THE URBAN PHYSICAL ENVIRONMENT AND PARASITIC INFECTION

The physical environment of urban cities can promote or hinder the proliferation and transmission of parasitic infections. The poor and unhygienic conditions prevailing in many cities of the developing countries encourage the transmission of parasitic infections via the air, food, water, human waste or insect-vectors. For example outbreak of gastrointestinal and skin infections is common in urban settings. Rates of certain epidemic infections, such as acute diarrhea (the second biggest killer of children under five years old worldwide) is very high in urban communities where there is lack of sufficient housing, sanitation and clean water. (Harpham et al; 1991).

            According to WHO, almost 137 million people in urban
populations have no access to safe drinking water and more than 600 million urban dwellers do not have adequate sanitation. The situation is particularly alarming in congested cities of sub-Saharan Africa. In Nigeria for example, only 30% of residents in Ibadan have access to piped water and in Lagos only 90% of its 10 million residents have access to portable water (Satterth; 2O1O). Unsafe water sources and inadequate sanitation and hygiene are prime contributors to diarrhea infection and might lead to cholera endemicity (Guevart et al; 2006). The overall prevalence of diarrhea can be very high in cities as shown by data from northern Jakarta, Indonesia where prevalence is 50 per 1000 people (Agtini et al; 2OO5).

Inadequate sanitation also affects the transmission of soil transmitted helminthiasis and intestinal parasites. Several surveys show a high prevalence of intestinal parasites among children-for example, 52.8% in Karachi Pakistan (Mehraj et al; 2008). In most urban settlements of the developing countries where children comprise a high proportion of the population, the impacts of parasitic infections are particularly heavy. Absence of sewerage systems can lead to the proliferation of rodents, as in El Salvador’s slums where rats carrying Leptospira interrogans proliferated (De faria et al; 20O8). During the rainy season, open drainage gutters tend to overflow, flooding streets and adjacent homes, and triggering out breaks of leptopirosis.

The distribution of sewage contaminated vegetables from urban gardens led to the propagation of cysticercosis in Mexico City (Vasquez; 1996). However, (Ikeh et al; 2006) in their comparative study of intestinal parasitism between rural and urban areas in North central Nigeria reported that the common practice of emptying the watery portion of filled septic tanks into the gutters, and burying the solid faecal waste in the soil contributed to the high prevalence of intestinal parasites of the urban centers. The watery portion eventually contaminated bodies of water used by humans and the buried wastes contaminated underground surface water. This was a very bad practice that affected the epidemiology of intestinal parasites in those urban areas.

Management of solid wastes is another problem posed by urbanization. The Asian Development Bank estimated that the waste quantities generated by Indian cities will increase from 46 million tones in 2001 to 65 million tones in 2010. In rural areas, most waste is reused as compost, burnt, or recycled to meet daily needs but in cities this is rarely possible and when municipal service are deficient, waste piles up in empty lots and street sides, leading to soil, air and water pollution. This might increase the prevalence of diarrhea and intestinal parasitic infections (Moreas, 2007).

Accumulated wastes can also be a breeding site for vectors. Phlebotomine Sandflies-the main vectors for leishmania parasites breed in organic waste from human being and domestic animals. In Teresina, Brazil, the risk of contracting visceral leishmaniasis is six times higher for people living in houses with no regular rubbish collection than for people living in houses with a regular rubbish collection(Costa et al; 2005).

Aedes spp mosquitoes and Anopheles spp which are vectors for dengue, yellow fever, chikungunya and malaria, have adapted well to the urban environment and often breed in cans, plastic bottles and tyres (Hayes et al; 2OO3).

On the other hand, urbanization can positively impact on vector – borne diseases. The expansion of urban areas can actually reduce the prevalence of parasitic infections by destroying the breeding grounds of some vectors (e.g. mosquitoes for malaria) (Trape et al; 1987). From the review of the demographical development of Brazzaville and previous malaria related entomological and parasite surveys, it revealed that inhabitants of Brazzaville were subject to reduced anopheles biting rates (0-7.36 versus 35-96 (L
bites per person per-night), reduced transmission intensities of an APfEIR of 22.5 versus 250 infected bites per person per annum (i.e. urban versus rural) (Trape et al; 1987). (APfEIR is Annual Plasmodium falciparum entomological inoculation rate). The above findings were corroborated in West Africa like Benin by (Akogbeto et al; 1992), Burkina Faso by (Rossi et al; 1986). Ghana by (Appawu et al; 2OO4) and Nigeria by (Awolola et al. 2OO2). Therefore there is clear evidence that urbanization affects Anopheline species in environment. Diversity, numbers, survival rates, infection rates with P. falciparum and the frequency with which they bite people are all affected, so fewer people acquire malaria infection, become ill and or die of its consequences in urban areas. The reason is simply because of lower vector densities that result from a paucity of clean fresh water, breeding sites (Lindsay et al; 199O).

