Meat plants—a new front line in the covid-19 pandemicBMJ 2020; 370 doi: https://doi.org/10.1136/bmj.m2716 (Published 09 July 2020) Cite this as: BMJ 2020;370:m2716
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Re: Meat plants—a new front line in the covid-19 pandemic. Are cold temperatures reducing host resistance to Covid-19 infection?
We read with interest the recent timely editorial by Professor Middleton and colleagues discussing Covid-19 outbreaks in slaughterhouses and meat packing houses (1). Inappropriate distancing, poor compliance with facemask wearing, presenteeism whilst unwell, voice projection against a background of loud machinery, whilst possible contributing factors, can also be seen in other workplaces. Meat processing plants function with temperatures between 10 degrees Celsius and refrigerating temperature. Middleton and colleagues note that the “virus thrives in lower temperatures and very high or very low relative humidity’ as well as surviving longer on metallic surfaces. We wish to highlight another possible detrimental effect of prolonged cold air exposure, that is on host resistance to Covid.
Perforin, expressed by some natural killer cells and T cells, is recognised as one of the primary means of human defence against viral infection. It is a potent pore-forming protein, permitting cytotoxic proteases, such as granzyme B, to enter the cytoplasm of virally-infected target cells (2). Epidemiological evidence appears to suggest that perforin expression and function is vital for human defence against severe SARS-CoV-2 infection (3). Perforin expression is greatest amongst children, twice as high in adult females versus males and substantially declines after the age of 70 years (3). Additionally, it has been shown to be reduced in Type 2 diabetics and obese people i.e. a consistently reduced expression in those population groups more susceptible to Covid (3). Indeed the immune profile of patients with severe Covid admitted to intensive care compared to non-intensive care patients demonstrates significantly reduced perforin expression (4).
Matsui and Yahoda, using incubated human lymphocytes in vitro, found that compared to normal body temperature (37oC), perforin expression by CD4+ and CD8+ T cells was significantly reduced at temperatures of 33oC by over 50% and 35% respectively but, interestingly, raised at the modestly higher temperature of 39oC (5). Similar in vitro effects of temperature on expression of Fas-Ligand, which is involved in the other main cellular means of killing virally-infected cells, have also been described (6). NLRP3 inflammasome, which releases cytokines in response to viral infection and thought to be vital in respiratory defence (7), also has reduced function at lower temperatures (8).
We are in agreement with both Middleton and colleagues and Mandal and Panwar, whose recent epidemiological study suggests that a cold environment may be an additional risk factor for COVID-19 cases (1, 9). We postulate that prolonged respiration of cold air could have a detrimental effect on the human respiratory immune response to SARS-CoV-2 which may be a contributory factor to the outbreaks of Covid-19 in food-processing workplaces.
1. Middleton J, Reintjes R, Lopes H. Meat plants-a new front line in the covid-19 pandemic. BMJ (Clinical research ed). 2020;370:m2716.
2. Voskoboinik I, Whisstock JC, Trapani JA. Perforin and granzymes: function, dysfunction and human pathology. Nature reviews Immunology. 2015;15(6):388-400.
3. Cunningham L, Simmonds P, Kimber I, Basketter DA, McFadden JP. Perforin and resistance to SARS coronavirus 2. The Journal of allergy and clinical immunology. 2020.
4. Bordoni V, Sacchi A, Cimini E, Notari S, Grassi G, Tartaglia E, et al. An inflammatory profile correlates with decreased frequency of cytotoxic cells in COVID-19. Clinical infectious diseases : an official publication of the Infectious Diseases Society of America. 2020.
5. Matsui T. Reduced perforin release from T cells as a mechanism underlyinghypothermia-mediated neuroprotection. Clin Exp Immunol. 2020;11(1):57-64.
6. Fu T, Blei AT, Takamura N, Lin T, Guo D, Li H, et al. Hypothermia inhibits Fas-mediated apoptosis of primary mouse hepatocytes in culture. Cell transplantation. 2004;13(6):667-76.
7. Lavelle EC, McNaughton A, McNeela E. NLRP3 in protective immunity and vaccination against respiratory infection. Expert review of vaccines. 2011;10(3):255-7.
8. Zhou M, Wang P, Yang Z, Wu H, Huan Z. Spontaneous hypothermia ameliorated inflammation and neurologic deficit in rat cardiac arrest models following resuscitation. Molecular medicine reports. 2018;17(2):2127-36.
