Eosinophils, basophils and myeloid-derived suppressor cells in chronic Loa loa infection and its treatment in an endemic setting.

BACKGROUND: Chronic infection by Loa loa remains an unsolved immunological paradox. Despite harboring subcutaneously migrating adult worms and often high densities of microfilariae, most patients experience only relatively mild symptoms, yet microfilaricidal treatment can trigger life-threatening inflammation. Here, we investigated innate cell populations hypothesized to play a role in these two faces of the disease, in an endemic population in Gabon. METHODOLOGY/PRINCIPAL FINDINGS: We analyzed numbers and activation of eosinophils and basophils, as well as myeloid-derived suppressor cell (MDSC) subsets and associated circulating cytokine levels by flow cytometry in sex- and age-matched L. loa-uninfected (LL-), -amicrofilaraemic (MF-) and -microfilaraemic (MF+) individuals (n = 42), as well as microfilaraemic individuals treated with albendazole (n = 26). The percentage of eosinophils was lower in LL- (3.0%) than in the combined L. loa-infected population, but was similar in MF+ (13.1%) and MF- (12.3%). Upon treatment of MF+, eosinophilia increased from day 0 (17.2%) to day 14 (24.8%) and had decreased below baseline at day 168 (6.3%). Expression of the eosinophil activation marker CD123 followed the same pattern as the percentage of eosinophils, while the inverse was observed for CD193 and to some extent CD125. Circulating IL-5 levels after treatment followed the same pattern as eosinophil dynamics. Basophil numbers did not differ between infection states but increased after treatment of MF+. We did not observe differences in MDSC numbers between infection states or upon treatment. CONCLUSIONS/SIGNIFICANCE: We demonstrate that both chronic infection and treatment of L. loa microfilaraemia are associated with eosinophil circulation and distinct phenotypical activation markers that might contribute to inflammatory pathways in this setting. In this first ever investigation into MDSC in L. loa infection, we found no evidence for their increased presence in chronic loiasis, suggesting that immunomodulation by L. loa is induced through other pathways.

Geostatistical modelling enables efficient safety assessment for mass drug administration with ivermectin in Loa loa endemic areas through a combined antibody and LoaScope testing strategy for elimination of onchocerciasis.

The elimination of onchocerciasis through community-based Mass Drug Administration (MDA) of ivermectin (Mectizan) is hampered by co-endemicity of Loa loa, as individuals who are highly co-infected with Loa loa parasites can suffer serious and occasionally fatal neurological reactions from the drug. The test-and-not-treat strategy of testing all individuals participating in MDA has some operational constraints including the cost and limited availability of LoaScope diagnostic tools. As a result, a Loa loa Antibody (Ab) Rapid Test was developed to offer a complementary way of determining the prevalence of loiasis. We develop a joint geostatistical modelling framework for the analysis of Ab and Loascope data to delineate whether an area is safe for MDA. Our results support the use of a two-stage strategy, in which Ab testing is used to identify areas that, with acceptably high probability, are safe or unsafe for MDA, followed by Loascope testing in areas whose safety status is uncertain. This work therefore contributes to the global effort towards the elimination of onchocerciasis as a public health problem by potentially reducing the time and cost required to establish whether an area is safe for MDA.

Optimization and evaluation of the Esperanza Window Trap to reduce biting rates of Simulium damnosum sensu lato in Northern Uganda.

BACKGROUND: Onchocerciasis, or river blindness, has historically been an important cause of blindness, skin disease and economic disruption in Africa and the Americas. It is caused by the filarial parasite Onchocerca volvulus, which is transmitted by black flies in the genus Simulium. Over the past decade, several international programs have been formed to control, or more recently eliminate onchocerciasis, using mass drug administration (MDA) of ivermectin. However, in many areas of Africa (particularly those which are endemic for the eyeworm, Loa loa, or where vector densities are very high) ivermectin MDA alone will not be sufficient to achieve elimination. In these situations, additional interventions may be necessary. METHODOLOGY/PRINCIPAL FINDINGS: The Esperanza Window trap (EWT), a simple trap originally developed to replace human landing collections for entomological surveillance of O. volvulus transmission was optimized, resulting in a 17-fold improvement in trap performance. The optimized trap was tested in trials in schools and in agricultural fields to determine if it could reduce vector biting locally. The traps resulted in a 90% reduction in biting in the school setting. In the field setting, results varied. In one location, the traps reduced biting by roughly 50%, while in a separate trial, the traps did not significantly reduce the biting rate. Examination of the two settings suggested that trap placement may be critical to their success. CONCLUSIONS/SIGNIFICANCE: These results suggest that the optimized EWT might be capable of reducing local vector black fly biting in areas commonly frequented by residents. Together with other recently developed methods of community directed vector control, the traps may augment ivermectin MDA, bringing the goal of onchocerciasis elimination within reach in much of Africa.

