16. Infectious Diseases Pathologies Flashcards
Infectious Pathologies
- A possible complication of an infection is sepsis (septicaemia), which occurs when the pathogen has infected the blood. It arises when the body’s response to the infection causes injury to the body’s own organs, potentially leading to multi-organ failure.
- The risk is higher in elderly populations (over 75), the very young (<1), alcoholics, diabetics, chemotherapy patients.
- Symptoms include lethargy, nausea, vomiting, abdominal pain, diarrhoea, coughing, etc.
Systemic Symptoms
•SYSTEMIC SYMPTOMS: –Fever (+ possibly chills). –Fatigue and weakness. –Headache. –Nausea.
Local Signs
–Pain and swelling.
–Redness.
–Warmth.
–Purulent exudate (bacterial).
Diagnostic Testing
- CULTURE / STAINING:
- BLOOD TESTS:
- STOOL TESTS.
- RADIOGRAPHY: (E.g. tuberculosis).
Culture /Staining
- Identification of micro-organisms.
* If required: Drug sensitivity test.
Blood Tests
- Bacterial infection: Often leukocytosis.
- Viral infection: Often leukopenia.
- High ‘erythrocyte sedimentation rate’ (ESR).
Cellulitis and Erysipelas
‘Cellulitis’ is a bacterial skin infection creating inflammation of dermal and subcutaneous layers.
‘Erysipelas’ is a more superficial bacterial skin infection of the dermis and upper subcutaneous layer, producing a well-defined edge.
•Both often co-exist, so it can be difficult to make a distinction between the two.
Cellulitis and Erysipelas: Cause
- Bacterial: Staphylococcus aureus, infections can enter the skin through minor trauma, eczema, IV drug abuse and ulcers.
- Can originate from streptococci bacteria in the subject’s own nasal passages (common in erysipelas — facial involvement).
Cellulitis and Erysipelas: Signs and Symptoms
- Very red, inflamed skin.
- Fever.
- Malaise.
Cellulitis and Erysipelas: Diagnosis
- Microbe analysis — can be difficult to detect.
* Usually diagnosed from clinical presentation.
Cellulitis and Erysipelas: Treatment
Antibiotics
Impetigo
Impetigo is a very contagious bacterial skin infection.
•Common in infants / young adults (poor hygiene / breaks in skin).
•Bacterial: Staphylococcus aureus or haemolytic streptococci.
Impetigo: Transmission
•Very contagious, spread by direct or indirect contact; e.g. towels.
Impetigo: Signs and Symptoms
- Pustules with round oozing patches and golden-yellow crusts that grow larger daily.
- Mostly affects exposed areas (hands and face) or in skin folds (particularly armpits).
Impetigo: Treatment
Antibiotics (e.g. flucloxacillin or erythromycin).
Oral Candidiasis
A superficial fungal yeast infection of mucous tissues.
Oral Candidiasis: Causes
•Mostly Candida albicans (less than 60% have candida in their
flora where it is commensal).
•Often presents after broad spectrum antibiotics or in immune compromised patients (normally skin / mucous membranes provide physical barrier with support of CD4 cells).
Oral Candidiasis: Signs and Symptoms
- White plaques.
* Can cause dysphagia and reduced appetite.
Oral Candidiasis: Complications
Can become systemic in severely immune-compromised patients (deposited on organs) ‘systemic candidiasis’.
Oral Candidiasis: Treatment
Antifungals (e.g. clotrimazole — topical or oral). These can significantly impact liver function and also damage the local skin or mucous membranes
Genital Candidiasis
A very common fungal infection (mycosis) of the genitals.
Genital Candidiasis: Triggers
- Not sex-related.
* Immune compromise, antibiotic treatment, diabetes mellitus, pregnancy, immune system disorders.
Genital Candidiasis: Signs and Symptoms
- Vaginal / genital itch, discomfort or irritation.
* Thick, clumpy discharge (‘cottage cheese’).
Genital Candidiasis: Yeast Infection
- Physical examination, fungal culture and analysis.
* Treatment as for oral candidiasis.
Lyme Disease
Lyme disease is caused by a bacterium called ‘borrelia’ which is often transmitted by tick bites.
•Different bacterial strains cause different clinical manifestations (hence differences between Europe and USA).
Lyme Disease: Signs and Symptoms
- A circular pink or red rash at the site of tick attachment that radiates from the bite, usually over 5 cm diameter.
