Models

Question 1

How do we study malaria? what models?

Answer 1

CHMI controlled human malaria infection
In currently infected human populations
Animal models (apes)
Rodent models
In vitro models
Looking at dead tissue/necropsy

Question 2

limitations of CHMI model

Answer 2

Overuse of 3D7 P. falciparum: Limited parasite diversity in studies reduces applicability to real-world infections.
Malaria parasites exhibit polymorphic antigens, necessitating the inclusion of other genotypes in CHMI studies.

Limited Generalisability Slow immune memory/resistance in malaria is due to the need for exposure to diverse strains over long period of time, which CHMI studies may not adequately replicate when using western volunteers,

Limited Generalizability: CHMI studies often involve healthy, malaria-naïve individuals, which may not represent populations in endemic areas with prior exposure.

Short Study Duration: CHMI studies typically focus on acute infection, providing limited insight into long-term immunity or chronic infections like asymptomatic malaria.
CHMI studies typically end after the acute phase, offering limited data on long-term immunity or the effects of repeated malaria exposure over years.

Severe Malaria: CHMI cannot study severe malaria syndromes, such as cerebral malaria or respiratory distress, as participants are treated before reaching these stages.

Inability to study Long-term immunity: CHMI typically focuses on acute malaria infections, providing limited insights into chronic or relapsing malaria, which are critical aspects of P. vivax and asymptomatic P. falciparum infections.

Exclusion of Vector Dynamics/artificial infection mechanisms: CHMI often uses injected sporozoites or controlled mosquito bites, which may not fully replicate natural transmission dynamics or immune responses associated with vector-mediated infection.

Controlled Environment Bias: Conditions in CHMI studies (e.g., low parasite doses, close monitoring, and early treatment) differ from real-world scenarios, potentially underestimating disease severity or immune complexity. Real-world factors such as co-infections, malnutrition, or varying exposure to mosquitoes cannot be effectively modeled in CHMI.

Question 3

Benefits of CHMI model?

Answer 3

Direct Human Relevance:
CHMI involves human participants, providing more accurate insights into human immune responses and pathophysiology compared to animal models.

Rapid and Controlled Testing:
CHMI allows for quicker evaluation of malaria vaccines, drugs, and diagnostics under highly controlled conditions, unlike field studies that depend on variable natural exposure.

Standardized Experimental Conditions:
Parasite dose, timing, and infection methods are tightly controlled, reducing variability compared to natural infections or endemic studies.

Ethical Use of Fewer Participants:
Compared to large-scale field trials, CHMI requires fewer participants to achieve statistically significant results.

Detailed Immune Response Data:
CHMI enables precise study of the immune system during the early stages of infection, providing insights that are difficult to obtain in uncontrolled settings or animal studies.

Testing Specific Parasite Strains:
Researchers can use defined Plasmodium strains or genotypes, enabling a focused study of parasite biology and host-pathogen interactions.

Early-Stage Validation of Interventions:
CHMI is ideal for early-phase testing of vaccines and drugs, identifying promising candidates before large-scale trials.

Minimized Confounding Factors:
CHMI participants are often malaria-naïve and healthy, reducing confounding variables such as prior immunity, co-infections, or environmental factors common in endemic populations.

Cost-Effective Alternative to Field Trials:
CHMI studies are more cost-effective than large-scale field studies, which require extensive logistical and financial resources.

Insights into Treatment Dynamics:
CHMI allows real-time tracking of parasite clearance following drug treatment, enabling precise pharmacodynamic studies.

Flexible Infection Methods:
CHMI can use mosquito-bite or direct injection of sporozoites, offering versatility in mimicking natural transmission or laboratory-controlled infection.

Addressing Ethical Concerns of Animal Models:
Reduces reliance on animal models, which often lack translational accuracy due to differences in immune systems between humans and animals.

Question 4

limitations of non-rodent animal models for studying malaria (ape)

Answer 4

Limitations
1. ethical concerns - endangered, high cognitive abilities, strict regulation considerations, expensive and logistically challenging
2. relevance to humans - Differences in immune mechanisms may fail to accurately model human-specific responses to malaria, disease progression often different compared to humans
Inability to Model Some Human-Specific Phenomena:
Certain aspects of malaria, such as pregnancy-associated malaria or cerebral malaria, may not manifest similarly in apes.

3. restricted study scope - ethical+logistical constraints can limit the size of the study population, reducing statistical power
4. fewer genetic modification/manipulation tools - Unlike rodent models, there are fewer tools for genetic manipulation in apes, making mechanistic studies more challenging

Question 5

advantages of ape animal model for studying malaria

Answer 5

Advantages

1. Closer Genetic and Physiological Similarity to Humans:
   apes share a higher degree of genetic, immunological, and physiological similarity with humans than rodent or in vitro models, making them better at mimicking human malaria. Good for studying host-parasite interactions or vaccine efficacy
2. Natural susceptibility to human-specific plasmodium species - like P. vivax and Falciparum, offering a natural model for studying human malaria without the need for adaptation.
3. Severe Malaria - Some ape species can exhibit severe malaria symptoms, enabling studies on pathogenesis and potential treatments for severe malaria syndromes.
4. Intermediary Model - Apes serve as a crucial intermediary model, offering insights that rodent models cannot provide while addressing some limitations of CHMI studies (e.g., long-term immunity studies).
   AND
5. Validation of results: Findings from rodent or in vitro studies can be validated in apes before transitioning to human trials, improving the reliability of results.

