**1. Introduction**

Population growth significantly contributes to water shortages in about 100 countries worldwide. It is estimated that by the year 2025, two-thirds of all people will be experiencing moderate to severe fresh water shortage [1]. Wastewater reuse has been considered as an alternative way of overcoming water scarcity in various parts of the world [2]. Treated and untreated wastewaters have been applied to economic and domestic activities including industry (applied in cooling and cleaning); recreation (swimming pools, irrigation of parks, and golf courses); and agriculture (irrigation) [3]. Globally more than 20 million hectares of agricultural

land is irrigated with either treated or untreated wastewater [4]. In addition to the direct uses, about 80% of all wastewater is discharged to the world's water bodies such as rivers, lakes, swamps, and streams [5].

Whether it is used directly or indirectly, an important consideration in wastewater reuse is its quality in terms of pollutant types and content. Wastewater reuse or discharge to surface water poses risks of disease transmission from animal and/or human-excreted waterborne pathogenic organisms to exposed communities [6, 7]. Transmissions of pathogenic bacteria are frequently a public health concern; however, the most important public health problem is parasite transmission [8]. Among the pathogenic parasites identified in wastewater, soil-transmitted helminths (STHs) are the most common. The problem of STH predominance in wastewater is measured in terms of how frequently the parasites are identified and their level of concentration [9]. The predominance of STHs in wastewater has been associated with the ability of their eggs to resist different types of environmental conditions compared to other organisms [10, 11].

In many countries, exposure to wastewater has been associated with high prevalence of STH transmission [12–14]. In addition, STHs are more prevalent in low- and middle-income countries where more than 72% of generated wastewater is discharged without being treated [15, 16]. To prevent the spread of helminthic diseases such as those caused by STH (e.g., ascariasis, trichuriasis, and hookworm), several measures to protect health have been practiced in wastewater reuse. These measures include wastewater treatment, crop restrictions, control of wastewater application, control of human exposure, and promotion of personal hygiene. Of these measures, wastewater treatment is the most commonly adopted approach in many controlled wastewater reuse schemes [17]. **Figure 1** presents an estimation of wastewater treatment capacities in 2015 in countries classified by level of income and their expected achievement by 2030. The estimation in 2015 shows that the capacity of wastewater treatment is 70% of all wastewater generated in high-income countries and 8% of all wastewater generated in low-income countries [5].

Compared to conventional treatment systems such as activated sludge and trickling filters, natural wastewater treatment systems have been reported to be more efficient at removing STH eggs from wastewater [18]. The potential of two types of natural wastewater treatment systems (waste stabilization ponds and constructed wetlands) for prevention of STH infections is discussed in this chapter.

**39**

with infective eggs.

*Natural Wastewater Treatment Systems for Prevention and Control of Soil-Transmitted Helminths*

STHs, are also known as geohelminths, are multicellular intestinal nematodes. Part of their life cycle depends on soil for maturation and they are transmitted through contaminated soil. The important STH species infecting humans include roundworm (*Ascaris lumbricoides*), whipworm (*Trichuris trichiura*), and hookworms (*Necator americanus and Ancylostoma duodenale).* These helminths are distributed throughout the world. Globally, about two billion people are infected with at least one species of STHs with those having heavy infections presenting considerable morbidities including malnutrition, allergy, and respiratory difficulties including asthma and Löffler's syndrome, diarrhea, intestinal obstruction, rectal prolapse, anemia, and cognitive development problems [19]. With limited access to clean and safe water often leading to poor hygiene and insufficient sanitation services, frequency of helminthiasis is higher in low- and middle-income

Transmission of STH occurs through the fecal-oral route by ingesting viable eggs of *Ascaris lumbricoides* and *Trichuris trichiura* from contaminated soil or food or, through skin penetration by third-stage hookworm larvae (filariform larvae). Based on the passage of young-stage worms (larvae), the STHs are divided into three groups. *Trichuris trichiura* undergoes a direct life cycle whereby the ingested eggs directly develop to adult worms inside human intestines. *Ascaris lumbricoides* undergoes a so-called modified direct life cycle whereby ingested eggs hatch to release larvae in the human intestine. The released larvae penetrate intestinal mucosa to the blood stream where they migrate to the liver, heart, lung, upper respiratory track, then return to the intestines where they develop into adults. Unlike *Ascaris lumbricoides* and *Trichuris trichiura,* eggs of hookworms hatch in the soil where they develop to the infective stage-three larvae (filariform larvae). The filariform larvae penetrate unbroken skin of human beings to the blood, and migrate to the liver, heart, lung, upper respiratory tract to the intestine where they mature to adults (**Figure 2**). In very rare cases, hookworm transmission occurs via the fecal-oral route. In the intestine, the sexually mature male and female adults mate and the female lays fertile eggs. In all these helminth species, eggs are excreted with feces to the environment. When they reach the soil, they mature and become infective (*Ascaris lumbricoides* and *Trichuris trichiura*), or hatch to rhabditiform larvae, which then develop into the infective filariform larvae (hookworms). STHs do not multiply in the host. Therefore, each one that is found in the intestine is the

**2. Soil-transmitted helminths in human and wastewater**

*DOI: http://dx.doi.org/10.5772/intechopen.92654*

**2.1 Soil-transmitted helminths in humans**

countries than in high-income countries [15].

**2.2 Life cycles of soil-transmitted helminths**

result of a single infection event [20].

**2.3 Soil-transmitted helminth treatment and control**

The drugs of choice for treatment of STHs are albendazole (400 mg) and mebendazole (500 mg). Measures used to control STH involve periodic deworming of at-risk groups to eliminate infective worms, health education to prevent infection and reinfection, and improved sanitation to reduce soil contamination

In 2011, the World Health Organization (WHO) opted for the use of periodic mass treatment with albendazole for at-risk people in STH endemic areas.

#### **Figure 1.**

*Wastewater treatment in countries as classified based on the level of income. Figure from [16].*

*Natural Wastewater Treatment Systems for Prevention and Control of Soil-Transmitted Helminths DOI: http://dx.doi.org/10.5772/intechopen.92654*
