Toxoplasma gondii, a microscopic parasite that gets inside our cells, is capable of infecting virtually all warm-blooded animals, and is commonly acquired by consuming raw meat or infected water or soil or handling cat litter. It can also be transmitted from mother to unborn baby and induce miscarriage. Indeed, in pregnant women, infection can result in congenital problems of the fetus, while in immune-compromised individual it can lead to severe neurological consequences. T. gondii is an important foodborne pathogen found in many domesticated animals used for human consumption in United States and human infection often develops after the ingestion or handling of undercooked or raw meat containing tissue cysts. Alternatively, it can result from direct contact with cat, soiled cat litter or from the consumption of water or food contaminated by oocysts excreted in the faces of infected cats. Toxoplasmosis continues to be a significant public health problem worldwide with several million people are believed to be infected with this parasite. Toxoplasma gondii, is present in about 10% of the population in the UK. But in tests on lung cancer patients, all were found to be infected with the parasite.
Reporting in the Journal the European Respiratory Journal, the team conducted diagnostic tests using five Toxoplasma specific PCR markers and specific immunohistochemistry demonstrated that the infection was present in lung biopsy samples. Drs Geoff Hide and Lucy Smyth’s work on lung tissue and chronic obstructive pulmonary disease (COPD) at Salford University, led them and Dr Jaro Bajnok, PhD, to carry out additional tests on the samples to see if any contained Toxoplasma. Working with Professor Dave Singh, clinical consultant at the Medicines Evaluation Unit at Manchester University, they tested 72 tissue samples from patients diagnosed with lung cancer and found the parasite in all of them. Further analysis of parasite life-cycle stages suggested that 96% of these patients had active infections. Control samples returned only a 10% positive match, consistent then with a national average. The team is now planning a much larger study of samples from a broad range of cancer centers, though at this time there is no declared association between Toxoplasma infection and human lung cancer.
Parasite infection as cause of human cancers is not a new concept. Scientists have long associated certain parasitic infection to the onset of tumors in internal organs. There is a specific section that can be found in textbooks of General Pathology concerning mechanisms of oncogenicity. There is no knowledge of substances produced by parasites that may act as a carcinogen. On the other side parasites, by recruiting the immune system, may trigger an inflammatory reaction. If they resist to immune attempt of erasing, inflammation may become longlasting. This inflammatory response is supposed to be the real oncogenic trigger. Inflammation is characterized by production of prostaglandins, lipid mediators whose production is impaired by NSAIDs like ibuprofen or ketoprofen. Prostaglandins may also stimulate cell proliferation, destabilize the cellular genome and, in time, they could become carcinogenic with this mechanism. This is the way how parasitic Schistosoma infection may cause bladder cancer; or Trichomonas infection may increase the risk for uterine cancers.
Geoff Hide, Professor of Parasitology, University of Salford commented: “It’s a remarkable result which we don’t fully understand yet. It is possible that the presence of the parasite in these patients is exacerbating their symptoms of cancer or interfering with their therapy. We need to find out why the parasite is so active in these patients. It may be age-related because these are people with lung cancer but that is clearly not the whole story. Our advice to clinicians at this stage is be aware of the presence of this parasite, do test for it because it may or may not interfere with any treatment regime”.
- Edited by Dr. Gianfrancesco Cormaci, PhD, specialist in Clinical Biochemistry.
Anvari D et al. Microb Pathog. 2019 Apr; 129:30-42.
Lu G et al., Wang L. Front Microbiol. 2019 Feb;10:181.
Thapa B et al. J Thorac Dis. 2018;10:S3446-S3457.
Cong W et al. Cancer Lett. 2015 Apr; 359(2):307-13.
Lu N et al. Int Med Case Rep J. 2015 Jan 22; 8:37-40.