Salmonellosis: A concise review of one of major zoonotic meat borne illness

Salmonellosis is one of the widely distributed foodborne diseases, causing a mild to severe type of diarrheal illness/acute gastroenteritis with tens of millions of human cases occurring worldwide every year (who.int/factsheet.com). The causative agent of Salmonellosis is Salmonella enterica, which is a gram-negative, rod-shaped, motile bacterium belonging to the family Enterobacteriaceae, capable of surviving in freezing, refrigeration and dry conditions (Optimal growth at 35-37°C and pH 7-7.5). The Salmonella spp have multiple serotypes out of which only a few are capable of producing infection showing clinical symptoms in healthy animals, presenting a classical example of a phenomenon termed as “serovar-host specificity” (the causative agent of a particular disease attacking only a narrow range of hosts).

Brief History:

An American scientist named Daniel E. Salmon is credited with the discovery of this bacteria in the late 1800s. Since then, scientists have identified more than 2,400 types of Salmonella bacteria. A summary of some of the important species of Salmonella has been formulated as:

Salmonellosis: A concise review of one of major zoonotic meat borne illness - Image 1

Risk Factors:

According to the World Health Organisation (WHO), over 21 million cases of typhoid fever are reported annually in the world, with 200000 deaths. The highest incidence of typhoid infection is in south-central Asia and South-East Asia regions (more than 100/100,000 persons per year). The incidence of Salmonella infection in Pakistan is 412 per 100 000 person-years, according to the WHO; amongst the highest in the world [Ochiai RL et al.2008; 86: 260-8]. Healthcare workers may be at greater risk of acquiring different infections compared to the general population. Typhoid is more prevalent in developing countries due to poor sanitary conditions, whereas in the developed countries it is a sporadic disease and occurs mainly in returning travelers.

Disease in Humans:

The Salmonellosis in humans has one of the major concern of antibiotic resistance while considering the treatment regimes. The incidence of multidrug-resistant (MDR) Salmonella Typhimurium (particularly phage type 104) infections in humans have increased substantially in many countries in the last 2 decades. Infections are often associated with increased illness. Diarrhea may last for several days and lead to potentially severe dehydration, especially in infants and children under 2 years old and in adults over 65 years old. Most people with diarrhea due to a Salmonella infection recover completely, although it may be several months before their bowel habits are entirely normal.

Transmission

Salmonella bacteria are widely distributed in domestic and wild animals. Salmonella bacteria typically live in animal and human intestines which are shed through feces.

Food-Borne Spread:

Salmonellosis in humans is generally contracted through the consumption of contaminated food of animal origin (mainly eggs, meat, poultry and milk), processed foods, although other foods, including green vegetables contaminated by manure, have been implicated in its transmission also.

Backyard poultry and pets:

Human cases also occur where individuals have contact with infected animals, including pets. These infected animals often do not show signs of disease.
The area where an animal lives, such as its cage or water in its tank or the places where an animal roams, may be contaminated with Salmonella, which can cause illness in people who come into direct contact with the animal area, cage, or tank water.

Unhygienic measures:

At Kitchens:

Foods can also be contaminated in the kitchen. Drippings from raw meat or poultry can contaminate surfaces and other foods in the refrigerator or shopping cart. When raw meat or poultry are prepared with a cutting board and knife without being washed thoroughly between uses, they can contaminate other foods.

At Slaughterhouses/Meat sales point:

When preparing raw meat or poultry, food handlers can transfer Salmonella on their hands to other foods if they do not wash their hands between food preparation steps. Food handlers who do not wash their hands with soap can also contaminate food with Salmonella.

Symptoms:

Sudden onset of diarrhea (which may be bloody).
Abdominal cramps.
Fever (almost always present).
Nausea, vomiting, and headache may appear as less frequent signs.

Invasive Salmonella Infections:

Sometimes, Salmonella infection can spread to urine, blood, bones, joints, the brain, or the nervous system, causing symptoms related to that body part or system. Some of these extra-intestinal infections can have long-term effects, depending on which part of the body is infected.

When Salmonella infections become invasive, they can affect the bloodstream, bone, joint, brain, or nervous system, or other internal organs which might be rarely life-threatening in case of people with weak immune systems. May occur as Bacteremia, Meningitis, Osteomyelitis or Septic arthritis.

Treatment:

Salmonella gastrointestinal infections usually resolve, or get better, in 5-7 days. Most patients do not require treatment other than oral fluids. People with severe diarrhea may require rehydration with intravenous fluids. Antibiotics are recommended only for patients who:

Have a serious illness (such as severe diarrhea, high fever, bloodstream infection, or condition requiring hospitalization).
Are considered at high risk for serious disease or complications (such as infants, adults over 65 years old, and people with weakened immune systems).

Antibiotic Resistance in Salmonella:

According to Food Safety news, News Desk, June 09, 2015 post titled as “CDC: Antibiotic Resistance Increasing in Certain Salmonella Serotypes”, Salmonella are resistant to some frequently used antimicrobial agents. Resistance varies with the serotypes of Salmonella. Salmonella Enteritidis accounted for 36 percent of infections resistant to nalidixic acid (resistance to nalidixic acid relates to decreased susceptibility to ciprofloxacin, a widely used fluoroquinolone drug). Salmonella serotypes Dublin, Heidelberg, Newport, and Typhimurium accounted for more than two-thirds of infections resistant to ceftriaxone [http://www.foodsafetynews.com/2015/06/cdc].

Prevention:

According to MSD Animal Health, reports of high incidence of Salmonellosis have been collected following the rise in environmental temperature. Some preventions have been listed below that may help prevent the major outbreaks of Salmonella:

“Cook thoroughly" is recommended as a preventive measure against Salmonellosis.
Pasteurized milk must be consumed.
Pet contact, wash hands afterward.
Keep pet/animal cages, feeding troughs and water reservoirs clean.
Hygiene at kitchens, slaughterhouses, meat sales point.
Processing of food.
Properly wash the utensils and kitchenware after contact with raw food.
Washing hands before eating meals.
Avoid the use of inadequately cooked or raw meat or eggs in the food.
Avoid cross-contamination of food (Use of raw vegetables along with the meat or contamination of raw meat with the adequately meat).

Conclusion:

Considering our eating habits, traditions, customs and the available food quality the number of unrecorded cases of Salmonellosis could be much higher than the internationally reported cases from the developed countries data. A strengthened surveillance system for Salmonellosis is needed at the farm levels along with the appropriate system of diagnosis and screening of unhealthy birds/carcass from the flock/processing plants and consumer outlets. Additionally, awareness and consumer education regarding proper cooking time and hygienic measures during cooking of food may be disseminated by public health workers. Furthermore, appropriate biosecurity at farms, improvement in slaughterhouse hygiene, in the food processing technology and adequate preventive measures at meat outlets is the need of the hour.