Housing conditions in urban centers are usually better than in rural areas as a result of the use of concrete floors and walls to build rather than houses built with leaves and mud. However, in many low-income countries, poor resident of slums generally build their own dwellings from flimsy, scrounged materials and with no concern for vector hygiene. In the suburbs of Arequipa, peru, about half of the houses are infested with Triatoma infestan, which transmits Trypanosoma cruzi (Levy et al; 2OO6). Infestans were also found in peri-urban areas of Cochabamba, Bolivia (Albarracin et al; 1999). Vectoral transmission of chagas disease has been documented in the peri-urban shanty towns in many cities in Latin America. In metropolitan Santiago, Chile 23% of the peri-urban substandard houses and 60% of the slums were infested with Triatoma infestans and 15% of the captured insects were infected by Trypanosoma cruzi, the causative agent of chagas disease (Shenone; 1985).

Urban areas may also encroach on rural environment where insects or arthropod vectors thrive facilitating exposure of increasing numbers of urban inhabitants to infection.

THE PROBLEM OF SLUMS

A slum, as defined by the United Nations agency UN HABITAT is a run-down area of a city characterized by substandard housing and squalor and lacking internal security. A United Nation expert group has created an operational definition of a slum as an area that combines to various extents the following characteristics-inadequate access to safe water, inadequate access to sanitation and other infrastructured; poor structural quality of housing. Over crowding and insecure residential status. (WHO, 2003) Slums have posed a huge problem for developing nations because they are by definition areas in which the inhabitants lack fundamental resources and capabilities such as adequate sanitation, improved water supply, durable housing or adequate living space.

While their physical forms vary by place and overtime, slums are uniformly characterized by inadequate provision of basic infrastructure_ and public services necessary to sustain health such as water, sanitation and drainage. Buildings made of flimsy materials that are prone to ignite, frequently collapse and offer scanty protection against the elements, leaving resident vulnerable to injury, violence, illness, crime, and death. Further since many of
these settlements are illegal, slum dwellers often have no official addresses and are commonly denied basic rights and entitlements like public education and health care. The characteristics and politics associated with slums equally vary from place to place.

It is usually characterized by urban decay, high rates of poverty, illiteracy, unemployment, lack of personal/community land ownership. They are commonly seen as “breeding grounds” for social problems such as crime, drug addiction, alcoholism, high rate of mental illness and suicide, high rate of diseases and malnutrition. The lack of services such as routine garbage collection allows rubbish to accumulate in huge quantities. The lack of infrastructure is caused by the informal nature of settlement and no planning for the poor by Government officials. UNESCO reports that over 2 billion people in the world live in slums and that number is expected to double by 2030(UNESCO, 2007) That means everyday approximately 250,000 children are born into slums. That is 250,000 more children each day are denied access to basic human rights such as health and clean water.

Recent years have seen a dramatic growth in the number of slums as urban population has increased in the third world.

In April 2005, the director of UN-HABITAT stated that the global community was falling short of the millennium Development Goals which targeted significant improvements for slum dwellers and an additional 50million people have been added to the slums of the world in the past two years (WHO, 2005).

According to a 2006 UN-HABITAT reports, 327million people live in slums in commonwealth countries which Nigeria belong. Example of slums in Nigeria are Maroko in Lagos, okpoko in Onitsha, mammy market Environs etc

SANITATION AND HYGIENE CHALLENGES IN SLUM:

