M.C.V. Ramón Alfredo Delgado González
Universidad Autónoma Agraria Antonio Narro, Unidad LAGUNA
Have been reported more than 400 outbreaks of diseases caused by protozoan parasites associated with the water, in the world, mostly in the industrialized countries. In these outbreaks have been described infections produced by aetiological agents such as Cryptosporidium parvum, Entamoeba histolytica, Cyclospora cayetanensis, Toxoplasma gondii, Isospora belli, Blastocystis hominis, Balantidium coli, Acanthamoeba and Naegleria sp., responsible for one or several outbreaks. Its presence in aquatic ecosystems makes it imperative to develop prevention strategies for water and food biosafety.
Cryptosporidium is a protozoan parasite that causes intestinal disease and induces acute infections with diarrhea and chronic infections often unnoticed. Often the raw water and drinking, treated with chlorine, presented oocysts of Cryptosporidium spp, (which are resistant to chlorine), and play an important role in the epidemiology of cryptosporidiosis, both in humans and in animals.
The interest in the contamination of drinking water by enteric pathogen protozoan has increased considerably during the last three decades. The parasite Cryptosporidium spp is a pathogen of great concern transmitted by the water. There are three characteristics of the life cycle of Cryptosporidium that increases the probability of the transmission by the water. In the first place, Cryptosporidium completed its life cycle within a single host, by which excretes a large number of oocysts in stool. Secondly, can occur zoonotic transmission, maintaining the reservoir of infection and therefore environmental pollution, increasing the probability of the transmission by the water. Thirdly, the infectious oocysts are resistant to the environment and are small enough to penetrate the physical barriers of water treatment and are insensitive to many disinfectants used in the water industry.
Water-borne diseases occur throughout the world, and the outbreaks caused by contamination of water systems in a community have the potential to cause disease in a large number of consumers. Outbreaks of water source have economic consequences beyond the cost of health care for the affected patients, their family members and contacts, and the economic costs of illness and disease in itself, since they also create a loss of confidence in the quality of drinking water and in the water industry in general. In addition to the outbreaks caused by contaminated drinking water, there are outbreaks caused by the accidental ingestion of water in recreation centers.
The statistics on outbreaks linked to contaminated water in the United States, dating from 1920 and from 1971, the Centers for Disease Control, have maintained a surveillance system for the collection of data relating to the occurrence and causes of outbreaks of water-borne diseases. In Europe, during the decades of the 80s and 90s, around 277 outbreaks associated with drinking water and recreational centers were reported in 16 countries.
Several outbreaks of cryptosporidiosis in industrialized countries have been associated with the contaminated drinking water. A case very remarkable happened in 1993 in Milwaukee and caused an estimated 400,000 cases of gastrointestinal diseases, indeed almost the entire population of the city.
The zoonotic transmission of Cryptosporidium parvum has been reported in cases of cryptosporidiosis in children after exposure with calves or lambs. Occupational exposure to infected animals (calves) has also given rise to the Human Infection
The Cryptosporidium oocysts are resistant to routine therapies of water and chemical disinfectants and a low number of viable oocysts can cause infection.
To detect Cryptosporidium oocysts in water provision requires much time. This method consists of multiple steps, including filtration and centrifugation to concentrate and purify oocysts, followed by immunofluorescence microscopy to identify and list the oocysts present. The limitations of this procedure include a poor recovery of oocysts. The microscopy with a special stain of modified Ziehl Neelsen, is also limited due to the volume of the sample that is required (around 60 liters of water) to retrieve a test sample of approximately 50 µL. The detection and enumeration of oocysts are further complicated by the composition and amount of sediment present in the samples.
Have been investigated alternative technologies to provide more efficient detection of Cryptosporidium in an aqueous base. These include Flow Cytometry, spectroscopy of visible light and UV rays, ELISA, microscopy sweep, polymerase chain reaction, immunomagnetic separation, microscopy with video, electrochemiluminescence, among others. Although the majority of these trials are suitable for the analysis of oocysts in water samples of low turbidity, are not satisfactory for the analysis of oocysts in samples with high turbidity.
