Pathogens are transmitted through vehicles such as water, food, and air. Waterborne disease transmission occurs due to contaminated water resulting from poor sanitation. In many parts of the world, waterborne diseases remain a severe issue.
According to the World Health Organization (WHO), polluted drinking water causes over 500,000 fatalities annually. Foodborne disease transmission can also result from contaminated food due to improper handling or storage (WHO, 2015).
Definition of Vehicle of Infection
A mechanism or medium through which disease-causing substances are conveyed is known as a vehicle of infection (Jim, 2007). This refers to the transmission of disease-causing agents from one person to another.
It is a method through which an infectious agent spreads to a host, which can occur through person-to-person transmission, food transmission, or vector-borne transmission, among other pathways.
It involves the spread of infectious diseases from a single source to all cases of a disease via a medium or vehicle like water, food, air, or blood. Having defined what a vehicle of infection is, it is important to understand how infections can spread.
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Common Vehicles of Infection
Food, water, biologic products (blood), and fomites are all vehicles that may indirectly convey an infectious pathogen (inanimate objects such as handkerchiefs, bedding, or surgical scalpels).
A pathogen can be carried by a vehicle in the same way as the hepatitis A virus can be transmitted by food or water. Alternatively, the vehicle may provide an environment in which the agent thrives, multiplies, or produces toxins, such as the environment in which Clostridium botulinum produces botulinum toxin when inadequately canned goods are present (CDC, 2000).
Food as a Vehicle for Pathogen Transmission
Food contaminated by infected individuals is a common way for infections to spread. Diarrhea, vomiting, open skin sores, boils, fever, dark urine, or jaundice are signs of infection by a pathogen that could be spread to others through food handling.
Foodborne transmission of these pathogens is caused by food workers failing to wash their hands in particular conditions (such as after using the restroom, handling raw meat, cleaning spills, or transporting rubbish), use clean disposable gloves, or use clean utensils (CDC, 2017). The following are several ways food can serve as a vehicle of infection.
1. Dairy Products as Infection Sources
a. Milk
Sheep, cows, goats, buffaloes, horses, and donkeys are just a few of the animals that produce milk. A common infection reservoir has been identified as milk. Examples of ailments include typhoid, bovine tuberculosis, and paratyphoid. Microbial hazards can be transferred through three main routes in milk:
- i. Fecal contamination: During the production of milk, excrement from cows, which is more liquid in nature than that of other animals, might contaminate the product. E. coli, Salmonella, and Listeria monocytogenes are some of the pathogens found in feces (Jim, 2007 in Jim et al., 2007).
- ii. Mammary gland inflammation: S. aureus has induced mammary gland irritation in some animals. This S. aureus, as well as a few other diseases, is found in large quantities in raw milk. S. aureus can produce and develop enterotoxin if it is not kept cool enough (Jim, 2007 in Jim et al., 2007).
- iii. Bacterial survival: V. cholerae O1 can live for more than two weeks in a variety of dairy items, such as milk, milk products, soft desserts, and cakes. Bacterial survival is improved when sugar and eggs are added. Although pasteurization of milk kills V. cholerae, the organisms can survive for up to four weeks in raw milk, even if refrigerated (WHO, 2000).
b. Cream
This is another dairy product. The cream may become contaminated during pasteurization in the bottle. The cream can cause infections such as S. aureus, VTEC, and S. Typhimurium when used with cakes and sweets.
c. Butter
When contaminated, butter is another dairy product that can cause food poisoning. Cultured butter and sweet-cream butter are both available. S. aureus, Staphylococcus intermedius, Salmonella, and Listeria monocytogenes, among others, are microorganisms that cause food poisoning outbreaks when tainted butter is consumed (Jim, 2007 in Jim et al., 2007).
d. Cheese
Another dairy product made from pasteurized milk and bacterial cultures with coagulation. Hard, semi-soft, and soft cheeses are available. Staphylococcal enterotoxins and aflatoxin are two microorganisms linked to cheese.
