Salmonellae are Gram-negative rods belonging to the family Enterobacteriaceae. Salmonellae are widely considered one of the most ubiquitous pathogens, both in humans and animals. There are more than 2000 serotypes, with different host specificity. In general, most Salmonellae can infect different species even if some have a very restricted biological niche. An increase in the frequency and severity of non-typhoidal strains of Salmonella has been reported in patients with AIDS and may be an initial manifestation of AIDS (Sperber and Schleupner, 1987). The most common species isolated are Salmonella typhimurium and Salmonella enteritidis (Levine et al., 1991) and infection often presents as recurrent diarrhoea with bacteraemia that relapses frequently despite therapy.
In the developing world, HIV infection and AIDS are important risk factors for non-typhoidal salmonellosis and bacteraemia. In recent surveys in infected African adults with documented bloodstream infections, non-typhoidal Salmonellae were isolated from up to 35 percent of adults (Hohmann, 2001).
Salmonella infection is generally acquired from animals or animal products including meat, poultry, milk and eggs. One frequent mode of transmission, often unrecognized, is by cross contamination in preparing food in the kitchen.
Salmonella spp. are found worldwide in domestic and wild animals, including reptiles, birds and insects (Morse and Duncan, 1974). Animals and their products represent the principal source of non-typhoidal Salmonella infection in humans. The organism can survive in the environment for a long time. The prevalence of Salmonella spp. in domestic animals has been the focus of many studies. Young, sick or immunosuppressed animals, especially if they are living in overcrowded conditions, are the most susceptible to Salmonella infection. Animals with salmonellosis may be asymptomatic carriers or be symptomatic with diarrhoea. Symptomatic animals often have a higher concentration of Salmonellae in their faeces (Fox, 1991).
Other pets are an important reservoir for humans. Reptiles in particular pose a significant risk: as many as 90 percent may be carriers of Salmonella spp. (Chiodini and Sundberg, 1981).
Salmonellosis is transmitted via the faecal-oral route; ingestion of contaminated food or water is the most important source of human infection. S. typhimurium is mainly present in beef and pork and raw or powdered milk. Poultry and poultry products are also responsible for a large number of outbreaks, especially due to S. enteritidis. Raw milk has been implicated in a number of S. dublin outbreaks associated with severe sequelae among patients with AIDS.
Salmonellosis usually causes transient diarrhoea, but can also manifest as an asymptomatic bacteraemia, especially in children or when predisposing factors are present. In HIV infected patients, salmonellosis is characterized by an intense and long-lasting diarrhoea, which is frequently associated with septicaemia. Relapse of infection, with recurrent bacteraemia, is a common feature of AIDS patients (Hohmann, 2001). Recurrent salmonellosis is mainly due to persistence of the original infecting strain, but can be also caused by reinfection with new bacterial strains (Rubino et al., 1999).
Bacteria belonging to the genus Campylobacter are Gram-negative microorganisms. They are among the most common pathogens isolated from patients with diarrhoea. The impact and importance of these micro-organisms in HIV infected or AIDS affected persons is relatively unknown, even if there is evidence that Campylobacter spp. in those people can represent a very important risk factor (Glaser, Angulo and Rooney, 1994). Campylobacter jejuni is the most common species isolated from HIV infected and AIDS affected people despite ample debate about the taxonomy of Campylobacter.
Campylobacter is a common pathogen of humans, but with different epidemiological scenarios in developing compared with developed countries (Coker et al., 2002). In developing countries, Campylobacter is the most commonly isolated bacterial pathogen from children less than two years old with diarrhoea. The disease does not appear to be important in adults. In contrast, infection occurs in adults and older children in developed countries. Poor hygiene and sanitation and the close proximity to animals in developing countries all contribute to the easy and frequent acquisition of any enteric pathogen, including Campylobacter.
Most estimates of incidence in developing countries are from laboratory-based surveillance of pathogens responsible for diarrhoea. Campylobacter isolation rates in developing countries range from 5 to 20 percent (Oberhelman and Taylor, 2000). Community-based case studies have provided estimates of 40 000 to 60 000 cases for every 100 000 children younger than five (Oberhelman and Taylor, 2000; Rao et al., 2001), and 300 cases for every 100 000 persons for developed countries (Tauxe, 1992).
Campylobacter species are commonly found in the gastrointestinal tracts of a wide variety of animals. They are thermophilic organisms and this feature is the reason they are commonly isolated in birds, which have a higher body temperature than mammals, and hence represent the animal reservoir (Whelan et al., 1988).
Several epidemiological trials have been conducted showing that Campylobacter spp. are also widely present in pets (Bruce, Zochowski and Fleming, 1980; Fox, Moore and Ackerman, 1983). Isolation rates are quite different, ranging from 0.5 to 45 percent in dogs and from 2 to 45 percent in cats. Although these results reveal quite a large range in rates, they support the concept that bacteria of the genus Campylobacter are common in pets. Thus, pets can act as transmitters of the micro-organisms in the environment and pose a great risk for people living in close contact with them.
People acquire infection by ingestion of micro-organisms with contaminated food. Infections due to Campylobacter spp. can be localized to the enteric environment or can generalize with bacteraemia and systemic involvement. Bacteraemia is more common in HIV infected and AIDS affected people, the old, or infants of less than 12 months, and people with underlying disease, suggesting a close correlation between the onset of the disease and the immune status of the patient.
Clinical features of Campylobacter spp. infections can be differently presented. They can be mild acute-onset febrile illness with self-limiting enteritis and shedding organisms with faeces, but infection can also induce a severe enteric syndrome with bloody diarrhoea, cramping and nausea. As mentioned above, Campylobacter spp. can cause a systemic infection with bacteraemia that induces fever and prostration.
PREVENTION OF INFECTION
Salmonella and Campylobacter micro-organisms are eliminated with faeces by infected hosts and they are mainly acquired by ingestion of contaminated foodstuff or direct contact with infected and eliminating animals. It means that HIV infected people need to follow several simple rules to reduce the risk of contracting infection:
They should avoid eating raw food, which can be contaminated. They should eat meat, poultry, seafood or eggs only after proper cooking. Raw eggs may be unrecognized in some food, including sauce, meringue, salad dressings, ice cream and mayonnaise. Unpasteurized milk should not be ingested unless cooked.
They should be trained in the proper hygienic handling and preparation of food in order to prevent cross contamination.
They should use water only after boiling, filtration or chemical disinfection.
In order to prevent faecal-oral spread directly from animals, HIV infected people in contact with animals should wash their hands after animal contact and not eat or drink during activities that involve animal contact.
Those with extensive exposure to animals, such as farmers, veterinarians and butchers should wear gloves when exposed to mucous membranes, secretions or tissue of animals.