The indirect transmission from person to person or the zoonotic transmission can occur by the contamination of the water used in the recreational centers, swimming pools, water to drink, or in the food. The surface water can be contaminated by untreated sewage and treated and the runoff from the manure. It is understood by surface water, the water on the surface of the planet as the form a stream, river, lake, wetland or ocean. Can be contrasted with groundwater and water from the atmosphere.
The Cryptosporidium oocysts can be in concentrations ranging from 0.01 up to 100 per liter. The highest concentrations are found in urban or agricultural waters, in addition around the 12% of underground water supplies in the United States are contaminated with Cryptosporidium spp, above all in the galleries of infiltration and horizontal wells (affected by the pollution of surface waters).
The largest outbreak of cryptosporidiosis has been attributed to contaminated drinking water, both by sources of surface water as by groundwater. Outbreaks have also been associated with exposure to recreational water and swimming and swimming pools. The seawater may contain Cryptosporidium but has not been implicated in outbreaks of cryptosporidiosis.
Cryptosporidiosis outbreaks have also been produced through the consumption of contaminated food. Food can contaminate by food handlers infected or by the irrigation with water contaminated with manure.
Cryptosporidium has been isolated from livestock throughout the world, the majority of the calves newborns have diarrhea by this agent, remain high the prevalence of the infection (5-100%). 90-100% of the herds may be infected. The clinical infection occurs primarily in the newborn calves, they can yield more than 1010 oocysts/day. The prevalence is lowest in the adult cattle. The high density of cattle in the watersheds and the excretion of a high number of oocysts make these animals important sources of pollution of the environment, which have been implicated in several outbreaks of water source of cryptosporidiosis.
Some features of Cryptosporidium that allow the survival in the environment and facilitate the transmission by the water are described below:
– The host specificity is low and increases the potential for the dissemination and pollution in the environment. Cryptosporidium infections occur in a wide variety of mammals including the human, domestic animals, pets, and wild animals.
– The infectivity of the Cryptosporidium oocysts is high; the ingestion of a single oocyst has a high probability of produce infection.
– Oocysts nature resistant enhance its survival during long periods of time in favorable environments. The survival of oocysts is reinforced in a wet environment and fresh environments. A high proportion of oocysts can survive for more than 6 months suspended in the water.
– The Extreme resistance to the chemical disinfection, above all to the disinfection with chlorine, has been a major barrier for pathogens in the water. The high resistance of Cryptosporidium oocysts in against the disinfection with chlorine makes this process of drinking water treatment is ineffective for the inactivation of oocysts. The chlorine dioxide is slightly more effective and the ozone is the most powerful chemical ooquisticide.
– The resistance and environmental persistence of the oocysts allow them to survive some processes of water treatment. Outbreaks transmitted by water indicate that the oocysts can survive the physical treatment and disinfection. The oocysts are resistant to disinfectants commonly used in the treatment of water. In addition, the oocysts can survive for months in surface waters and estuaries, and its longevity in fresh water has been observed since the 4 to 25°C. The survival of the oocysts in soil is approximately 120 days.
– In comparison with other protozoan parasites, the Cryptosporidium oocysts are small (4-6 micron), which allows the penetration through sand filters. Due to its small size, its elimination is less efficient through filtration of the ground.
– Few infectious oocysts must be ingested to establish an infection in guests susceptible. Five to nine oocysts can cause infection in humans and animals.
– The excretion of oocysts in stool, in large numbers during the acute infection, facilitates the diffusion in the water. The oocysts can be found in large quantities in the feces of the host, due to the autoinfection. At the peak of infection, deleted until 105-7 oocysts per gram of feces. The concentration of oocysts in wastewater can be up to 300-14,000 Cryptosporidium oocysts per liter in untreated water. In treated wastewater can be found up to 50 oocysts per liter.
– Several studies show that infected cattle, especially the newborn calves, show a high number of oocysts. Approximately 1010 Cryptosporidium oocysts are excreted during the symptomatic infection. The excretion of oocysts usually occurs after 7 days and the peaks around 14 days. At the peak of the infection, 106-7 is excreted oocysts per gram of feces. Have been found concentrations of oocysts in stool up to 104-7/gram in calves of 1-6 weeks of age, 90% of the herds.
– Unlike other coccidian and helminths parasites, the Cryptosporidium oocysts do not require a period of maturation after the excretion in feces because they are immediately able to infect a new host.