Transmission dynamics of lymphatic filariasis: vector-specific density dependence in the development of Wuchereria bancrofti infective larvae in mosquitoes

Mathematical models of transmission dynamics of infectious diseases provide a useful tool for investigating the impact of community based control measures. Previously, we used a dynamic (constant force-of-infection) model for lymphatic filariasis to describe observed patterns of infection and disease in endemic communities. In this paper, we expand the model to examine the effects of control options against filariasis by incorporating the impact of age structure of the human community and by addressing explicitly the dynamics of parasite transmission from and to the vector population. This model is tested using data for Wuchereria bancrofti transmitted by Culex quinquefasciatus in Pondicherry, South India. The results show that chemotherapy has a larger short-term impact than vector control but that the effects of vector control can last beyond the treatment period. In addition we compare rates of recrudescence for drugs with different macrofilaricidal effects.

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Progress towards elimination of lymphatic filariasis in the Americas region

International Health ◽

10.1093/inthealth/ihaa048 ◽

2020 ◽

Vol 13 (Supplement_1) ◽

pp. S33-S38

Author(s):

Gilberto Fontes ◽

Eliana Maria Mauricio da Rocha ◽

Ronaldo Guilherme Carvalho Scholte ◽

Rubén Santiago Nicholls

Keyword(s):

Dominican Republic ◽

Lymphatic Filariasis ◽

Wuchereria Bancrofti ◽

World Health ◽

Vector Species ◽

Effective Coverage ◽

The Third ◽

Assessment Survey ◽

Health Organization ◽

Important Progress

Abstract In South and Central America, lymphatic filariasis (LF) is caused by Wuchereria bancrofti, which is transmitted by Culex quinquefasciatus, the only vector species in this region. Of the seven countries considered endemic for LF in the Americas in the last decade, Costa Rica, Suriname and Trinidad and Tobago were removed from the World Health Organization list in 2011. The remaining countries, Brazil, Dominican Republic, Guyana and Haiti, have achieved important progress in recent years. Brazil was the first country in the Americas to stop mass drug administration (MDA) and to establish post-MDA surveillance. Dominican Republic stopped MDA in all LF-endemic foci: La Ciénaga and Southwest passed the third Transmission Assessment Survey (TAS) and the Eastern focus passed TAS-1 in 2018. Haiti passed the TAS and interrupted transmission in >80% of endemic communes, achieving effective drug coverage. Guyana implemented effective coverage in MDAs in 2017 and 2018 and in 2019 scaled up the treatment for 100% of the geographical region, introducing ivermectin in the MDA in order to achieve LF elimination by the year 2026. The Americas region is on its way to eliminating LF transmission. However, efforts should be made to improve morbidity management to prevent disability of the already affected populations.

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Semiannual Treatment of Albendazole Alone is Efficacious for Treatment of Lymphatic Filariasis: A Randomized Open-label Trial in Cote d'Ivoire

Clinical Infectious Diseases ◽

10.1093/cid/ciab194 ◽

2021 ◽

Author(s):

Allassane F Ouattara ◽

Catherine M Bjerum ◽

Méité Aboulaye ◽

Olivier Kouadio ◽

Vanga K Marius ◽

...

Keyword(s):

Lymphatic Filariasis ◽

Primary Outcome ◽

Central Africa ◽

Wuchereria Bancrofti ◽

Bancroftian Filariasis ◽

Loa Loa ◽

Open Label ◽

Treatment Groups ◽

Open Label Trial ◽

To Receive

Abstract Background Ivermectin (IVM) plus albendazole (ALB), or IA, is widely used in mass drug administration (MDA) programs that aim to eliminate lymphatic filariasis (LF) in Africa. However, IVM can cause severe adverse events in persons with heavy Loa loa infections that are common in Central Africa. ALB is safe in loiasis, but more information is needed on its efficacy for LF. This study compared the efficacy and safety of three years of semiannual treatment with ALB to annual IA in persons with bancroftian filariasis. Methods Adults with Wuchereria bancrofti microfilaremia (Mf) were randomized to receive either three annual doses of IA (N=52), six semiannual doses of ALB 400mg (N=45), or six semiannual doses of ALB 800mg (N=47). The primary outcome amicrofilaremia at 36 months. Findings IA was more effective for completely clearing Mf than ALB 400mg or ALB 800mg (79%, CI 67-91; vs. 48%, CI 32-66 and 57%, CI 41-73, respectively). Mean % reductions in Mf counts at 36 months relative to baseline tended to be greater after IA (98%, CI 88-100) than after ALB 400mg (88%, CI 78-98) and ALB 800mg (89%, CI 79-99) (P=0.07 and P=0.06, respectively). Adult worm nest numbers (assessed by ultrasound) were reduced in all treatment groups. Treatments were well tolerated. Interpretation Repeated semiannual treatment with ALB is macrofilaricidal for W. bancrofti and leads to sustained reductions in Mf counts. This is a safe and effective regimen that could be used as MDA to eliminate LF in areas ivermectin cannot be used.

