Four-winged spineless nematodes and tubular nematodes

Four-winged acanthocephalan disease is an intestinal parasitic infection in rodents caused by the four-winged acanthocephalan, while rodent cryptic tubular nematode disease is a parasitic condition characterized by the presence of cryptic tubular nematodes and rodent tubular nematodes, which respectively infest the intestines of mice and rats.

The cryptic tubular nematode resembles the four-winged acanthocephalan nematode in morphology, with the primary distinction being its narrowly defined neck wings. Adult worms are white, featuring a simple mouth opening without a buccal capsule. The esophageal bulb is round, and the neck-wing membrane is narrow and gently curved. Male worms are extremely small, measuring 1.25–1.65 mm in length, and appear as fine, hair-like structures under magnification. They have three ventral papillae, with the middle one located near the mid-body region. The tail curves sharply downward toward the ventral side, tapering abruptly just behind the cloacal opening; males possess a slender, elongated copulatory bursa equipped with a guiding structure. Female worms measure 3.45–5.95 mm in length, with the vulva situated approximately at the anterior one-sixth of the body. Their eggs exhibit a typical left-right asymmetrical shape: one side is relatively straight, while both ends are pointed and tapered, measuring 118–153 μm by 33–35 μm. The rat tubular nematode closely resembles the cryptic tubular nematode, making it challenging to distinguish between the two species. Adult worms have a blunt, rounded anterior end and a long, pointed posterior end, characterized by three distinct lips. Male worms measure 1.2–1.3 mm in length and 0.1 mm in width, while females reach 2.8 mm in length and 4.0 mm in width, with the vulva positioned about one-fourth of the way along the body. In contrast, the four-winged acanthocephalan nematode has adult worms that are white and cylindrical, with a prominent anterior protrusion and finely transverse striations on their cuticle. The mouth is encircled by three lateral lips, lacking an oral cavity, and the esophageal bulb is oval-shaped. Notably, there are conspicuous semi-elliptical cephalic bulbs flanking the mouth opening. The neck-wing membrane is well-developed, forming an arrow-like structure that spans roughly one-tenth of the worm's body length. Male worms range from 2 to 4 mm in length, with a smooth body surface and a tail that curves sharply downward toward the ventral side. They lack both a copulatory bursa and a guiding structure. Female worms measure 3–4 mm in length, with the vulva positioned around the anterior one-third of the body. Their tails are gently rounded and conical in shape. Eggs of this species are oval or spindle-shaped, exhibiting bilateral symmetry, with thin shells measuring 89–93 μm by 36–42 μm. Newly laid eggs contain a single embryonic cell at the mulberry-stage development.

The images show the four-winged apospore nematode and the tubular nematode observed during our experiment.

Hidden tubular nematodes and four-winged spineless nematodes are two common pinworm species found in laboratory mice, and their parasitic sites overlap—while the former primarily inhabits the cecum, the latter is most commonly found in the colon, with occasional infections also occurring in the cecum. Studies have shown that hidden tubular nematodes and four-winged spineless nematodes can coexist harmoniously within mice, and mixed infections involving these two parasites consistently rank highest among all types of mixed infections.

These two parasites cause relatively mild disease in the rodents themselves. In mice with mild or moderate infections, clinical symptoms are often subtle; however, severe infections exhibit similar signs, leading to stunted growth and development, poor coat condition—characterized by dull, disheveled fur—and reduced reproductive capacity, even resulting in cannibalism of offspring. In more advanced cases, these parasites can damage the intestinal tract, causing conditions such as rectal prolapse, intestinal obstruction, intussusception, and mucous enteritis.

After infection with the tubular nematode, no obvious pathological changes are observed; however, severe infections can lead to enteritis. Under microscopic examination, thickening of the intestinal wall, edema, fibrosis, and inflammatory cell infiltration on the mucosal surface become evident. In mice severely infected with the four-winged, spineless nematode, the primary site of pathology is the colon, with lesions resembling those caused by the cryptic tubular nematode.

According to national standards, dissect mice to collect intestinal contents, process the samples using conventional methods, and then examine them under a microscope. Alternatively, multiplex PCR combined with sequencing technology can be used for rapid and accurate detection and identification.

The reasons for parasitic infections in laboratory mice may include: (1) poor housing conditions for experimental animals, such as cages that are too small, inadequate ventilation, and failure to promptly remove waste; (2) ingestion of food or water contaminated with infectious eggs—due to insufficient cleanliness of food and drinking water, incomplete disinfection procedures, or cross-contamination from wild animals; and (3) the animals themselves having compromised health, with weakened immune systems and reduced resistance. To address these issues, it is recommended to improve the living conditions of experimental animals by housing higher-quality mice within barrier facilities. Additionally, strengthen the disinfection processes for feed, bedding, and drinking water, regularly sterilize and sanitize the animal housing areas, and enhance personnel management protocols. As a preventive measure, anti-parasitic agents can also be added to the animals' diet.

References

1. Isolation and Identification of Intestinal Nematodes from C57BL/6 Mice

2. Morphological Description and Molecular Identification of *Aphelenchoides* Parasitizing the House Mouse

3. Morphological and Molecular Identification of the Four-Winged Acanthocheilonema Species

4. Morphological Study of Cryptolaimus, Tetradichosoma, and Hymenolepis nana

5. Investigation of Intestinal Parasite Infections in Closed-Group ICR Mice

6. Laboratory Animal Epidemiology

7. Illustrated Guide to Medical Parasites

8. Veterinary Parasitology

9. National Standard of the People's Republic of China. GB 14922-2022