Introduction
Ascaris lumbricoides has a worldwide distribution. It is particularly common in tropics and subtropics in places where environmental sanitation is inadequate and infected human faeces are used as fertilizers (night soil). World Health Organisation estimated that there were 1.45 billion persons infected with Ascaris lumbricoides and annually 60,000 dying from ascariasis (World Health Organisation, 2002).
Ascaris lumbricoides are large intestinal roundworms which cause a disease called ascariasis, the disease is the third most frequent helminth infection. Ascaris lumbricoides is spread by faeces pollution of the environment. A person becomes infected by ingesting infective egg in contaminated food or from hands that have become faecially contaminated (Adeoye, 2007).
The mature worms live freely in the intestine. Fertilized female worms produce many eggs per day. The egg can remain viable in the soil and dust for several years. These factors contribute to the widespread and often heavy Ascaris lumbricoides which can be found especially among children of 3 – 8 years whose fingers becomes contaminated while playing on an open ground (Chessbrough, 2000).
Eggs past in the faeces are non-embryonated and requires about 30-40 days in the soil environment to mature to infective stage. Infection in man is acquired when man ingests the embryonated eggs. The eggs hatch in the stomach, liberate the larvae that eventually penetrates the wall of the small intestine. In the capillaries the lungs and the larvae are filtered out of the blood vascular system, these penetrate the alveoli of the lungs for several days before migrating or coughed up in the bronchioles, bronchi and trachea. They are swallowed by the epiglottis and enter the small intestine where the larvae grow into adult worms within 8 weeks. The adult live for about 6-12 months and lay eggs that are passed in faeces (Adeoye, 2007).
Epidemiology of Ascaris Lumbricoides
Ascaris lumbricoides has a worldwide distribution. It is prevalence in most warm climates and in areas with poor sanitation. It is one of the commonest human parasites. Infection in humans is acquired through ingestion of embryonated eggs from faecally polluted soil (Ochei and Kolhatkar, 2007).
It is estimated that more than 1.4 billion people are infected with Ascaris lumbricoides representing 2.5 percent of the world population. A number of features account for its high prevalence including an ubiquitous distribution, durability of eggs under a variety of environmental and conditions, high number of eggs produced per parasite, poor socio-economic conditions that facilitate its spread. Transmission is enhanced by the fact that individuals can be symptomatically infected and can continue to shed eggs for years, yet poor infection does not centre protective immunity (Seltzletet al.,1999).
Haswell et al. (2000) stated that ascariasis occurs at all ages, it is most common in children 2 to 10 years old and prevalence tends to cluster in families, and worm burden correlates with the number of people living in a home. Infection with Ascaris lumbricoides has not been reported to be higher in patients infected with human immunodeficiency (HIV) (Anand et al., 1998; Lindo et al., 1998).
More than 796 Ascaris lumbricoides worms weighing up to 550g (19 ounce) were recovered at autopsy from a 2 years old South African girl. The worm had caused torsion and gangrene of the ileum which was interpreted as the cause of death (Baird, 1986). The prevalence is also greatest in areas where suboptimal sanitation practices lead to increased contamination of soil and water. The majority of people with ascariasis live in Asia (73 percent), Africa (12 percent) and South America (8 percent), where some populations have infections rates as high as 99 percent. (Sarinas et al., 1997; Reedel, 1998).
Ova can survive in the environment for prolong periods and prefer warm, shady, moist conditions under which they can survive for up to 10 years (Tietzeet al., 1991). The eggs are resistant to usual methods of chemical water purification but are removed by filtration or by boiling. Developing larvae will be destroyed by sunlight.
Mode of transmission
Transmission occurs mainly via ingestion of water or food (raw vegetables or fruits in particular) contaminated with Ascaris lumbricoides eggs and occasionally inhalation of contaminated dust. Children playing in contaminated soil may acquire the parasite from the hands. Transplacental migration of larvae has also occasionally been reported (Chu et al., 1999). Co-infection with other parasitic diseases occurs with some regularities because of similar predisposing factors for transmission (Tletzeet al., 1991).
Morphology of Ascaris lumbricoides
Ascaris lumbricoides worms are pink or yellow – white in colour. The female is larger (20 – 35 x 0.3 – 0.6 cm) than the male (15 – 30 x 0.2 – 0.4). The tail of the male is curled and has two rod-like projections (spicules). A small mouth is surrounded by three lips.
Fertilized egg; it is round over, measures 60 x 11m yellow-brown in colour and is covered by an outer coarsely mammilated thick albuminous covering. The egg contains a mass of unsegmented embryo, densely impregnated with lecithin granule. Sometimes the albuminous coat of the egg may be absent, it may appear pale yellow with smooth shell and it is described as “decorticated” (Ochei and Kolkatkar, 2007).
Unfertilized egg, the eggs are found in about two-fifth of infections because of the continuous copulation and mass production of eggs. The unfertilized eggs are also found where there are no male adult worms. The eggs are usually more oval (90cm x 45cm) and albuminous coat that completely surround the amorphous mass of protoplasm and the refractile granules (Adeoye, 2007).