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Lymphatic filariasis, infection status in Culex quinquefasciatus and Anopheles species after six rounds of mass drug administration in Masasi District, Tanzania

Infectious Diseases of Poverty ◽

10.1186/s40249-021-00808-5 ◽

2021 ◽

Vol 10 (1) ◽

Author(s):

Eliza Lupenza ◽

Dinah B. Gasarasi ◽

Omary M. Minzi

Keyword(s):

Vector Control ◽

Lymphatic Filariasis ◽

Drug Administration ◽

Mass Drug Administration ◽

Wuchereria Bancrofti ◽

Elimination Phase ◽

Anopheles Species ◽

The Status ◽

Household Environment ◽

Indoor And Outdoor

Abstract Background Lymphatic filariasis (LF) elimination program in Tanzania started in 2000 in response to the Global program for the elimination of LF by 2020. Evidence shows a persistent LF transmission despite more than a decade of mass drug administration (MDA). It is advocated that, regular monitoring should be conducted in endemic areas to evaluate the progress towards elimination and detect resurgence of the disease timely. This study was therefore designed to assess the status of Wuchereria bancrofti infection in Culex quinqefasciatus and Anopheles species after six rounds of MDA in Masasi District, South Eastern Tanzania. Methods Mosquitoes were collected between June and July 2019 using Center for Diseases Control (CDC) light traps and gravid traps for indoor and outdoor respectively. The collected mosquitoes were morphologically identified into respective species. Dissections and PCR were carried out to detect W. bancrofti infection. Questionnaire survey and checklist were used to assess vector control interventions and household environment respectively. A Poisson regression model was run to determine the effects of household environment on filarial vector density. Results Overall, 12 452 mosquitoes were collected of which 10 545 (84.7%) were filarial vectors. Of these, Anopheles gambiae complex, An. funestus group and Cx. quinquefasciatus accounted for 0.1%, 0.7% and 99.2% respectively. A total of 365 pools of Cx. quinquefasciatus (each with 20 mosquitoes) and 46 individual samples of Anopheles species were analyzed by PCR. For Cx. quinquefasciatus pools, 33 were positive for W. bancrofti, giving an infection rate of 0.5%, while the 46 samples of Anopheles species were all negative. All 1859 dissected mosquitoes analyzed by microscopy were also negative. Households with modern latrines had less mosquitoes than those with pit latrines [odds ratio (OR) = 0.407, P < 0.05]. Houses with unscreened windows had more mosquitoes as compared to those with screened windows (OR = 2.125, P < 0.05). More than 80% of the participants own bednets while 16.5% had no protection. Conclusions LF low transmission is still ongoing in Masasi District after six rounds of MDA and vector control interventions. The findings also suggest that molecular tools may be essential for xenomonitoring LF transmission during elimination phase.

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An analysis of the safety of the single dose, two drug regimens used in programmes to eliminate lymphatic filariasis

Parasitology ◽

10.1017/s0031182000007423 ◽

2000 ◽

Vol 121 (S1) ◽

pp. S147-S160 ◽

Cited By ~ 63

Author(s):

J. HORTON ◽

C. WITT ◽

E.A. OTTESEN ◽

J.K. LAZDINS ◽

D.G. ADDISS ◽

...

Keyword(s):