During the maturing or production process, they are created. B. melitensis, B. abortus, VTEC, L. monocytogenes, and Salmonella are some of the bacteria that can be found in cheese (Jim, 2007 in Jim et al., 2007).
iv. Fruits and Vegetables as Infection Sources
Another way infections can be transferred is through fruits and vegetables. This is due to the possibility of contamination during production or storage. Plant-based meals and food components, like most other food commodities, can get contaminated with microbial hazards throughout their growth in fields and orchards, harvesting and post-harvest processing, storage, and distribution, according to Jim (2007) in Jim et al. (2007).
Cholera outbreaks have been widespread in many nations, according to Rabbani and Greenough (1999), as a result of the habit of fertilizing gardens with untreated night soil and the ingestion of raw vegetables. Vegetables can become infected if they are washed in dirty water.
When polluted water is injected into fruits like watermelons to maintain their weight and flavor, this can happen (Feachem, 1981). V. cholerae infection is strongly influenced by the pH of a particular fruit. Sour fruits, such as lemons and oranges, have a lower pH (below 4.5) and thus do not promote the growth of V. cholerae, offering no cholera danger.
Wild animals that naturally defecate in areas where food is grown, gathered, processed, or stored, as well as cattle, can cause direct fecal contamination (Jim, 2007 in Jim et al., 2007).
Long et al. (2002) found that 85 of the 1518 food poisoning outbreaks of intestinal infectious illness in England and Wales between 1992 and 2000 were caused by salad vegetables or fruits.
v. Seafood as a Vehicle for Pathogens
Fishes are more likely to be infected by V. cholerae when the surrounding water is contaminated by sewage or other V. cholerae O1 environmental sources, according to Rabbani and Greenough (1999). In the presence of zooplankton, V. cholerae has been found to survive in seawater (copepods).
When the surrounding water is contaminated by sewage or other environmental sources of V. cholerae O1, fish are more likely to be infected with V. cholerae.
Plankton-feeding seafood such as mollusks, crustaceans, crabs, and oysters can become infected with V. cholerae (Huq, Small, West, Huq, Rahman, and Colwell, 1983). Even if refrigerated, clams and oysters, in particular, can carry V. cholerae for weeks once infected (Depaola, 1981).
vi. Meat and Poultry as Infection Sources
Meat and poultry are two of the most popular foods in the United States. These are meats that have had their surfaces infected during the slaughtering and butchering process. Cross-contamination is a common method of disease transmission during butchery.
It can also spread from raw to cooked foods and throughout storage periods before and after cooking. This is supported by Kolvin and Roberts (1982) that contamination of meat of animal origin occurs exogenously during processing, cooking, storage, or consumption, and it has been shown that V. cholerae can live and grow on cooked chicken, with an increase in numbers of V. cholerae from 10³ to 10⁶ within 16 hours.
According to Jim (2007) in Jim et al. (2007), the movement of organisms from raw to cooked meals, as well as the time spent in storage between preparation and consumption, play a significant role in contamination.
Food poisoning would be significantly decreased, according to Jim, if freshly prepared, roasted, boiled, or fried meats were always eaten hot. In the processing, retailing, and cooking steps, viruses can spread.
Pathogens can be disseminated by hand, as well as by using surfaces such as chopping blocks, cutting boards, and slicing machines. Food handlers are not immune; by touching the food, they can contaminate it (Jim, 2007 in Jim et al., 2007).
Eating prepared foods cold or warm might potentially transmit foodborne illness. During long durations of slow cooking and storage, C. perfringens spores survive, germinate, and multiply rapidly.
Hamburgers and sausages, perishable cooked uncured meats, perishable cooked cured meats, canned and pickled cured meats, dried meats, pies, and pastries are just a few examples of meat items that can be used as pathogen spreaders (Jim, 2007 in Jim et al., 2007).
vii. Eggs as a Vehicle for Pathogens
Poultry is a significant source of infections such as Salmonella. Contact with feces in the nest, barn, or cages can contaminate the shells of hen eggs, even during storage, packing, processing, distribution, and preparation.
