Filariasis in the Igwun River Basin, Nigeria: an epidemiological and clinical study with a note on the vectors

Lymphatic filariasis baseline survey in two sentinel sites of Ogun state, Nigeria

Introduction

In preparation for Mass Drug Administration by National Lymphatic Filariasis Elimination Programme, a baseline epidemiological investigation on lymphatic filariasis (LF) was conducted in two sentinel sites of Ogun State, Nigeria. The study was carried out in Ado-Odo Ota and Abeokuta South Local Government Areas (LGAs) to determine LF prevalence, microfilarial density and the abundance of Wucheraria bancrofti in the mosquito vectors.

Methods

Microscopic examination of thick blood smears of 299 and 288 participants from Ado-Odo Ota and Abeokuta South LGAs was conducted. Visual observations of clinical manifestations of chronic infection and questionnaire administration were also conducted. Indoor resting mosquitoes were collected using the pyrethrum spray technique and CDC light traps and mosquitoes were dissected for filarial larvae.

Results

Microfilaria prevalences were 4.0% and 2.4% in Ado-odo Ota and Abeokuta South LGAs. The microflarial density (mfd) was 30.6mf/ml and 23.9 mf/ml in the same areas. No clinical manifestations of the infection were found at both sites. Knowledge of LF by inhabitants was very low in the two areas. Anopheles gambiae s.l and Culex species mosquitoes were collected but none was found positive for stage L3 infective larvae.

Conclusion

Mass awareness campaigns on the goal of mass drug administration, cause of LF, mode of transmission, the relationship between infection and clinical signs/symptoms is advocated so as to increase acceptance and support of the control programme by the community.

Co-endemicity of loiasis and onchocerciasis in rain forest communities in southwestern Nigeria

Background

Loiasis is currently receiving attention as a disease of public health importance because of the possibility of increased risk of developing neurologic serious adverse event following mass ivermectin treatment against onchocerciasis in individual co-infected with Onchocerca volvulus and Loa loa.

Methodology/Principal Findings

Rapid assessment procedure for loiasis (RAPLOA) was conducted in 12 communities covering the 3 senatorial districts of Osun State, Nigeria. A total of 960 people were interviewed for history of eye worm using the WHO guidelines for rapid assessment. The survey confirmed the presence of loiasis in all the 12 communities with 4 in Osun East/Ife south senatorial district being at high risk with a prevalence of over 40%. Based on the RAPLOA results, communities within Osun East/Ife south senatorial district were selected for microfilaraemic assessment of L. loa and O. volvulus. A total of 1115 and 1091 individuals were screened for L. loa and O. volvulus microfilaria worms respectively. 160 (14.3%) had L. loa microfilaria detected in their blood with 8 (5.0%) individuals having L. loa loads above 8000 mf/ml. 166 (15.2%) subjects had O. volvulus microfilaria (range 4-504 mf/ml) detected in their skin snip. 30 (2.69%) subjects were co-infected with both L. loa and O. volvulus. There was a significant variation in the prevalence (2.1% to 33.3%) of onchocerciasis in the communities studied (p = 0.001). Five (41.7%) of the studied communities had a prevalence that is equal to or greater than 20%.

Conclusions/Significance

Low prevalence of onchocerciasis and loiasis co-infection in this study suggests that loiasis may not pose a serious epidemiological threat to the continuous distribution and sustainability of ivermectin for the treatment of onchocerciasis. Evaluation of the interruption of onchocerciasis transmissions in this region using all the indicators set forth by WHO is therefore suggested.

