by Microbiology Doctor-Dr
Foodborne Giardiasis- Food Poisoning By Giardia Species
Table of Contents
- Diseases connected to diarrheal illness are brought on by parasites, which are widely dispersed in the environment.
- The sickness is mostly linked to parasites that are water- and food-borne, and these parasites represent the biggest threat to food production.
- The greatest threat to human health and economic loss to the country is posed by parasitic protozoa, particularly in underdeveloped countries.
- Cryptosporidium, Cyclospora, Giardia, and Toxoplasma are a few of the parasitic protozoans that pose a concern to humans.
- The main parasite known to cause human disease is giardia, and each year, several epidemic cases are documented.
- Giardia duodenalis, Giardia lamblia, Giardia intestinalis, and Giardia muris are the giardiasis-causing species that affect people and other mammals.
- Although there are many cases of food-borne parasites each year, there aren't very many cases recorded, which may be because surveillance and detection methods aren't particularly good.
Sources of foodborne giardiasis contamination
- The primary source of contamination is the excrement of domesticated animals, wild animals, and cattle, and it is often spread by the fecal-oral pathway.
- Giardia cysts may also be found in shallow spring water and sewage effluent. These cysts are very contagious and can survive for a long time in a cold, moist environment.
- Giardia may withstand several conventional water treatments and is resistant to chlorine, posing a serious threat to water sources.
- They can be eliminated through the filtering process, however Cryptosporidium cannot due to their tiny size.
Characteristics of Giardia
- Flagellated protists
- Diplomonads with tumbling motility, or two bodies with separate nuclei
- Mitosomes take the place of mitochondria
- utilises anaerobic glycolysis to metabolise
- Two stages—the reproductive trophozoite and the cyst stage—mark the end of the life cycle.
- asexual reproduction
- Giardia cysts are 9–12 mm long and the reproductive trophozoite is 9–21 mm long. Giardia cysts are sensitive to chlorine, iodine, and chlorine dioxide as disinfectants.
Clinical manifestations of Foodborne Giardiasis
- Giardia can be spread by 10 to 100 cysts, and symptoms generally appear 1 to 2 weeks after infection.
- The initial symptoms include gas, nausea, stomach bloating, abdominal cramps, and diarrhoea.
- Dehydration and weight loss under extreme circumstances may result in a persistent infection and possibly death.
- There are also situations when the patients are asymptomatic carriers but the illness only lasts a week or five days.
Lifecycle of Giardia Species
- Giardia cysts may contaminate surfaces, food, and water, and when consumed during this contagious stage of their life cycle, they can result in giardiasis. When a person ingests Giardia cysts from contaminated water, food, hands, surfaces, or items, they get infected.
- When Giardia cysts are ingested, they go from the mouth, oesophagus, and stomach into the small intestine where, via a process known as excystation, each cyst produces two trophozoites. The Giardia trophozoites then consume the infected person's nutrition and feast on them.
- Giardia trophozoites remain in the small intestine where they can be free or adhere to the inner lining of the small intestine and reproduce by splitting in two through a process known as longitudinal binary fission.
- The Giardia trophozoites then advance into the colon and undergo encystation, reverting to cyst form. The stage most frequently discovered in stools is the Giardia cyst.
- Giardiasis can be identified by looking for Giardia cysts and trophozoites in a patient's faeces and by seeing them under a microscope. Giardia cysts can live for several months in cold water or soil and are instantly contagious when discharged in the stool or shortly after.
Pathogenesis of Giardia species
- Giardia's two-stage life cycle ends with the vegetative trophozoite, which multiplies and produces sickness, and the cysts that cause infection.
- The cysts' outer filamentous layer, which is formed of N-acetyl-galactosamine and three proteins called CWPs 1–3, which enable them to survive for a long time, makes them resistant to the environment, especially at low temperatures.
- When a cyst gets past the stomach acid and into the duodenum, it has a 10–100% chance of infecting that area.
- Each cyst divides into two trophozoites upon entry into the duodenum, which populate the small intestine by consuming vital nutrients and ailing the host.
