Moniliformis moniliformis

Moniliformis moniliformis is a species of acanthocephalan parasite that can infect humans, though it rarely does. Human infections have been reported in the United States, Iran, Iraq, and Nigeria. It has been found in rats all over the world, and usually is found in cats, dogs and, in Poland, red foxes. Intermediate hosts are usually beetles and cockroaches.

This parasite, like other acanthocephalans, does not have a digestive tract. It absorbs nutrients through the tegument (external layer). The scolex (anterior end) of the worm has a cylindrical proboscis and a multitude of curved hooks. The main parts of the worm body are the proboscis, neck, and trunk. The male is generally 1.5 to 2 inches long, while the female ranges from 4 to 12 inches in length. The female has floating ovaries within a ligament sac where fertilization occurs.

The eggs of this parasite typically infect intermediate hosts (beetles or cockroaches) and usually remain premature until ingestion occurs by a larger definitive host, where it attaches to the small intestine and matures and then mates again, with eggs being excreted with feces, to be ingested yet again by another intermediate host to renew the cycle.

Reproduction only occurs in the definitive host. The adult male has cement glands in the posterior end. The widely-held theory is that the mucilaginous and proteinaceous substance that these glands secrete is used by the male to seal up the female after copulation in order to prevent leakage of the inseminated sperm and further insemination by other males. It has also been found that the male may create this seal on other males in order to prevent them from copulating. These seals, or copulatory caps, last for a week.

In what is commonly known as “brain-jacking,” the parasite induces a behavioral change in its intermediate host that increases the risk of predation for the host. It is thought that this behavioral change holds an evolutionary advantage for the parasite by increasing its chances of getting to its definitive host. When Moniliformis moniliformis infects its intermediate host, the cockroach species, Periplaneta americana it changes the cockroach’s escape response. In one study, it was concluded that cockroaches infected by M. moniliformis took longer to respond to wind stimuli simulating the approach of a potential predator and displayed fewer escape responses implying that the parasite infection renders its intermediate host more vulnerable to predation by hindering its ability to detect and escape from its predator.

While this species rarely infects humans, there have been several human cases reported. The earliest known human infection was found in Utah in the feces of a prehistoric man. In 1888 in Italy, Calandruccio infected himself by ingesting larvae, reported gastrointestinal disturbances, and then shed the eggs in two weeks. This was the first report of the clinical manifestations of an M. moniliformis infection in humans (or acanthocephaliasis). Because infection of humans would require human consumption of infected raw beetles or cockroaches, human acanthocephaliasis is rare.

There are not many case studies on acanthocephaliasis but of the ones that exist, many of the patients described were asymptomatic. When the patients exhibited symptoms, they normally experienced abdominal pain, diarrhea, dizziness, edema, and anorexia. In some patients, giddiness has also been reported. In rodents, acanthocephaliasis is fatal and manifests itself through similar hemorrhaging and gastrointestinal disturbance. Acanthocephaliasis is treated with anti-helminthics.

Because the only way of developing acanthocephaliasis is through ingesting the intermediate hosts, the most effective means of prevention is avoiding the consumption of beetles and cockroaches. This is especially difficult in children exhibiting pica and in areas with poor hygiene. Awareness campaigns on the risks of consuming infected beetles and cockroaches would be effective. Moreover, preventing entry of the intermediate hosts into the home, and especially the kitchen where it is at risk of getting into the food, would help curb the risk of becoming infected.

Image Caption: An adult of Moniliformis moniliformis (Acanthocephala: Archiacanthocephala: Moniliformida). Credit: Division of Parasitic Diseases and Malaria team/Wikipedia