Welcome to Science with Shrike! Today we lay the groundwork for considering risk from existing and emerging diseases. While emerging diseases grab attention, there are many known diseases that kill tens to hundreds of thousands of people annually. Having a risk management plan in place will give you peace of mind when considering new pathogens.
COVID Fatigue
Many people associate ‘new infectious disease’ with ‘lockdowns and endless masking’ due to the COVID pandemic, and want nothing to do with it. There is also a lot of distrust in public health authorities given the handling of the COVID pandemic. While these are understandable feelings, infectious disease is always with us, and new ones continually emerging. We need to be prepared.
Notice that Shrike did NOT say ‘be scared’ or ‘freak out’. We want to assess risks and make decisions based on our risk tolerance and assessment of the risks. While heuristics like ‘do the opposite of what the government says’, and ‘ignore all diseases the media promotes’ may be tempting to employ, these are not the most effective heuristics out there for infectious disease. To decide what you want to do, you need to start with a risk framework, and consider your approach for diseases in general. We’re going to start general and then return to monkeypox.
Infectious Disease Hygiene
If we ground ourselves in a general consideration of infectious disease hygiene, we will be better placed to evaluate new diseases as they emerge. Depending on your assessment, it may lead you to cleaner practices in general. To assess, we need to consider routes of infection, and then decide what we will do to minimize access by pathogens.
In general, pathogens are transmitted via 6 different ways:
skin
respiratory
oral
sexual
mucosal contact w/infectious material
vectors
Skin pathogens are prepared to deal with penetrating the hardest barrier of all—your skin. Many pathogens need to wait for a break in the skin to start an infection, but some don’t need a break to cause an infection. Infectious fungi that eat or penetrate skin don’t need a break in the skin to cause problems. Similarly, parasitic worms like schistosomes and hookworms burrow through the skin. Since you need to avoid contact with these pathogens, general precautions include wearing shoes, especially around carpeted, common use areas or outdoors, and improving sanitation to break the infectious cycle. Avoid swimming in natural freshwaters in endemic areas.
Respiratory pathogens are the hardest to defend against. While most of these pathogens are transmitted by aerosols, some may be transmitted by respiratory droplets. Aerosols hang around in the air for 15-20 min, and penetrate deep into the lungs. To stop aerosols, good ventilation is needed or a properly-fitted N95 (or better, like a PAPR or P100) is needed to filter pathogens out. Tuberculosis and SARS-CoV2 are examples of pathogens spread by aerosols.
Respiratory droplets fall quickly to the ground, and may spread 6-10 feet depending on the strength of ejection. Approaches like “cover your cough” or surgical masks block these droplets and the pathogens on them. Strep throat can be spread by respiratory droplets.
Oral pathogens must be consumed to cause pathogenesis. These pathogens can survive passage through the stomach and often cause gut issues. The most common exit strategy for these pathogens is the fecal route. Fecal contamination of food or drinking water helps these pathogens spread. Oral-anal contact can also spread these pathogens. The riskiest area is daycares because young children do not have sanitary practices. Cooking food kills pathogens prior to consumption. Handwashing helps deal with these pathogens. Finally, advances in sanitation, especially handling wastewater and water purification, have made many of these pathogens rare in the developed world.
Sexually transmitted pathogens are transmitted via sexual contact. While some pathogens have trouble establishing infections outside of the genitals, others just require a mucous membrane for spread. For example, Chlamydia, Trichomonas and Gonorrhea are spread between genital-genital contact. In contrast, pathogens like herpes, and yeast infections/thrush can be spread via oral-genital contact. Condoms reduce spread of these pathogens. Limiting sexual partners, especially high risk ones, and regular testing also reduce the risk of sexually transmitted infections.
Mucosal contact with infectious material summarizes many of the pathogens discussed above. If the pathogen comes in contact with most mucosal membranes, it can infect. These may also include blood-borne pathogens, which are transmitted by contact with infectious blood, and vertically transmitted pathogens (spread from mother to child). These pathogens may be transmitted when infectious material is aerosolized and inhaled. The infection cycle will determine how the pathogen can be transmitted. Practices to reduce spread of these pathogens includes limiting contact of your mucosal membranes with potentially infectious materials. Gloves, and reducing aerosol risk are the primary approaches. Eye protection and respirators are often considered overkill, but reasonable if you are concerned about those routes of infection.