Loiasis recently emerged as a disease of public health importance because of the risk of rare severe adverse events (SAEs) associated with the rapid killing of Loa loa microfilariae in heavily parasitized individuals following ivermectin treatment. for onchocerciasis. The possibility of developing these SAEs has been slowing down the control of onchocerciasis in some endemic communities. Based on information available at the Osun State Ministry of Health, the detailed geographic distribution of L. loa in Osun State is still awaiting elucidation. The results of this study revealed an overlap in geographic distribution of loasis and onchocerciasis in many communities in Osun State. The overall Community Microfilaria Load (CMFL) for L. loa was below the threshold level of endemicity that could be associated with the risk of SAEs after ivermectin treatment. Most individuals with slightly high L. loa microfilaria are either O. volvulus microfilaria free or have very low microfilaria load. The low prevalence of co-infection of both diseases in the study area is an indication that loiasis may not pose any serious epidemiological threat to the distribution and sustainability of ivermectin in the treatment of onchocerciaisis.

Lymphatic filariasis in Nigeria; micro-stratification overlap mapping (MOM) as a prerequisite for cost-effective resource utilization in control and surveillance

Background

Nigeria has a significant burden of lymphatic filariasis (LF) caused by the parasite Wuchereria bancrofti. A major concern to the expansion of the LF elimination programme is the risk of serious adverse events (SAEs) associated with the use of ivermectin in areas co-endemic with Loa filariasis. To better understand this, as well as other factors that may impact on LF elimination, we used Micro-stratification Overlap Mapping (MOM) to highlight the distribution and potential impact of multiple disease interventions that geographically coincide in LF endemic areas and which will impact on LF and vice versa.

Methodology/Principal findings

LF data from the literature and Federal Ministry of Health (FMoH) were collated into a database. LF prevalence distributions; predicted prevalence of loiasis; ongoing onchocerciasis community-directed treatment with ivermectin (CDTi); and long-lasting insecticidal mosquito net (LLIN) distributions for malaria were incorporated into overlay maps using geographical information system (GIS) software. LF was prevalent across most regions of the country. The mean prevalence determined by circulating filarial antigen (CFA) was 14.0% (n = 134 locations), and by microfilaria (Mf) was 8.2% (n = 162 locations). Overall, LF endemic areas geographically coincided with CDTi priority areas, however, LLIN coverage was generally low (<50%) in areas where LF prevalence was high or co-endemic with L. loa.

Conclusions/Significance

The extensive database and series of maps produced in this study provide an important overview for the LF Programme and will assist to maximize existing interventions, ensuring cost effective use of resources as the programme scales up. Such information is a prerequisite for the LF programme, and will allow for other factors to be included into planning, as well as monitoring and evaluation activities given the broad spectrum impact of the drugs used.

Nigeria is estimated to have the highest burden of lymphatic filariasis (LF), a disease also known as elephantiasis, which is transmitted by mosquitoes and caused by the parasite Wuchereria bancrofti. The National LF Elimination Programme is planning to scale up the elimination programme through mass drug administration of ivermectin and albendazole. However, a major constraint to this expansion is the risk of serious adverse events (SAEs) associated with the use of ivermectin in areas co-endemic with Loa, the causative agent of tropical eye worm (loiasis). To better understand this and other factors that may impact on LF elimination, we collated and mapped all available LF data, and highlighted the overlaps with predicted loiasis prevalence distributions, onchocerciasis ivermectin treatment areas, and bed net distributions for malaria. This study provides a baseline overview for the LF Programme and will help to maximize existing disease interventions, ensuring cost effective use of resources as the programme scales up.

The Abundance and Biting Patterns of Culex quinquefasciatus Say (Culicidae) in the Coastal Region of Nigeria

This study was aimed at determining the abundance and biting patterns of Culex quinquefasciatus in the coastal region of Nigeria. Collections were done by human landing catch and by CDC miniature light traps from September 2005 to August 2006. A total of 3798 C. quinquefasciatus females were collected. The highest number of females was caught in the month of August and it represented nearly a quarter (24.0%) of the total females collected. In all, 38.8% of females dissected were parous. The abundance of C. quinquefasciatus followed the pattern of rainfall with the population starting to expand at the onset of the rains. The highest increase was found after the temperature had peaked. The mean of biting was 3.2 times more in the rainy season than in the dry season, whereas the transmission potential was higher in the dry season. C. quinquefasciatus is presently regarded as a biting nuisance having no significant epidemiological importance yet. Efforts at its control should be intensified before it is too late.