- Giardia reproduces asexually; as a result, trophozoites are tetraploid, or four sets of one chromosome, and multiply through binary fission.
- When the cyst exits the stomach's acidic environment and enters the duodenum and small intestine, excystation occurs, and encystation then follows.
- The body's immune system activates T cells in reaction to the trophozoite, disrupting and shortening the epithelial microvilli.
- Additionally, it damages the epithelial tight junctions, increasing permeability and causing diarrhoea.
- Additionally, the cyst undergoes bile salt and cholesterol deprivation before beginning to replicate, splitting into two trophozoites, and infecting the other host.
- It is also clear that a strong immune response helps the host develop immunity to the illness.
- According to antigenic variation, the organism is said to have adapted to the various intestinal habitats.
- Some organisms with variant-specific proteins (VSPs) develop resistance to antibodies while not producing any poisons or virulence factors.
Epidemiology of Foodborne Giardiasis
- The parasitic protozoan Giardia outbreaks affect 4 to 20 people per 100,000 people annually, and the majority are thought to be spread by fecal-oral contact.
- According to the Food and Agriculture Organization (FAO) and WHO, out of 24 foodborne parasites, giardia is listed in position 11 of these rankings.
- Giardiasis epidemiology is more common in developing nations and is connected to climatic and environmental factors.
- Children under the age of five are at greater risk than adults, and 60 to 80 percent of infections are asymptomatic; chronic infections, however, account for less than 4 percent of cases.
- In Peru, 95% of children under the age of 2 were infected, but 6 months after treatment, the virus returned.
- Children's early growth is stunted as a result of the condition, which is typically asymptomatic.
- More than 3000 persons were infected by a recent widespread outbreak in Bergen, Norway, which was brought on by drinking water contamination.
- Due to the excretion dose being larger than the infective dose each day, it was declared to be a waterborne outbreak.
- Although an infected individual can discharge up to 109 cysts each day, it takes 10 to 100 cysts to develop an infection.
- In impoverished nations where people drink tap water, shallow wells, and surface water, the potential for contamination is significant.
- These water sources are full with zoonotic parasites that can infect humans when drank without filtration.
- Due to increased water intake and the fact that most afflicted children attend daycare facilities, the giardiasis infection often peaks in the late summer.
- A Minnesota outbreak was brought on by the intake of home-canned salmon, which infected 60 staff members at a school.
- However, because asymptomatic Giardia carriers were responsible for the outbreak, it was not classified as giardiasis.
Detection Methods of Giardia species
- Using a microscope to identify the Giardia cysts in stool samples is a common practise, although it lacks specificity and sensitivity.
- Enzymatic immunoassays (EIAs) and immunochromatographic tests are two more immunoassay techniques that are employed, however they also lack specificity because of antibody cross-reactivity.
- The immunomagnetic technique of cyst separation is the one most frequently utilised by the US Environmental Protection Agency (EPA).
- The cysts are separated, then stained with fluorescent dye and differential interference contrast to be seen under a microscope (DIC).
- As it distinguishes the pathogens at the species and genotype levels, the PCR-based approach, when compared to other detection methods, offers increased specificity and sensitivity.
Prevention and Control measures of Foodborne Giardiasis
- While asymptomatic infections are simple to cure, they are harder to find and must be monitored once they develop into chronic conditions.
- Tinidazole, nitroimidazole, and metronidazole are the initial treatments of choice.
- In comparison to metronidazole, which takes 5–10 days to achieve the effective dose, tinidazole is more effective since it has a high effectiveness in a single dose.
- Paromomycin is advised for pregnant women even though it is less efficient than nitroimidazole and nonabsorbed aminoglycoside.
- Giardiasis in humans may be avoided by providing treated municipal water sources, which breaks the life cycle of the parasite and stops it from spreading.
- Cysts and other pathogens are effectively eliminated by the coagulation, clarifying, filtering, and chlorination processes used in municipal water systems.
- Giardia cysts can also be removed by using household portable filters with a size smaller than 1 m, as well as heat treatment at 55°C and higher for 5 minutes.
- The risk of asymptomatic infection can also be reduced by food workers washing their hands and using protective gloves when preparing meals.
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