Spatial Distribution of PCR-Identified Species of Anopheles gambiae senu lato (Diptera: Culicidae) Across Three Eco-Vegetational Zones in Cross River State, Nigeria.

Anopheles gambiae sensu lato complex (An. gambiae s.l.) describes a group of nine morphologically indistinguishable members that vary in their distribution, ability to transmit malaria, and susceptibility to pyrethroids. Here, we recorded the spatial patterns of PCR-identified An. gambiae s.l. complex species collected from four sites in Cross River State, Nigeria that represented three different ecological zones. Trapping was conducted between October 2015 and June 2016. Anopheles gambiae s.l. complex species identification was performed using species-specific primers followed by An. gambiae and An. coluzzii differentiation using the restriction fragment length polymorphism (RFLP) method. Bivariate and multivariate logistic regression models were used to identify ecological and seasonal variables closely associated with An. coluzzii and An. gambiae distribution. Out of 1,388 An. gambiae s.l. successfully amplified, 1,074 (77.4%) were An. coluzzii, 278 (20%) were An. gambiae, and 25 (1.8%) were hybrids (An. coluzzii/An. gambiae). A very small number of An. arabiensis (0.8%, n = 11) were also collected. Statistical analysis indicated that An. coluzzii is predominant in Guinea-savannah and tropical rainforest, and is highly associated with rainy seasons, while, An. gambiae is prevalent in mangrove swamp forest during dry seasons. Only 13 An. gambiae s.l. females were infected with Plasmodium falciparum (P. falciparum). The sporozoite infection rate was higher in mangrove swamp forest (53.8%, n = 7) than in rain forest (38.5%, n = 5) followed by Guinea-savannah (7.7%, n = 1) ecological zones. These results provide important insights for strategic planning of malaria control programs in Nigeria.

Species Composition of Anopheles (Diptera: Culicidae) in Selected Forested Tourist Areas of Nigeria Endemic for Malaria.

The study was carried out to determine relative abundance, species diversity, of Anopheles species (Diptera: Culicidae) in selected forested areas in Cross River State, Nigeria and the prevalence of malaria infection in the specimens. Mosquitoes were collected using pyrethrum spray catch and Centre for Disease Control light traps modified with yeast and sugar to generate carbon dioxide (CO2) and identified using morphological identification keys. We used a multiplex polymerase chain reaction followed by restriction fragment length polymorphism (PCR-RFLP) to simultaneously distinguish sibling species of the An. gambiae s.l, including separation of An. gambiae s.s. and An. coluzzii (Diptera: Culicidae). The samples were also screened for Plasmodium infection using the enzyme-linked immunosorbent assay. One hundred and four Anopheles specimens were collected during the study of which 97% was An. gambiae complex and 3% was An. rufipes (Diptera: Culicidae). Only 77% of the An. gambiae s.l. was identify to species level. The result shows that 41.6% was An. gambiae s.s. and 34.6% was An. coluzzii. No sporozoite of Plasmodium was detected in the Anopheles species. The study also found a hybrid form of An. gambiae s.s. and An. coluzzii. These findings suggest the first documented evidence of hybrid forms of An. gambiae s.s./An. coluzzii in South Eastern Nigeria although its epidemiological implication is still not clear.

The distribution of M and S molecular forms of Anopheles gambiae in Nigeria.

The distribution of M and S molecular forms of Anopheles gambiae sensu stricto across Nigeria was determined. The molecular form of 40 to 45 specimens per locality from 9 localities was determined using mostly the same specimens from our recent study of genetic differentiation of A. gambiae across Nigeria (Onyabe & Conn, 2001). These samples were previously genotyped at 10 microsatellite loci, 5 located within chromosome inversions and 5 outside inversions. Both molecular forms occurred throughout the country, with no apparent relationship to the ecological transition from dry savannah in the north to humid forest in southern Nigeria. In all localities, however, 1 form or the other occurred virtually exclusively. No hybrids between forms were found. Across all loci, F(ST) values were as high within molecular forms as between forms. Regardless of molecular form, F(ST) values calculated across loci within inversions were much higher (range 0.0016 to 0.1988) than those calculated across loci outside inversions (range -0.0035 to 0.0260). Genetic distance was not significantly correlated with geographical distance within either form (P> 0.05). These observations suggest that, in addition to partial reproductive barriers between molecular forms, selection is a major factor shaping genetic differentiation of A. gambiae across Nigeria.

