Abstract

To determine the role of soils in dissemination of enteric protozoan cysts and intestinal eggs and/or larvae of helminths, a study was carried out on muddy soils around springs and wells of six districts in Yaounde, Cameroon from February to July 2015. Protozoan cysts and helminth eggs and larvae were observed microscopically after concentration by standard scientific methods. Flagellated enteric protozoa cysts were detected at an average density of 245 ± 145 cysts/L for Giardia intestinalis, 308 ±190 cysts/L for Chilomastix mesnili, 105 ± 106 cysts/L for Enteromonas hominis and 96 ± 118 cysts/L for Retortamonas intestinalis. Cyst densities were higher during the short rainy season (277 ± 119 cysts/L) than in the short dry season (147 ± 60 cysts/L). The helminths identified were Ascaris sp., Enterobius sp., Necator americanus and/or Ancylostoma duodenale, Strongyloides sp., Taenia sp., Hymenolepis sp., Diphyllobothrium sp. and Fasciola sp. Size varied between 40 μm and 200 μm for eggs and between 100 μm and 600 μm for the larvae assessed. Densities of environmental forms of the helminths were also higher during the short rainy season (176 ± 77 agents/L) than during the short dry season (117 ± 49 agents/L). These results show that muddy soils could contribute to the contamination of wells and springs and should be considered in epidemiological studies of intestinal parasites.

INTRODUCTION

Access to drinking water and sanitation is a major problem in the cities of developing countries (Lenton 2007). The lack of access to drinking water and sanitation is at the root of environmental degradation and the emergence of water-borne diseases (Hutton et al. 2007). The agents responsible for biological contamination include viruses, bacteria, fungi, protozoa and helminths. Most of this pollution is of faecal origin, due to the spread of human and animal wastes. These water-borne pathogens cause nearly 99% of diarrheal diseases, according to the World Health Organization (WHO 2011). The WHO (2004) reported that worldwide infectious and parasitic diseases account for 9.5 million deaths a year (16.2% of all deaths recorded). Many households carry out poor water management, so the water is unable to find appropriate drainage channels. This water originates mostly from springs and wells that are close to homes. Their exploitation for household activities leads to the release of wastewater or stagnant water which mixes with top soil and organic matter to form mud that is spread around the vicinity. In a study on environmental parasitology Ajeagah et al. (2016) showed contamination of springs and wells by the resistant forms of entero-parasites. To better understand the potential sources of groundwater contamination, it is important to collect, evaluate and analyse soils around wells and springs. The objective of this research is to assess the role played by soils around wells and springs in the spread of intestinal parasitic forms.

MATERIALS AND METHODS

Study site

Our study site in Yaounde, the political capital of Cameroon, lies between latitude 3°51′ and 3°52′ North and between longitude 11°31′ and 11°33′ East (Suchel 1972). It is located at nearly 750 m altitude, characterized by a seasonal climate known as the ‘Yaoundéen climate’ (Suchel 1972) comprising a long dry season (LDS) which extends from mid-November to mid-March, a short rainy season (SRS) which runs from mid-March to the end of May, a short dry season (SDS) from June to August and a long rainy season (LRS) which extends from September to mid-November.

Sampling points

The study proceeded in two phases. The first phase was the prospection from November 2014 to January 2015. Multiple field trips made it possible to choose the sampling points according to their proximity to springs and wells and to human activity. Samples were chosen, from six muddy areas in the surroundings of springs denoted as MoS, NkS, MeS, MlS, EtS and ObS and six points in the surroundings of wells denoted as MoW, NkW, MeW, MlW, EtW and ObW in the districts, respectively, of Mokolo, Nkomkana, Melen I, Melen VII, Etoug-Ébé and Obili as presented in Figure 1. The second phase was the sampling which extended over six months from February to July 2015, and samples were collected monthly.

Figure 1

Map of the locations of sampling points.