Vector-borne pathogens avoid all of these hassles and let the vector deliver them. A vector in microbiology is an organism necessary to transmit a pathogen to the pathogen’s host. Most vectors are blood-sucking arthropods—ticks, fleas, flies, and bugs, though snails are the vector for schistosomes. Not every pathogen can use a vector—pathogens need to be adapted to life inside the vector. For example, Plasmodium species, the causative agents of malaria, have to migrate from the mosquito’s midgut to the salivary glands to be transmitted. Yersinia pestis, the causative agent of the Plague, forms a biofilm in the flea’s foregut to starve it (so it bites more animals), and make the flea regurgitate the bacteria when it tries to dislodge the biofilm. This is why mosquitos do not transmit HIV or many other bloodborne pathogens. Defense against these pathogens focuses on vector control. Prevent them from biting you and/or kill them. Malaria is no longer present in the US because it was driven out by killing all of the mosquitoes carrying it with DDT. Insecticide-treated mosquito nets help reduce malaria in Africa.
Risk Management
Given all of these ways for pathogens to infect you, how do you deal with these challenges? This answer will depend on your relative risk level, which vary by your personal situation, and the cost of mitigating those risks. For example, getting pregnant increases infectious disease risk, but the benefit outweighs that risk. Living in a tropical region, or city may also be worth the risks. Risk management is a spectrum of trade-offs, not an all-or-none. Just be intentional about your risks.
At the personal level, you need to determine your level of general risk to infectious diseases. Some factors leading to disease risk, like Severe Combined Immunodeficiency (SCID), Chronic Granulatomous Disease (CGD), and other primary immunodeficiencies, are genetic. If you have those, and survived long enough to learn how to read, you should know more about your immunodeficiency than Shrike, and how best to manage it. Other factors, like age or need for cancer treatment, are similarly hard to avoid. However, some risk factors, like type 2 diabetes and obesity, are within your power to fix. BowtiedOx can get you started on a fitness program. The important take-away is that your risk may be different, and you may need to adjust your lifestyle based on your risk.
The next large risk to consider is geographic. While some diseases are world-wide, many others are regional, especially if they are fecal-oral (eliminated by sanitation) or vector-borne (limited by vector range). In general, sub-Saharan Africa has the most diseases, though tropical regions in general carry a greater variety of diseases than elsewhere. Cooler regions tend to have a lower variety of diseases, and developed nations have extirpated many diseases.
Outside of climate, population density, sanitation, and exposure to wildlife/livestock are the next geographic considerations. The rate of disease spread is driven primarily by susceptible population density, which is why cities and day cares are hotbeds of germ spread. Poor sanitation, especially poor water quality, allows infection, especially from fecal-oral pathogens. Wildlife/livestock exposure carries the risk of infections from those reservoirs. For example, chickens may carry Salmonella (fever + diarrhea), cows may carry Brucella (diarrhea + weakness), bats may carry rabies (fatal), and deer may carry Mycobacterium tuberculosis.
After you know the risks of where you live, and your personal risks, consider any lifestyle risks. What occupational risks do you have? Do you travel to higher risk areas? Do you have sex with strangers? Are you exposed to vectors that might bear diseases? Does anyone living with you engage in any high risk activities (including children attending day care or elementary school)? To whose blood or other bodily fluids are you regularly exposed? How well ventilated are the places you frequent?
Once you have a list of all your risks, it’s time to decide what can be done, if anything, to mitigate them. You also have to balance the mitigation against all of the costs. Some of these may be easy changes to implement (wash your hands after using the bathroom or handling the chickens), while others may be more challenging, and/or require trade-offs.
Personal protective equipment is the last step of risk mitigation. This comes when the risk cannot be engineered away by structural changes in your life. If you have to clean up someone’s blood, nitrile or latex gloves can provide a protective barrier so you can do this safely. If you have to clean mouse scat out of cabins in New Mexico, a respirator will reduce your risk of hantavirus exposure.
Make a Plan
This is where it is helpful to develop a plan—list those risks and what your options are for mitigation, and the costs of that mitigation. General precautions will help against a wide variety of diseases, even if you are not familiar with the particulars of the latest plague. To go more in depth, look at the disease stats for your region—this is often provided by your health authority, and/or regional clinics on what diseases are present. If you do not trust your health authority, you can discount or multiply their estimates based on how much you think they are incorrect.
While you want to plan for risks and mitigate them, you will not be able to drive the risk to zero. Worse, there is evidence that completely avoiding microbes is bad for you. The hygiene hypothesis suggests that improvements in some aspects of sanitation that reduced our environmental exposure to microbes causes an increase in asthma and allergies. Studies in germ-free mice shows that their immune system is more aggressive, which leads to autoimmunity.
Balance is a necessary part of risk management, and the risk profile for you, and your family will be different than others. Diseases that are only annoying, yet hard to control (eg common colds), may only be worth minimal mitigation. Diseases that carry mortality for your risk group (eg rabies) should be mitigated more aggressively. Having this framework in place will help you evaluate new diseases when they arise. Are they worse than diseases you currently live with? How do you categorize them?
With risk management as a background, we will be ready to dive into the current monkeypox pandemic in the next post.