- Flu-like symptoms. Can lead to neurological disease, cardiovascular disease and arthritis especially if untreated.
Lyme Disease: Treatment
Antibiotics
Diptheria
A highly contagious upper respiratory tract infection affecting primarily the nose and throat.
Diptheria: Cause
Bacterial: Corynebacterium diphtheriae (gram-positive), transmitted by droplets.
Diptheria: Signs and Symptoms
- Sore throat and fever.
- Grey membrane (necrosis) grows across the tonsils / pharynx or nose (impairs breathing).
- Enlarged cervical lymph nodes.
Diptheria: Diagnosis
Throat culture
Diptheria: Complications
•Exotoxins cause endothelial necrosis by inhibiting protein synthesis. Can cause myocarditis and paralyse diaphragm. The membrane can block the airways.
Diptheria: Treatment
• Medical emergency: Anti-toxins and antibiotics may be required; respirator.
• DPT vaccine introduced in 1941 (diphtheria /
tetanus / whooping cough / polio).
Scarlet Fever
An infectious disease resulting from exotoxins released by Streptococci pyogenes bacteria.
• Bacteria secrete haemolytic enzymes and exotoxins (damage capillaries which both cause red rash).
• It usually only occurs in children (90% <10yoa).
• Much less common and less serious than it once was. Full recovery is usual.
Scarlet Fever: Cause
•Bacterial: Streptococcus pyogenes (haemolytic streptococcus).
Scarlet Fever: Transmission and Incubation Period
Droplet transmission
3-4 days
Scarlet Fever: Signs and Symptoms
- Sore throat, fever, scarlet rash (blanches under pressure, unlike meningitis spots).
- Haemorrhagic spots on palate.
- First two days: white tongue with red papillae. After this, more raw / red.
Scarlet Fever: Treatment
Antibiotics (penicillin)
Cold Sores
Cold sores are caused by the herpes simplex virus (Type I).
•The virus remains dormant in the trigeminal nerve.
Cold Sores: Transmission
• Direct contact or indirect — saliva (viruses can be present in saliva for weeks after symptoms).
Cold Sores: Signs and Symptoms
- Commonly asymptomatic.
- Begins as tingling on lip as virus travels down nerve.
- Painful fluid lesions around mouth that scab then heal.
- Re-occurrence can be triggered by infection, stress, sun, etc.
Cold Sores: Complications
Spreading to the eyes
Cold Sores: Treatment
Acyclovir
Chicken Pox
Highly infectious viral disease, mostly in children (90%).
Chicken Pox: Cause
•Varicella zoster virus (part of herpes viral family).
Chicken Pox: Transmission and incubation time
- Droplets into upper respiratory tract mucosa and direct contact.
- Two–three weeks.
Chicken Pox: Signs and Symptoms
- Duration approx. two weeks: Prodromal fever and malaise.
- Vesicular eruptions on the skin appear over three–five days mostly on head / neck / trunk. Itchy.
- Infective two days before rash until all lesions at ‘crusting’.
Chicken Pox: Complications
- Infection because of scratching.
- Encephalitis.
- Viral pneumonia.
Chicken Pox: Treatment
None or acyclovir
Shingles
Infection by the Varicella zoster virus following chicken pox infection.
Shingles: Cause
- Varicella zoster virus — travels down infected nerve causing neuritis (nerve inflammation) in an immune-compromised individual.
- Commonly affects thoracic nerves or trigeminal nerve (head / face).
Shingles: Signs and Symptoms
- For one–two days before rash, burning / itching / tingling.
- Then ‘eruptive phase’, producing skin lesions similar to chicken pox, causing severe dermatomal pain, altered sensation and vesicular rash only in the affected dermatome.
Shingles: Treatment
Acyclovir
Whooping Cough
A bacterial infection with characteristic coughing attacks where there is a desperate attempt to breathe in, creating ‘whooping’.
Whooping Cough: Cause
Bordetella pertussis (bacterial).
Whooping Cough: Signs and Symptoms
- Initial one–two weeks ‘cold-like symptoms’.
- Then a cough which does not respond to usual cough medication. The cough gets worse and presents with attacks (for three–six weeks).
Whooping Cough: Complications
Pneumonia
Rib fracture
Death (esp if < 6m)
Tuberculosis
A systemic infection usually caused by pyogenic bacteria — Mycobacterium tuberculosis.
•A chronic granulomatous disease.
