Large roundworm of pigs - AbsoluteAstronomy.com

Introduction

Ascaris suum, also known as large roundworm of pigs, is a parasitic

Parasitism

Parasitism is a type of symbiotic relationship between organisms of different species where one organism, the parasite, benefits at the expense of the other, the host. Traditionally parasite referred to organisms with lifestages that needed more than one host . These are now called macroparasites...

nematode

Nematode

The nematodes or roundworms are the most diverse phylum of pseudocoelomates, and one of the most diverse of all animals. Nematode species are very difficult to distinguish; over 28,000 have been described, of which over 16,000 are parasitic. It has been estimated that the total number of nematode...

that causes ascariasis

Ascariasis

Ascariasis is a human disease caused by the parasitic roundworm Ascaris lumbricoides. Perhaps as many as one quarter of the world's people are infected, with rates of 45% in Latin America and 95% in parts of Africa. Ascariasis is particularly prevalent in tropical regions and in areas of poor...

in pig

Pig

A pig is any of the animals in the genus Sus, within the Suidae family of even-toed ungulates. Pigs include the domestic pig, its ancestor the wild boar, and several other wild relatives...

s. Until recently it was believed that Ascaris suum could also infect humans; however, it has now been established that humans are affected by a related parasite, Ascaris lumbricoides

Ascaris lumbricoides

Ascaris lumbricoides is the giant roundworm of humans, belonging to the phylum Nematoda. An ascarid nematode, it is responsible for the disease ascariasis in humans, and it is the largest and most common parasitic worm in humans. One-sixth of the human population is estimated to be infected by this...

. Ascaris suum is distributed worldwide and grows up to 40 cm in length. Ascaris infections are treated with ascaricide

Ascaricide

Ascaricides are drugs to treat ascariasis that is caused by infections with parasitic nematodes of the genus Ascaris...

s. Ascaris suum is in the family of Ascarididae, and is one of the oldest association to mankind.

Genetics

A 273 megabase draft genome for Ascaris suum was published in 2011 in Nature.

Life cycle

Life cycle can be direct or indirect with paratenic

Paratenic

In parasitology, the term paratenic describes a host which is not needed for the development of the parasite, but nonetheless serves to maintain the life cycle of the parasite. Alaria americana may serve as an example: the so-called mesocercarial stages of this parasite reside in tadpoles, which...

hosts. The pig ingests the egg with an L2 larva

Larva

A larva is a distinct juvenile form many animals undergo before metamorphosis into adults. Animals with indirect development such as insects, amphibians, or cnidarians typically have a larval phase of their life cycle...

inside. The larvae undergo hepatic

Liver

The liver is a vital organ present in vertebrates and some other animals. It has a wide range of functions, including detoxification, protein synthesis, and production of biochemicals necessary for digestion...

migration, molt to the L3 form, and then migrate to the lung

Lung

The lung is the essential respiration organ in many air-breathing animals, including most tetrapods, a few fish and a few snails. In mammals and the more complex life forms, the two lungs are located near the backbone on either side of the heart...

s. Larvae enter the alveoli, are coughed up and then swallowed. This process is known as hepato-tracheal migration. They then molt two times and become adults.

Paratenic hosts ingest the eggs and the L2 larvae remains in the tissues of the paratenic host until a pig eats it. These may include beetles and earthworms, as well as large to jumbo sized chicken eggs from at-risk fowl.

Morphology

In addition to their large size, these species also have the three prominent lips. Each lips contains dentigerous ridge, and no interlabia or alae.

Males are about 15 cm to 31 cm long, and 2mm to 4mm wide. The posterior end is curved toward the ventral side with a pointed tail. They have simple spicules that measure 2.0mm to 3.5mm long.

Females are larger than males, measuring in at 20 cm to 49 cm long and 3mm to 6mm in diameter. From the anterior end, the vulva occupy about one-third in body length. Females lay 200,000 eggs per day, and the uteri can contain up to 27 million eggs at a time. When the parasite infect a pig, female stop producing eggs after two to three weeks, then resume egg production when there’s a male worm present. Fertilized eggs are ovoid, ranging from 45 µm to 75 µm length and 35 µm to 50µ in diameter. The uterine wall contributes to the lumpy and thick outer layer of the egg. The mammillated layer is stained golden-brown by the bile when the eggs are passed in feces. Before insemination, female would deposit unfertilized eggs that are narrower and longer than normal fertilized eggs, ranging from 88 µm to 94 µm in length, and 44 µm diameter. Only proteinaceous layer can be seen in unfertilized eggs, because after fertilization the vitalline, chitinous, and lipid layers form.

Epidemiology

Infection of Ascaris suum occurs when its eggs, containing a third stage juvenile, are swallowed. The eggs are ingested via contaminated food and water. This contamination occurs when the host defecates in soil that is near habitations. The eggs remain viable anywhere from months to as many as four years, even in freezing conditions. The eggs are able to survive on their own for so long because they are resistant to strong chemicals, low temperatures, and dehydration. Their strong viability aids in the success of the parasite, and is due to the lipid layer of the eggshell that contains ascarosides. With this type of longevity with these eggs it is almost impossible to prevent reinfection once the soil has been contaminated.

Pathogenesis

When juvenile worms are hatched, little damage is done by their penetration into the intestinal mucosa. Symptoms can be difficult to diagnose and confused with other diseases. Juveniles get into the respiratory system by breaking out of lung capillaries and causing small hemorrhages. Heavy infections cause small pools of blood to accumulate and causes edema. This, along with the accumulation of white blood cells and dead epithelium, causes congestion of the air pathways and is called Ascaris pneumonitis. With this condition the lung can become diseased and when bacterial infections become involved, it can lead to death.

Diagnosis and Treatment

Clinical signs include coughing, rapid shallow breathing called "thumps", unthriftiness, colic

Colic

Colic is a form of pain which starts and stops abruptly. Types include:*Baby colic, a condition, usually in infants, characterized by incessant crying*Renal colic, a pain in the flank, characteristic of kidney stones...

, weight loss or reduced weight gain.

Diagnoses by finding eggs (not in paratenic hosts) in the feces by fecal floatation and/or clinical signs.

Ascaris infections are treated with ascaricide

Ascaricide

Ascaricides are drugs to treat ascariasis that is caused by infections with parasitic nematodes of the genus Ascaris...

Incidents and Outbreaks

In Canada in 1970, a postgraduate student tainted his roommates' food

1970 ascariasis poisoning incident

The 1970 ascariasis poisoning incident was a poisoning incident that took place in Quebec in February, 1970. At least seven people were infected with parasitic worm eggs by Eric Kranz, a disgruntled postgraduate student from Hempstead, New York...

with Ascaris suum. Four of the victims became seriously ill; two of these suffered acute respiratory failure.