Figure 1

Map of the locations of sampling points.

Description of some intake points

Overall, the samples resulting from wastewater, stagnant water and domestic effluents (muds) in the surroundings of springs and wells near dwelling houses (less than 10 m distance from the springs and wells as presented in Table 1). Water from the springs and wells around the collecting points is usually used for drinking, bathing, teeth cleaning, cooking food, watering crops around the living areas and other domestic activities. Ajeagah et al. (2016) demonstrated the contamination of this groundwater by parasites around the study areas.

Table 1

Geographic coordinates of sampling points and distance to toilets

Sampling point Geographic coordinates Altitudes (m) DM-W/Sa (m). DM-Tb (m) 
MoS 03°52′48.5′′N, 011°29′52.3′′E 722 
MoW 03°52′46.7′′N, 011°29′53.8′′E 726 2.5 
NkS 03°53′15.5′′N, 011°29′45.3′′E 762 15 
NkW 03°53′13.1′′N, 011°29′52.2′′E 756 
MeS 03°51′53.1′′N, 011°30′08.1′′E 731 0c 3.5 
MeW 03°51′52.9′′N, 011°30′06.6′′E 733 
MlS 03°51′58.2′′N, 011°29′27.4′′E 724 
MlW 03°51′56.1′′N, 011°29′35.9′′E 747 
EtS 03°51′27.7′′N, 011°29′04.9′′E 727 
EtW 03°51′36.6′′N, 011°29′07.7′′E 727 16 
ObS 03°51′32.2′′N, 011°29′25.2′′E 721 
ObW 03°51′30.7′′N, 011°29′18.8′′E 715 
Sampling point Geographic coordinates Altitudes (m) DM-W/Sa (m). DM-Tb (m) 
MoS 03°52′48.5′′N, 011°29′52.3′′E 722 
MoW 03°52′46.7′′N, 011°29′53.8′′E 726 2.5 
NkS 03°53′15.5′′N, 011°29′45.3′′E 762 15 
NkW 03°53′13.1′′N, 011°29′52.2′′E 756 
MeS 03°51′53.1′′N, 011°30′08.1′′E 731 0c 3.5 
MeW 03°51′52.9′′N, 011°30′06.6′′E 733 
MlS 03°51′58.2′′N, 011°29′27.4′′E 724 
MlW 03°51′56.1′′N, 011°29′35.9′′E 747 
EtS 03°51′27.7′′N, 011°29′04.9′′E 727 
EtW 03°51′36.6′′N, 011°29′07.7′′E 727 16 
ObS 03°51′32.2′′N, 011°29′25.2′′E 721 
ObW 03°51′30.7′′N, 011°29′18.8′′E 715 

a0 means that muddy soils are less than 1 m from the wells or springs.

bDM-W/S: Distance between muddy soils and wells or springs.

cDM-T: Distance between muddy soils and toilets (m).

Sampling of muds for parasitic elements

Sampling for the identification of the dissemination forms of protozoa and helminths was carried out in muds at places characterized by an accumulation of organic matter. The mud samples collected were immediately introduced into sterile polyethylene bottles of 1,000 mL then transported to the Laboratory of Hydrobiology and Environment in a refrigerator. At the laboratory, the samples were stored for 24–48 hours before decanting. The supernatant was discarded and the pellet was measured and kept for parasitological analysis by various methods.

Sedimentation method

After homogenization of the pellet, 5 mL of sample was collected and placed in a test tube. To this, 1 mL of 10% formaldehyde (fixative), 5 mL of distilled water and two drops of Lugol's iodine were successively added. The mixture was centrifuged at 500 rpm for 5 minutes using a laboratory centrifuge (MEDIFRIGER). Subsequently, a drop of sample was removed, placed on a microscope slide and covered with a cover slide for identification and enumeration.

