Are plant pathogens (Virus, Bacteria and Fungus) fatal to human?: A brief review

Image: Tobacco Mosaic Virus (TMV) under microscope (Science photo library)

Editor: M A Mannan

Effect of plant pathogens on human

Although infection of plants by pathogens can have serious consequences on plant health, human health can be affected by one of the several ways. Viruses, bacteria and fungi that infect plants do not usually cause infection in humans. However, a study reported that Pepper mild mottle virus may react with the immune system of humans and induce a clinical symptom, but the study did not provide a clear evidence on the pathogenic role of this plant virus in humans. Despite the question about the possible direct effect of plant pathogens on humans, several plant pathogens can affect humans by reducing the available food or by contaminating human food with toxic compounds. Human health can also be affected by bacterial species living in agricultural soils and used as bio-control agents for plant diseases.

One of the most common ways by which plant diseases can affect humans is through the secretion of toxic metabolites ’mycotoxins’ by fungi infecting plant products. Although the fungi producing these mycotoxins infect plants but not humans, these mycotoxins can have direct effects on humans and animals, resulting in diseases and death. Examples of fungal species producing mycotoxins include Aspergillus flavus, Fusarium spp. and Penicillium spp. There are several groups of mycotoxins under which several types are included. Aflatoxins are one of the most common and serious groups (types = B1, B2, G1 and G2), which are produced by some Aspergillus species. Aflatoxin B1 is one of the most serious mycotoxins, because it is lethal at high doses and is carcinogenic to humans at low doses and can result in reduced liver function, vomiting and abdominal pain. Annual deaths in some parts of Africa due to the effect of aflatoxin have been reported to reach 250,000 annually. Mycotoxins can be found in several products, especially peanuts, pistachios and maize. Infection of these products by mycotoxin-producing fungi can occur in the field or during storage. In addition, mycotoxins can be consumed indirectly by humans through the consumption of meat from animals fed on food contaminated with mycotoxins.

Humans Have Antibodies against a Plant Virus

Tobacco mosaic virus (TMV), a widespread plant pathogen, is found in tobacco (including cigarettes and smokeless tobacco) as well as in many other plants. Plant viruses do not replicate or cause infection in humans or other mammals. This study was done to determine whether exposure to tobacco products induces an immune response to TMV in humans. Using a sandwich ELISA assay, we detected serum anti-TMV antibodies (IgG, IgG1, IgG3, IgG4, IgA, and IgM) in all subjects enrolled in the study (20 healthy smokers, 20 smokeless-tobacco users, and 20 non-smokers). Smokers had a higher level of serum anti-TMV IgG antibodies than non-smokers, while the serum level of anti-TMV IgA from smokeless tobacco users was lower than smokers and non-smokers. Using bioinformatics, we also found that the human protein TOMM40L (an outer mitochondrial membrane 40 homolog – like translocase) contains a strong homology of six contiguous amino acids to the TMV coat protein, and TOMM40L peptide exhibited cross-reactivity with anti-TMV antibodies. People who smoke cigarettes or other tobacco products experience a lower risk of developing Parkinson’s disease, but the mechanism by which this occurs is unclear. Our results showing molecular mimicry between TMV and human TOMM40L raise the question as to whether TMV has a potential role in smokers against Parkinson’s disease development. The potential mechanisms of molecular mimicry between plant viruses and human disease should be further explored.

Acknowledgment: IJNPND, PLOSONE