Efficacy and tolerability of a low-dose mefloquine-sulfadoxine-pyrimethamine combination compared with chloroquine in the treatment of acute malaria infection in a population with multiple drug-resistant Plasmodium falciparum.

The efficacy and tolerability of single, low-dose mefloquine, sulfadoxine-pyrimethamine (MSP) combination was compared with chloroquine (CQ) for malaria treatment in a malaria-endemic area of Nigeria with multiple drug-resistant Plasmodium falciparum. The two drug regimens (MSP and CQ) were tested in a 12-month prospective population study. The patients were divided into two groups. Group 1 patients were treated presumptively, based on malaria symptoms. Group 2 patients were treated based on a parasitologic diagnosis using the World Health Organization seven-day in vivo test and extended to a 28-day follow-up period. Tolerability was assessed by the incidence and intensity of adverse events. One thousand nine hundred thirty-five patients visiting 10 health facilities, including the University of Calabar Teaching Hospital, were enrolled. The study showed that the low-dose MSP was efficacious, with day 7 response rates of 95% and 91% for (presumptive) Group 1 and (in vivo) Group 2, respectively, while CQ had day 7 response rates of 82% and 66% in Groups 1 and 2, respectively. The low-dose MSP was significantly (P < 0.0001) more efficacious, with faster fever and parasite clearance times than CQ in this area of CQ-resistant P. falciparum malaria. Eight patients treated with CQ, including seven severe cases (RII-RIII) were successfully re-treated with MSP. Adverse events were generally more common among those treated with MSP (29%) than those treated with CQ (17%). However, the adverse events caused by both drugs were mild to moderate and self-limited. The MSP combination appears to be a good substitute for CQ, in view of multiple drug resistance, especially in areas with severe (RII-RIII) malaria.

Chloroquine-resistant Plasmodium falciparum among children in Calabar, south eastern Nigeria.

Sixty-nine children aged between 6 and 60 months with parasitologically proven Plasmodium falciparum malaria were treated with chloroquine (2.5 mg/kg) in the Children's Emergency Room of the University of Calabar Teaching Hospital (UCTH) in 1993. Thirty subjects (mean age 27.8 months) and 39 (mean age 29.5 months) received chloroquine phosphate suppository (Pharma Deko) and chloroquine sulphate syrup (May & Baker), respectively. The World Health Organization (WHO) 14-day in vivo field test was used in evaluating the response to treatment. In both treatment groups the responses were similar. Overall, parasitological cure occurred in 24 subjects (34.8%) and in the remaining 45 subjects (65.2%) treatment failed (chloroquine resistance). This level of chloroquine resistant Plasmodium falciparum (CRPF) is higher than 53.6% reported in this centre in 1989. Furthermore, in the present study the proportion of RII (46.4%) is significantly higher than 21.4% (P < 0.02) obtained in 1989. Our findings show a worsening of CRPF in Calabar with RII being the main contributor. This observation indicates the need for continued surveillance of the response of P. falciparum to chloroquine and alternative antimalarials as a means of evolving an effective treatment policy for malaria.

New trends in chloroquine efficacy in the treatment of malaria: significance of low (scanty) parasitaemia in an endemic area, with emerging chloroquine-resistant P. falciparum.

In a continuous malaria therapy surveillance, using in vivo (WHO) seven-day-test, extended to 14 days follow up, we evaluated the significance of low (scanty) parasitaemia, in an area with chloroquine resistance P. falciparum (CRPF), where self-medication is widely practised. We found that 30.9 pc of the patients screened had Plasmodium species, and 71.4 pc of these had low parasite counts of less than 500 parasites/mm3, whole blood. Eight pc of these were febrile and 41.7 pc of the parasite strains were not susceptible to chloroquine. Parasite strains from four of the patients were also resistant to other antimalarials. These patients gave psychosomatic symptoms, and were seen by a psychiatrist. We conclude that 41 pc of the patients with low parasite counts consist of patients with CRPF and/or multiple-drug resistant P. falciparum in this area. These do not only cause chronic anaemia, but also may be responsible for moderate psychosomatic symptoms in all ages.

