ROUNDWORMS

ROUNDWORMS


Roundworms belong to the phylum Nematoda, which contains worms that are round and unsegmented. Members of this phylum are called nematodes. There are thousands of genera of nematodes, but only five are of zoonotic importance in North America: Toxocara canis, T. cati, Baylisascaris procyonis, Ancylostoma braziliense, and Trichinella spp. A. braziliense is a nematode parasite that is discussed under Hookworms. Trichinella spp. are discussed under trichinosis.



MORBIDITY: +




MORTALITY: + TO ++++




ETIOLOGY: PARASITIC


T. canis, T. cati, and B. procyonis are roundworms of zoonotic importance when the infective eggs of these parasites are ingested by abnormal, or atypical, dead-end mammalian hosts, such as people.



HOSTS


T. canis is the roundworm of dogs, T. cati is the roundworm of cats, and B. procyonis is the roundworm of raccoons. Other mammals, including humans, are abnormal or suboptimal hosts.



TRANSMISSION


Adult roundworms live in the intestines of their hosts. Transmission starts with passage of roundworm eggs in the feces. A single T. canis female can produce up to 100,000 eggs per day; a single B. procyonis female can produce up to 45,000,000 eggs per day. If the host is harboring hundreds of roundworms, the potential exists for the production of millions of infective eggs in a single day. Roundworm eggs can become infective within 2 weeks and can remain infective in the environment for years. Eggs often live in soil, and the next host is infected when it eats infective eggs containing live larvae or immature worms.


After ingestion the eggs hatch, and the larvae are released into the intestinal tract. They burrow through the intestinal wall and into a blood vessel, where they are then carried on a circuitous journey through the host’s body. Eventually they end up back in the host’s intestines when they are ready to become adults. The cycle begins again after the adult female roundworms produce eggs, which are then passed in the host’s feces (Figure 31).


The zoonotic problem arises when the infective roundworm eggs are ingested by atypical or suboptimal hosts, such as people. The eggs still hatch in the intestine, and the larvae will enter the blood stream to begin migration routes that are abnormal because the larvae are in an atypical host. These abnormal migration routes do not lead back to the intestines, but along the way the larvae are deposited in various tissues in the body, causing tissue damage as they continue to migrate through the tissue.



ROUNDWORM INFECTIONS IN ANIMALS


Damage due to roundworms is most often seen in young animals. Puppies can be infected with T. canis before they are born, through the mother’s milk, or by ingesting infective eggs. Sometimes migrating larvae in a bitch will go dormant in tissue until she becomes pregnant. If she has been treated for roundworms, she most likely is not shedding roundworm eggs in the feces, so she appears to be roundworm-free. The pregnancy activates the larvae to finish the life cycle, and they find their way back to the intestines, where they mature and produce eggs. Puppies can thus become infected from a mother that appears roundworm-free.


Kittens are not infected with T. cati before they are born, but are most likely to be infected through the mother’s milk and through ingestion of infective eggs.


Adult worms absorb nutrients from the host’s intestines. Because of their large size, they can interfere with digestion and may even damage the intestinal wall. In large numbers they can cause intestinal obstruction and constipation. Animals with low numbers of adult worms may show no roundworm-specific clinical signs. Puppies with heavy infections will be thin, but will have a potbelly. They may vomit or have diarrhea in which adult worms may be present. Adult worms may also be passed in the puppy’s normal feces. Puppies with heavy infections do not do well, and often act as though they are in pain. T. canis and T. cati larvae migrate through the lungs, causing a dry cough.


The life cycle of B. procyonis is similar to the life cycles of T. canis and T. cati. The adult worms do not seem to do much damage in raccoons.



LARVA MIGRANS IN HUMANS


When people swallow roundworm eggs, they can develop diseases known as visceral larval migrans, ocular larva migrans, or neural larva migrans (Figure 32). As with animals, most of the damage seen with T. canis, T. cati, or B. procyonis infection in people occurs in young children. Most infections happen when children play in areas contaminated with infective roundworm eggs. Children like to put interesting things in their mouths, including dirt, dirty toys, or dirty hands, all of which may have been contaminated with infective roundworm eggs. The eggs hatch as usual in the intestine, and the released larvae burrow through the intestine wall into the blood stream, which carries them to various parts of the body, depositing them in tissues. The larvae can remain alive for many weeks in the tissues, where they migrate around causing tissue damage and destruction. This is known as visceral larva migrans (VLM). The tissues most often affected are the liver, lungs, eye, and brain. The damage caused by the migrating larvae is permanent and can result in severe visual, respiratory, or neurological conditions. The degree of damage or destruction is dependent on the number of larvae meandering through the tissue. Eventually the larvae die, and small abscesses or granulomas may form around them. In people, the larvae never fully mature.


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FIGURE 32 Visceral, ocular, and neural larva migrans.

Related posts:

  1. ABOUT THE DISEASES
  2. CAMPYLOBACTERIOSIS (VIBRIOSIS)
  3. MYCOBACTERIUM INFECTIONS (TUBERCULOSIS)
  4. PSITTACOSIS

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Oct 1, 2016 | Posted by in EXOTIC, WILD, ZOO | Comments Off on ROUNDWORMS

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