TABLE OF CONTENTS
Gnathostoma spinigerum: Morphology, Life Cycle, Hosts, Classification & Diseases
Gnathostoma spinigerum is a spirurid nematode of veterinary and zoonotic importance that primarily infects the stomach of cats, dogs, and various wild carnivores. Adult worms are typically found embedded in the gastric wall, where they can cause chronic gastritis and nodular lesions. Humans serve as accidental hosts and may develop larval migration in the subcutaneous tissues and other organs following the ingestion of infective larvae.
This article provides a comprehensive overview of Gnathostoma spinigerum, including its taxonomy, morphology, life cycle, hosts, pathogenicity, and clinical significance in veterinary parasitology.
Parasite Overview
- Definitive Hosts: Cats, dogs, and various wild carnivores (adult worms inhabit the stomach)
- Accidental (dead-end) Hosts: Humans (larvae migrate through the subcutaneous tissues)
- First Intermediate Host: Cyclops
- Second Intermediate Host: Frogs, fish, and reptiles
Taxonomical Classification
- Kingdom: Animalia
- Phylum: Nematoda
- Class: Chromadorea (Secernentea)
- Order: Spirurida
- Suborder: Spirurina
- Superfamily: Gnathostomatoidea
- Family: Gnathostomatidae
- Genus: Gnathostoma
- Species: Gnathostoma spinigerum
Morphology
- The body is typically pink and is covered anteriorly with concentric rows of flat, toothed spines.
- It is characterized by a bulbous head (head bulb) with a pair of lateral lips surrounding the mouth.
- The cephalic region is covered with transverse rows of cuticular spines.
- Internally, the head contains four glandular cervical sacs that attach near the esophagus, as well as four hollow spaces called ballonets, each continuous with a cervical sac through a central canal.
Pathology and Clinical Signs
- Adult Gnathostoma spinigerum causes chronic gastritis and gastric nodules in cats and dogs.
- Migration of the larvae through the subcutaneous tissues in humans causes intermittent, painful, pruritic migratory swellings, a condition known as cutaneous gnathostomiasis.
Cutaneous Gnathostomiasis
Cutaneous gnathostomiasis is the most common clinical manifestation of human infection caused by the migrating third-stage larvae (L3) of Gnathostoma spinigerum. Humans are accidental hosts and become infected by consuming raw or undercooked freshwater fish, frogs, eels, poultry, or other paratenic hosts containing infective larvae, or less commonly by drinking water contaminated with infected Cyclops.
After ingestion, the larvae penetrate the gastric wall and migrate through the subcutaneous tissues, producing intermittent, migratory swellings. These lesions are typically painful, pruritic, erythematous, and edematous, and may recur over weeks or months as the larvae continue to migrate. Peripheral eosinophilia is a common laboratory finding.
Although the skin is the most frequently affected site, migrating larvae may occasionally invade deeper tissues, including the eyes, lungs, and central nervous system, resulting in severe complications such as ocular or neurological gnathostomiasis.
In humans, cutaneous gnathostomiasis is typically treated with albendazole or ivermectin. Surgical removal may be performed when the migrating larva is localized.
Life Cycle
The eggs hatch in fresh water, and the larvae are ingested by copepods of the genus Cyclops, where they develop into second-stage larvae. When infected copepods are eaten by freshwater fish, frogs, reptiles, or other paratenic hosts, the larvae develop into infective third-stage larvae (L3). Carnivores, usually cats and dogs, become infected after consuming these intermediate or paratenic hosts.
The larva bores through the stomach wall and migrates throughout the host’s body for about three months before returning to the stomach and attaching to the gastric mucosa. It then takes another six months to mature.
The eggs are passed in the host’s feces, and if they reach fresh water, the life cycle begins again.
