Analysis of the prevalence of infection and associations between human gastrointestinal nematodes among different age classes living in the urban and suburban communities of Port Harcourt, Nigeria.

Fresh stool samples from 300 subjects presenting at out-patient clinics in two major hospitals in Port Harcourt were analysed for the prevalence and intensity of gastrointestinal (GI) nematode infections and 85.3% were found to carry at least one of the four species of GI nematodes recognized during the study. The most common species was Ascaris lumbricoides (54%), followed by Trichuris trichiura (43.7%) and Necator americanus (42.7%) and lastly Strongyloides stercoralis (33%). Peak prevalence for A. lumbricoides was among the < or = 9 years age cohorts, whilst those for the remaining species all coincided among the 15-19 years age cohort. The frequencies of single, double and triple-species infection categories, across the species and within most of the specific combinations were lower than the expected frequencies calculated from overall prevalence data for each species. Observed cases of non-infected individuals and those carrying all four species were higher than expected, suggesting that a greater than expected subset of the population was free from infection, particularly among subjects > or = 30 years old and another subset more prone to infection by all four species, predominantly among the age cohorts < or = 29 years. N. americanus and T. trichiura were more commonly encountered among multiple species infection combinations than expected, but the intensity of the former declined as the number of other concurrently infecting species increased. In contrast, the intensity of infection with S. stercoralis increased as the number of other species increased. Positive associations between A. lumbricoides and T. trichiura, N. americanus and S. stercoralis, and T. trichiura and N. americanus were identified in respect of greater than expected co-occurrence of these combinations and significant positive correlations between their respective intensities of infection. These were related to specific age cohorts which were identified as particularly prone to multiple infections.

Assessment of the effectiveness of primary health care interventions in the control of three intestinal nematode infections in rural communities.

In a 30 months' longitudinal study, primary health care intervention was effective in reducing the prevalence of three common intestinal nematode infections (Ascaris lumbricoides, Trichuris trichiura and Necator americanus) in three communities. This was achieved by training school leavers and auxiliary aides as microscopists, health inspectors and field assistants and deploying them to provide screening, surveillance, environmental sanitation, and mass-expulsion chemotherapy (MEC). Post-control surveillance confirmed that the prevalence of these infections had been greatly reduced. The prevalence of Ascaris lumbricoides had declined from 49.3% (pre-intervention) to 10.5% (post-intervention). Hookworm had fallen from 31.4% (pre-intervention) to 4.1% (post-intervention) and whipworm from 40.7% (pre-intervention) to 6.5% (post-intervention). Overall percentage decreases of 78.7%, 86.9% and 84.0% were recorded for Ascaris lumbricoides, Necator americanus and Trichuris trichiura respectively. The initial decline in prevalence was due to the MEC campaign, but the improved sanitation and health education presumably reduced the reinfection rate. If the entire population participated, periodic repetition of the mass expulsion therapy campaign at appropriate intervals combined with continued attention to environmental hygiene and prolonged health education could bring these infections under control within a few years.

PIP: In the late 1980s and early 1990s in Nigeria, parasitologist evaluated the effectiveness of health education, environmental sanitation, and mass expulsion chemotherapy (MEC) in controlling endemic parasitic infections (Ascaris lumbricoides, Trichuris trichiura, and Necator americanus) in the population served by health care centers in Ndele, Emohua, and Aluu (in the eastern area of the Niger Delta Basin). 240 dropouts from primary and secondary schools and 45 auxiliary nurses from the communities underwent 6 months, training to become health inspectors, microscopists, field assistants, and surveillance staff. About 120 people/day frequented each community health education forum at the centers. The communities worked together to build ventilation-improved pit latrines, resulting in a considerable decline of open air defecation. 54.5% of the population provided stool samples so researchers could determine the prevalence of intestinal nematode infections. Health workers administered a single dose of either Alcopar or Zentel to all people diagnosed with nematode infection. The infected people also received nutritional supplements as required. Initial prevalence was 49.3% for A. lumbricoides, 40.7% for T. trichiura, and 31.4% g for N. americanus. The interventions contributed to a decline in overall prevalence ranging from 70.6% (A. lumbricoides in Ndele) to 88.2% (N. americanus in Emohua). The percentage of reduction of A. lumbricoides infection increased as age increased (e.g., 73.5% reduction for 5 year old children and 86% reduction for 45 to 54 year olds). Little difference in reduction with age existed for N. americanus and T. trichiura infections, however, 30 months after intervention prevalence was 10.5% for A. lumbricoides, 6.3% for T. trichiura, and 3.9% for N. americanus. These findings indicated that health education campaigns, MEC campaigns, and improvement in environmental sanitation result in considerable reduction of nematode infections.