Lymphatic filariasis and associated morbidities in rural communities of Ogun State, Southwestern Nigeria

Lymphatic filariasis caused by Wuchereria bancrofti is a serious public health problem in rural communities of Nigeria. The study assessed the prevalence of lymphatic filariasis and associated clinical morbidities in Ado-Odo Ota Local Government Area of Ogun State. Microscopic examination of thick blood smears of 500 participants of both sexes and age ranging from 1 to 79 years was conducted. Visual observations of clinical manifestations of chronic infection were also conducted. The overall prevalence and intensity of infection were 21% and 21.4 mf/mL of blood respectively. Microfilaraemic prevalence was significantly higher in males (27.1%) than in females (16%) (P < 0.001). However, intensity of infection was not gender and age dependent (P > 0.05). The overall prevalence of all clinical manifestations of infection due to W. bancrofti is 15% with hydrocele, limb and breast elephantiasis constituting 16.9%, 4.6% and 5.1% of the total population respectively. Prevalence of hydrocele and limb elephantiasis was significantly higher in the older age groups (P < 0.05). Occurrence of elephantiasis of the breast in women however was not associated with age (P > 0.05). Integrated approach through chemotherapy and vector control is therefore advocated to reduce morbidity due to infection in this study area.

Mansonella perstans filariasis in Africa

Mansonella perstans is a vector-borne human filarial nematode, transmitted by tiny blood-sucking flies (biting midges). It is widespread in many parts of Sub-Saharan Africa and also occurs in parts of Central and South America. Despite the commonness of this parasite very few studies have been carried out on its epidemiology and on the morbidity resulting from it, and only few thorough drug trials have been conducted to look for effective and suitable drugs and drug regimens for treatment and control. Here, we review currently available knowledge on M. perstans infections in Africa, including documented aspects of biology, vectors, transmission, diagnosis, epidemiology, morbidity and treatment. It is concluded that there is an urgent need for more research on this widespread but greatly neglected infection in order to properly assess its public health significance and as a background for identifying and recommending optimal means and strategies for treatment and control.

Assessment of loiasis and outcomes of ivermectin masstreatment in Ijebu-North, Nigeria

A total of 286 individuals from 3 selected communities (Areedi-Aje, Ipakodo/Ojokodo, and Ijebu-Igbo) of Ijebu-North, southwestern Nigeria were examined for Loa loa microfilaremia using finger prick blood smear, between December 2008 and March 2009. Rapid assessment procedure for loiasis (RAPLOA) was used to obtain information, from 187 Ijebu-Igbo residents, on adverse reactions experienced from retrospective treatments with ivermectin and history of eye worm. Only 33.9% of the respondents reported having had a history of eye worm while 33.2% had microfilaremia. The demographic factor of gender was not significant determinants of the prevalence (P>0.05) while age was significant (P<0.05). The highest prevalence of eye worm history and microfilaremia were recorded in 61-70 and 15-20 years of age categories, respectively. Ijebu-Igbo had 27.3% eye worm history, 32.1% microfilaremia, and the highest intensity of 140 microfilariae (mf)/ml. Ipakodo area had the highest eye worm history of 54.4% and the highest intensity of 420 mf/ml. Areedi-Aje had the highest occurrence of 45.2% microfilaremia and the highest intensity of 460 mf/ml. Predictably, Areedi-Aje and Ipakodo areas were high risk communities. The low intensity of L. loa infection with an insignificant (2.1%; P>0.05) adverse reactions from 187 subjects involved in the retrospective ivermectin administration confirmed that ivermectin delivery may be considered safe. The community-directed treatment with ivermectin (CDTI) programme was most probably responsible for the low prevalence and intensity.

