This episode moves from luminal infections to protozoa that invade blood and deep tissues. Drawing from Murray’s Chapter 73, it examines organisms that establish systemic infection, often requiring vector transmission.

Major pathogens include:

* Plasmodium species - malaria; intraerythrocytic replication

* Babesia species - tick-borne haemoparasites

* Trypanosoma species - African sleeping sickness and Chagas disease

* Leishmania species - cutaneous and visceral leishmaniasis

* Toxoplasma gondii - congenital and immunocompromised disease

These organisms frequently replicate within host cells - red blood cells, macrophages, or neural tissue - evading immune detection.

Clinical manifestations include:

* Anaemia

* Fever cycles

* Organomegaly

* Neurological involvement

Conceptually, blood and tissue protozoa illustrate immune evasion through intracellular survival. Clinically, vector exposure, travel history, and host immunity shape risk assessment.

Key Takeaways

* Many systemic protozoa are vector-borne

* Intracellular replication promotes immune evasion

* Malaria involves cyclic red cell destruction

* Leishmania survives within macrophages

* Toxoplasma poses risk in pregnancy and immunosuppression

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