Zinc sulphate flotation or faust technique

The Faust technique was described by Faust et al. (1938). This method enables the suspension of cysts in water. After homogenization of the pellet, 5 mL of the sample was collected and placed in a test tube. To this, 1 mL of 10% formaldehyde and 3 mL of 33% zinc sulphate (specific gravity 1.18) were successively added. The mixture was centrifuged at 500 rpm for 5 minutes. A drop of the supernatant, in which the parasites can be found, was taken and spread on a slide which was then covered with a cover slip. Sedimentation and flotation methods were used for the observation of protozoa cysts.

Kato-Katz technique

For the Kato-Katz technique, a portion of the pellet produced by centrifugation at 500 rpm for 5 minutes was taken and deposited on the centre of a slide. The latter was covered by a rectangle of cellophane soaked in glycerol, the sample was spread out between the slide and the cellophane to form a smear.

Formalin-ether concentration technique

For the formalin-ether concentration technique, 5 mL of the sample pellet, 2 mL of 10% formalin and 3 mL of ether were introduced into a 10 mL test tube. Four layers were observed in the test tube after homogenisation. The fat layer (debris) was removed with a stick, and the sediment was resuspended by inverting the tube with a quick motion. Finally, two or three drops of Lugol's iodine were added to the suspension which was used for observation and enumeration after mounting between the slide and cover slip. Kato-Katz and formalin-ether techniques were used for the observation of eggs and larvae of helminths.

Identification and enumeration of parasitic elements

The parasitic elements were identified on the basis of their morphology using the identification keys of the World Health Organization (WHO 1994). The (X) number of parasitic elements in 1 L of sample was found starting with the following formula (Ajeagah et al. 2010): 
formula
where, Vx = pellet volume of 1 L of sample, Vy = pellet volume considered in the identification; y = a number of cysts, eggs and larvae counted in Vy.

Observations were made using an Olympus CK2 inverted microscope at a magnification of 40× for protozoa and 100× for helminths.

Statistical analysis

The graphs were prepared using MS Excel 2010. The average densities of parasitic elements and the standard errors were also determined by the same software. The Bray Curtis index was applied by SPSS to measure the level of affinity between the different sampling points that have been considered in our investigations.

RESULTS

Flagellated enteric protozoa

Total abundances of the cysts of the protozoa for the period of study in muds

Throughout the duration of the study, the abundance of the flagellated enteric protozoa cysts varied from 2,521 cysts for Retortamonas intestinalis to 8,192 cysts for Chilomastix mesnili. The values of the cysts of Giardia intestinalis and Enteromonas hominis, respectively, were 6,481 and 2,588 cysts (Figure 2).

Figure 2

Total abundance of the cysts of the flagellated enteric protozoa in muds.

Figure 2

Total abundance of the cysts of the flagellated enteric protozoa in muds.

Seasonal variation of cysts' abundance in mud

The mud samples in the surroundings of wells and springs near the dwelling houses revealed contamination of all the intake points (100%) considered in our investigation. In general, the highest densities of cysts were recorded during the SRS and in all the samples of mud collected except that of Nkomkana in the SDS.

Seasonal variation and diversity of the densities of cysts in mud

As a whole, the densities of protozoa cysts were higher in the SRS (Figure 3; Figure 4(a)) than in the SDS (Figure 4(b)), except at the sampling points MoW, NkS, M1 W and EtS. Muddy soils in the surroundings of Etoug-Ébé well (SRS) and spring (SDS) were distinguished from the others by their more significant density. An absence of cysts in the mud samples was also observed at NkW in the SDS. The cysts of Giardia intestinalis and Chilomastix mesnili are represented at all sampling points.

Figure 3

Partial and seasonal variation of relative abundance of the cysts in muds for the study period.

Figure 3

Partial and seasonal variation of relative abundance of the cysts in muds for the study period.

Figure 4

Spatiotemporal variation of the average densities of the cysts per season: (a) (SRS), (b) (SDS).

