatment: prednisolone 30mg daily and prolonged course of itraconazole (up to 4 months)

ii) Aspergilloma
- masses of fungal mycelia that grow in pre-existing lung cavities
- hemoptysis is common symptom
- CXR: round lesion with air halo above it
- high serum precipitins (continuing antigenic stimulation), negative skin prick test
- treatment: surgical resection, itraconazole (if unfit for resection), arterial embolisation if life threatening hemoptysis

iii) Invasive aspergillosis
- occurs in immunosuppressed
- presents with acute pneumonia, meningitis or intracerebral abscess, lytic bone lesions, granulomatous lesions in liver
- treatment: IV voriconazole or amphotericin B

Progressive multifocal leukoencephalopathy (PML)

-infection of oligodendrocytes by JC virus (a polyomavirus)
- characterised by progressive damage or inflammation of white matter at multiple locations
- occurs almost exclusively in immunosuppressed individuals
- presents with focal neurological deficits such as aphasia, hemiparesis, behavioural changes and cortical blindness.
- MRI: multifocal non enhancing lesions without mass effects
- viral PCR for JC virus
- brain biopsy (asymmetric foci of demyelination and intranuclear inclusion containing JC virus) has sensitivity of 74-92% and specificity of 92-100%
- no effective treatment but progression can be slowed by initiation of antiretroviral therapy

Trypanosomiasis

American trypanosomiasis (Chagas' disease)
- caused by T.cruzi
- spread by reduviids (triatomine bugs)
- erythematous indurated nodule (chagoma) at side of infection which may then scar
- fever, myalgia, rash, lymphadenopathy, hepatosplenomegaly, unilateral conjunctivitis, periorbital edema (Romana's sign), myocarditis, meningoencephalitis
- trypomastigotes seen or grown from blood in acute disease, serology in chronic disease
- treatment: nifurtimox, benznidazole

 

African trypanosomiasis (sleeping sickness)
- T.gambiense (slow, wasting illness), T.rhodesiense (rapidly progressive illness)
- spready by tsetse flies
- tender subcutaneous nodule (chancre) at site of infection
- 2 stages
  i) haemolymphatic
     - fever, rash, rigors, headache, hepatosplenomegaly, lymphadenopathy
     - Winterbottom's sign (posterior cervical node enlargement)
  ii) meningoencephalitic
     - convulsion, agitation, confusion,apathy, depression, ataxia, dementia, hypersomnolence, coma
- treatment: suramin, melarsoprol

 

Pneumocystis jirovecii (carinii) pneumonia

- one of the AIDS defining illness
- identified on microscopy by methenamine silver staining which shows a cystic phase of organism or Giemsa staining which demonstrates sporozoites and trophozoites with small punctate nuclei
- organism confined to alveolar space with interstitial infiltration of lymphocytes and plasma cells
- presents with high fever, dry cough, exertional dyspnea and type I respiratory failure (arterial oxygen level strikingly lower than expected from symptoms)
- CXR: diffuse bilateral alveolar and interstitial shadowing beginning in perihilar regions and spreading out in a butterfly pattern
- diagnosis can be made in 90% by staining sputum using indirect immunofluorescence with monoclonal antibodies
- prophylaxis/treated with cotrimoxazole (or pentamidine or clindamycin + primaquine if allergic)
- adjunctive steroids have been shown to reduce mortality in severe PCP

Botulism

- paralytic disease caused by neurotoxins of Clostridium botulinum
- due to inhibition of acetylcholine release at neuromuscular junction
- associated with trauma, surgery, subcutaneous heroin injection and sinusitis from intranasal cocaine abuse
- incubation period is 4-14 days
-  cranial nerves, bulbar, symmetrical paralysis (diplopia, dysarthria, dry mouth, generalised weakness)
- respiratory failure arises from airway obstruction and diaphragmatic weakness
- diagnosis confirmed by isolation of toxin from serum
- antitoxin is avaiable but risk of anaphylaxis

Immune reconstitution inflammatory syndrome (IRIS)

- occurs in people who have been profoundly immunosuppressed and begin on HAART
- as immune system recovers, patient able to mount inflammatory response to a range of pathogens
- exacerbation of symptoms with new or worsening of clinical signs
Examples
- unusual mass lesions or lymphadenopathy associated with mycobacteria
- deteriorating radiological apperance associated with TB
- inflammatory retinal lesions associated with cytomegalovirus
- deteriorating liver function in chronic hepatitis B carrier
- vigorous vesicular eruption with herpes zoster

Chancroid

- caused by Haemophilus ducreyi
- painful ulcer with necrotic base and ragged edge
- ulcer commonly on prepuce and frenulum in men; vaginal entrance and perineum in women
- inguinal lymphadenopathy that can progress to large buboes which suppurate
- diagnosis by isolating organism from swab taken from lesion and culture on chocolate based media
- treatment: azithromycin 1g orally or ceftriaxone 250mg IM or ciprofloxacin 500mg bd for 3 days

Creutzfeldt Jakob disease (CJD)

- human prion disease
- prions are glycoproteins which codes for a membrane protein
- definitive diagnosis is post mortem neuropathological examination
- tonsillar biopsy and CSF 14-3-3 (marker of rapid neuronal destruction) helps in diagnosis


New variant CJD
- young adults (mean age 29) presents with painful sensory symptoms, psychiatric symptoms, ataxia, dementia, myoclonus, upgaze paresis and chorea
- MRI : high signal on T2 weighted image in pulvinar (posterior thalamus)
- EEG normal



Sporadic CJD
- older age, shorter disease duration
- rapidly progressive dementia, cerebellar ataxia, pyramidal and extrapyramidal signs and myoclonus
- EEG : triphasic waves

Granuloma inguinale

- a.k.a donovanosis
- caused by Klebsiella granulomatis, encapsulated gram negative bacillus
- mode of transmission: sexual contact
- characteristic heaped up ulcerating lesion with prolific red granulation tissue
- rarely painful
- extension of primary infection to inguinal regions produces pseudo-bubo
- donovan bodies can be identified intracellularly in scrapings or biopsies of an ulcer
- treatment: doxycycline, bactrim or azithromycin

Diphtheria

- caused by Corynebacterium diphtheriae (Gram positive bacillus)
- produces a toxin which affects myocardium, nervous and adrenal tissues
- most common presentation is with pharyngitis
- areas of grey or white fibrinous exudate coalesce to produce a tough grey-yellow membrane that bleeds when removed (pseudomembrane)
- regional lymphadenopathy produces "bull-neck"
- cutaneous diphtheria may occur, typically ulcer is punched-out with undermined edges covered with a greyish white to brownish adherent membrane
- neuritis frequently follows bulbar distribution
- treatment: anti-toxin (risk of anaphylaxis) and benzylpenicillin 1.2gm QID for 1 week

Mucocutaneous leishmaniasis

- caused by L.b.braziliensis
- indurated or ulcerating lesions affecting mucosa or cartilage typically on lips or nose (espundia)
- diagnosis by culture of parasite or PCR
- treatment: sodium stibogluconate

Katayama fever

- acute schistosomiasis
- occurs 6 weeks to 3 months after initial infection especially by S.mansoni and S.japonicum
- snail vectors release cercariae that penetrates skin causing itchy papular rashes. Cercariae shed their tails to become schistosomules and migrate via lungs to liver.
- presents with fever, rash, myalgia, diarrhea, hepatosplenomegaly and pneumonitis
- diagnosis by serology and rectal biopsy (look for eggs)
- treatment: praziquantel