Zoonoses are diseases and infections that are naturally transmissible between vertebrate animals and humans. There are believed to be in excess of 250 zoonotic diseases recognised worldwide, and new diseases continue to be identified. Transmission may occur due to direct occupational, recreational or domestic contact with animals, via indirect contact or due to consumption of contaminated food or water. Some zoonotic agents can cause serious disease in humans but have little or no effect on animals (e.g. verotoxin-producing producing E. coli O157), whereas others cause serious disease in both humans and animals (e.g. rabies).
This report summarises laboratory-confirmed cases of selected zoonotic infections reported in Scotland (Table 1), excluding the main gastro-intestinal pathogens which are covered in detail on separate surveillance reports (http://www.hps.scot.nhs.uk/giz/surveillance.aspx?databaseid=1)
Most frequently reported zoonotic organisms
During 2016, reports of Lyme borreliosis, pasteurellosis, toxoplasmosis and taeniasis accounted for around 95% of these reports (Table 1). These are discussed in more detail below.
Lyme borreliosis, known as Lyme disease, is caused by the bacterium Borrelia burgdorferi and is transmitted to humans and animals through the bite of an infected tick (Ixodes species). It is the most common tick-borne infection in humans in the temperate northern hemisphere. The majority of cases in Scotland are indigenously acquired, usually through recreational activities including country or hill walking, running, orienteering or gardening. There were 170 laboratory-confirmed reports of cases of current infection with Borrelia burgdorferi in 2016 in Scotland. It is recognised that this underestimates the true incidence as many cases are treated on the basis of symptoms and will not be tested (see British Infection Association position statement at https://www.britishinfection.org/index.php/download_file/view/218/202/). The Scottish Health Protection Network’s Gastrointestinal and Zoonoses Group has established a multi-agency sub-group to lead on work to reduce the burden of Lyme disease in Scotland. The group has identified three priority areas for action, namely increasing awareness among the public and health professionals, improving diagnosis and accurate surveillance.
Pasteurellosis is a zoonotic bacterial disease with a worldwide distribution. Pasteurella multocida is the most commonly reported organism in this group, and is well known as both a common commensal (part of the normal bacterial flora) and pathogen in a variety of animal species. Human infections are usually contracted following exposure to domestic pets such as cats and dogs. The most common manifestation of pasteurellosis in humans is a local wound infection, usually following an animal bite, scratch or licks. Animals do not have to be ill to pass the bacterium to humans, as they can carry the organism without showing symptoms. Broad spectrum antibiotics are usually effective against Pasteurella in the setting of simple wound infections. Pasteurella species can also cause meningitis, eye and respiratory infections.
In 2016, 199 cases of pasteurellosis were reported, four of which had dual infection with two different types of Pasteurella. Of the total, 74% (N=148) were associated with wound infections and, while information was not available for all cases, 68% of wound infection cases reported a dog or cat bite/scratch. A further 30 cases (15%) were associated with respiratory illness. Information on the remaining reports indicated that they were obtained from ear or eye swabs, or were isolated from blood cultures.
Toxoplasmosis is caused by the protozoan parasite Toxoplasma gondii. Cats are the definitive host for the organism although many warm-blooded animal species can be infected as intermediate hosts. Human infection can occur. People most at risk are pregnant women, who can pass congenital toxoplasmosis on to their unborn baby, and people with weakened immune systems. The T. gondii parasite is sometimes found in the afterbirth and on newborn lambs after an infected sheep has given birth and there is a small risk during the lambing season of toxoplasmosis infection passing from sheep to humans.
In 2016 there were 17 laboratory-confirmed reports of toxoplasmosis made to HPS.
Taeniasis is an intestinal infection caused by three species of tapeworms -Taenia solium (pork tapeworm), Taenia saginata (beef tapeworm) and T. asiatica (Asian tapeworm). Humans can become infected when they consume beef (T. saginata) or pork (T. asiatica and Taenia solium) which is either raw or has not been adequately cooked. Taeniasis can cause mild gastrointestinal symptoms and T. solium infections may develop into cysticercosis. In 2016 there were 10 reports of taeniasis in Scotland (all T. saginata). All cases reported in Scotland were imported infections.