Written by Dr. Declan J. Bolton
Food Safety Department, Teagasc Food Research Centre, Ashtown and a member of the Knowledge Network Expert Group
Mental illness covers a wide range of mental health conditions, but refers generally to disorders that affect mood, thinking, and behaviour. Although the causes of mental illness are often unknown, it is clear that biological, psychological, and environmental factors all play a role, acting either individually or together. Among the biological factors, genetics (hereditary) resulting in abnormal functioning of nerve cell circuits or pathways are important, as are brain injury due to trauma, non-infectious diseases such as epilepsy, and birth trauma (oxygen starvation). While infections such as malaria, Legionnaire’s disease, syphilis, typhoid, diphtheria, HIV, and herpes are relatively well recognized as causing psychiatric symptoms, others are less well documented and are more often associated with a symptom spectrum that does not include mental disability.
It has long been suspected and recent research from the Republic of Ireland has demonstrated that a healthy gut micro ora (community of bacteria and other microbes residing in the gut) has an effect on emotional activity. When foodborne infections are investigated and treated, the focus is solely on the physical symptoms.
With correct treatment, diarrhea, abdominal cramps, vomiting and fever usually clear up in 7-10 days. In contrast, associated psychological symptoms such as depression, anxiety and general malaise are chronic illnesses that must be endured for many years. This phenomenon was recently demonstrated after the 2011 Shiga-toxin producing Escherichia coli (STEC) O104:H4 outbreak, which occurred primarily in Germany and France although cases were reported in 14 other countries. By July, when the outbreak was declared over, 852 of the 4,321 cases were suffering from kidney failure and 54 had died. Six months after the outbreak, almost half of those who had been infected were suffering from poor psychological health with 43% complaining of persistent fatigue and 3% suffering post-traumatic stress disorder.
When a person is suffering from an infection they often display social withdrawal, reduced appetite and lethargy. These are perfectly normal responses as the body focuses resources on ghting the infection and recovering full health. However, these ‘sickness behaviors’ may persist long after the infection has cleared up if the infective agent establishes chronic carriage or there is a dysfunctional immune response. If we are to treat these conditions it is essential we obtain a better understanding of the underlying mechanisms. Some foodborne parasites, for example, such as the larval stage of the tapeworm (Taenia solium) or the tissue cysts of Toxoplasma gondii affect mental health by directly infecting the brain. In contrast, other parasitic and bacterial infections may contribute to mental illness indirectly via the immune system or by in uencing neurotransmission pathways.
Several studies have shown that foodborne infections may cause the development of depression, for example, in vulnerable individuals or exacerbate the illness in patients already suffering depression, by directly impacting on the brain or via the nervous system. Foodborne infections, such as salmonellosis and campylobacteriosis have also been associated with hypochondriasis and anxiety. There may also be a link between bipolar and/or related disorders and bacterial infections. Research from the USA suggests that children that are genetically predisposed to bipolar disorder may develop pediatric autoimmune neuropsychiatric disorders associated with streptococcal infections (PANDAS). Recent research from Germany also reported an association between these bacteria and Tourettes Syndrome.
Given the enormity of mental health issues in terms of personal suffering, adverse quality of life and costs to our health services, the link between psychological conditions and microbial infections can no longer be ignored. There is sufficient data currently available to prioritize the initial research objectives, which should include establishing the proportion of mental illness that may be directly or indirectly attributed to microbial infections and obtaining a better understanding of the mechanisms involved.
This article is a summary of the review paper ‘Mental health disorders associated with foodborne pathogens’ by Dr. ‘Declan J. Bolton and Lucy J. Robertson, recently (2016) published in the Journal of Food Protection, volume 79 (11), pages 2005-2017.
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