**3. Giardiasis epidemiology**

**1. Introduction**

148 Current Topics in Giardiasis

Gastrointestinal diseases have caused up to 871,000 deaths worldwide, which have been related to unsafe drinking water, health, and hygiene. Mortality rate is greater in African countries where death risk is 4.3 × 10−1 [1, 2]. Such data justify that the main risk factors are unsafe water and deficient cleaning linked to malnutrition and immunosuppression, invariable characteristics in marginalized communities. The microscopic parasite *Giardia* is among the main pathogens that cause gastrointestinal diseases at world level. In developing countries, 200 million people have been diagnosed with giardiasis symptoms, which are related to inadequate sanitation problems and access to safe drinking water. Giardiasis does not make a distinction between humans and animals by fecal-oral transmission using different routes:

The strategy used in this research was assessed by analyzing different literature studies related to *Giardia* risk assessment; the search was performed in databases from October 2000 to October 2016, using the following terms: giardiasis risk factors; *Giardia* cysts in water, air, soil, and food; quantitative microbial risk assessment (QMRA); and cyst treatments. No restriction was found in language. This chapter focuses on reviewing world incidence of *Giardia* in water, soil, air, and food, including giardiasis prevalence, risk factors, and finally a system to reduce

*Giardia* is one of the most primitive eukaryotic protozoa initially described by Leeuwenhoek in 1681; its taxonomy was confusing and complicated throughout the first half of the twentieth century. The name *Giardia lamblia* was well-known in the 1970s, but it was consolidated and changed to *Giardia duodenalis* or *Giardia intestinalis* in the 1990s. It is classified within the class Zoomastigophorea in the order Diplomaida and family Hexamitidae. Historically, 41 species have been described based on their hosts. To date, eight of these species have been detected in mammals: *duodenalis, enterica, canis, bovis, muris, cati, simondi*, and *microti* (**Table 1**) [6–9].

*Giardia* exists in two forms: an active form called a trophozoite and an inactive form called a cyst. The cyst measures 5 × 7 to 10 μm in diameter, containing four nuclei covered by a wall from

zoonotic, anthropogenic environmental, food, and water [3–5].

cysts in the environment, emphasizing on QMRA.

**2.** *Giardia* **generalities**

**Species\* Host**

*G. agilis* Amphibian *G. muris* Rodents *G. ardeae* Birds *G. psittaci* Birds

*G. microti* Rats and moles

**Table 1.** Giardia species.

*G. intestinalis* Humans and mammals

#### **3.1.** *Giardia* **in the environment**

The necessary dosage for giardiasis to start is from 10 cysts, which have been found in all environmental matrices: water, soil, air, and food. In drinking water, up to 24 cysts/L have been reported [16]; 87 cysts/L in soil; 0.0087 cysts/L in air [17]; and 40 cysts/L in leafy vegetables [18]. Most research has monitored *Giardia* cysts in water (**Table 2**). Giardiasis life cycle includes illness in several mammal species mediated by the environment, which is why climate factors such as humidity and temperature influence in cyst exposure, which are very persistent and their viability is preserved more in temperate and humid climates. *Giardia* cysts can maintain their infectious capacity from 15 days up to 2 months in water; 15 days to 1 month in soil; and from 2 to 10 days in vegetables; because of their small size and weight, they can be found suspended in air. Their resistance in the environment is a natural advantage to invade new hosts and expand their


**Table 2.** Occurrence and density of Giardia cyst in water.

progeny, which is why they have been identified as a potential danger to food products that are equally contaminated with animal feces or with contaminated water [17, 32]. Fecal runoff and vectors increase pathogen dissipation and thus the risk of acquiring the disease [33].

#### **3.2. Genotypes**

*Giardia* has many species characterized, but *G. intestinalis*, *lamblia*, or *duodenalis* is more recognized as a pathogen for human beings and a wide range of hosts including wild animal species. Currently, eight genetic groups from A to H (**Table 3**) are recognized; nonetheless, the species that are harmful for humans are divided into two genotypes: A (or Polish) and B (or Belgian), of which B is the most pathogenic in man [34]. Recent studies have revealed that genotype E has also been identified in humans [32].

The majority of research studies report that genotypes A and B have been found in clinical samples, and their distribution in the world is related to social and economic factors. The mix of both genetic groups (A and B) has also been reported in one sample, which suggests multiple infections [1] and confirms constant exposure to contaminated sources. It is common to find assemblages or genotypes A and E in superficial water [27].

*Giardia* genotypes can appear mixed as in the case of Scotland where both genotypes turn up, of which A is more prevalent [35]; the same case happened in Malaysia [36] and in Egypt, where A subtype I was the most prevalent [37]. In Latin America, particularly in Mexico, genotype A


**Table 3.** Recognized *Giardia* genotypes.

type II is only present [38]. While in Argentina, genotype A type II showed low seroprevalence, genotype B was found in high number of cases that included children and adults [39].

