Joan Ribi

 

The EU Urban Indicators for Sustainable Cities (Science for Environmental Policy) take a metabolism approach focusing on resources needed to exist and function and the elimination of pollution and waste.  The concept of a   'liveable world' also includes aspects such as Environmental Hygiene and Cleanliness.

 

Out of sight, out of mind

Rats are stealthy creatures. One does not see them out in the open environment. Nevertheless they are agents which can cause substantial harm in terms of spreading diseases.  If Environmental Hygiene and Cleanliness were included as an indicator in the list of EU Urban indicators for Sustainable Cities, this might stimulate the relevant authorities to take positive action. Cities overrun by rats are breeding places for some of the worst human diseases - certainly a major threat to the concept of Sustainable Cities.

Rats feed on pigeon chicks and eggs that fall from nests perched on window sills.  The rat-pigeon food chain needs to be addressed in order that the indicator is addressed holistically. Vermin, in particular rats and pigeons as indicators of Environment, Hygiene and Cleanliness relate to two pillars of sustainable development:  Environmental and Social; Environmental Health in cities is central to EU Policy. Indicators of health are related to water such as water quality and sanitation, to life expectancy and health care services. Urban vermin are also a serious threat to citizens' health.  Vermin, in particular rats and pigeons are an indicator of Environmental Hygiene and Cleanliness that concurs with the three criteria for usability defined by Cash et al (2003):  Salience, Credibility and Legitimacy.

If Environmental Hygiene and Cleanliness were included as an indicator in the list of EU Urban indicators for Sustainable Cities, this might stimulate the relevant authorities to take positive action. Cities overrun by rats are breeding places for some of the worst human diseases - certainly a major threat to the concept Sustainable Cities.

Salience, credibility and legitimacy are the criteria for using rats as indicators of Environment, Hygiene and Cleanliness in Urban Environments.

 

Food and shelter

The Urban Environment provides an excellent breeding place for rats, particularly where there are large populations of birds, food strewn on pavements for cats, and garbage bags torn open by dogs and cats. The rat- pigeon food chain supports a large array of vermin: cockroaches, several species of flies, mites and mosquitoes. Rats are the least obvious. The Black Rat (Rattus sp,) thrives comfortably in dirty buildings, stores and piled up street garbage. In urban areas they are found in and around residential buildings and stores. Rats climb trees and vines to gain entry into upper floors of buildings.  

The rat grows at least to 23 cm in body length (excluding tail). They are intelligent animals with a well developed hearing and sense of smell. Stealthy, fast and noiseless, they may be only a few meters away from you as you walk along the pavement. Broken pavements, cracks in the wall, stinking cellars and disused storage rooms full of rotting household effects provide excellent hiding places. Easy access to the streets provides a source of abundant food available in the form of pigeon chicks and eggs which fall off nests on ledges and window sills. Food in the form of half eaten human meals scattered on the pavement for cats and bird seeds thrown out for pigeons supplement the bounty that falls from above.

Rats are generalists, and thus not very specific in their food preferences, which is indicated by their tendency to feed on any urban meal that becomes available be it pigeons, eggs,  small birds, or food and water put out on pavements for cats and dogs. Food stores in homes are particularly vulnerable to being ruined because rats tend to urinate and defecate where they feed, contaminating food stores. They eat about 15 grams per day and drink about 15 millilitres water per day.  They are a threat not only to humans and dwellings but also to revegetated urban habitats.  These animals strip bark off of trees and dig burrows

 

Foraging

As generalists, black rats express great flexibility in their foraging behaviour. They often meet and forage together in close proximity. Although it has been reported that rats tend to forage after sunset, their behaviour is flexible, adapting to the behaviour pattern of humans.

 

Reproduction.

Black rat populations demonstrate explosive population growth under favourable circumstances. The species is polygynous, and generally, the dominant male is the most successful breeder. If environmental conditions allow it, successful breeding may occur all year, the peak breeding seasons are summer and autumn. Females can produce up to 5 litters in one year. Young rats are able to reproduce within 3 to 5 months of their birth. Weaning and independence from the mother occur at about 3 to 4 weeks of age. 

 

Rodent-borne diseases and their risks to public health

Rats serve as outstanding vectors for transmittance of diseases because they carry a large array of  bacteria and viruses in their systems. A number of disease- causing bacteria common to rats, include Streptococcus pneumoniae,  Corynebacterium kutsheri, Bacillus piliformis, Pasteurella pneumotropica, and Streptobacillus moniliformis, to name a few. All of these bacteria are disease-causing agents in humans. In some cases, these diseases are incurable.   Rat endoparasites include trypoanosomes (blood parasite), nematodes, trematodes, cestodes (gut parasites causing abdominal pain and diarrhoea).

Black rats (or their ectoparasites) are able to carry a number of pathogens which cause rabies, fevers, typhus, Weil's disease, toxoplasmosis and trichinosis which are the best known.  Rats transmit the spread of bacterial diseases as leptospirosis to humans. Rats played a primary role in spreading the bacteria Yersinia pestis, which is responsible for bubonic plague and pneumonic plague in humans. The urban plague is spread via flea bites.

 

Dust as a vector of disease

On windy days a major nuisance is blown dust. It is also a vector of diseases. Rat and pigeon faeces and dog faeces dry out and are reduced to dust which is carried by winds in all directions.  Blown into our eyes, noses and mouth, bacteria and viruses in faeces dust cause infections from ulcers to major diseases. When walking in the street on a windy day it is wise to cover nose and mouth and wear eye protection to avoid infections. The environment inside the house can be protected to some extent by keeping the windows closed.

 

Population control

Rat populations are killed off with chemical pest control programs or controlled by removing their food source, in this case pigeons. Rat control is undertaken in urban environments for health purposes.  Repetitive treatment is necessary because rat populations are known to rebound, a phenomenon which is not yet fully explained.