This Week in Parasitism (TWiP) episode 259 features hosts Vincent Racaniello, Daniel Griffin, and Christina Naula. The episode begins by confirming the diagnosis of a previous clinical puzzle: a man in Kuching, Malaysia, presenting with daily fevers and shaking chills, was infected with Plasmodium knowlesi malaria. The hosts review numerous listener responses that accurately pinpointed P. knowlesi based on symptoms, geographic location, and association with primate hosts. A detailed discussion follows, exploring the predominantly zoonotic nature of P. knowlesi, its transmission dynamics, diagnostic challenges due to morphological similarities with other Plasmodium species, and the surprising historical use of malaria (possibly P. vivax or P. knowlesi) for treating syphilis. The episode concludes with a new clinical case for listeners to solve: a 32-year-old pregnant woman in Northern Tanzania suffering from over three weeks of bloody, sticky diarrhea, dehydration, low hemoglobin, and elevated creatinine, who reportedly sources her water from a nearby river.
TWiP 259: Unraveling Plasmodium knowlesi and a New Tanzanian Mystery
0:00 Introduction & Hosts: The episode opens with Vincent Racaniello, Daniel Griffin, and Christina Naula introducing TWiP 259, recorded on May 23rd, 2025.
0:44 Lighthearted Banter: Daniel Griffin's Trichomonas-themed bowtie sparks a brief, humorous discussion.
1:36 Call for Listener Support: Vincent Racaniello encourages listeners to support MicrobeTV's ad-free science podcasts, emphasizing their commitment to providing factual information and combating misinformation.
2:08 Solved Case Presentation (Kuching, Malaysia): Daniel Griffin reviews the previous case of a man in his late 30s from Kuching, Malaysia, admitted in December with daily fevers, shaking chills, and headache, following a jungle visit.
2:55 Patient's Symptoms & Labs: The man presented with a fast heart rate, increased respiratory rate, low white blood cells, anemia, thrombocytopenia (<50,000 platelets), abnormal coagulation, elevated serum creatinine, and elevated serum aminotransferases.
3:30 Listener Guesses β Plasmodium knowlesi (Confirmed): Multiple listeners, many from a University of Washington parasitology class, correctly identified Plasmodium knowlesi as the likely pathogen, citing:
Geographic & Exposure Factors: Patient's visit to the Malaysian jungle (specifically Sarawak), known for P. knowlesi endemicity; close proximity to macaque monkeys (natural hosts, which can interact with orangutans); mosquito transmission (Anopheles, active in the evening/night); and the rainy season (November-March) increasing mosquito populations.
Discrepancy Noted: Chan points out that while P. knowlesi typically causes normal or elevated white blood cell counts, this patient had a low count.
13:21 Historical Context of P. knowlesi: Jay highlights that P. knowlesi was initially identified in 1931 but believed to infect only monkeys. It was later discovered to cause significant human disease (2,500 cases, 9 deaths in Malaysia in 2022), reflecting an evolution in scientific understanding.
15:11 Diagnostic Challenges: Michelle and Alexander, along with other listeners, emphasize that P. knowlesi can morphologically resemble P. malariae on blood smears, necessitating molecular methods like PCR for accurate diagnosis, especially as P. knowlesi can cause rapid, severe disease, unlike typically milder P. malariae.
30:54 Treatment Considerations: Listeners suggest artemisinin-based combination therapies (ACT) for uncomplicated cases, and intravenous artesunate for severe infections, noting the importance of prompt treatment due to P. knowlesi's rapid replication cycle.
41:17 Case Solution Confirmed: Daniel Griffin confirms the diagnosis as Plasmodium knowlesi, stating that a blood smear was done and this species is prevalent in the area.
42:42 Primarily Zoonotic: Christina discusses studies showing P. knowlesi is predominantly zoonotic (animal-to-human) with very unlikely sustained human-to-human transmission, possibly due to low gametocyte production in human hosts, which are necessary for mosquito uptake.
45:55 Underestimation of Prevalence: Daniel suggests that P. knowlesi might be more widespread and severe than historically recognized, partly due to diagnostic difficulties and past medical dogma regarding malaria severity.
48:33 Historical Malaria-Syphilis Treatment: Christina and Daniel recount the historical practice, pioneered by Julius Wagner-Jauregg (Nobel Prize in 1927), of intentionally infecting neurosyphilis patients with malaria (likely P. vivax) to induce therapeutic fevers. This practice ceased with the advent of penicillin.
52:28 New Clinical Case Presentation (Northern Tanzania): Daniel Griffin presents a new clinical puzzle:
Patient: A 32-year-old pregnant woman (second trimester, second pregnancy) admitted to a hospital near the Kenya border.
Symptoms: Dehydrated, reporting 3+ weeks of diarrhea described as "sticky," "hard to get herself clean," and containing "blood mixed in the stool." She feels weak but has no fever or chills.
Exposures: She obtains her water from a nearby river. She lives with her husband and a 2-year-old child; the family is healthy. She is HIV negative.
Clinical & Labs: Appears tired and worn down but is feeling better. Labs show low hemoglobin and elevated creatinine. Stool studies are pending.
Hint: "Ockham would be confused but Dr. Hickam would know what to do," implying a diagnosis that accounts for all symptoms, possibly without multiple diseases.
55:17 Call for New Case Guesses: Listeners are invited to send their case guesses to twip@microbe.tv (subject: TWIP 259 case) before June 20th.