New trends in chloroquine efficacy in the treatment of malaria: chloroquine-resistant Plasmodium falciparum in Anambra and Benue States of Nigeria.

Increasing malaria treatment failures with chloroquine (C25) and reports of chloroquine resistant Plasmodium falciparum (CRPF) led to the field survey of two sites (Agbani and Jato-Aka) both in Primary Health Zone A, using WHO--in vivo seven-day test, modified to 14-day follow-up period. Of the 922 children studied, high transmission rates of 40 pc and 59.2 pc were found in Agbani and Jato-Aka respectively. Varying degrees of parasitologic failures (CRPF), 52 pc in Agbani and 60 pc in Jato-Aka were confirmed. However, chemotherapy with C25 significantly reduced the clinical symptoms of malaria infection, even in the CRPF-cases. The clinical success in the two study sites were 69 pc ad 94 pc respectively.

Malaria and its treatment in rural villages of Aboh Mbaise, Imo State, Nigeria.

We examined the malaria situation among 489 children under 5 years of age in the rural villages of Aboh Mbaise, Nigeria, using a combination of a standard questionnaire technique and laboratory diagnosis to confirm clinical observations. The results show a high prevalence rate of 52.8% for Plasmodium falciparum in this area. The geometric mean parasite density (GMPD) was 19,361.4/mm3. The proportion of children with fever and/or parasitaemia was not related to age, although the numbers in the febrile group appeared to increase with age. Using 37.5 degrees C as the threshold for fever, 48.7% of the heavily infected group (more than 1000/mm3) were afebrile while 51.3% were febrile. High grade temperatures above 38 degrees C were associated with high parasitaemia above 10,000 parasites/mm3. Of the 911 children who died in the area within the last five years, 22.4% died of fever of unknown origin, 39.7% from malaria, 22.5% from convulsion, 10.5% from diarrhoea and 4.6% from cough. Chloroquine is the drug of choice for the treatment of malaria and there were many cases of drug abuse, and use of sub-curative doses prescribed by non-medically qualified staff.

Efficacies of chloroquine and pyrimethamine-sulphadoxine in a Nigerian population with chloroquine resistant P. falciparum malaria.

A modification of the standard World Health Organisation 7--day in vivo test was used to assess the parasitologic and, to limited extent, the clinical response of children less than 5 years of age to defined oral dosages of chloroquine and pyrimethamine-sulphadoxine during the 14 days following the initiation of treatment. The study took place in Jato-Aka, a rural community in Benue State of Nigeria. 471 children were screened and 271 (59%) of these had plasmodium parasites thus showing a high transmission rate at a time of the year with scarce rainfall. Of the 42 children on chloroquine and who were followed up to day 2, 4 or 9.5% of them were parasitologic failures while none of the 45 children on pyrimethamine-sulphadoxine (P-S) failed parasitologically. By day 7, 21 (50%) of the children on chloroquine and 4 or 8.9% of those on P-S. had become parasitologic failures. The total number of parasitologic failures on day 14 were 21 (50%) and 4(8.9%) for chloroquine and P-S groups respectively. Chloroquine improved the clinical state of the patients better than P-S. However, P-S appears superior in clearing the parasites. These results confirm the existence of both chloroquine and pyrimethamine-sulphadoxine resistant strains of P. falciparum in some regions of Nigeria. The routine chloroquine chemoprophylaxis of children under 5 years of age should be discontinued so as not to hasten the intensification of chloroquine resistance and because of its probable marginal efficacy at chemoprophylaxis dosages. There is also need for a national policy on pyrimethamine-sulphadoxine usage in order not to hasten its resistance to P. falciparum.