Figure 4

Spatiotemporal variation of the average densities of the cysts per season: (a) (SRS), (b) (SDS).

Intestinal eggs and/or larvae of the helminths

Partial variation of the density of the intestinal eggs and larvae of the helminths in muds

The densities of the dissemination forms of helminths in muddy soils around springs and in soils around the wells vary from one point to another. Overall, the highest densities were obtained in the mud samples from the surroundings of the springs compared to those from the surroundings of the wells. Soils at the various points harbour the same species of helminth. The environmental forms of the helminths were found in all muds from the surroundings of the wells and springs. The minimum density of eggs and larvae of helminths was obtained in the muds at NkS (54 agents/L), and the maximum density in Melen 1(274 agents/L) (Figure 5).

Figure 5

Spatial variation of densities of eggs and larvae.

Figure 5

Spatial variation of densities of eggs and larvae.

Spatiotemporal variation of the densities of dissemination forms of the helminths in the muds

The minimum density of eggs and larvae of helminths are obtained from the muddy soils of NkS during the SDS (43 ± 16 agents/L) and the maximum density in the muddy soils from MeS during the SRS (333 ± 69 parasitic elements of helminths/L). At all the points, the highest densities of eggs and larvae of helminths in muds are obtained during the SRS (Figure 6).

Figure 6

Spatiotemporal variation of the averages of the densities of intestinal eggs and/or larvae of the helminths.

Figure 6

Spatiotemporal variation of the averages of the densities of intestinal eggs and/or larvae of the helminths.

Parasite infections

The presence of protozoa and helminth in mud suggests the role of mud in the dissemination of pathogens. The abundance of identified parasites is presented for each species. The high concentrations of protozoa and helminths in mud are responsible for waterborne disease (Table 2).

Table 2

Overall number of parasitic forms (cysts, eggs and larvae)

Group Species Abundance (% of total) Disease 
Protozoa Giardia intestinalis 6,481 (25.39%) Giardiasis 
Chilomastix mesnili 8,192 (32.09%) Chilomastidiasisa 
Enteromonas hominis 2,588 (10.14%) Non-pathogenic 
Retortamonas intestinalis 2,521 (9.87%) Non-pathogenic 
Helminths Ascaris sp. 1,532 (6.00%) Ascariasis 
Enterobius sp. 532 (2.08%) Enterobiosis 
Ancylostoma duodenale and/or Necator americanus 558 (2.19%) Ancylostomosis 
Strongyloides sp. 882 (3.45%) Strongyloidiosis 
Taenia sp. 948 (3.71%) Taeniasis 
Hymenolepis sp. 165 (0.65%) Hymenolepiosis 
Diphyllobothrium sp. 351 (1.37%) Diphyllobothriosis 
Fasciola sp. 369 (1.45%) Fascioliasis 
Schistosoma sp. 411 (1.61%) Schistosomiasis 
Total 25,530  
Group Species Abundance (% of total) Disease 
Protozoa Giardia intestinalis 6,481 (25.39%) Giardiasis 
Chilomastix mesnili 8,192 (32.09%) Chilomastidiasisa 
Enteromonas hominis 2,588 (10.14%) Non-pathogenic 
Retortamonas intestinalis 2,521 (9.87%) Non-pathogenic 
Helminths Ascaris sp. 1,532 (6.00%) Ascariasis 
Enterobius sp. 532 (2.08%) Enterobiosis 
Ancylostoma duodenale and/or Necator americanus 558 (2.19%) Ancylostomosis 
Strongyloides sp. 882 (3.45%) Strongyloidiosis 
Taenia sp. 948 (3.71%) Taeniasis 
Hymenolepis sp. 165 (0.65%) Hymenolepiosis 
Diphyllobothrium sp. 351 (1.37%) Diphyllobothriosis 
Fasciola sp. 369 (1.45%) Fascioliasis 
Schistosoma sp. 411 (1.61%) Schistosomiasis 
Total 25,530  

aPathogenicity uncertain.