Prevalences of loiasis in Ondo state, Nigeria, as evaluated by the rapid assessment procedure for loiasis (RAPLOA)

The rapid assessment procedure for loiasis (RAPLOA) was used to assess the prevalences of loiasis among 4800 subjects in 60 villages in Ondo state, south-western Nigeria. Coverages for community-directed treatment with ivermectin (CDTI) were assessed in the same communities, which were located in the Owo, Akure North, Ifedore, Akure South, Ondo East and Ondo West local government areas (LGA). In addition, fingerprick blood samples were collected from 80 individuals in each of six villages (i.e. one village in each LGA investigated) and checked for Loa loa microfilaraemia. Microfilaraemias were only detected in three of the villages where blood samples were collected and then only at low prevalences (1.25%-5.0%) and intensities (267-1600 microfilariae/ml). No serious adverse events were or ever had been related to the CDTI but mild or moderate adverse reactions were quite common, especially in Akure North (55.0%) and Owo (40.2%). A female subject was more likely to report an history of eye worm than a male subject (20.3%-35.7% v. 20.8%-26.5%, according to LGA). Although the subjects aged 41-50 years formed the age-group most likely to report an history of eye worm (32.7%), the highest CDTI coverage was recorded in the subjects aged 61-70 years (54.7%). The results indicated that CDTI had helped to reduce the prevalence and intensity of Loa microfilaraemia and that ivermectin can continue to be used for mass administrations in Ondo state with little risk of serious adverse events.

Biting of anthropophilic Culicoides fulvithorax (Diptera: Ceratopogonidae), a vector of Mansonella perstans in Nigeria

Anthropophilic Culicoides were investigated in a rural community endemic for Mansonella perstans in Ijebu North area of western Nigeria between December 2003 and October 2004. Three hundred and fifty-nine adults of Culicoides fulvithorax collected by human bait in the morning were dissected for Mansonella perstans larvae, and 1.95% of infection rate was found. Seasonal abundance of C. fulvithorax was investigated by monthly biting rates, and showed that higher prevalence was observed in rainy season, with peak in September. Culicoides prevalence was positively correlated with rainfall and relative humidity, but not temperature. Human perceptions on the behavior of these biting midges were determined by interviewing 854 self-selected villagers, of which 86.5% of the interviewees confessed having experienced Culicoides bites. Between 76.5 and 99.1% of the various age groups complained body reactions to Culicoides bites. Itching was the most frequent body reaction. No interviewees associated Culicoides with transmission of any parasitic infections. The results showed need to adequately control Culicoides in the community.

Analysis of Wuchereria bancrofti infections in a village community in northern Nigeria: increased prevalence in individuals infected with Onchocerca volvulus

Infections with Wuchereria bancrofti causing lymphatic filariasis still represent one of the major health problems in the tropics, with 120 million people infected and over 750 million exposed to this filarial parasite. We have studied lymphatic filariasis infections as part of a multi-parasite survey in a village community in the savannah of northern Nigeria. We analysed serum samples from 341 individuals aged 5-70 years, detecting a W. bancrofti circulating antigen using the commercially available ICT Filariasis card test. The prevalence of infections was 10% and clearly age-dependent, increasing from below 2% in children to over 20% in subjects older than 40 years. Measuring IgG4 antibodies against the recombinant W. bancrofti antigen SXP1 showed that 36% of all tested individuals had been at least exposed to the parasite. Antibody levels also increased very significantly with age. A further analysis measuring Onchocerca volvulus-specific IgG4 antibodies showed a very significant association between infections with O. volvulus and those with W. bancrofti. Our data show that infections with W. bancrofti in Nigeria are still a frequently occurring health problem, since they are more prevalent than previously reported, and that individuals with an O. volvulus infection are more often infected with W. bancrofti than expected statistically.

