Day: May 1, 2024

AIDS This is a condition caused by the human immunodeficiency virus (HIV). The virus gains entry in CD4+ T cells. As the infection progresses, it leads to depletion of the CD4 cells, leading to a decrease in immune function. This leads to acquired immunodeficiency syndrome (AIDS).   Transmission Sexual Transmission Vertical (mother to baby) IVDU   Symptoms Seroconversion (3–12 weeks following infection) Flu-like symptoms with fatigue, fever, lymphadenopathy, sore throat, and arthralgia Erythematous papular rash and mouth ulcers Persistent generalised lymphadenopathy (swollen lymph nodes lasting > 3 months)   Chronic infection This is usually asymptomatic until complications of immunosuppression develop

Short incubation periods   Staphylococcus Aureus A Gram-positive bacterium which produces toxins causing intestinal inflammation. The bacteria makes enterotoxins to compete with other bacteria in cooked and processed foods, but these end up being ingested by humans, causing symptoms The symptoms are due to the toxin rather than the bacteria, which gives the short incubation period of 1–6 hours.   Symptoms Nausea and explosive vomiting up to 24 hours Abdominal pain, weakness and headache   Key tests Stool culture to assess if bacterium is present Management Fluid and electrolyte replacement as illness quickly resolves within a couple days   Bacillus

Chlamydia This is a condition which is caused by the bacteria Chlamydia trachomatis. It is the commonest sexually transmitted disease in the UK. It is spread through all types of sex and can be passed to the baby during childbir   Symptoms  Often the infection is asymptomatic In females, can cause vaginal bleeding, discharge and deep dyspareunia In males, can cause urethritis (dysuria and discharge) Eye disease – can cause blindness Joints – often a cause of reactive arthritis Risk factor for pelvic inflammatory disease (PID) in women, leading to infertility   Key tests Investigation of choice is nuclear acid

Lyme disease This is a condition which is caused by the bacteria Borrelia burgdorferi. Transmission occurs via the Ixodes tick bite, so it is important to ask a detailed travel history to places where these ticks live e.g., forests, parks (e.g., Richmond Park in London has a higher incidence). It initially causes an expanding area of redness on the skin at the site of the tick bite. The bacteria can become systemic and spread to the heart, joints and CNS where they can persist for years. It is thought that the bacteria induce an autoimmune disease secondary to molecular mimicry,

Malaria This is a mosquito borne infection which injects the parasite Plasmodium into the blood. There are 4 main variants of the parasite and the natural vector is the female anopheles’ mosquito Pre-erythrocytic stage Mosquito injects sporozoites into human blood These migrate to liver and infect hepatocytes, multiplying by mitosis They can stage in the liver for up to 2 years remaining immature as hypnozoites These differentiate into merozoites which are released from the liver into the bloodstream   Erythrocytic stage Trophozoites infect RBCs, feeding on haemoglobin using the enzyme haem polymerase These form a schizont and multiply asexually, and

Pneumocystis Jirovecci This is a fungal infection that is seen in immunocompromised patients. It is an AIDS-defining disease, typically causing a pneumonia in HIV positive patients.   Symptoms Atypical pneumonia (SOB, dry cough, fever) but very few chest signs The classic symptom is desaturation of SpO2 during exercise/exertion Can lead to secondary pneumothorax, hepatosplenomegaly and lymphadenopathy   Key tests Blood tests show raised inflammatory markers and fungal markers (beta-glucan) CXR/HRCT shows bilateral interstitial pulmonary opacifications Sputum culture – this can be taken directly or from bronchoalveolar lavage if needed Lung biopsy may be required if diagnostic doubt   Management Co-trimoxazole is

Malaria This is a mosquito borne infection which injects the parasite Plasmodium into the blood. There are 4 main variants of the parasite and the natural vector is the female anopheles’ mosquito Pre-erythrocytic stage Mosquito injects sporozoites into human blood These migrate to liver and infect hepatocytes, multiplying by mitosis They can stage in the liver for up to 2 years remaining immature as hypnozoites These differentiate into merozoites which are released from the liver into the bloodstream   Erythrocytic stage Trophozoites infect RBCs, feeding on haemoglobin using the enzyme haem polymerase These form a schizont and multiply asexually, and

Lyme disease This is a condition which is caused by the bacteria Borrelia burgdorferi. Transmission occurs via the Ixodes tick bite, so it is important to ask a detailed travel history to places where these ticks live e.g., forests, parks (e.g., Richmond Park in London has a higher incidence). It initially causes an expanding area of redness on the skin at the site of the tick bite. The bacteria can become systemic and spread to the heart, joints and CNS where they can persist for years. It is thought that the bacteria induce an autoimmune disease secondary to molecular mimicry,

AIDS This is a condition caused by the human immunodeficiency virus (HIV). The virus gains entry in CD4+ T cells. As the infection progresses, it leads to depletion of the CD4 cells, leading to a decrease in immune function. This leads to acquired immunodeficiency syndrome (AIDS).   Transmission Sexual Transmission Vertical (mother to baby) IVDU   Symptoms Seroconversion (3–12 weeks following infection) Flu-like symptoms with fatigue, fever, lymphadenopathy, sore throat, and arthralgia Erythematous papular rash and mouth ulcers Persistent generalised lymphadenopathy (swollen lymph nodes lasting > 3 months)   Chronic infection This is usually asymptomatic until complications of immunosuppression develop

