Giardia is a gastrointestinal parasite that causes infections in humans worldwide. In developing countries, giardiasis is an emerging infection because it plays an important role in diarrhea outbreaks linked to water and food consumption affecting the population in general. Giardiasis is referred to as zoonosis because its biological etiological agent is transmitted to humans through animal reservoirs by oral-fecal route. Detection and occurrences of Giardia cysts have been documented in water, food, soil, and air. The principal risk factors for developing giardiasis include environmental contamination associated with malnutrition and immunosuppression. The small size of cysts and their environmental resistance together with the small infection dose to produce the disease allow giardia dissemination especially in marginalized populations; however, parasitism is present in all countries and at different economic levels. This zoonotic illness contains several species of Giardia duodenalis, infecting mammals and humans with eight serotypes, of which A and B are of public health importance. Quantitative microbiological risk assessment (QMRA) is a methodology used for predicting health risk to establish regulations for permissible Giardia risk in water and food. This chapter focuses on worldwide reviews of Giardia incidence in environmental samples including giardiasis prevalence, serotypes, risk factors, and finally options for cyst reduction in the environment, emphasizing on QMRA.
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
The strategy used in this research was assessed by analyzing different literature studies related to
|Humans and mammals|
|Rats and moles|
The vital cycle of
For the parasite to survive within the host and avoid the immune response,
3. Giardiasis epidemiology
Giardiain 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 ; 87 cysts/L in soil; 0.0087 cysts/L in air ; and 40 cysts/L in leafy vegetables . Most research has monitored
|Waste water||EU, Italy, Ireland, Spain||25–100||3.2 × 103–4.2 × 104||[19–22]|
|Surface water||Belgium, Germany, Ireland, the Netherlands, Malaysia, Taiwan, EU, México, China||10–81||0.2–18.6 × 104||[23–27]|
|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]|
|A||Humans, cats, dogs, horses, calves, pigs, deers, lemurs, beavers, Guinea pigs, and sloths|
|B||Humans, dogs, monkeys, beavers, rabbits, guinea pigs, muskrats, and chinchilla|
|E||Cows, goats, lams, and pigs|
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  and confirms constant exposure to contaminated sources. It is common to find assemblages or genotypes A and E in superficial water .
Genotype A is linked to diarrhea  and more in human origin than in zoonotic ; 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 .
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 .
|Source||Location||Quantity of cases||Reference|
|Water sources||New Zealand||14|||
|Swimming pool||Victoria, Australia||30|||
|Drinking water||New Hampshire, EU||31|||
|Water sources||New York, EU||36|||
|Recreational water||California, EU||50|||
|Water supply||Izmir; Turkey||196|||
|Contaminated water||Bergen, Norwegian||2500|||
|Foodborne/anthropogenic||All states in EU||19,140|||
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 . Divers have a high risk of contracting parasitosis even more than swimmers .
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
4. Detection methods in the environment
Detection techniques in environmental samples are diverse. Molecular biology methods are used to differentiate genotypes by using hybridization DNA probe DNA and polymerase chain reaction (PCR) techniques, starting from diverse fragments of nucleic acids as ribosomal RNA, los genes
The techniques to number
Fluorescent staining as acridine orange, propidium iodide (PI), and 4,6-diamidino-phenylindole (DAPI) are prone to have false positives and have variable stain characteristics depending on the viability state of the microorganism; nonetheless, the use of these stains, especially DAPI, can be very useful in identification when used together with other microscopy techniques such as fluorescence and phase contrast and differential interference contrast (DIC) .
Immunomagnetic separation (IMS) methods and the 1623 method have been developed to concentrate bacteria and protozoan pathogens. These methods use specific antibodies on the surface of paramagnetic particles to link target pathogens, followed by a magnet used to separate them from the matrix sample . The assay method of immunoabsorption linked to enzymes (ELISA) is more sensitive than the microscopy techniques for (oo)cyst detection .
Flux cytometry (FC) is a method by means of fluorescent activators capable of classifying cells according to their fluorescence and size. Detection and selective enumeration of
Knowing cyst concentration in environmental samples and the necessary dosage when giardiasis starts allows us to estimate pathogen exposure; with this information and using the appropriate mathematic model, it is possible to calculate health risk. This methodology called quantitative microbial risk assessment (QMRA) is based on a series of steps that convey predicting daily and annual risks. In developed countries, QMRA has been adapted to assess permissible risk limits for
5. Quantitative microbial risk assessment
The Codex Committee on Food Hygiene and the National Advisory Committee on Microbiological Criteria for Foods have proposed a framework for conducting QMRA. These guidelines also provide methods and approaches used to evaluate potential health effects and assess risks from contaminated source media, i.e., soil, air, and water. One of the key benefits of this method is the development of models describing the complex nature of pathogen populations in water or food supply .
