Climate Change

33 recommended. The whole community is treated irrespective of age, sex, infection status, or other social characteristics. The treatment should be organized once a year. The efficacy of this measure is higher if the whole population is treated simultaneously. Women of childbearing age, pre-school and school-age children suffer more from morbidity related to the infections, so they must be treated more intensively (two or three times a year). Communities within category I usually have extremely low standards of sanitation: reduction of transmission through interventions based on information, education and communication (IEC) strategies, and improvements in sanitation and water supply should be a long-term aim.

For communities in category II, targeted treatment is recommended. The groups identified for treatment are women of childbearing age, pre-school and school-age children. Treatment must be organized at least once a year. These communities usually also have insufficient standards of sanitation but reduction of transmission may be obtained by implementing information, education and communication (IEC) strategies and supporting the improvement of sanitation.

For communities in category III, case management is the recommended measure, i.e. the treatment of positive cases diagnosed by the health units. Information, education and communication (IEC) strategies have a great impact on this category and should be extensively implemented.⁸⁸

34 1.3.2 Poverty, Sanitation and Potable water supply

Sub-Saharan Africa harbours between 30% and 40% of the estimated 1.4 billion people living in chronic poverty and these are areas where helminth disease rates are also the highest.⁹³ The transmission of STHs depends on environments contaminated with egg-carrying faeces.

Consequently, helminths are intimately associated with poverty, poor sanitation, and lack of clean and potable water.^{94, 95.} They result in part from poverty and contribute to further poverty and there is a striking relationship between hookworm prevalence and low socioeconomic status in all regions.⁴ Hookworm infection is closely associated with poverty and inadequate sanitation, poor housing construction, and lack of access to essential medications are major factors in this relationship.⁹⁶ As countries develop and these factors improve, hookworm infestation has been found to decrease as reported when the socioeconomic status of 94 countries was assessed according to several commonly used indicators, with poverty measures divided into quartiles ranging from the most poor (1st quartile), very poor (2nd quartile), poor (3rd quartile), to the least poor (4th quartile).⁹⁷ Places like the coastal regions of East Texas, Louisiana, Mississippi, Florida, Georgia, and the Carolinas, at the turn of the 20^th century exhibited high prevalence rates of hookworm and other tropical diseases including malaria and typhoid fever, as well as epidemics of yellow fever. This is no more the story because the extreme poverty also needed to sustain the endemicity of these diseases no longer exists.⁹⁷ 1.3.3 Behaviour, Household Clustering, and Occupation

STHs prevalence and intensity, particularly hookworm, in which the highest intensities occur among adult are influenced by specific occupations, household clustering, and behaviours as found in Brazil in which a suite of covariates, which included demographic, socioeconomic, water supply and water contact behaviour terms, contributed 15% to the variance in faecal egg counts and shared residence alone accounted for 28% of the variance in faecal egg excretion.

35 When both the suite of covariates and shared residence were considered in the same model, shared residence still contributed 22% to the variance in infection intensity.^{98, 99}

Behavioural and occupational factors, through their effect on water contact, interact with environmental factors to produce variation in the epidemiology of STH. Agricultural labourers have traditionally been at high risk of hookworm infection. Improper disposal of human faeces and the common habit of walking barefoot are important epidemiologic features.⁹⁶ There is also evidence of familial and household aggregation of infection, with the relative contribution of genetics and common household environment debated.³⁸

1.3.4 Genetics

No genes that control for human helminth infection have yet been identified. However, recent genome scans have identified loci possibly responsible for controlling A. lumbricoides intensity on chromosomes 1 and 13 and a locus for S. mansoni infection intensity on chromosome 5q31-33. There is also evidence for genetic control of pathology attributable to S.

mansoni, with linkage reported to a region containing the gene for the interferon gamma receptor 1 subunit.¹⁰⁰

1.3.5 Age dependency

Changes with age in the average intensity of infection tend to be convex, rising in childhood and declining in adulthood. For A. lumbricoides and T. trichiura, the most intense infections are found in children aged 5 to 15 years, with a decline in intensity and frequency in adulthood.