The human environment, occupation, and possible water-borne transmission of the human hookworm, Necator americanus, in endemic coastal communities of the Niger Delta, Nigeria.

A 15-month longitudinal study was carried out in four riverine communities of the Niger Delta to ascertain the impact of the environment and occupation on the transmission and infection pattern of the human hookworm Necator americanus. A total of 925 (50.10%) individuals were found to be infected. Male and female infection rates were 54.26% and 47.96% respectively. The difference was statistically significant (P less than 0.05). The prevalence of infection, the egg counts, and the seasonal incidence were related to the occupations and mode of transmission. The highest occupation prevalence of 60.92% occurred among the fishermen through water-borne transmission, while prevalence rates of 52.96% and 52.4% were recorded respectively through soil transmission. The difference between fishermen's prevalence and farmers' prevalence was statistically significant (P less than 0.01). Farmers' egg counts varied from 1,500 eggs per gram (epg) in the dry season to 7,500 epg in the rainy season. Fishermen's egg counts ranged from 3,000 epg in the rainy season to 8,000 epg in the dry season. The difference was not significant (P greater than 0.05). Among farmers the highest monthly incidence of 25% occurred in June, while the highest incidence of 35% occurred in fishermen in April. Incidence of infection among fishermen remained significantly higher (P less than 0.05) than in other occupation groups during the dry season months. Water-borne transmission of hookworm probably increases the incidence and egg counts among fishermen during the dry season.

Human community ecology of urinary schistosomiasis in relation to snail vector bionomics in the Igwun River Basin of Nigeria.

In a 15-months filed study of the human community ecology of urinary schistosomiasis 15.0% prevalence rate was recorded in 1,625 individuals examined. 37.0% of infected individuals had infections of low intensity. 34.0% were of moderate intensity, while 28.7% had high intensity in infections. Male prevalence of 16.7% was not statistically different (P less than 0.05) from the female prevalence of 13.3%. The population of the Bulinus snail intermediate host showed seasonal fluctuations with a peak in May, and a trough in January. Infection rates of snails rose gradually from 60% in February to 75% in May. Cercarial burdens of snails rose from 500 cercariae per snail per month to a peak count of 900 cercariae per snail per month in June. Water contact activities were either complete and long term, partial and medium term or limited and short term. Age, sex, and occupation were important determinants of the type, duration and period of water contact activities. Results also suggest that high exposure indices were related to high infection prevalence and intensity.

Clinical field trials of praziquantel in pulmonary paragonimiasis due to Paragonimus uterobilateralis in endemic populations of the Igwun Basin, Nigeria.

A clinical field trial of praziquantel was carried out on patients infected with Paragonimus uterobilateralis in the Igwun Basin, Nigeria. 332 patients were subjected to the praziquantel therapy. 290 (87.3%) reverted to negative status. The pattern of reduction in sputum and faecal egg counts was related to the quantity of praziquantel administered. With 45 mg daily dose reduction in sputum egg counts ranged from 83.2% to 87.3% with reversion rate of 71.1%; with 60 mg daily dose, 84.8-88.3% reduction was recorded with 85.4% cure rate. With 75 mg daily dose reduction rate ranged between 90.8-96.8%, with cure rate of 97.6%. A cure rate of 100% was recorded in 15-29 year old patients treated with 75 mg daily dose. The recommended effective dose treatment of Paragonimus uterobilateralis infection with praziquantel is therefore 75 mg/kg body weight/day for two days.

Bancroftian filariasis in the Igwun Basin, Nigeria. An epidemiological, parasitological, and clinical study in relation to the transmission dynamics.