Genotype A is linked to diarrhea [40] and more in human origin than in zoonotic [1]; in disagreement, another study indicated that humans are the greatest source of assemblage B and that domestic animals are the greatest hosts of assemblage A [41].

#### **3.3. Outbreaks and risk factors**

An outbreak is a spontaneous increase of a disease occurrence. These cases are epidemiologically linked with at least one confirmed laboratory case. Numerous giardiasis outbreaks transmitted in water have occurred in the USA, Canada, England, France, Australia, Japan, and other industrialized nations due to contamination of water and food sources (**Table 4**). The factors that could be attributed to the increase of parasitic disease outbreaks produced by water and food are diverse. The increase of international travelers and migrants produces a rapid dissemination of the symptoms. Globalization of food sources, food imports as exotic fruits and vegetables are now necessary to satisfy consumption demands. Unfortunately, transportation conditions as controlled temperature have favored parasite survival in fruits and vegetables [50].

Two significant factors that contribute to the risk of contracting giardiasis are age and gender. Children from 1 to 5 years of age are more prone to the disease; in addition, infection incidence is greater in men than in women [38]. Divers have a high risk of contracting parasitosis even more than swimmers [51].

#### **3.4. Impact in public health**

Political, legal, economic, and public health is very committed to having reliable and safe drinking water sources for human consumption. An important concern is having them contaminated with pathogenic microorganisms such as *G. intestinalis*. The World Health Organization


**Table 4.** Giardiasis outbreaks.

**Genotype Hosts**

**3.2. Genotypes**

150 Current Topics in Giardiasis

C, D Dogs

F Cats G Rats

E Cows, goats, lams, and pigs

genotype E has also been identified in humans [32].

find assemblages or genotypes A and E in superficial water [27].

**Source Location Percent** 

Malaysia, Taiwan, EU, México, China

Surface water Belgium, Germany, Ireland, the Netherlands,

**Table 2.** Occurrence and density of Giardia cyst in water.

Waste water EU, Italy, Ireland, Spain 25–100 3.2 × 103

H Marine vertebrates

**Table 3.** Recognized *Giardia* genotypes.

A Humans, cats, dogs, horses, calves, pigs, deers, lemurs, beavers, Guinea pigs, and sloths

progeny, which is why they have been identified as a potential danger to food products that are equally contaminated with animal feces or with contaminated water [17, 32]. Fecal runoff and

Drinking water Bulgaria/Russia, Spain 5–27 0–62 [28, 29] Ground water Bulgaria/Russia, Brazil, France 8–62.5 6–3.61 × 103 [29–32]

**positive\***

**(oo)cyst 100 L−1\***

10–81 0.2–18.6 × 104 [23–27]

**Reference**

–4.2 × 104 [19–22]

*Giardia* has many species characterized, but *G. intestinalis*, *lamblia*, or *duodenalis* is more recognized as a pathogen for human beings and a wide range of hosts including wild animal species. Currently, eight genetic groups from A to H (**Table 3**) are recognized; nonetheless, the species that are harmful for humans are divided into two genotypes: A (or Polish) and B (or Belgian), of which B is the most pathogenic in man [34]. Recent studies have revealed that

The majority of research studies report that genotypes A and B have been found in clinical samples, and their distribution in the world is related to social and economic factors. The mix of both genetic groups (A and B) has also been reported in one sample, which suggests multiple infections [1] and confirms constant exposure to contaminated sources. It is common to

*Giardia* genotypes can appear mixed as in the case of Scotland where both genotypes turn up, of which A is more prevalent [35]; the same case happened in Malaysia [36] and in Egypt, where A subtype I was the most prevalent [37]. In Latin America, particularly in Mexico, genotype A

vectors increase pathogen dissipation and thus the risk of acquiring the disease [33].

B Humans, dogs, monkeys, beavers, rabbits, guinea pigs, muskrats, and chinchilla

(WHO) estimates that at least 10<sup>9</sup> cases of gastrointestinal diseases occur per year in one-third of the countries in the world, causing mortality of more than 5 × 106 persons at early age. The economic costs of diseases are alarming and cause financial losses. For this reason, social institutions have decided to work in developing better techniques for researching and controlling parasites in such a way that water turns out to be a safe liquid. Knowing the relative importance of specific transmission routes of intestinal protozoa, including potential sources of environmental contamination, constitutes fundamental aspects that allow understanding the epidemiology of parasitic diseases. In this manner, corrective measures can be applied to minimize prevalence and incidence of these diseases in the population. In developed countries, giardiasis is an emerging infection because it plays an important role in diarrhea outbreaks linked to water and food consumption that affect the population in general. As to developing countries in Asia, Africa, and Latin America, approximately 200 million people experience giardiasis symptoms [1, 52].