Whether such age dependency indicates changes in exposure, acquired immunity or a combination of both remains controversial.¹⁰¹ Although heavy hookworm infections also occur in childhood, frequency and intensity commonly remain high in adulthood, even in elderly people.¹⁰² Some of the strongest evidence for protective immunity to human helminth infection

36 has come from epidemiological observations of a “peak shift” in prevalence and intensity of infection with age.¹⁰³ Briefly, if age-infection data are compared across host populations, the peak level of infection intensity (e.g., epgs for intestinal helminths) is higher and occurs in younger individuals when transmission is also higher, but the peak intensity of infection is lower and occurs in older individuals when transmission is lower. This shift in the peak level of infection intensity and the age at which this peak occurs is consistent with mathematical models that assume a gradually acquired protective immunity, an interpretation supported by experimental studies in animals.¹⁰³

1.3.6 Nutritional Status

The fundamental basis of the relationship between an infectious organism and its host is nutritional because the host is the source of all nutrients needed by the organism for maintenance, growth, and reproduction.¹⁰⁴ Undernutrition also increases susceptibility to infection and increases the severity of disease which can lead to a downward spiral of increasing under nutrition and repeated or persistent disease, and is thus a major component of illness and death from disease.14,15,20-22 There is strong evidence that undernourished hosts are in general at greater risk of dying of infectious diseases than well-nourished hosts mostly based on analysis of the relationship between underweight and the risk of dying. ^105,106

Both host-specific and environmental factors such as behaviour; household clustering, occupation, poverty, sanitation and availability of potable water have been identified as affecting the risk of acquiring or harbouring heavy intensity helminthic infections.95,107,108 In 2009, among elementary school children of Zarima town in Northwest Ethiopia, age group 5-9 years showed statistical significant association compared to other categories and significant association in parasite prevalence was observed between family water sources. Frequency of hand washing habit with soap was also significantly associated with children infection with

37 increased risk seen for infrequent hand washing habit with soap.¹⁰⁹ In Zanzibar, Tanzania, people consuming raw vegetables or salad were more likely to be infected with A.

lumbricoides (OR = 2.54, 95% CI 1.27–5.10). Participants belonging to the least poor wealth quintile were at a significantly lower risk of a T. trichiura infection than their counterparts belonging to the most poor wealth quintile (OR = 0.28, 95% CI 0.10–0.82). In peri-urban area, washing hands after defecation was determined as a protective factor against a T. trichiura infection (OR = 0.06, 95% CI 0.01–0.26).¹¹⁰ A study done in South Indian fishing village identified that children from fishing families with low levels of education of the mother had the highest intensity of A. lumbricoides infection.¹¹¹ Hookworm infections were more prevalent among those 12 years of age or older (OR 2.9; 95% CI 1.2-7.1) and children of mothers with educational attainment of secondary school or higher had a protective effect against T. trichiura (OR 0.18; 95% CI 0.06-0.54) and hookworm (OR 0.21; 95% CI 0.09-0.51) infections in a village survey in rural South-West China.¹¹² Some studies in many countries has proved that parasitic infections, especially Ascaris, Trichuris and co-infections were associated with stunting in school-age pupils and that de-worming treatment can improve children's nutritional status.^113,114 An Ugandan study among primary school children revealed that 26.6%, 46% and 10.3% of the incidences of stunting, underweight and moderate acute malnutrition (MAM) cases respectively are attributable to the potential effects of intestinal helminthes infections.¹¹⁵ A study done in Nigeria between two schools found that the prevalence rate of hookworm was lower in students of boarding school (0.4%) as compared to staff school students (5.9%) and has been explained by the fact that the boarding school regimented the movement of student and placed emphasis on good sanitary habit while students in the staff school engaged in outdoor activities such as helping on the farm, playing at the backyard on moist soil that may be contaminated with filariform larvae there making the children to be more at risk.³⁷

38 There was a relationship between intensity of infection and wasting in school children in Ilie, Osun State since there were fewer underweight pupils (13%) with normal stool than those moderately infected (35%)(P<0.05). There was statistically significant association between type of latrine use and prevalence of infection; and also between water treatment and infection.⁶⁷ Another study in Ile- Ife, also in Osun State showed the nutritional indices of the pupils who were found helminth-infected were generally lower than those of the pupils who appeared free of intestinal helminths. The mean values for weight-for-height, for example, were higher in the apparently uninfected pupils than in those found infected with any intestinal helminth (P =0.02) or only with Ascaris lumbricoides (P=0.05). Similarly, the mean height-for-age of the pupils who were apparently uninfected was higher than the corresponding value for the pupils found hookworm-positive (P=0.003).The pupils who were each found infected with two or more species of intestinal infection had significantly lower weights-for-heights, weights-for-ages and heights-for-ages than the pupils who appeared to be helminth-free.¹¹⁶ In a study in the peri urban area of Lagos state, intestinal parasitic prevalence among the school pupils in the institution with potable water was found 52.7% while the prevalence among pupils in the institution without potable water was 70.6%.The difference was found to be statistically significant (p < 0.01).⁹⁵