Chlamydia This is a condition which is caused by the bacteria Chlamydia trachomatis. It is the commonest sexually transmitted disease in the UK. It is spread through all types of sex and can be passed to the baby during childbir   Symptoms  Often the infection is asymptomatic In females, can cause vaginal bleeding, discharge and deep dyspareunia In males, can cause urethritis (dysuria and discharge) Eye disease – can cause blindness Joints – often a cause of reactive arthritis Risk factor for pelvic inflammatory disease (PID) in women, leading to infertility   Key tests Investigation of choice is nuclear acid

Short incubation periods   Staphylococcus Aureus A Gram-positive bacterium which produces toxins causing intestinal inflammation. The bacteria makes enterotoxins to compete with other bacteria in cooked and processed foods, but these end up being ingested by humans, causing symptoms The symptoms are due to the toxin rather than the bacteria, which gives the short incubation period of 1–6 hours.   Symptoms Nausea and explosive vomiting up to 24 hours Abdominal pain, weakness and headache   Key tests Stool culture to assess if bacterium is present Management Fluid and electrolyte replacement as illness quickly resolves within a couple days   Bacillus

C. difficile This is a Gram-positive bacterium which colonises the gut in the absence of one’s commensal harmless bacteria. The commensal flora in the gut can be killed due to the use of broad-spectrum antibiotics, leaving the individual vulnerable to a C. diff infection. The bacteria make a toxin which leads to inflammation in the colon, causing pseudomembranous colitis. It is a common hospital-acquired infection and can spread rapidly between patients.   Causes Most commonly secondary to antibiotics beginning with the letter “C” like cephalosporins, clindamycin. Also associated with PPI use.   Symptoms Diarrhoea, abdominal pain, fever If severe, can

Short incubation periods   Staphylococcus Aureus A Gram-positive bacterium which produces toxins causing intestinal inflammation. The bacteria makes enterotoxins to compete with other bacteria in cooked and processed foods, but these end up being ingested by humans, causing symptoms The symptoms are due to the toxin rather than the bacteria, which gives the short incubation period of 1–6 hours.   Symptoms Nausea and explosive vomiting up to 24 hours Abdominal pain, weakness and headache   Key tests Stool culture to assess if bacterium is present Management Fluid and electrolyte replacement as illness quickly resolves within a couple days   Bacillus

Chlamydia This is a condition which is caused by the bacteria Chlamydia trachomatis. It is the commonest sexually transmitted disease in the UK. It is spread through all types of sex and can be passed to the baby during childbir   Symptoms  Often the infection is asymptomatic In females, can cause vaginal bleeding, discharge and deep dyspareunia In males, can cause urethritis (dysuria and discharge) Eye disease – can cause blindness Joints – often a cause of reactive arthritis Risk factor for pelvic inflammatory disease (PID) in women, leading to infertility   Key tests Investigation of choice is nuclear acid

Fungi are eukaryotes with a nucleus, cytoplasm and a cell membrane made of ergosterol. – They also have a cell wall made of an outer matrix of B-1,3-linked glucans and inner layer of chitin, which is made up of chains of B-1,4-linked n-acetyl glucosamine. Fungi can exist in many different forms: Yeasts: These are round unicellular organisms which multiply asexually by a process called budding   Filamentous moulds: These form hyphae, which form an interwoven mass called a mycelium   Dimorphic: These change morphologies depending on the external environment.   Fungi classically are grouped into 2 types of pathogens: Systemic

Viruses are composed of a genome (nucleic acid) with a protein shell (capsid). This is sometimes surrounded by a phospholipid membrane called an envelope. – The most important part of the life cycle is being able to replicate the viral DNA within host cells. DNA viruses These use a host DNA-dependent RNA polymerase to make mRNA – The mRNA is translated in cytoplasm and used to make protein components – These protein components are put together in the cytoplasm to make new virus particles which can be released from the cell.     RNA viruses These can be subdivided according

Bacteria are unicellular microorganisms which are composed of a naked DNA chromosome, cytoplasm, cell membrane and cell wall. They can be divided into Gram Positive and Negative bacteria i) Gram Positive: These have a cell wall made of peptidoglycan, take up Gram stain   ii)Gram Negative: These have a cell wall of peptidoglycan but then an additional outer membrane too, do not take up Gram Stain Bacteria can be classified by Gram Stain, shape, enzymes and whether they are aerobic or anaerobic. This will all affect diagnosis and treatment options.   Gram Positive Bacteria   Cocci These look like round

The immune response can be split into the innate and adaptive system:   Innate Immunity This is immunity which is dependent on antigen receptors that are germline encoded   The innate immune system recognizes 3 types of stimulants, which activate the innate response: – Pathogen associated molecular patterns (PAMPs) – molecular shapes specific to the pathogen – Danger associated molecular patterns (DAMPs) – self-molecules released by host stressed cells – Missing-self – Infected cells do not show normal self-antigens which protect host cells from NK cells.   The activation of these receptors gives acute inflammation and activation of the following