Life cycle
Ascaris lumbricoidesis a roundworm, infects humans when an ingested fertilised egg becomes a larva worm that penetrates the wall of the duodenum and enters the blood stream. From there, is carried to the liver and heart, and enters pulmonary circulation to break free in the alveoli, where it grows and molts. In three weeks, the larva passes from the respiratory system to be coughed up, swallowed, and thus returned to the small intestine, where it matures to an adult male or female worm. Fertilization can now occur and the female produces as many 200,000 eggs per day for a year. These fertilised eggs becomes infections after two weeks in soil, they persist in soil for 10 years or more.
The eggs have a lipid layer which makes them resistant to the effects of acids and alkalis, as well as other chemicals. This resilience helps to explain why this nematode is such an ubiquitous parasite. Ascaris lumbricoidesis characterised by its great size male are 2-4mm (0.08 – 0.2in) in diameter and 15-31cm(5.9-12in) long. The male’s posterior end is curved ventrally and has a bluntly pointed tail. Females are 3-6mm (0.1-0.2in) wide and 20-49cm (7.9 – 19m) long. The vulva is located in the anterior end and account for about one third of its body length. Uteri may contain up to 27 million eggs at a time with 200,000 being laid per day. Fertilized eggs are oval to round in shape and are 45 – 75µm (0.0018 – 0.0030in) long and 35 – 50µm (0.0014 – 0.0020in) wide with a thick outer shell. Unfertilised eggs measure 88 – 94µm (0.0035-0.0037in) long and 44µm (0.0017in) wide (Murray et al., 2005; Piper et al., 2007; Roberts et al., 2009).
Pathophysiology
Most of the time, there are no symptoms. If there are symptoms, they may include:
- Bloody sputum
- Cough
- Low grade fever
- Passing worms in stool
- Shortness of breath
- Skin rash
- Stomach pain
- Vomiting worms
- Wheezing
- Worms existing through the nose or mouth
Ascariasis is also the most common cause of Loffer’s Syndrome worldwide. Accompanying symptoms include pulmonary infiltration, eosinophilia and radiographic opacities (Medlineplus Encyclopaedia, 2005).
The symptoms and complications of infections can be classified into the following;
- Pulmonary and hypersensitive manifestation
- Intestinal symptoms
- Intestinal obstruction
- Hepatobiliary and pancreatic symptoms
Intestinal obstruction
A mass of worms can obstruct the bowel lumen in a heavy Ascaris infection, leading to acute intestinal obstruction occurs most commonly at the illececal valve. Symptoms include; colicky abdominal pain, vomiting and constipation vomits may contain worms. Approximately 85 percent of obstructions occur in children between the ages of one and five years. Sometimes an abdominal mass that change in size and location on several examinations may be appreciated (Tenezaet al., 2006).
The overall incidence of obstruction is approximately 1 in 500 children. In endemic areas, it has been shown that, between five and thirty five percent of all cases of bowel obstruction are due to Ascaris lumbricoides(Rhuroo, 2000).
Ascaris is said to be the most common cause of acute abdominal surgical emergencies in certain countries including South Africa and Myanmar (Reeder, 2001).
Hepatobillary and pancreatic symptoms
Symptoms related to the migration of adult worms into the bilary tree can cause abdominal pain, bilary colic, acidulous cholecysticide, ascending chelangit obstructive jaundice, or bile duct perforation with peritonils. Structures of the bilary tree may occur. Hepatic abscesses can also result (Javidet al., 2001). Retained worms fragments can serve as an Indus for recurrent pyogenic cholangitis. The pancreatic duct may also be obstructed, leading to pancreatitis and the appendix resulting in appendiatis
Occasionally, migrating adult worms emerge from the mouth, nose, umbilicus or luginal canal and lacrimal ducts. High fever, diarrhoea spicy funds, anesthesia and other stresses have all been associated with an increased likelihood of worm migration. Complications associated with Ascaris lumbricoides infections are fatal in up to five percent of cases. It is estimated that 20,000 deaths from ascariasis occur annually, primarily as a consequence of intestinal obstruction (Khuroo, 2001).
Pulmonary and hypersensitivity manifestation
Transient respiratory symptoms can occur in sensitized hosts during the stage of larval migration through the lungs symptoms associated with pneumoritis which are known as Loffler’s syndrome, tend to occur one or two weeks after ingestion of the eggs. The severity of symptoms tends to correlate with larval burden, but pulmonary symptoms are also less common in countries with continuous transmission of Ascaris lumbricoides.
Urticaris and other symptoms related to hypersensitivity usually occur toward the end of the period of migration through lungs.
- Intestinal symptoms
Heavy infections with Ascaris are frequently believed to result in result in abdominal discomfort, anorexia, nausea and diarrhoea. However, it has not been confirmed whether or not these non-specific symptoms can truly be attributed to Ascariasis.
