L-8 Bartonella henselae & Cat-Scratch Disease

• No normal flora exists in the cardiovascular and lymphatic systems
• The primary role of the lymphatic system is to return leaked interstitial fluid from capillaries back into the cardiovascular system
• Interstitial fluid can contain pathogens like bacteria, viruses, and fungi
• Lymphatic capillaries drain into larger vessels, eventually reaching the superior vena cava, via the left side, or the right subclavian vein, via the right side
• As lymph moves through the system any pathogens present activate the immune system and lymphocytes are produced

Bartonella henselae

• It is a rod-shaped, gram-negative bacterium
• Infection leads to cat-scratch disease
• Symptoms include: fever, malaise, and lymphadenopathy (swollen lymph nodes)
• Atypical presentations include: Leber neuroretinitis, encephalitis, and endocarditis
• Transmitted to humans via cat saliva, often through a bite or scratch
• Bacteria enters human tissue and is phagocytosed by macrophages
• Macrophages transport bacteria to lymph nodes, releasing proinflammatory cytokines that cause swelling and fever
• Found all over in the United States
• Diagnosis is mainly clinical, based on a history of cat exposure and characteristic lymph node presentation
• 90% of infections are self-limiting, but azithromycin may help in cases of extensive lymph node swelling
• Flea control is important for prevention, because fleas spread in cats

Sporothrix schenckii

• It is a dimorphic fungus, switching between filamentous and yeast forms
• Found globally in the environment, especially in soil, moss, decaying wood, and vegetation
• Typically infects agricultural workers or outdoor hobbyists
• Enters the body when soil or plant material containing S. schenckii is introduced under the skin
• Causes cutaneous sporotrichosis
• A single nodular lesion appears on the skin near the inoculation site weeks after the initial infection
• Cells containing the yeast form can travel through the lymphatic system, causing more skin nodules along lymph vessels, known as nodular lymphangitis
• Pulmonary sporotrichosis can occur if spores are inhaled
• Disseminated sporotrichosis may occur in immunocompromised individuals
• Diagnosed through biopsy of the cutaneous lesion, which may reveal granulomatous inflammation and signs of inflammation
• Itraconazole (antifungal) is the treatment
• Wear gloves and protective clothing when working outdoors to avoid infection

Leishmania species

• Protozoan parasites that are single-celled eukaryotes and obligate intracellular to host cells
• Leishmania exists worldwide
• L. tropica and L. mexicana are found in Central and South America, Northwest Africa, and Central Asia, causing cutaneous leishmaniasis
• L. donovani causes visceral leishmaniasis and found in Central and South America, Eastern Africa, and India
• L. braziliensis causes mucocutaneous leishmaniasis
• Sandflies transmit Leishmania to humans by biting and taking up blood from an infected mammal
• Parasites replicate within macrophages, eventually leading to cell death and tissue destruction at the bite site

Cutaneous, mucocutaneous, and visceral Leishmaniasis symptoms

• L. tropica: Macrophages in the skin are destroyed, leading to ulcerated scarring skin lesions
• L. braziliensis: Macrophages travel to mucocutaneous tissue, leading to ulcerated lesions in both the oropharynx and also genital areas
• L. donovani: Macrophages travel to visceral tissue like the liver or spleen, leading to cell death, tissue destruction and high fever, splenomegaly, and anemia. It also has a very poor prognosis
• Diagnosed via a Polymerase Chain Reaction (PCR)
• Histology of skin biopsy
• Performing an ELISA
• Treatment includes sodium stibugluconate, amphotericin B, and cyloguanil pamoate
• Vaccines are under development
• Use of bed nets, insecticides, and screens can help with prevention

Parvovirus B19

• Non-enveloped DNA virus
• Common worldwide
• Human-to-human transmission
• Spread via respiratory droplets, blood products, or across the placenta
• It affects erythroid precursor cells
• Causes fifth disease/erythema infectiosum
• Symptoms include:
• low-grade fevers
• aches and pains
• potential anemia
• A few weeks later, a rash develops, which is a "slapped cheek rash" and joint pain
• The rash starts as prominent red cheeks and spreads to various extremities. Aplastic crisis, and Hydrop fetalis are rare complications
• Diagnosis based on symptoms
• Treatment includes self-limiting and prevention includes hand-washing

Babesia microti

• Protozoan parasite
• United States, predominantly in the Northeast and upper Midwest
• Transmitted to humans via Ixodes tick
• The symptoms take weeks to develop
• Babesia gametocytes mature in erythrocytes, leading to hemolysis
• Causes babesiosis
• Symptoms of babesiosis include anemia, malaise, and fatigue, with fever increasing the rate of hemolysis
• Diagnosed via peripheral blood smear
• "Maltese cross” pattern
• PCR confirms the presence of Babesia microti
• Treatment consists of atovaquone + azithromycin
• Prevention includes insect spray, avoiding tick bites, long sleeves, and nets