•When first encountered, macrophages in the lungs engulf the bacteria and carry them to the hilar lymph nodes. Some organisms can spread to distant areas.
•In 80% of cases the granulomas formed will be eliminated by the immune system. If not, the bacteria can become active immediately, later, or may remain dormant.
•Primarily affects the lungs (75%) because highly aerobic (oxygen plentiful!).
•Also affects CNS, lymph, circulation, genitourinary, bones, joints and skin.
Tuberculosis: Transmission
- Droplet, inspiration of dust, dry excretions, contaminated milk.
- Immunity of the patient plays an important role.
TB: Signs and Symptoms
Pulmonary TB: Fever, chronic cough, purulent / bloody sputum, night sweats, severe malaise. Weight loss, anorexia.
TB: Diagnosis
- Blood tests: High ESR, leukocytosis.
* X-rays and other imaging.
TB: Treatment
Antibiotics for six months! BCG vaccine.
Measles
Acute and very infectious viral disease mainly in children.
•Small outbreaks of the disease.
Measles: Cause
Measles virus
Measles: Transmission and Incubation
Droplet infection
11 days
Measles: Complications
•Middle ear infection, pneumonia, encephalitis.
Measles: Signs and Symptoms
- For three–five days: non-specific cold symptoms (cough, runny nose and red eyes, fever). ‘Koplik spots’: Small grey spots on oral mucosa opposite molar teeth.
- Eruptive phase: Measles-like rash that initially begins on face / forehead. Rash fades within one week (contagious four days before and after rash).
Measles: Treatment
No specific treatment, only symptomatic
Mumps
Acute viral infection associated with the mumps virus causing swelling of the parotid / salivary gland.
Mumps: Signs and Symptoms
- Feeling generally unwell, fever, head and joint pains, swollen parotid glands, first one then both sides.
- Pain at jaw angle.
Mumps: Complications
•After puberty about 30% of males get testicular inflammation. However, these rarely lead to sterility.
Mumps: Treatment
Self-limiting, MMR vaccine
Rubella
‘German measles’. A rare, usually harmless viral infection, that often passes unnoticed, caused by the Rubella virus.
Rubella: Signs and Symptoms
- Sore throat, fever, headache. Petechiae on hard palate.
* Pink rash with small macules that starts on face and behind ears.
Rubella: Complications
•Abnormal foetal development (birth defects) and can cause miscarriage and foetal death.
Rubella: Treatment
Self-limiting
Viral Hepatitis
An acute viral infection of the liver.
Viral Hepatitis: Cause
- Hepatitis virus (types: A, B, C, D and E).
* The most common types of hepatitis are A, B and C.
Hepatitis: Transmission
- A and E — faecal-oral
* B, C, D — blood and other bodily fluids
Hepatitis: Diagnosis
•Blood test (liver function test).
Hepatitis: Complications
•Chronic liver disease: Cirrhosis, liver cancer (85% of hep. C becomes chronic).
Hepatitis: Signs and Symptoms
- Pre-icteric stage: Malaise and diarrhoea.
- Icteric stage: Jaundice, pale stools, dark urine (hepatic stasis), pruritic skin, enlarged liver, impaired blood clotting.
Hepatitis: Treatment
- Limited: Antiviral therapy.
* Hep B vaccine in ‘vulnerable’ groups.
Poliomyelitis
Acute viral infectious disease.
•Faecal-oral transmission.
•Targets anterior horn cells of CNS (motor) and has no cure.
Poliomyelitis: Causes
Poliovirus
Poliomyelitis: Signs and Symptoms
- 90% of polio infections are asymptomatic.
- Initially: Fever, fatigue, headache, vomiting, neck stiffness.
- In 1% of cases, the virus enters the CNS and causes paralysis.
- 5–10% die from respiratory failure.
HIV
- Human immunodeficiency virus (HIV).
- An STI which attacks the immune system.
- A retrovirus — a double-strand RNA virus.
- First patient with HIV in 1981.
- Uses special enzymes — reverse transcriptase that converts RNA to DNA inside the host cell.
- Dies quickly outside of body.
- Directly transmissible.
AIDS
Acquired immune deficiency syndrome.
•Describes the later stages of HIV when the immune system is severely impaired and life-threatening, opportunistic infections occur.
•Used less often now (‘late stage’ / ‘advanced’ HIV used more often).
•Non-transmissible: develops from HIV.
HIV Pathophysiology
• HIV binds to CD4 receptors, which are found on:
- T-helper cells.
- Macrophages.
