Entomologists estimate that there are about 4,400 species of cockroaches in the world. They, together with the termites (formerly order Isoptera), constitute the order Blattodea. Currently, there are at least 130 species of cockroaches in the Philippines. In nature, cockroaches perform important roles in nutrient cycling in forests, caves, and other ecosystems. They also serve as prey items for many insectivorous wildlife and as hosts of parasitic insects and mites. Many species also exhibit a great variety of forms, color, and behavior patterns.
The interesting life and diversity patterns of cockroaches, however, are often overshadowed by the few, mostly invasive species, about five or six in the Philippines, that have become domestic pests. They are not only a nuisance in the household (kitchen, dining area, toilets, etc.) but also a formidable and omnipresent scavenger in garbage dumps and canals. American cockroaches are acknowledged allergens that can trigger asthma.
Many common house cockroaches, most notably the American cockroach, Periplaneta americana (L.), are almost cosmopolitan species. P. americana was probably introduced accidentally the world over through early trade. In the Philippines, it is suggested that this most abhorred species arrived via commercial routes after the Spanish colonial rule.
They are confirmed carriers of pathogenic coliforms and other bacteria including Salmonella as well as some viruses like the Polio virus (WHO, 1997). The manner of transmission is mechanical. As we have explained in the earlier parts of this series, in mechanical transmission, multiplication of the virus or any pathogen, for that matter, inside the body of the insect is not necessary. Aspects of the behavior of the insect play the major part in its potential as a mechanical carrier. Such behavioral aspects include those that are associated with foraging and feeding, as well as gregariousness and frequency of encounters with humans or places that humans visit or things that humans touch.
Cockroaches have probably lived in close association with humans since the time when tribes or families also sought the safety of caves during the last Ice Age, roughly the Last Glacial Period that ended around 12,000 years ago. In modern times, pest cockroaches although mainly tropical in origin have also reached temperate regions and live in parts of houses and other buildings where it is warm, moist and abundant with food. They are gregarious, that is they live in groups. They are nocturnal, meaning they are active at night for the most part of their lives but hide during the day in cracks or crevices in walls, food cabinets and cupboards, under kitchen sinks, and secure spaces in toilets, canals, drains and sewer systems. Garbage or rubbish bins, unwashed dishes, pots, pans, and utensils, even dining tables and work areas are, likewise, favorite foraging areas for cockroaches.
Food items for cockroaches are as diverse as their group, which include items used as human food and animal feeds. Starchy and sugary substrates are preferred, but I have also personally observed them nibble at styrofoam (polystyrene) boxes and their own cast skins, dead animals including their own kind. Cockroach bites are not common, although I had been bitten by Periplaneta australasiae (Fabricius) while sleeping in a village hut during one fieldwork. They also carry the eggs of intestinal parasites and may trigger asthma and other allergic reactions. The main public health issue concerning cockroaches, however, lies in their ability to and habit of moving freely from one building to another, from garbage dumps and rubbish bins, and sewers and latrines to houses, apartments, condos, and shanties, and most significantly because they feed on human feces, sputum, and other discarded items. They contaminate not only food but also all surfaces where they walk, run, or crawl. All these make them mechanical carriers of microorganisms and viruses that cause diseases although generally, their role is considered supplementary. Cockroaches are suspected or experimentally proven mechanical carriers of the organisms that cause diarrhea, dysentery, cholera, leprosy, black plague, typhoid fever, and as mentioned already, polio (WHO, 1997).
As in the case of filth flies, the high rate of positivity of the coronavirus in fecal samples makes cockroaches potential spreaders in places where their populations are high, especially in urban poor communities. Moreover, if the initial data on the persistence of coronaviruses in feces of bats (Le Gouil & Manuguerra 2012; Wu et al. 2020) will be extrapolated to those of humans in urban poor communities, then the possibility of cockroaches helping in local spread of the virus may also increase.
A Note on Household Ants
There number of species of ants present in Filipino households is increasing. Lit (2010) made an initial survey in Laguna Province and came up with 10 species. Pancho et al. (2019) listed about the same number for Tangub City in Mindanao. Household ants are mainly invasive or tramp species. Preliminary studies have indicated that they may also spread coliform bacteria within the household depending on where they nest, forage, pass through. The spread is effected mainly by their legs walking on as well as their portions of their bodies touching contaminated food sources. Their potential contribution to domestic spread of the virus may be essentially similar to those of cockroaches. However, their ability to produce certain antimicrobial secretions may reduce the potency of microbial pathogens possibly including viruses.
What Do We Do Now?
Again, the above discussions should be taken with ‘a big grain of salt.’ The tentative explanations are, largely, statements of hypotheses. They need to be subjected to replicated experiments so that empirical evidence may confirm or reject them. Investigations on these aspects may not be considered a priority, at the moment. However, policies are at their best when they are science-based. In turn, a thorough and holistic understanding of the ecological aspects of COVID-19, its causal virus – SARS-CoV-2, and humans and associated organisms, including insects, will be best achieved with total evidence generated through research involving collaborations of scientists.
All of these, notwithstanding, the data provided in the table we have mentioned in Part 2 support the best practices available to us today – with or without the contributions of these domiciliary insects.
- Follow doctors’ orders.
- Observe social physical distancing.
- Dispose of wastes properly.
- Do not spit in public places.
- Wear face masks.
- Wash hands often and properly.
- Uphold science and respect scientists.
- Stay at home, stay safe.
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