Similarities between the sampling points based on parasites

The similarities between the sampling points based on the biological variation are presented in a dendrogram (Figure 7). They were assessed by the application of the Bray–Curtis dissimilarity index, which is a statistical tool used to quantify the compositional dissimilarity between two different sampling points, based on the counts of the cysts and eggs/larvae identified. It shows 80% similarity between points EtS, EtW, MlS MlW, MoS and ObW which share the same branch and directly receive piggery effluent. Points MeW and NkS show 50% similarity. Points MeS, ObS, NkW and MoW show 50% similarity, representing low parasite contamination.

Figure 7

Dendrogram showing the similarities between the points.

Figure 7

Dendrogram showing the similarities between the points.

DISCUSSION

These results indicate the presence of cysts, eggs and larvae in these study areas revealing, according to WHO (2012), contamination of faecal origin and would expose the inhabitants to the risks of contamination if the areas were not sanitized. According to Bloomfield & Nath (2009), microbiological contamination of muds or soils is widespread due to large-scale practice of open defecation.

Concerning protozoa, the total abundance of the four species of protozoa studied was 19,782 cysts found in muddy soils greater than that of groundwater (14,037 cysts) in the same locality (Ajeagah et al. 2016), proving that protozoa cysts were more important in the muddy soils around the wells and springs. This can be interpreted as showing that the dissemination of cysts is more important in muddy soils than in groundwater. The highest densities of cysts were recorded during the SRS and in all the samples of muddy soils collected except that of Nkomkana in the SDS. This can be explained by the fact that muddy soils are the major recipients of pollutants through draining water which plays a major role in the distribution of resistant forms of the pathogens in the environment. In this regard, Bertrand et al. (2004) show that the percentages of contamination of mud by cysts, eggs and larvae are always between 37% and 100% and Hanus (2005) confirmed that muddy soils around water points would worsen the risks of pollution of the wells. This is also applicable to unprotected springs and other water bodies in local communities.

The high density observed in muddy soils at Etoug-Ébé during the study period would be due to a favourable topography that is related to a low sanitation conditions. An absence of cysts in the mud samples has also been observed in Nkomkana well in the SDS. The cysts of Giardia intestinalis and Chilomastix mesnili are represented at all the intake points. This could be explained by the influence of the size of the cysts, coupled with the thickness of the wall. In fact, the large cysts of the flagellated enteric protozoa (8–17 μm) and (5–10 μm) for Giardia intestinalis and Chilomastix mesnili, respectively, would resist better in a disturbed environment than the small cysts such as Enteromonas hominis (5–7 μm) and Retortamonas intestinalis (4–6 μm). In the same way, the work of Ajeagah et al. (2016) on groundwater treated with sodium hypochlorite has shown the greater resistance of large flagellated enteric protozoa (Giardia and Chilomastix) rather than small cysts (Enteromonas and Retortamonas).

The biological analysis of mud samples also reveals the presence of helminth eggs and larvae such as Ascaris sp., Enterobius sp., Ankylostomes (Necator sp. and/or Ancylostoma sp.), Strongyloides sp., Taenia sp., Hyménolepis sp., Diphyllobothrium sp., Fasciola sp. and Schistosoma sp. According to Bouhoum et al. (1997), the pathogenic organisms present in the muddy areas of the community reflect its health state. Indeed, the number and the varieties of parasites found in muddy soils are related to the level of infestation of the human population and/or animal population present. These parasites are excreted in the external area in the form of eggs or larvae with the faeces of its host during open faecal defecation. The eggs of Ascaris sp. are highly represented among the helminth eggs in this study. In this situation, WHO (1989) mentioned that the eggs of Ascaris are resistant in the environment and considered as indices of parasitoses and poor sanitation conditions. The densities of the dissemination forms of helminths in muddy soils around the springs and wells vary from one point to another. The maximum density of eggs and larvae of helminths in the muds around springs were obtained at Melen 1 (274 agents/L) while the minimum density was recorded in the muddy soils around the Nkomkana spring (55 agents/L). This could be explained by the unhealthy behaviours that the populations close to the muddy points adopt. These muddy soils could also constitute a source of pollution for water in the wells and springs in the SRS. For this reason, Kassim (2005) affirms that waste water forms pools during the rainy season and from time to time overflows into the water collection point, which could be a spring or well or tap water.