• The viral envelope and cell membrane fuse and viral RNA enters the cell. It is converted by an enzyme called ‘reverse transcriptase’ into viral DNA.
• Using ‘integrase’ it integrates into the host cell DNA.
• The viral DNA forces the host cell to produce viral RNA and proteins.
• Assembles in cytoplasm and buds off.
• As the viral load goes up, T-cell count goes down.
HIV Transmission
- HIV is fragile so easily destroyed outside the body — only active for a short time outside the body.
- Primarily through blood and semen (low risk with saliva and vaginal secretions).
- NOT transmitted by casual contact — e.g. on toilet seats or sharing eating utensils.
- Primarily spread via unprotected anal sex. Recent increase in heterosexual transmission.
- Only 6–7% from intravenous drug use.
HIV Transmission: Mothers
Risk of transmission during pregnancy.
• Increased risk during birth.
• There may be a risk of transmission through breastfeeding (although actual risk is unknown).
• Recommended that mothers opt for a caesarean birth and must not breastfeed.
HIV: Avoiding the Immune System
As with all viruses: HIV can mutate, uses few structures of its own, does not have its own metabolism. HIV also destroys CD4 cells leading to immune compromise.
HIV: Diagnosis
- Blood test for antibodies — there is a delay in the appearance of HIV antibodies (two weeks–six months) — during this time window, tests are inaccurate.
- Remember babies will have antibodies from mother.
- Anonymous blood tests available from sexual health clinics.
HIV Progression
1.Initial stages:
• One–six weeks after infection.
• 50% symptomatic.
• Flu / glandular fever-like sore throat, fever, malaise, muscle / joint pain, rash, swollen lymph nodes.
• Negative antibody (IgG) tests, but viral RNA and p24 core protein high.
2. Late stage:
• Huge reduction CD4 count and rise in viral load.
• Severely impaired immune function.
• Opportunistic infections can cause disease.
• AIDS diagnosis based on T-helper cell count (<14%) and presence of opportunistic infections.
HIV: Signs and Symptoms
- Fatigue.
- Anaemia.
- Anorexia, diarrhoea, cachexia (weight loss, muscle wasting).
- Neurological disease with no other cause.
- Peripheral neuropathy.
- Neutropenia and thrombocytopenia.
- Dementia (HIV dementia).
- Cognitive / motor dysfunction.
HIV: Opportunistic Infections
–Recurrent pneumonia. –Active TB. –Candida (esp. oral, vaginal). –Lymphoma. –Cervical cancer. –Kaposi’s sarcoma (cancer of blood vessels). –Herpes zoster (shingles). –Herpes simplex. –Cytomegalovirus.
HIV: Opportunistic Infections Stages
Opportunistic infections become more serious as the CD4 count lowers:
•CD4 < 500: Herpes infections, candidiasis, Kaposi’s sarcoma.
•CD4 < 200: Toxoplasmosis (parasite), pneumonia.
•CD4 < 50: Severe mycobacterium infection, HIV dementia.
HIV: Prognosis
- Increased with highly active anti-retroviral therapy (HAART).
- Use of anti-retrovirals increases life expectancy, but causes a variety of adverse effects due to high toxicity from the drugs. Most patients will have a combination of two or three drugs.
- Currently no cure — focus is on slowing progression and prevention.
Dysentery
Dysentery is an infection of the intestines that causes diarrhoea containing blood and / or mucus.
•More prevalent in developing countries / poor sanitation — travellers.
Dysentery: Causes
- Bacterial (shigella).
- Amoebic (protozoan).
- Via faecal–oral contamination.
Dysentery: Signs and Symptoms
- Diarrhoea (watery stools) with mucus and blood.
* Cramping and possible nausea / vomiting.
Dysentery: Diagnosis
•Stool microscopy.
Dysentery: Treatment
Anti-parasitic / anti-bacterial. Rehydration: Fluid and mineral replacement.
Dysentery: Complications
Dehydration can be severe
Malaria
Malaria is a tropical infectious disease spread by anopheles mosquitoes that are infected by plasmodium species.
•Five million affected each year.
Malaria: Causes
Plasmodium species (protozoa) • Five types / species of the plasmodium parasite can infect humans. • Spread by vector / host mosquito.
Malaria: Transmission and Incubation
- Infected female anopheles mosquito bites human.
- Plasmodium parasites (‘sporozoites’) taken up by the liver where they proliferate and mature — some varieties may lie dormant for up to a year.
