Bacteria

Bacteria can be found both within the gut of an insect and on its surface, as they are with any animal, us included. Bacterial content in itself is not, however, the issue; it is whether bacteria pathogenic to humans can be propagated through the farming of insects, either for human or animal consumption.

The EFSA was not so much concerned with bacteria that were pathogenic to the insects themselves, since insects are genetically so different from us that a case of “entomopathogenic” bacteria developing the ability to infect human hosts would be highly unlikely. They were, however, concerned with the potential for insects to act as vectors for known human and animal pathogens such as Salmonella, E. coli and Campylobacter. Studies have indeed shown that this is possible (Holt et al., 2007; Leffer et al., 2010), but unlike poultry and larger animal livestock, these pathogenic bacteria are unable to replicate inside the insect gut, meaning that this risk can essentially be mitigated as long as substrate choice and processing methods are carefully regulated.

Nevertheless, this opinion is based on scarce evidence in the scientific literature. The ESFA therefore recommends further research into the prevalence of human pathogens in farmed insects.

An additional concern involves antimicrobial resistance, since antibiotics are made use of in insect farms in cases of pathogenic outbreaks, or simply in order to improve insect yields and longevity (Hirose et al., 2006; Eilenberg et al., 2015). It is therefore advised to introduce controlled antimicrobial use for insect farming, and to keep a close watch on bacterial populations in case resistance develops.

Viruses

The story for viruses is much the same as for that of bacteria. Insects have a multitude of viruses that affect them, but they are all specific at either the family or species level so are of no threat to humans. The EFSA did consider whether some insect viruses with taxonomically related groups affecting vertebrates (e.g. viruses for polio, Hepatitis A, etc.) had the potential to jump to humans, but some studies have shown that insect viruses do not replicate in human cells (El Far et al., 2004), and there is no evidence of such a jump having ever occurred.

Insects do, however, act as vectors for some human viruses (e.g. dengue fever, West Nile disease, etc.) which are actually able to replicate within the insect (King et al., 2012). There is therefore a need to determine whether these kind of viruses can be found in farmed insects, but there is no evidence of this to date.

Similarly, it will be necessary to investigate the potential survival of vertebrate viruses within insects in order to evaluate whether insects may aid in the propagation of viral disease outbreaks, regardless of whether the virus is able to replicate within the insect.

Parasites

Insects are known to harbour parasites and there have been rare occurrences of transmission of these to humans, although all instances were non-European.

Most of these reports involved trematodes (parasitic flatworms, or flukes). These animals tend to have very complex life cycles involving at least two hosts, one of which is almost always a specific species of snail. An example of such a life cycle for Dicrocoelium dendriticum, a trematode worm that can infect humans through eating ants (Jeandron et al., 2011), is shown below.

The EFSA notes that the risk of parasite infections such as this can be significantly reduced in properly managed closed farming environments, since the parasites will not have access to all of the hosts required to complete their life cycle, nor will the farmed insects be exposed to the parasites in the first place.

Prions

Prions are a strange one. They are not living organisms; they are composed entirely of protein – misfolded protein – yet it is widely accepted that they are able to replicate by stimulating their normally folded counterparts found in humans and animals to take on their own misfolded configuration. Since the immune system does not recognise them, they can’t be fought in this way, leading to diseases such as Creutzfeldt-Jakob Disease (CJD) and variant CJD, taking on the apparent behaviour of an unregulated viral infection.

Any animal would need the properly folded prions in their system (found naturally in our cell membranes) in order for a misfolded prion infection to replicate by using them as templates. Insects, however, do not have prion-encoding genes, so the risk of insect-derived prions infecting us is zero. Where the risk lies is in whether they can act as vectors for our own prions. Fortunately, due to the same genetic basis, mammalian prions cannot replicate within insects, but studies have found that they can be carried by them (Thackray et al., 2012; 2014).

The key issue with prions is that farmed insects would need to be fed on human- or animal-derived substrates, such as slaughterhouse by-products or human sewerage, for any potential risks to arise, but this is only going to be a possibility for insects raised for feed since these substrates are not made use of in the farming of insects for human food.

Chemicals

Chemical contaminants that may accumulate in insects through their substrate can be broken down into the following categories:

Heavy Metals

Data on heavy metal uptake by insects is mostly limited to studies on cadmium and lead, but it has been shown that these metals are accumulated in insects through their substrate or from the soil (Vijver et al., 2003; Diener et al., 2011). More research is needed on the uptake of other metals and on the heavy metal content found in different forms of substrate.

Toxins

Insect toxins are naturally produced by some insect species, but they usually advertise their toxicity through the use of vivid colours to ward of predators. There is no evidence that the most commonly farmed insect species produce these kinds of toxins. Insects do have the ability to accumulate toxins from plants and fungi, so the issue for farmed insects is primarily related to the control of toxin levels in their substrate.

Hormones & Veterinary Drugs

Veterinary drugs, hormones and antimicrobial agents are sometimes added to substrates to fend off disease or promote growth in farmed insect populations, and residues have been found to accumulate in the insects (Charlton et al., 2015). The EU veterinary drug legislation does not currently cater for insect farming, but testing for these kind of compounds can be managed in much the same way as is practised with other foods of animal origin.

Pesticides & Biocides

Very little data exists on the accumulation of pesticides in farmed insects, but most insects tested had levels below the danger threshold (Charlton et al., 2015). Pesticide accumulation is obviously a concern for insect farming, especially if the insects are destined for the plate, but again, close control and traceability of the substrate used should be practised. Similarly, care must also be taken with the use of any biocides for the cleaning and disinfecting of farming equipment.

Allergens

This is a big one for insect farmers, since there have already been cases of allergic reactions and even anaphylactic shock in humans (Siracusa et al., 2003; Ji et al., 2009). Moreover, the potential for allergic reactions cannot be controlled by choice of substrate, as has been the case for most of the risks discussed so far.

Allergic reactions occur in individuals either because they are already sensitised to insect allergens, the allergen has cross-reactivity with something else they are allergic to (e.g. shellfish), or the allergen is responsible for a completely new food allergy in the individual. The ESFA advises risk assessments need to be informed by further research into these three types of allergic reactions and their relative potential to develop in the population.

The obvious solution, provided that the risks assessed through research are not higher than acceptable levels, is to inform consumers of the insect content and potential allergenicity and/or cross-reactivity of insect-derived products through adequate food labelling.

Farming Methods

The processing and storage methods used following insect harvesting are also key considerations for food safety, as contamination can occur after the farming process, as was the case when five people in Kenya died of botulism after eating termites stored in plastic bags for four days during transport (Knightingale & Ayim, 1980).

Environmental Risks

Environmental Risk Assessment (ERA) takes into account many of the risk factors already discussed in this article, their potential to be released into the environment, and any knock-on effects that this may cause. The sustainability of our food sources is another factor that is becoming increasingly more important, and was also therefore considered by the EFSA.

The environmental risks involved in insect farming largely depend on the waste management strategies in place, as is the case for any type of livestock agriculture, but also on the levels of some of the contaminants already mentioned (heavy metals, pesticides, etc.) that might be present in the insect waste. Insect frass, for example, is known to be nutrient-rich and therefore may act as an efficient fertiliser, but risks of environmental contamination may then come into play if the safety criteria for them are not adhered to in the first place.

As far as the sustainability of insect farming is concerned, it does appear to be more favourable than traditional livestock farming (more details here), but the EFSA suggests that more data is required to evaluate the extent to which this is the case, specifically for the mass-rearing of insects compared to that of larger livestock.