A 12-month field and laboratory study was carried out to determine the epidemiology, clinical features, and transmission dynamics of bancroftian filariasis in the Igwun Basin, Nigeria. A total of 1,418 individuals (768 males, and 650 females) were examined for clinical signs of filariasis. 690 day provocative blood samples (DPS), and 728 night blood samples (NBS) were examined for microfilaremia. 14.3% of males and 11.1% of females were mf positive. 5.8% of DPS, and 19.5% of the NBS were mf positive. An overall microfilaria rate of 12.8% was recorded in the basin. Prevalence and microfilarial density increased with age. The highest average density of 35 mf/20 ml NBS occurred in the 40-59-year-old male individuals. The mean microfilarial density in DPS and NBS were 7.9 and 28.0 per 20 ml blood in males, respectively, and 6.2 and 20.0 per 20 ml DPS and NBS in females, respectively. Disease rates of 55.5% were recorded for males, and 68.1% for females. The clinical signs observed were: Chyluria (9.1% for males, 16.7% for females); hydrocele (15.5%); elephantiasis (15.5% in males, 29.2% in females); and enlarged groin glands (15.5% in males, 22.2% in females). All clinical signs were associated with microfilariae. Anopheles gambiae s.I., and Culex pipiens s.I. were the two mosquito vectors identified. The estimated mean annual biting rates were 5508 and 10448 for A. gambiae s.I. and C. pipiens s.I., respectively. Their respective mean infection rates were 21.7% for A. gambiae s.I. and 22.7% for C. pipiens s.I.; with microfilarial densities of 4.1 and 6.6.(ABSTRACT TRUNCATED AT 250 WORDS)

Experimental and field studies on the viability of eggs, and the infectivity of third-stage larvae of the human hookworm Necator americanus recovered from the creek waters of the Niger Delta, Nigeria, and their epidemiological significance.

In a combined field and laboratory study, the eggs and 3rd-stage infective larvae of the human hookworm Necator americanus were recovered from the creek waters of the Niger Delta, Nigeria. They were tested for viability and infectivity. Eggs recovered from fresh water creeks showed a viability or hatching index of between 17.5 and 23.7%. Eggs recovered from brackish water showed a viability index of 18.8-21.4% in 'normal' cultures, and a maximum index of 6.3% when cultured in brackish water. The differences in the viability indices of these eggs were not significant (P greater than 0.05). Infective 3rd-stage larvae were recovered from both fresh creek water (205-258 L3/litre of water), and brackish water (45 L3/litre of water). Larvae hatched from brackish water eggs that were cultured in the brackish water were 20% infective by 3 days, but lost all infective potential by 7 days post-hatching. Larvae from fresh water eggs, cultured in fresh water and 'normal' laboratory cultures reached 50% infectivity in 3-5 days, losing potential infectivity in 11-15 days post-hatching. The infectivity patterns of larvae recovered directly from fresh and brackish waters did not differ significantly (P greater than 0.05) from the infectivity patterns of larvae recovered from laboratory cultures of eggs from all the experimental sources. Although larvae recovered directly from fresh and brackish waters survived in these respective media under laboratory conditions, there was a significant difference (P less than 0.05) in their survival patterns. The survival and infectivity rates of field larvae were considerably reduced over time relative to control larvae.(ABSTRACT TRUNCATED AT 250 WORDS)

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

In a cross-sectional, epidemiological and parasitological study of human filariasis, 845 individuals were examined in settlements along the Igwun Basin, Imo State, Nigeria. Four different filarial nematode species were identified. Two hundred and fifty-six (30.3%) of the individuals examined were positive for Onchocerca volvulus, 113 (13.4%) for Mansonella perstans, 76 (9.6%) for Wuchereria bancrofti and 77 (9.1%) for Loa loa. Microfilarial rates increased with age of individuals and showed a tendency towards higher prevalence rates in males than in females. The intensity of O. volvulus infection was high, with the highest microfilarial density of 44 mf mg-1 snip which occurred in the 40-49-year-old individuals. In W. bancrofti and L. loa infections, infections of over 1000 mf 20 ml-1 blood were recorded in 15.8% and 19.5% of individuals, respectively. Observed clinical signs were associated with inflammatory, lympho-obstructive and ocular manifestations. In M. perstans infections all clinical cases were inflammatory. In W. bancrofti, 44.4% of clinical cases were inflammatory, and lympho-obstructive manifestations consisted of 23.8% chyluria, 12.7% hydrocele and 19.1% elephantiasis. In L. loa infections all clinical cases were inflammatory with indications of Calabar swellings. In O. volvulus infections 23.5% of clinical cases were inflammatory, while 76.5% showed ocular manifestations. The absence of blindness despite high O. volvulus infection rates was remarkable. The presence of potential insect vectors and the occurrence of clinical signs are indications of active transmissions.

Bancroftian filariasis in the Igwun basin, Nigeria: an epidemiological, parasitological, and clinical study in relation to the transmission dynamics.