Hazard identification involves pathogen detection in terms of concentration in water, for example. Next is exposure assessment where the quantity of water consumed for the people at risk is determined. In these two steps, one should take into account the recovery efficiency of the method, the characteristics of the people (age, sex, immune state, and customs), and pathogen survival. Then, the dose-response curve is calculated with the mathematical models described in the literature; finally, the integration of all the parameters provides the risk characterization that results in the likelihood of infection risk per day and year per person .
Quantitative microbial risk assessment has become a standard; the UK has pronounced a mandate that establishes that risk assessment be carried out by local government on many water supplies . The US Environmental Protection Agency (EPA) handled permissible water
6. Quantitative microbial risk assessment for
Giardiain environmental samples
The QMRA is an approach that has been widely used around the world to estimate the risk of infection by giardiasis in different sources of exposure. Most research studies have been performed in water samples, but the method has been applied in food, soil, and air samples.
In the last few years, the most relevant studies where QMRA has been used to evaluate giardiasis infection risks are the following:
In New Jersey, USA, the risk by accidental water ingestion (50 mL) of the Lower Passaic River was assessed resulting in a probability of 1:1 . In Amsterdam, risk probability was calculated from 9 × 10−4 to 1.2 × 10−2 in recreational waters , while in Eastern Europe a giardiasis risk was predicted from 3 × 10−1 for water consumption from a well contaminated with sewage water . In Mexico, a risk of 1.09 × 10−2 was estimated by lettuce consumption .
In France and England,
In Brazil, giardiasis risk for drinking water consumption was estimated at 1.92 × 10−2 . In Venezuela, the risk for bathers swimming in seawater was 3.6 × 10−2 . In Switzerland, the risk by indirect contact with water from a lagoon contaminated with residual water was 3.5 × 10−1 , whereas risk by joint exposure to soil and dust transported by air was assessed at 1:1 in a rural town in Mexico .
In all the previous studies (Figure 2), the risks were greater than those allowed by the regulating commissions (1 × 10−4), which is why these studies show that the microorganism concentration is enough to produce the disease in a percentage of the populations. Based on this information, it should be solved how to make these sources not harmful for humans and implement the necessary treatments for decreasing or eradicating giardiasis risk.
Using the concentrations reported in the literature, annual risk by giardiasis was calculated. To estimate infection probabilities (Pi), a consumption exposure of 1.46 L was taken into account , and then the exponential model equation Pi = 1−exp(−
|Drinking water||Québec, Canada||8.4 × 104|||
|Reclaimed water||California, EU||1.58 × 10−1|||
|Surface water||NJ, EU||1|||
|Surface water||Arizona, EU||4.2 × 10−4|||
|Urban flooding||Netherlands||6 × 10−3|||
|Treated water||Saint Lawrence River, Canada||1.46 × 10−3||, |
|Tank water||Queensland, Australia||1.2 × 10−1|||
|Small water supplies||England||9.1 × 10−2|||
|France||2.6 × 10−2|
|Well water||Sao Paulo, Brazil||9.9 × 10−1|||
|Drinking water||Zhejiang, China||6.25 × 10−6|||
|Drinking water||Sao Paulo, Brazil||1.92 × 10−2|||
|Tap water||Gorges Reservoir, China||1.3 × 10−1|||
|Reclaimed water||Tianjin, China||9.83 × 10−3|||
|Well water||Sonora, Mexico||9.9 × 10−1|||
|Small private systems||Canada||3.3 × 10−2|||
7. Treatments decrease giardiasis risk
It has been proven that the use of effective removal treatments for
The stabilization ponds are biological treatment systems that consist of excavated deposits with the sufficient surface and volume to provide the treatment periods; depending on oxygen requirements, the artificial lagoons can be aerobic, facultative, and anaerobic; it has been reported that these lagoons eliminate up to 2 logarithmic units of
Currently, the best
After water, the most important infection route with
The consumption of raw food increases the risk of infection, which is why international recommendations exist to provide innocuousness in food preparation. It is especially important to (1) practice adequate hand hygiene for protection against this parasite; (2) buy food from reliable providers; (3) maintain food packed or closed; (4) perform pest control frequently; (5) make sure refrigerator temperature is below 5°C; (6) avoid cross-contamination by surfaces and recipients; (7) separate cooked from raw food; (8) use purified or boiled water especially if food is consumed raw; and (9) make sure food is cooked at high temperatures (≥70°C).
One of the main regulators of food innocuousness is the system ISO 22000, which is a combination of preliminary programs, such as the hazard analysis and critical control point (HACCP) principles, the implementation steps defined by the
8. Impact of climate change on giardiasis epidemiology
Climatic change is actually being considered as a triggering infection risk factor of zoonotic diseases because certain temperature conditions may increase the pathogens’ infective capacity. In the case of
Escobedo et al.  in their ecological study verified statistically that giardiasis increases significantly during the climate change that occurs with the “El Niño” phenomenon by using nonlinear Poisson models similar to those in QMRA and proving that
The authors would like to thank Grelda Yañez and Diana Dorantes for editorial services in English.