- Spread to erythrocytes and proliferate further. Symptoms begin (i.e. fever).
- Infected cells burst and spread infection.
- Protozoan gametes are formed and are taken up by mosquito during a blood meal. (three stages in malaria life cycle: Mosquito / human liver / erythrocyte stage).
Up to nine months
Malaria: Signs and Symptoms
•Cyclical fever attacks depending on type of malaria.
- First chills, then fever for several hours followed by extreme sweating and then shivering.
• Headache, fever, malaise, arthralgia, nausea, vomiting, diarrhoea, anaemia (haemolysis), haemoglobinuria and convulsions.
Malaria: Signs
Splenomegaly, hepatomegaly, jaundice (because of excessive haemolysis).
Malaria: Complications
- Death (can be misdiagnosed as flu).
* Relapses.
Malaria: Treatment
- Quinine / chloroquine (tetracycline, anti-inflammatories, antipyretics, analgesics).
- Preventative drugs — adverse effects!
- Resistance is becoming common.
Chlamydia
A very common sexually-transmitted infection, most commonly affecting under-25s.
Chlamydia: Causes
Chlamydia trachomatis (bacteria).
Chlamydia: Incubation
•Several weeks.
Chlamydia: Diagnosis
Urine, cervical, urethral swab tests.
Chlamydia: Signs and Symptoms
- Males: 50% asymptomatic, milky-white or yellow discharge from penis, epididymitis, urethritis (dysuria).
- Females: 80% asymptomatic, yellow vaginal discharge.
Chlamydia: Complications
Pelvic inflammatory disease and subsequent risk of infertility.
Chlamydia: Treatment
Antibiotics (e.g. erythromycin and tetracycline).
Gonorrhoea
Gonorrhoea is another very common bacterial STI.
Gonorrhoea: Cause
Neisseria gonorrhoea (bacteria) — infects epithelium of GU tract, rectum, pharynx and conjunctiva.
Gonorrhoea: Transmission
- Direct: Oral, anal or genital sex, occasional spread from the genital area to rectum.
- Mother to baby during birth.
Gonorrhoea: Diagnosis
- Swab culture of urethra, throat (90% asymptomatic), cervix or rectum, urine — but less reliable.
- Presumptive on-the-spot diagnosis often made.
Gonorrhoea: Signs and Symptoms
- Males: 90% symptomatic, yellow penile discharge, dysuria.
- Females: 50% asymptomatic, yellow vaginal discharge, dysuria, irregular vaginal bleeding, lower abdominal pain, pain during sex.
Gonorrhoea: Treatment
Antibiotics. Abstain from sexual activity until self and all partners are clear.
Gonorrhoea: Complications
Permanent complications (particularly in women) if untreated. PID, and infertility.
Genital Herpes
Herpes simplex virus (mostly Type II).
Genital Herpes: Transmission
Direct contact — sexually transmitted: genital-genital or oro-genital.
Genital Herpes: Signs and Symptoms
- Always symptomatic. After initial infection the viruses move to sensory nerves, where they remain at latent viruses.
- Initially painful vesicles, then shallow ulcers.
Genital Herpes: Treatment
Acyclovir
Syphilis
A chronic contagious systemic disease.
Syphilis: Cause
Treponema Pallidum (bacteria)
Syphilis: Transmission
Enters body via damaged skin or mucous membranes; e.g. sexual contact, pregnancy (crosses placenta).
Syphilis: Treatments
•Penicillin, avoid sex until confirmation the infection is no longer present. Regular blood tests to ensure NO re-occurrence.
Syphilis: Stage 1
A hard, painless ulcer on the infection point. Heals completely within 4 weeks of appearance & becomes asymptomatic.
Syphilis: Stage 2
General, flat, erythematous rash (very contagious!) potentially covering entire body. Not itchy, lasting several weeks.
• Latent stage: no symptoms - untreated person may remain infectious for up to 2 years!
Syphilis: Stage 3/3*
Years later if untreated may lead to:
- Chronic Gummas (granulomas).
- Neurological syphilis
- Cardiovascular syphilis
Genital Warts
•Human papillomavirus (HPV).
Incubation: Up to 6m
Genital Warts: Signs and Symptoms
•Soft, fleshy projections / cauliflower-like masses / small pointed masses / flat lesions on the vagina, cervix, penis.
Genital Warts: Treatment
Surgery, laser, cryotherapy. Re-occurrence is common.