Hygiene is commonly known as cleanliness or conditions and practices that serve to promote or preserve health. A population that does not take into consideration hygiene is at risk of infection and illness. Improved housing, improved nutrition and improved hygiene are the essential components for war against infectious diseases (Greene, 2OO1). Lack of resources such as water, results in poor hygiene level, toilets cannot be washed and there is not enough water to shower. This, however, promotes parasitic infection. United Nations Habitat (2006) has described sanitation and hygiene challenges in terms of poor basic services like access to sanitation facilities and safe water source, the lack of water collection service, poor rain water drainage system, poor infrastructure and absence of electricity supply, substandard and inadequate houses overcrowding and congestion. The cohabitation of different families and more single rooms (one room unit in slum. Often shared by five or more people which they use for cooking sleeping and living). The lack of path ways, the uncontrolled dumping of water and polluted enrolments result to unhealthy living encouraging the transmission of parasitic infection and their vectors such as malaria, filariasis, schistosomiasis, amoebiasis, trypanosmiasis, leishmaniasis and chagas disease etc. Houses may be built in dungeons locations which are unsuitable for human settlement for example near waste disposal sites.

The living conditions in slums are often sub-human as the denial of government services lead to children playing in gutters of human feaces, houses mounted on heaps of trash and cesspools that serve as incubators for infectious diseases.

According to (Bradley et al;1991) many surveys have demonstrated a prevalence of intestine parasite infection in children of slums, shanty towns and squatter settlements. Among them include Entamoeba histolytica, Giardia lamblia, Ascaris lumbricoide, Trichuris trichuria and the less frequently encountered one like Necator americanus.

According to (crompton et al; (1993) the table below shows the Results from epidemiological surveys of intestinal parasite infections in poor pen urban (slum) and urban communities in developing countries.

Table 1: Prevalence of intestinal parasite infections in poor peri-urban and urban communities in some developing countries.

Prevalence (%)

Crompton et al, (1993)

Peri-Urban/Urban Community And Country

About a third of the population in the cities of developing countries lives in slums and shanty towns. In the year 2000 it was estimated that the number will grow to 2200 million and by 2025 about 57% of the population in developing countries will live in peri urban areas. (Crompton et al; 1993) The prevalence of infections caused by Entamoeba histolytica and Giardia intestinalis and the prevalence and intensity of Ascaris lumbricoides and Trichuris trichura infection  may increase among the rural population who are migrating to these sub-urban settings owing to the favorable conditions for transmission.

Urban consideration should therefore be given to improving sanitation in slums and to treating periodically these populations to reduce the worm burden especially in school age children (Crompton et al; 1993).

URBANIZATION AND PROBLEM OF EPIDEMIOLOGY

The epidemiology of parasitic infection is usually influenced by rapid urbanization, unplanned urbanization, uncontrolled population growth, agricultural developments, socio-economic factors, disease and vector control operation and health care delivery system.

Owing to population growth, poor level of hygiene and increasing urban poverty, the urban environment in many developing countries is rapidly deteriorating. Densely packed housing in shanty towns or slums and inadequate drinking water supplies, carbage collection services and surface water drainage system all combine to create favorable habitats for the proliferation of vectors and reservoirs of communicable diseases. As a consequence, vector-borne diseases such as malaria, lymphatic filariasis, and dengue are becoming major public health problems associated with rapid urbanization in many tropical countries. At the present time, the urban health authorities in many countries are alarmed by the rise in vector-borne diseases due to increased densities of vectors and other pests which present ever greater burdens on their vector and pest control programs.

The escalation of diseases is closely related to overcrowded urbanization, which is the result of population growth and rural to urban migration taking place much faster than ever before since the dawn of man. In many cities, slums and poor neighborhoods are spreading, with the appalling living and working conditions, lack of safe drinking water and sanitation. The exposure to emission from traffic and in many places, also from factories is the daily burden of a rapidly growing proportion of city dwellers.

            The major urban arthropod vectors are those of dengue, malaria, filariasis, chagas disease, plague and typhus. In addition most urban enviroment favours the breeding of nuisance mosquitoes, cockroaches, mice and nuisance bird species.

            According to (Bradley et al; 1991) many surveys have demonstrated a prevalence of intestine parasite infection in children of slums, shanty towns and squatter settlements. Intestinal parasite infections persist and flourish wherever poverty, inadequate sanitation, insufficient health care and over crowding are entrenched. Ascariasis is a mirror of socioeconomic status, a reflection of environmental sanitary practices and an indicator of the presence, or lack of health awareness and health education (Crompton et al; 1993). In the poor urban habitation, environmental factors promote the survival and transmission of intestinal parasites.

However, a well planned urban setting usually records reduced incidence of parasitic infection when compared to rural centers.