With relatively heavy infections, impaired absorption or dietary proteins, lactose, and vitamin A has been noted, and Steatorrhoea may occur. One review concluded that Ascaris-free or treated children should better nutritional status in terms of growth, lactose tolerance, vitamin A and C,and albumin levels than Ascaris-infected children based upon almost 20 years of published cross-sectional and intervention studies from Africa, Asia and South America (Hlaing, 1993). This review also found significant improvement in weight or height following therapy from Ascaris lumbricoides. However, other studies have not confirmed these conclusions and the true effect of Ascaris on nutrition is still widely debated, especially as additional nutritional deficiencies commonly co-exist in infected children (Rousham et al., 1999). It has also been proposed that, heavy infections may be associated with impaired cognitive development in school children (Hadidjaja et al., 1998).
Diagnosis
The diagnosis is usually by:
Detection of eggs in faeces
Identification of the adult worm passed out from the anus or the mouth/nose (Ocheland Koltalktar, 2000).Other forms of diagnosis are through microscopy, eosinophilia, imaging, ultrasound or serology examination.
Microscopy
Microscopy characteristic of eggs may be seen on direct examination of faeces or following concentration techniques by sedimentation method (Unfertilized eggs do not float on Nacl or Zinc Sulphate). (Ochel, and Koltalktar,2000). However, eggs do not appear in the stool for at least 40 days after infection this, the main drawback of recycling upon eggs in faeces at the sole diagnostic marker for Ascaris infection is that, an early diagnosis cannot be made, including during the phase of respiratory symptoms in additions, no eggs will be present in stool if the infection is due to male worms only.
Sometimes an adult worm is passed, usually per rectum. If an Ascaris worm is found in the faeces, a stool specimen can checked for eggs to document whether or not additional worms are present prior to instituting therapy,
Eosinophilia
Peripheral eosinophilia can be found particularly during the phase of larval migration through the lungs but also sometimes at other stages of Ascaris infection (Weller, 1999). Eosinophilia levels are usually in the range of 5 to 12 percent but can be also high as 30 to 50 percent. serum levels of IgG and IgF, are also often elevated during early infection.
Imaging
In heavily infested individuals particularly children, large collections of worms may be detectable on plain film of the abdomen. The mass of worms contrasts against the gas in the bowel, typically producing a “Whirpool” effect (Reeder, 2001). Radiologic detection of adult worms is sometimes made by detecting elongated filling detects following barium, meal examination of the small bowel. The worm may sometimes ingest barium, in which the alimentary canal appears as a white thread bisecting the length of the worms body (Reeder,2001) Radiographs will also show when there is associated intestinal obstruction (Kakihara et al., 2004).
Ultrasound
Ultrasound examinations can help to diagnose hepatobiliary or pancreatic ascariasis single worms, bundles of worms or a pseudotum or like appearance body segments of worms may be visible, and on prolonged scanning, the worms will show curling movement (Malden 1999) computed temographic (CT) scanning of magnetic resonance imaging (MRI) may also be used to identify worm(s) in the liver or bile duct this is not usually necessary. Imaging the worm in cross-section gives a “bull” eye” appearance when ascariasis involving the biliary tree or pancreatic duct is suspected, an ERICP will not only establish the diagnosis but also allows for the direct removal of the worm (Misraet al., 2000).
Serology
Infected individuals make antibodies to Ascaris lumbricoides, which can be detected. However, serology is generally reserved for epidemiologic studies rather than in the diagnosis in a particular individual (Seltzer, 1999). IgG antibodies are not protective against infection (Ocheland Katalktar,2000). Antibodies to Ascaris also often cross react with antigens from other helminths.
Prevention
Prevention of re-infection poses a substantial problem since Ascaris parasites are abundant in soil good sanitation to prevent fercal contamination of soil is required. An education programme advising against the use of human faeces as a fertilizer is also needed in some areas. Soil treatments have been attempted but are generally not practical. Mass treatments with single dose Mebendazole for all school age children and reducing the overall worm burden in the community. Indeed, mass community therapy has been shown to reduce Ascaris burden and transmission, although it has a greater effect on the intensity of infection than on the overall prevalence (Hall et al, 2000). This approach has been shown to be cost-effective (Holland et al 1996). Because re-infections occur so frequently, shorter intervals between treatments have been found to be preferable. Targeted treatments help to control the morbidity of infection but do not have a substantial effect on transmission, (Anderson 1999). In a large randomized trial of school-based de-worming performed in Zanzibar, for example, single dose Mebendazole, given either twice or trice (three times) a year, decreased intensity of Ascaris lumbricoides infection by 63 and 67 percent, respectively, compared to control children who received no mebendazole (Albonico et al., 1999).
Prevention include; use of toilet facilities, safe excreta disposal, and protection of food from dirt and soil, through washing of product and hand washing. Food dropped on the floor should never be eaten without washing or cooking, especially in endemic area. Fruits and vegetables should always be washed thoroughly before consumption.
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