Ascaris lumbricoides - Host Immunity, Clinical Manifestation, Complications, Prognosis
Host Immunity of Ascaris lumbricoides
Although the exact mechanism of host resistance is not known, host immunity against Ascaris lumbricoides develops with age. Both humoral and cell-mediated immunity are developed in roundworm infection.
Humoral Immunity
Humoral immunity functions to defend the host from the parasite by:
specific secretion of IgE antibodies
elevated IgG antibodies in the host serum
production of heterotrophic antibodies including anti-A and anti-B isoagglutinin
These antibodies function by
altering biochemical activities – blocks the excretory pores of the roundworm with immune precipitates
increasing adherence to cytophilic eosinophils and activated macrophages to the Ascaris lumbricoides larvae teguments
Cell-mediated immunity
The host cell-mediated immunity against Ascaris lumbricoides infestation involves delayed hypersensitivity reactions which are manifested by the granulomatous reaction around the larvae.
Clinical Manifestations of Ascaris lumbricoides
In the majority of cases, clinical manifestations of Ascaris lumbricoides i.e. symptoms are absent.
In cases where symptoms are present, the parasitic infection may clinically manifest as:
Intestinal ascariasis
Pulmonary ascariasis
Intestinal ascariasis
The severity of intestinal disease caused by Ascaris lumbricoides depends on the roundworm load in the intestine as well as the nutritional status of the infected host.
Symptoms include nausea, vomiting, fever, weight loss, abdominal pain, and diarrhea.
In cases of heavy infections, nutritional impairment in the host occurs. This may result in malabsorption of proteins, vitamins, and carbohydrates. In children, hindrance in growth and development occurs.
In younger children, heavy Ascaris lumbricoides infection may lead to a life-threatening illness called intussusceptions with partial or full obstruction of the intestinal lumen. This is due to the smaller diameter of the lumen in contrast to the size of the adult parasites.
Conditions such as administration of general anesthesia, subtherapeutic doses of antihelminthics, and high temperature during febrile illness may cause the adult Ascaris lumbricoides to migrate to other parts of the host body such as the appendix, biliary duct, and the bile duct. In addition, these roundworms may enter and block small orifices. In extreme cases, the parasites have been passed out from lacrimal glands, nose, and umbilicus.
Pulmonary ascariasis
Pulmonary ascariasis is more common at the initial stage of infection. This is caused by the migrating larvae when it reaches the host lung. Common symptoms in newly infected individuals include coughing, wheezing, etc.
In previously sensitized hosts, Ascaris lumbricoides may clinically manifest as eosinophilic pneumonia (Loeffler’s syndrome).
Loeffler’s syndrome
Loeffler’s syndrome is an allergic hypersensitivity reaction from the host induced by allergens produced by the migrating larvae. Symptoms include cough, low-grade fever, eosinophilia, urticaria, dyspnoea, rales, and pulmonary infiltrates.
These symptoms usually reside 10 to 14 days after larvae leave the lung i.e. at the end of the larval tour.
Complications of Ascaris lumbricoides
Migrating Ascaris lumbricoides can cause intestinal perforation when they enter the peritoneal cavity, respiratory tract, vagina, urethra, and in some cases placenta and fetus.
Biliary tract obstruction due to adult roundworm is another important complication of the parasitic infection.
Prognosis of Ascaris lumbricoides
Ascariasis caused by Ascaris lumbricoides can be successfully treated by the administration of anthelmintics and is rarely fatal. However, death can occur in children mostly due to intestinal obstruction caused by heavy parasitic load.