Module 10: Veterinary Ectoparasites
Module 10.1: Introduction to Veterinary Ectoparasites
Introduction to Veterinary Ectoparasites
Ectoparasites are organisms, typically arthropods, that live on the exterior surfaces of their hosts and obtain nutrition by feeding on their blood, skin, or tissue fluids. They primarily target the skin and its associated structures. In veterinary practice, common ectoparasites include ticks, mites, lice, and fleas. This chapter will provide an overview of the key morphological characteristics that differentiate these parasites, enabling you to accurately identify them when presented with specimens. As a veterinarian, your role extends to identifying invasive or non-native parasites that may be introduced through animal movements, thereby safeguarding animal and public health.
General characteristics of insects and arachnids
Arthropods are a diverse group of invertebrates characterized by their exoskeletons, segmented bodies, and jointed appendages. In the context of veterinary ectoparasites, they are primarily categorized into two groups: insects and arachnids.
Arachnids
This class of ectoparasites includes ticks and mites. Adult arachnids are distinguished by having eight legs (four pairs). Unlike insects, arachnids undergo a type of development called gradual metamorphosis. This means that the various developmental stages—egg, larva, nymph, and adult—look quite similar, making it challenging to distinguish between them. Notably, ticks and mites can be found in different developmental stages on their hosts.
Arachnid Metamorphism
Eggs: Laid in the environment.
Larvae: Six-legged stage
Nymphs: Eight-legged stage, often resembling adults but smaller. Differentiation between stages is based on size, host, and season
Adults: Eight-legged stage
It’s crucial to note that while nymphs and adults both have eight legs, larvae only have six legs, which is an important distinction in the identification of ticks and mites at different stages of their life cycle.
Insects
Insects of veterinary importance include lice, fleas, and flies, though this chapter will focus on lice and fleas. Unlike arachnids, adult insects have six legs (three pairs). Insects can undergo either complete or incomplete metamorphosis.
Insect Metamorphism
Complete Metamorphosis: This process involves four stages—egg, larva, pupa, and adult. Each stage is distinct in form, making identification straightforward. Fleas are an example of insects that undergo complete metamorphosis.
- Egg: Laid by the adult.
- Larva: Often involves multiple instars (larval stages).
- Pupa: A transitional stage where the larva transforms into the adult.
- Adult: The final, reproductive stage.
Incomplete Metamorphosis: This involves three stages—egg, nymph, and adult. The nymphs resemble the adults but are smaller and undergo multiple molts, growing larger with each stage. Lice are an example of insects with incomplete metamorphosis.
- Egg: Laid by the adult.
- Nymph: Resembles the adult but is smaller and non-reproductive. Multiple instars occur as the nymphs grow.
- Adult: The reproductive stage that is morphologically similar to the nymphs but fully developed.
Incomplete vs Complete Metamorphosis
Summary Table
Ectoparasite |
Type of Arthropod |
Pairs of Legs |
Type of metamorphosis |
|---|---|---|---|
Ticks |
Arachnida | 4 pairs of legs (8 legs) | Simple (gradual) |
Mite |
Arachnida | 4 pairs of legs (8 legs) | Simple (gradual) |
Lice |
Insecta | 3 pairs of legs (6 legs) | Incomplete |
Fleas |
Insecta | 3 pairs of legs (6 legs) | Complete |
Knowledge check
This is a type of development in which the immature stage (nymph) is a smaller version of the adult.
Complete Metamorphosis: Involves a radical transformation between stages (egg → larva → pupa → adult).
Incomplete Metamorphosis: Involves gradual growth without significant change in form (egg → nymph → adult).