With regard to these results, it is well accepted that muddy soil can become contaminated with protozoa and helminths in high concentrations, and that it can act as a vehicle and source of the spread of intestinal diseases (Bloomfield & Nath 2009). The presence of various pathogens in our environment can lead to polyinfection and cause more health disorders. The infection of humans and animals by the same parasite is called zoonosis. Protozoa and helminths are among the most common causes of infection and disease in humans and other animals. The diseases have a major public health and socio-economic impact. Indeed children between 5 and 16 years would be most exposed to these sources of contamination due to the defects of hygienic conditions and the negligence of the community when fetching water from wells and springs, uncontrolled playing of the children around these water points and absence of a collection system, treatment and water drainage. It is therefore necessary to improve the water supply and sanitation facilities. According to Hutton et al. (2007), improved water supply generally involves better physical access and the protection of water sources, including standpipes, boreholes, protected springs or wells or collected rainwater, and improved sanitation generally involves physically closer facilities, less waiting time and safer disposal of excreta, including septic tank, simple pit latrine or ventilated improved pit latrine. In cases of contamination of muddy soils, the risk of epidemic is not to be excluded at the family level or beyond in the event of the consumption of water around muddy soils. The distribution of environmental forms of protozoa and helminths vary from one point to another according to the level of contamination (Figure 7).

It would also be crucial to mention that these muds could support contamination of the water table by the process of infiltration or draining water into unprotected wells and springs and also of streams via domestic effluents. In this regard, Nanfack et al. (2014) and Ajeagah et al. (2010) demonstrate that contamination of wells and springs would be related to the sources of pollution in the neighbourhood. It can also be related to domestic effluents, cattle ranching and lack of toilet facilities. These results show that not only are soils reservoirs of the cysts, eggs and larvae, but can also be a crucial factor of contamination of groundwater. In all, the high level of soil contamination constitutes a potential source of parasitic infection and suggests that the treatment and disposal of human and animal excreta continues to be a public health concern in our urban municipalities (Moura et al. 2010).

CONCLUSION

This study showed that soils around water points are reservoirs for the dissemination of the environmental forms of protozoa and helminths. The analysis of the results reveals that muds shelter the cysts of flagellated enteric protozoa (Giardia intestinalis, Chilomastix mesnili, Enteromonas hominis and Retortamonas intestinalis) and the eggs and/or larvae of the helminths (Ascaris sp., Enterobius sp., Necator americanus and/or Ancylostoma duodenale, Strongyloides sp., Taenia sp., Hymenolepis sp., Diphyllobothrium sp., Fasciola sp. and Schistosoma sp.) revealing a contamination of faecal origin. Overall, the dissemination forms were commoner in the SRS than in the SDS due to the impact of drainage and infiltration of water charged with faecal matter. The contamination of soils in proximity to dwelling places can be a factor in groundwater contamination and would expose the households to health risks. Given the results of this research we recommend that the population conduct sustainable water management, to cleanse and treat the surrounding soils of springs, wells and water points, to practice good rules of hygiene, to plan water drainage systems and to adopt an eco-citizen approach.