A 12-months study on bancroftian filariasis was carried out in the Igwun basin, Nigeria. A total of 1,418 individuals (768 males, and 650 females) were examined for microfilaremia and clinical filarial stigmata. There were 14.3% and 11.1% male and female point prevalence rates, respectively, and an overall prevalence of 12.8%. Prevalence rates and microfilarial density increased with age. The highest mff density of 35 mff/20 ml blood occurred in the 40-49 year old male individuals. Disease rates of 55.5 and 65.3% were recorded for males and females respectively. Chyluria (9.3% males, 16.7% females), hydrocele (17.8%), elephantiasis (15.9% males, 29.2% females), and enlarged groin glands (16.4% males, 19.4% females) were the major clinical signs, all associated with microfilaremia. Anopheles gambiae and Cules pipiens were the principal vectors. The estimated mean daily, weekly, and monthly per capita biting densities were 26, 161, and 753 respectively. The overall infection rate of mosquitoes was 22.3%, with a mean mff density of approximately 5 mff/mosquito. These vector parameters were indicative of active transmission in the area, and may be responsible for the high prevalence of infection, the diversity of clinical signs, and high morbidity rates.

Dracontiasis in the Igwun River Basin, Nigeria: its distribution, epidemiology, and transmission dynamics.

In a cross-sectional dracontiasis survey of the Igwun Basin, Nigeria, 879 persons from seven communities were examined. Ninety-five (10.8%) had dracontiasis blisters and ulcers. Male prevalence of 14.9% was significantly higher (P less than 0.001) than the female prevalence of 6.9%. Infection increased with age, rising from 2% in 1-4 years old children to 15.8% in the 35-44 years old adults. Sixty-five percent of infected males had blisters, 34.4% had ulcers. Among females, 48.4% had blisters, 51.6% had ulcers. Among the males, blisters and ulcers showed seasonal variations, with 80% cases of blisters between November and April, and 20% between June and October. Seasonal morbidity pattern in females did not show any significant variation (P greater than 0.20). The density of cyclopoid copepods increased in the dry season in relation to decreasing rainfall. The highest cyclops count was 18 cyclops per litre of water recorded between January and February, while the lowest was zero recorded in July in some areas. The infection rates of cyclops rose from 10% in November to a peak value of 20% between January and February, with the lowest rate of 5% in July. Larval burden of cyclops also rose from 3L3's/cyclops in June, to 5L3's/cyclops in January. Dracontiasis appears to be a relatively new disease in the area, and its spread has been enhanced by the interaction of human behavioural, and parasite-vector ecological factors which are seasonally modulated.

Necator americanus: temperature, pH, light, and larval development, longevity, and desiccation tolerance.

The effect of incubation temperature and pH on the hatch rate of eggs of Necator americanus, and the desiccation tolerance of the resulting infective stage-3 larvae were investigated in the laboratory under controlled conditions. Hatching did not occur below 15 C and above 35 C. A 21% hatch rate was obtained at 15 C while a 10.6% hatch rate was obtained at 35 C. The highest hatch rate (93.7%) was obtained at 30 C. The optimum pH for hatching was 6.0, but the larvae did not reach the infective stage. Incubation temperature of the eggs affected the longevity and desiccation tolerance of resultant infective larvae. Larvae hatched at 30 C and maintained at 26 C under bright fluorescent light had a 50% survival time (S50) of 4 days. In the dark or shade, the S50 for larvae raised at 30 C was 5 weeks, while that of larvae hatched at 20 C was 7 weeks. Incubation temperature also affected the desiccation tolerance of larvae. Larvae developed at 20 C were more resistant to desiccation at various relative humidity values than larvae hatched at 30 C.

Endemic Paragonimus infection in upper Igwun Basin, Nigeria: a preliminary report on a renewed outbreak.

In a 24-month longitudinal study on a renewed outbreak of Paragonimus infection in Igwun Basin, Nigeria 1973 individuals were examined. A total of 332 (16.8%) individuals were found infected with Paragonimus uterobilateralis. There was evidence of increasing annual prevalence rates from 15.0% in 1983 to 16.7% in 1984, and 18.7% in 1985. Infection was present in all age groups, with prevalence of 18.9% in males and 14.5% in females. 12.3% of the infections were of high intensity, over 100 eggs in 5 ml of sputum; 20.5% were moderate infections, 50-100 eggs in 5 ml of sputum; the remaining 67.2% were of low intensity, less than 50 eggs in 5 ml of sputum. The increasing annual prevalence rates and intensity of infection resulted from increased crab consumption. The commonest crab was Sudanautes africanus, whose population and level of infection with metacercariae showed seasonal fluctuations with peaks during the dry season months. There was evidence that snails of the genus Melania are involved in the transmission of P. uterobilateralis in the area.

The status of human filariasis in relation to clinical signs in endemic areas of the Niger Delta.