Under certain humidity and temperature circumstances, Salmonella can enter the shell. Contamination can occur when using it as a liquid or dried product, as minute shell pieces drop into the liquid egg for freezing or drying (Jim, 2007 in Jim et al., 2007).
Air as a Vehicle for Disease Transmission
Another mode of disease transmission from one infected individual to another is through the air. This can happen when an infected person laughs, coughs, sneezes, etc., and the disease spreads into the air and stays there for a time, causing airborne transmission if an individual comes into contact with the agents.
According to the Centers for Disease Control and Prevention (CDC), airborne transmission occurs when infectious organisms are transported by dust or droplet nuclei suspended in the air. Material that has settled on surfaces and been resuspended by air currents, as well as infectious particles carried from the soil by the wind, are examples of airborne dust.
Droplet nuclei are dried residues with a diameter of less than 5 microns. Droplet nuclei, unlike droplets that fall to the earth within a few feet, can stay suspended in the air for lengthy periods of time and be blown long distances.
Because the measles virus remained suspended in the air after a child with measles had departed, measles has arisen in children who came into a doctor’s office after that child had left (Remington, Hall, Davis, Herald, and Gunn, 1985).
An individual with a typical cold may sneeze, causing droplets to land on a fomite such as a tablecloth or carpet, or she may wipe her nose and then transfer mucus to a fomite such as a doorknob or towel, according to CDC (2000).
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Water as a Vehicle for Disease Transmission
When water contains germs that might cause waterborne illness when swallowed, it can act as a vehicle for transmission. According to Nwabor, Nnamonu, Martins, and Ani (2016), waterborne infections are diseases spread by drinking contaminated water.
When contaminated drinking water is used to prepare food, the same germs can cause food poisoning. Diarrhea is a symptom of most waterborne infections, and it is characterized by excessive stooling, which can lead to dehydration and mortality (Nwabor, Nnamonu, Martins, and Ani, 2016).
Waterborne transmission, according to Macy and Quick (n.d.), is the acquisition of disease by intake of water contaminated with feces or inorganic chemicals, which can become polluted at the source, during delivery to the residence, in storage containers, or through incorrect treatment.
A disease that enters a population through water, according to Jeffrey (2017), can spread through additional pathways, such as person-to-person transmission or wastewater pollution of crops. Similarly, a disease that transmits from person to person can infiltrate water supplies via the fecal stream and become waterborne.
The World Health Organization estimates that diarrheal disease accounts for 4.1 percent of the total daily global burden of disease and kills 1.8 million people each year.
According to further estimates, 88 percent of the burden is due to inadequate water supply, sanitation, and hygiene, with the majority of the load falling on children in underdeveloped nations (WHO, 2000; WHO, 2005; and Prüss-Üstün, Bos, Gore, Bartram, 2008 in Nwabor et al., 2016).
According to the World Health Organization (WHO, 2013), children under the age of five die annually as a result of unclean water and a lack of basic sanitation. This figure shows a remarkable improvement over the predicted 2.2 million fatalities from diarrheal illnesses in 1998, which included both adults and children.
According to Prüss-Üstün and Corvalán (2006), insufficient water, sanitation, and hygiene are responsible for at least 88 percent of diarrheal episodes worldwide. Most waterborne infections, on the other hand, are commonly transferred by the fecal-oral channel, which occurs when human feces are swallowed through contaminated water or food, which is primarily caused by poor sewage management and sanitation.
Drinking-water feces contamination can be intermittent, and the level of fecal contamination can be minimal or fluctuate substantially. In places with modest levels of contamination, supplies may not pose a life-threatening threat, and residents may have relied on the same source for years (Nwabor et al., 2016).
Cholera, amoebic dysentery, bacillary dysentery (shigellosis), cryptosporidiosis, typhoid, giardiasis, paratyphoid, balantidiasis, salmonellosis, campylobacter enteritis, rotavirus diarrhea, E. coli diarrhea, hepatitis A, leptospirosis, and poliomyelitis are only a few of the organisms (Cheesbrough, 2006).
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