Onchocerciasis in Taraba State, Nigeria: clinical-epidemiological study of at-risk males in Bakundi District

An epidemiological study of 1366 adult males from fourteen communities of Bakundi district of Taraba State, Nigeria was carried out to establish the prevalence and intensity of onchocerciasis. The findings of the study showed that 45.2% of subjects were infected. Ten communities had infection rates in excess of 30%. Lizard skin and leopard skin were seen in 3.5% and 2.0%, respectively, and increased with increasing age. Hanging groin (2.6%) and scrotal enlargement (8.6%) were also observed. There was a good correlation between the infection rate on one hand and the presence of nodules (r = 0.85, P < 0.05), hanging groin (r = 0.56, P < 0.05) and scrotal enlargement (r = 0.62, P < 0.05) on the other. There was also a significant correlation between the intensity of infection on the one hand and lizard skin (r = 0.67, P < 0.05), leopard skin (r = 0.88, P < 0.05) and hanging groin (r = 0.82, P < 0.05) on the other. Those who worked in the fields (such as hunters, farmers and fishermen) had higher infection than others because of frequent contact with the vector. Extensive surveys of all suspected river valleys must be carried out to identify all those communities which will benefit from ivermectin treatment.

Re-assessing the global prevalence and distribution of lymphatic filariasis

This paper estimates the global burden of lymphatic filariasis based on a review of the published literature on infection and disease surveys. A method for aggregating and projecting prevalence data from individual studies to national, regional and global levels, which also facilitates the estimation of gender and age-specific burdens, is presented. The method weights in favour of the larger, and hence presumbably more reliable, studies and relies on estimated empirical relationships between gender, age, infection and disease in order to correct studies with incomplete data. The results presented here suggest that although the overall prevalence of filariasis cases is 2.0% globally (approximately totalling 119 million cases), the disease continues to be of considerable local importance, particularly in India and Sub-Saharan Africa. Estimates by age and gender clearly show that, unlike other helminth infections, filariasis is mainly a disease of the adult and older age-classes and appears to be more prevalent in males. This work suggests that the derivation of more accurate estimates of the burden of filariasis will require a better understanding of both the epidemiology and the spatial aspects of infection and disease. It also suggests that filariasis is preventable based on a geographically targeted strategy for control.

Human onchocerciasis in the lower Jos Plateau, central Nigeria: the prevalence, geographical distribution and epidemiology in Akwanga and Lafia local government areas

An investigation of human infection with Onchocerca volvulus and the resulting clinical disease was carried out for the Nigerian National Onchocerciasis Control Programme between July and August 1989 [corrected]. The survey covered 10.6% of the rural population in 41 savanna villages of central Nigeria. Of the 8451 self-selected individuals examined, 900 (10.6%) had skin microfilariae (Mf). There were differences between villages in both endemicity and intensity of infection, but in general the number of both Mf carriers and cases of clinical onchocerciasis increased with age. The disease in the Mf carriers showed as blindness (0.8%), onchocercal nodules (0.6%), leopard skin (1.6%) and pruritus (2.8%). Of 35 persons with lymphatic complications, 19 had hanging groin, 10 had elephantiasis and six had hydrocoele. Onchocerciasis was mesoendemic in the rocky northern escarpments, and became hypoendemic and sporadic in the southern uplands of sedimentary geological origin.

The occurrence of loiasis, mansonellosis and wuchereriasis in the Jarawa River Valley, central Nigeria

In a study to assess the status of filariasis in the Jarawa River Valley of the savanna area of Nigeria, 940 self-selected residents from 10 villages were examined between March 1984 and April 1987. Overall results showed 105 (11.2%) had microfilaraemia and/or clinical signs of filariasis. Sixty-four (6.8%) and 20 (2.1%) persons, respectively, were infected with Mansonella perstans and Loa loa microfilariae (mff). Four of the 28 villagers examined had Wuchereria bancrofti mff in their night blood samples whereas 17 (1.8%) of all residents surveyed had clinical filariasis mainly due to lympho-obstructive manifestations: hydrocele (n = 11, 64.7%); enlargement of the inguinal nodes (n = 8, 47.1%) and elephantiasis (n = 2, 11.8%).