A study was carried out in selected parts of the Niger Delta Basin on human filariasis and its relationship to clinical signs. One hundred and seventy-six (13.0%) of 1351 individuals examined were infected with microfilaria. Forty-six percent of microfilaria positive cases had M. perstans; 25.6% had W. bancrofti, 19.3% had L. loa, and 9.0% had O. volvulus. The prevalence of filariasis increased with age. Microfilarial density was generally low, 28.4% of infected individuals had counts of 50-100 microfilaria per 20 mm3 blood, 12.5% had counts less than five microfilaria per 20 mm3 blood. Onchocerca microfilariae did not exceed five microfilaria per snip. Microfilarial density was high among individuals aged between 20 and 49 years, but declined with increasing age above 50 years. Acute clinical signs of febrile attack, sink eruptions, and chronic clinical signs of chyluria, hydrocoele, elephantiasis and ocular lesions were observed in 61.9% of infected individuals, 73.4% of clinical cases were febrile attack and skin eruptions, 5.5% were chyluria, 12.8% were elephantiasis of the leg and scrotum, 7.3% were hydrocoele and 0.9% were ocular lesions. Chronic clinical signs were more prevalent in individuals over 40 years of age.

Studies on the co-occurrence of two species of human hookworm in a riverine community in Nigeria.

A total of 1,623 stool specimens from different individuals were examined to assess the infection prevalence and the pattern of occurrence of Necator americanus and Ancylostoma duodenale in a riverine community in Nigeria. 56.3% of 823 males and 52.63% of 800 females were positive for both species of hookworm, 25.1% of infected males, and 26.1% of infected females had A. duodenale while 46.7% of infected males and 51.2% of infected females had N. americanus. 28.2% of males and 22.7% of females had mixed infections of both species. The occurrence of each species was independent of the other. The distribution of infection was age-dependent, while sex had no effect on infection pattern. In A. duodenale infection, egg counts rose between 15 and 25 years of age, but declined with increasing host age. Egg counts in N. americanus infection were more stable with increasing age of the host. The probability of recovering N. americanus eggs in the faeces was higher than that of A. duodenale. In mixed infections, egg out put of N. americanus was higher than that of A. duodenale as indicated by the higher conditional probability of recovering N. americanus eggs in the presence of A. duodenale. The egg production of A. duodenale seems to be suppressed by N. americanus when both co-occur.

Changes in lipid contents of infective third-stage larvae of Necator americanus during desiccation and revival.

Changes in lipid content of infective third-stage larvae of Necator americanus were investigated after short periods of induced desiccation and revival. A fall in lipid reserve from an outset level of 86% to 74% was recorded in the first 2 h of desiccation. With increased desiccation, lipid reserves did not show significant decline, probably as a result of decreased lipid metabolism in the desiccated larvae. During revival, there was a drastic fall in lipid reserves as a result of increased lipid utilisation by the reviving larvae. The results showed that desiccated larvae with lipid levels less than 10% did not revive. The presence of lipid did not appear to prevent desiccation but was an essential factor for revival. The ecological significance of these findings in field larvae is discussed.

Necator americanus infection: a longitudinal study of an urban area in Nigeria.

A longitudinal study was carried out in Owerri, capital of Imo State, Nigeria, to assess the pattern of Necator americanus infection during a 27-month period. The mean annual prevalence fell from 59.0% in 1978, to 55.5% in 1979 and 51.1% in 1980. The egg count (apparent intensity of infection) fell in a similar pattern. Maximum and minimum conversion rates were 55.2 and 13.7%, respectively, and conversion rates fell by approximately 20% between 1979 and 1980. The highest reversion rate was 55.0% between 1979 and 1980. The population density of available third-stage larvae fluctuated seasonally and this was significant in determining the pattern of infection.

Necator americanus: population structure, distribution, and fluctuations in population densities of infective larvae in contaminated farmlands.

Observations have been made over a 15-month period on the frequency distribution of human faecal deposits and infective larvae of Necator americanus in a hookworm endemic area. The agestructure of infective larvae in a field population and their vertical distribution in soils were determined. These studies were undertaken to examine the hypothesis that hookworm transmission in the tropics is discontinuous and limited mainly to the rainy season. The distribution of larvae was found to be overdispersed statistically and in general much greater numbers of L3s were recovered during the rainy season. The degree of overdispersion was also reduced during this season, and there was a tendency for larvae to be confined to the surface/topsoil. The implications of these findings have been discussed in relation to human hookworm parasitism in endemic areas of the tropics.