Parasitic Protozoa and Helminths

Introduction

Protozoa

Helminths

Biologic properties

 

Small

Variable in size

Unicellular

Multicellular

Multiply in host

Usually do not multiply in host

Short generation time

Long generation time

High basic reproductive rate

Low basic reproductive rate

Clinical properties

 

Random or behavior influenced distribution

Aggregated distribution

Infection is usually transient

Tend to induce persistent infection

Disease may be initiated by a small innoculum

Disease is related to intensity of infection

Varies from asymptomatic to acute disease

Asymptomatic to chronic disease

Immunological properties

 

Strong transient immune response

Moderate, sustained immune response

Solid immunity is rare

Partial immunity may occur

Infection is not associated with eosinophilia

Tissue infective stages are associated with eosinophilia

Elaborate evasive mechanisms

Unclear evasive mechanisms

Protozoa

Helminths – "worms"

Pathogenesis and Host Response

Host Immune Response – "Examples of effective acquired resistance"

 

Leisch recidivans

Diffuse cutaneous Leisch

# lesions

Usually one

++++

# lymph/lesion

+++

+/-

Skin test

+++

-

In vitro response

+++

-

# parasites/macrophage

+

++++

Evasion – "Examples of how protozoa escape host defenses"