Question 6

Advantages of rodent models

Answer 6

Advantages of Rodent Models in Malaria Research:

Fluorescent Imaging and Genetic Labeling:
Rodent models allow for advanced techniques like fluorescent labeling of parasites, enabling real-time visualization of host-parasite interactions with immune cells.

Genetic Manipulation:
Mice are highly genetically modifiable, allowing researchers to study specific genes, immune responses, and host-parasite interactions in detail. Can do humanised mice

Cost-Effective and Accessible:
Rodents are inexpensive to breed, maintain, and study, making them a practical choice for high-throughput studies.

Controlled Experimental Design:
Rodent models allow for tightly controlled studies with minimal confounding factors, improving reproducibility.

Variety of Rodent Malaria Strains:
Species like Plasmodium berghei and P. yoelii can model various aspects of malaria biology, such as liver-stage infection or cerebral malaria. Thicket rat natural host for berghei

Short generation time: can study infection throughout the animal’s life

Question 7

Limitations of murine/rodent models

Answer 7

Useful for studying molecular interactions and drug efficacy but cannot replicate the complexity of host immune responses or disease progression.

2. Different Clinical Symptoms and Pathology:
   Mice exhibit hypothermia instead of fever, and their disease course lacks the hallmark severe symptoms seen in human malaria, such as cerebral malaria or respiratory distress.

2B. Poor Translation to Human Results:
Despite 30–40 new treatments suggested by rodent studies, none proved effective in humans, highlighting limited translational accuracy.

2C. Key aspects of Human Malaria Pathogenesis Missing:
Rodent malaria parasites do not cause red blood cell (RBC) sequestration, a critical feature of severe P. falciparum infections.
Differences in parasite biology mean rodent models cannot replicate the full spectrum of human malaria symptoms and complications.

2D: Disease Course is Significantly Different:
The speed of parasite replication, immune clearance, and overall disease progression differ greatly between rodents and humans.

3. Rapid Immune Development:
   Rodents become immune to malaria very quickly due to differences in their immune system, making it hard to study chronic infections.
4. Limited Lifespan:
   Their short lifespan (1–2 years) restricts the ability to study long-term immunity or chronic malaria dynamics.
5. Variation in Outcomes depending on Mouse Strain (see next card)

Question 8

How does the genetic background of the mouse effect its response to P. Berghei

Answer 8

Certain mouse strains, such as C57BL/6 or BALB/c, show differing susceptibility to P. berghei.

For example:
C57BL/6 mice are more susceptible to cerebral malaria when infected with P. berghei ANKA.

BALB/c mice are relatively resistant to severe malaria syndromes and may exhibit milder disease.

The variability response however, makes them a useful tool for studying genetic and immune factors influencing malaria severity.

Question 9

advantages of in vitro models?

Answer 9

1. Cost-Effective:
   In vitro systems are significantly cheaper than in vivo models, requiring fewer resources and infrastructure.
2. Fewer Ethical Concerns:
   Avoids ethical issues associated with infecting animals or humans, making these models more widely acceptable and easier to implement.
3. Controlled Environment:
   Provides a high level of control over experimental conditions, reducing variability and allowing precise manipulation of factors such as parasite concentration, immune cell types, or drug dosage.
4. Genetic Manipulation of Parasites:
   In vitro models are ideal for studying genetically modified Plasmodium strains, helping to identify genes involved in drug resistance, virulence, or immune evasion.
5. Specific Immune Cell Interactions:
   Allows researchers to isolate and test hypotheses about specific immune cell responses (e.g., T-cells, macrophages) or molecules involved in malaria immunity.
6. Rapid Experimental Turnaround:
   Experiments can be completed more quickly compared to in vivo models, facilitating high-throughput studies of drugs, vaccines, or parasite behavior.
7. Drug Screening and Mechanistic Studies:
   In vitro systems are well-suited for screening potential antimalarial compounds and studying parasite biology, such as the mechanisms of drug action or resistance.
   Accessibility:
8. Accessibility
   No need for specialized facilities like animal housing or mosquito insectaries, making in vitro research more accessible to a wider range of laboratories.

Question 10

Limitations of in vitro models?

Answer 10

1. Lack of Complexity:
   Cannot replicate the full host immune response, organ interactions, or disease pathology seen in vivo. Reductionist and lacking in complexity
2. Simplified Environment:
   Parasite behavior and drug responses may differ due to the absence of host factors like immune cells, cytokines, and metabolic conditions.
3. Limited Longevity:
   Difficult to study long-term parasite development (e.g., liver-stage or chronic infections).
4. No Modeling of Severe Malaria:
   In vitro models cannot replicate features like RBC sequestration, cerebral malaria, or multi-organ involvement.
5. Reduced Translatability:
   Findings may not directly apply to human infections without validation in animal or human models.