Epidemiology of Ascaris Lumbricoides

WHO estimated that more than 1.4 billion people are infected with Ascaris lumbricoides, representing about 25 percent of the world population.

In Malaysia, it is estimated that up to 90 percent are infected in rural areas (especially among Orang Asli) whereas only 4 percent in are reported urban areas.

A number of features account for its high prevalence including:
1)a ubiquitous distribution the durability of eggs under a variety of environmental conditions
2)the high number of eggs produced per parasite
3)poor socioeconomic conditions that facilitate its spread.
Transmission is enhanced by the fact that individuals can be asymptomatically infected and can continue to shed eggs for years, yet prior infection does not confer protective immunity.

Although ascariasis occurs at all ages, it is most common in children 2 to 10 years old, and prevalence decreases over the age of 15 years. Infections tend to cluster in families, and worm burden correlates with the number of people living in a home. Infection rates for ascariasis have not been reported to be higher in patients infected with the human immunodeficiency virus (HIV).

The highest prevalence of ascariasis occurs in tropical countries where warm, wet climates provide environmental conditions that favor year-round transmission of infection. This contrasts to the situation in dry areas where transmission is seasonal, occurring predominantly during the rainy months.
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 infection rates as high as 95 percent.

The rate of complications secondary to ascariasis ranges from 11-67%, with intestinal and biliary tract obstruction representing the most common serious sequelae. Although infection with A lumbricoides is rarely fatal, it is responsible for an estimated 8,000-100,000 deaths annually, mainly in children, usually from bowel obstruction or perforation in cases of high parasite burden

Ova can survive in the environment for prolonged periods and prefer warm, shady, moist conditions under which they can survive for up to 10 years. 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 and desiccation. There is no significant animal reservoir, but A. suum, which infects pigs, is morphologically similar to A. lumbricoides, and the larval forms can occasionally infect humans.

Transmission - How the parasites were spread?
Transmission occurs mainly via:
1)ingestion of water or food (raw vegetables or fruit in particular) contaminated with Ascaris lumbricoides eggs
2)inhalation of contaminated dust
3)Children playing in contaminated soil may acquire the parasite from their hands
4)Transplacental migration of larvae has also occasionally been reported
5)Co-infection with other parasitic diseases occurs with some regularity because of similar predisposing factors for transmission