Symptom

Definition

A subjective indication of disease, injury, or physiological disturbance reported by a host organism, as distinguished from an objective sign observable by an examiner. In medical and veterinary entomology, symptoms describe the internal experiences of infection or envenomation—such as pain, pruritus, fever, malaise, or nausea—resulting from arthropod-borne pathogens, venoms, or allergic responses. Symptoms contrast with signs, which are externally measurable (e.g., a mosquito bite wheal, detectable parasitemia, or visible necrosis). The distinction matters in field diagnostics, where patients or wildlife cannot communicate symptoms, and in epidemiological surveillance, where symptom-based case definitions shape outbreak detection.

Etymology

From Greek symptōma 'a happening, accident, disease symptom', from sympiptein 'to fall together, happen'

Example

A human patient infected with Plasmodium falciparum by Anopheles mosquitoes may report symptoms of cyclic fever, chills, and headache, while the clinician observes signs such as splenomegaly, anemia, or detectable parasitemia in blood smears.

Related Terms

• sign
• Pathology
• vector-borne disease
• envenomation
• parasitemia
• clinical manifestation
• case definition

Usage Notes

In strict clinical usage, symptoms are always subjective and patient-reported; applying 'symptom' to non-human animals requires anthropomorphic inference, so veterinary contexts often use 'clinical sign' more broadly. In entomological research, symptom-based surveys (e.g., self-reported allergic reactions to Hymenoptera stings) carry inherent bias compared to sign-based field assessments (e.g., measured wheal diameter). The symptom/sign boundary can blur with behavioral proxies: a lethargic, anorexic insect vector might show 'signs' of infection, while the vertebrate host's fever remains a 'symptom'.