Lymphatic Filariasis ◽

Wuchereria Bancrofti ◽

The Philippines ◽

Data Set ◽

Direct Observations ◽

National Public Health ◽

Total Data ◽

Drug Regimens ◽

At Risk Populations ◽

Health Programmes

This review of the safety of the co-administration regimens to be used in programmes to eliminate lymphatic filariasis (albendazole+ivermectin or albendazole+diethylcarbamazine [DEC]) is based on 17 studies conducted in Sri Lanka, India, Haiti, Ghana, Tanzania, Kenya, Ecuador, the Philippines, Gabon, Papua New Guinea, and Bangladesh. The total data set comprises 90635 subject exposures and includes individuals of all ages and both genders. Results are presented for hospital-based studies, laboratory studies, active surveillance of microfilaria-positive and microfilaria-negative individuals, and passive monitoring in both community-based studies and mass treatment programmes of individuals treated with albendazole (n=1538), ivermectin (9822), DEC (576), albendazole+ivermectin (7470), albendazole+DEC (69020), or placebo (1144). The most rigorous monitoring, which includes haematological and biochemical laboratory parameters pre- and post-treatment, provides no evidence that consistent changes are induced by any treatment; the majority of abnormalities appear to be sporadic, and the addition of albendazole to either ivermectin or DEC does not increase the frequency of abnormalities. Both DEC and ivermectin show, as expected, an adverse event profile compatible with the destruction of microfilariae. The addition of albendazole to either single-drug treatment regimen does not appear to increase the frequency or intensity of events seen with these microfilaricidal drugs when used alone. Direct observations indicated that the level of adverse events, both frequency and intensity, was correlated with the level of microfilaraemia. In non microfilaraemic individuals, who form 80–90% of the ‘at risk’ populations to be treated in most national public health programmes to eliminate lymphatic filariasis (LF), the event profile with the compounds alone or in combination does not differ significantly from that of placebo. Data on the use of ivermectin+albendazole in areas either of double infection (onchocerciasis and LF), or of loiais (with or without concurrent LF) are still inadequate and further studies are needed. Additional data are also recommended for populations infected with Brugia malayi, since most data thus far derive from populations infected with Wuchereria bancrofti.

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Transmission Dynamics of Lymphatic Filariasis: A Mathematical Approach

ISRN Biomathematics ◽

10.5402/2012/930130 ◽

2012 ◽

Vol 2012 ◽

pp. 1-9 ◽

Cited By ~ 4

Author(s):

C. P. Bhunu ◽

S. Mushayabasa

Keyword(s):

Numerical Simulations ◽

Lymphatic Filariasis ◽

Reproduction Number ◽

Epidemiological Model ◽

Transmission Dynamics ◽

Effective Control ◽

Mathematical Approach

An epidemiological model for the spread of lymphatic filariasis, a mosquito-borne infection, is developed and analysed. The epidemic thresholds known as the reproduction number and equilibria for the model are determined and stabilities analysed. Results from the analysis of the reproduction number suggest that treatment will somehow contribute to a reduction in lymphatic filariasis cases, but what it does not show is the magnitude of the reduction, a part answered by the numerical simulations. Numerical simulations show that even when all lymphatic filariasis cases displaying elephantiasis symptoms are put on treatment it will not be able to eradicate the disease. This result suggests that effective control of lymphatic filariasis may lie in treatment for those displaying symptoms as well as chemoprophylaxis for the exposed.

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An assessment of mosquito collection techniques for xenomonitoring of anopheline-transmitted Lymphatic Filariasis in Ghana

Parasitology ◽

10.1017/s0031182018000938 ◽

2018 ◽

Vol 145 (13) ◽

pp. 1783-1791 ◽

Cited By ~ 8

Author(s):

Millicent Opoku ◽

Corrado Minetti ◽

Worlasi D. Kartey-Attipoe ◽

Sampson Otoo ◽

Joseph Otchere ◽

...

Keyword(s):

Lymphatic Filariasis ◽

Close Contact ◽

Wuchereria Bancrofti ◽

Northern Region ◽

Trapping Efficiency ◽

Mosquito Collection ◽

Control And Prevention ◽

Specific Species ◽

High Degree ◽

Collection Methods

AbstractMonitoring vectors is relevant to ascertain transmission of lymphatic filariasis (LF). This may require the best sampling method that can capture high numbers of specific species to give indication of transmission. Gravid anophelines are good indicators for assessing transmission due to close contact with humans through blood meals. This study compared the efficiency of an Anopheles gravid trap (AGT) with other mosquito collection methods including the box and the Centres for Disease Control and Prevention gravid, light, exit and BioGent-sentinel traps, indoor resting collection (IRC) and pyrethrum spray catches across two endemic regions of Ghana. The AGT showed high trapping efficiency by collecting the highest mean number of anophelines per night in the Western (4.6) and Northern (7.3) regions compared with the outdoor collection methods. Additionally, IRC was similarly efficient in the Northern region (8.9) where vectors exhibit a high degree of endophily. AGT also showed good trapping potential for collecting Anopheles melas which is usually difficult to catch with existing methods. Screening of mosquitoes for infection showed a 0.80–3.01% Wuchereria bancrofti and 2.15–3.27% Plasmodium spp. in Anopheles gambiae. The AGT has shown to be appropriate for surveying Anopheles populations and can be useful for xenomonitoring for both LF and malaria.

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