9. Mandal CC, Panwar MS. Can the summer temperatures reduce COVID-19 cases? Public health. 2020;185:72-9.
Competing interests: No competing interests
The outbreak of COVID-19 in meat-markets should serve as a stark warning to developing countries like Pakistan, preparing to celebrate Eid-ul-Azha on 31st of July, 2020. Eid-ul-Azha is an annual Islamic ritual where Muslims sacrifice animals on the 10th, 11th, and 12th of ‘Zul-Hajj’, the twelfth month of Islamic lunar calendar.(1) According to some estimates, on Eid-ul-Azha of 2017, 8.1 million animals were sacrificed in Pakistan.(2) In preparation for this festival, cattle-markets spring up in a large number of localities, many of them illegal and unregulated. (3,4) These cattle markets, mostly located out in the open, are visited by throngs of people. Lack of hygiene measures like the availability of running water, limited available space leading to over-crowded, cramped conditions along with the frequent movement of buyers between different markets, could spell a looming disaster for Pakistan.
If there is one lesson that governments all over the world could learn from COVID-19, it is that timely preventive measures are the most effective strategy for combating a pandemic. Pakistan has already suffered from the lack of insight displayed by its policy-makers in combating COVID-19 outbreak. Back in May, while the government had imposed a lock-down all over the country, with the situation still somewhat under control, the Supreme Court of Pakistan termed the lock-down illegal and ordered the opening of shopping malls on the 19th of May. (5) As people rushed to markets, the under-capacitated, under-resourced hospitals battled with a sharp increase in the number of COVID-19 patients, going from 31,812 on 20th May to 104,780 on 20th of June subsequent to the opening of markets. (6) This also indicates the importance of involving healthcare experts in taking decisions regarding national health crisis, a role visibly lacking in Pakistan. If Pakistan wants to avoid a similar disaster again, the government must come up with an effective roadmap for ensuring the set-up of cattle markets with strict implementation of those guidelines.
The primary goal in this scenario is to reduce human-to-human contact. Although some voices in the government are proposing online transactions for the sale of animals as an alternative, this does not take into account the fact that majority of the vendors of sacrificial animals are uneducated farmers from peripheral rural areas of Pakistan with limited prowess in digital technology. For guidelines to be effective, they must take into account the ground-realities of the country. In this context, one of the most important steps would be to involve the local government and health authorities to educate the sellers regarding the possible risks they face and the preventive measures they must take to protect both themselves and the people who visit them. The government should allocate adequate area to set up the cattle markets, where social distancing protocols can be followed. It must ensure the supply of both running water and disinfectant. The whole market must be cleaned and disinfected regularly. The availability of a doctor on the premises to regularly examine the sellers on the market, in order to identify and quarantine possible COVID-19 patients and their contacts at the earliest possible would help prevent large outbreaks within a market. Taking all these steps on a large scale requires efficient planning; therefore, the government should involve all the stake-holders, i.e public health authorities, police and farmer associations to come up with a practical roadmap for implementation of its guidelines. Never was the maxim, “A stitch in time saves nine” truer.
1. Eid ul Adha [Internet]. [cited 2020 Jul 14]. Available from: https://www.timeanddate.com/holidays/muslim/eid-al-adha
2. (24) 8.1 million animals sacrificed on this Eid ul Adha, Pakistan Tanners Association - YouTube [Internet]. [cited 2020 Jul 14]. Available from: https://www.youtube.com/watch?v=LILP96P-xeE
3. Illegal cattle markets mushroom | The Express Tribune [Internet]. [cited 2020 Jul 12]. Available from: https://tribune.com.pk/story/2252627/illegal-cattle-markets-mushroom
4. Only eight cattle markets in Karachi are legal | Pakistan Today [Internet]. [cited 2020 Jul 12]. Available from: https://www.pakistantoday.com.pk/2019/08/03/only-eight-cattle-markets-in...
5. SC orders opening of all shopping malls - Newspaper - DAWN.COM [Internet]. [cited 2020 Jul 15]. Available from: https://www.dawn.com/news/1558179
6. Pakistan Coronavirus: 255,769 Cases and 5,386 Deaths - Worldometer [Internet]. [cited 2020 Jul 15]. Available from: https://www.worldometers.info/coronavirus/country/pakistan/
Competing interests: No competing interests