REFERENCES

REFERENCES
Ajeagah
G. A.
,
Njine
T.
,
Bilong Bilong
C. F.
,
Foto
S. M.
,
Wouafo
N. M.
,
Nola
M.
,
Di Giovanni
G. D.
&
Huw
S.
2010
Seasonal distribution of enteric opportunistic Cryptosporidium spp.Oocysts and Giardia spp. cysts in a tropical water basin
.
Water
2
,
44
57
.
Ajeagah
G. A.
,
Asi
Q. A.
&
Nola
M.
2016
Bioquality of dissemination forms of flagellated enteric protozoa in groundwater (springs and wells) in an urban area (Yaounde-Cameroon)
.
European Scientific Journal
12
(
33
),
554
557
.
[In French]
.
Bertrand
I.
,
Gantzer
C.
,
Chesnot
T.
&
Schwartzbrod
J.
2004
Improved specificity for Giardia lamblia cysts in quantification & wastewater by development of real-time PCR
.
Journal of Microbiological Methods
57
,
41
53
.
Bloomfield
S. F.
&
Nath
K. J.
2009
Use of ash and mud for handwashing in low income communities. International Scientific Forum on Home Hygiene (IFH).
Bouhoum
K.
,
Mahmid
O.
,
Habba
K. H.
&
Schwartzbrod
J.
1997
Fate of helminth eggs and protozoan cysts in an open channel receiving raw wastewater from Marrakech
.
Revue des Sciences de L'eau
2
,
217
232
.
[In French]
.
Faust
E. C.
,
D'Antni
J. S.
,
Odom
V.
,
Miller
M. J.
,
Peres
C.
,
Sawitz
W.
,
Thomen
L. F.
,
Tobie
J.
&
Walker
J. H.
1938
A critical study of clinical laboratory technics for the diagnosis of protozoan cysts and helminth eggs in feces
.
American Journal of Tropical Medicine and Hygiene
18
,
169
183
.
Hanus
J.
2005
Evaluation of the healthiness of the water of the wells of Pointe-Noire. Characterization and studies of health. The University of Louvain D.E.S. in science and management of the environment. [In French].
Hutton
G.
,
Haller
L.
&
Bartram
J.
2007
Global cost-benefit analysis of water supply and sanitation interventions
.
Journal of Water and Health
5
,
481
502
.
Kassim
C.
2005
Study of the Physicochemical and Bacteriological Quality of the Water of the Wells of Certain Districts of the District of Bamako
.
Thesis in Pharmacy (Diploma of State)
,
Faculty of Medicine of Pharmacy and D’ Odonto-Stomatology, University of Bamako
,
Mali
.
Lenton
R.
2007
Water and sanitation for poor disservice
.
Suden Cooperation
1
,
42
53
.
Moura
F. T.
,
Falavigna
D. L. M.
,
Mota
L. T.
&
Toledo
M. J. O.
2010
Enteroparasite contamination in peridomiciliar soils of two indigenous territories, State of Paraná, southern Brazil
.
Review Panam Salud Publica
27
(
6
),
414
422
.
Nanfack
N. A.
,
Fontehm
F.
,
Vincentm
K.
,
Katte
,
&
Fogoh
J.
2014
Nonconventional water: a risk or a solution with the problems of water for the poor classes
.
Larhyss Journal
17
,
47
64
.
[In French]
.
Suchel
B.
1972
The distribution of the rains and the pluviometric modes in Cameroun
.
Work and Documents of Tropical Geography
5
,
1
288
.
WHO
1989
Health Guidelines for the Use of Wastewater in Agriculture and Aquaculture
.
Technical Report 778
,
World Health Organization
,
Geneva
.
WHO
1994
Bench Aids for the Diagnosis of Intestinal Parasites
.
World Health Organization
,
Geneva
.
WHO
2004
The Global Burden of Disease
.
World Health Organization
,
Geneva
.
WHO
2011
Guidelines for Drinking-Water Quality
,
4th edn
.
World Health Organization
,
Geneva
.
WHO
2012
Directives WHO for the use Without Risk of Used Water, the Excreta and Waste Waters
.
Use of waste water and the excreta in aquiculture, World Health Organization
,
Geneva
.