Mouse models of Loa loa.

Elimination of the helminth disease, river blindness, remains challenging due to ivermectin treatment-associated adverse reactions in loiasis co-infected patients. Here, we address a deficit in preclinical research tools for filarial translational research by developing Loa loa mouse infection models. We demonstrate that adult Loa loa worms in subcutaneous tissues, circulating microfilariae (mf) and presence of filarial biomarkers in sera occur following experimental infections of lymphopenic mice deficient in interleukin (IL)-2/7 gamma-chain signaling. A microfilaraemic infection model is also achievable, utilizing immune-competent or -deficient mice infused with purified Loa mf. Ivermectin but not benzimidazole treatments induce rapid decline (>90%) in parasitaemias in microfilaraemic mice. We identify up-regulation of inflammatory markers associated with allergic type-2 immune responses and eosinophilia post-ivermectin treatment. Thus, we provide validation of murine research models to identify loiasis biomarkers, to counter-screen candidate river blindness cures and to interrogate the inflammatory etiology of loiasis ivermectin-associated adverse reactions.

Comparison of different drug regimens for the treatment of loiasis-A TropNet retrospective study.

BACKGROUND: Loa loa infection is endemic in limited areas of West-Central Africa. Loiasis has been associated with excess mortality, but clinical studies on its treatment are scant, particularly outside endemic areas, due to the rarity of cases diagnosed. METHODOLOGY/PRINCIPAL FINDINGS: With this retrospective TropNet (European Network for Tropical Medicine and Travel Health) study, we aimed at outlining the treatment schedules followed by different reference centers for tropical medicine across Europe. We gathered information about 238 cases of loiasis, 165 of which had follow up data. The regimens followed by the different centers were heterogeneous. The drugs most frequently administered were: diethylcarbamazine alone (74/165, 45.1%), ivermectin alone (41/165, 25%), albendazole + ivermectin (21/164, 11.6%), ivermectin + diethylcarbamazine (16/165, 9.7%). CONCLUSIONS/SIGNIFICANCE: The management of loiasis substantially differs across specialized travel clinics in Europe. These discrepancies could be due to different local protocols as well as to (un)availability of the drugs. An harmonization of clinical protocols for the treatment of loiasis would be suggested across reference centers for tropical medicine in Europe.

Removal of adult subconjunctival Loa loa amongst urban dwellers in Nigeria.

Loiasis is a neglected tropical disease caused by infection with the filarial parasite Loa loa. It is a disease considered by many to be benign. Several reports of trans border importation of the Loa loa worm amongst immigrants and visitors from endemic regions of the world exist. In most cases an adult subconjunctival worm is removed from the patient. An interventional case series is reported and examines the practice of removal of subconjunctival adult Loa loa worms amongst urban dwellers in Nigeria. Four cases of ocular loiasis seen amongst urban dwellers in Nigeria exemplify the different presentations and removal methods of the subconjunctival adult worm. There were 2 males and 2 females aged 35years, 23years, 25years and 30years respectively. Each patient gave a history of having been raised in a rural community in childhood years, during which they were exposed to streams and muddy farm land; and then migrated to the urban community in later years. They all present with the finding of a subconjunctival adult worm, which was successfully removed and identified to be Loa loa. There are more urban dwellers in Nigeria who present with symptoms of foreign body sensation that may be related to the manifestation of a subconjunctival worm and are not recognized. This is because the emphasis on this disease has erstwhile been on the rural, village dwellers and not on urban dwellers. Eye care practitioners working in urban centers need to be aware of the possibility of this presentation, and be ready to remove any subconjunctival worm when it presents.

Increasing evidence of low lymphatic filariasis prevalence in high risk Loa loa areas in Central and West Africa: a literature review.

In West and Central Africa, there is a need to establish the prevalence of Wuchereria bancrofti in areas that are co-endemic for Loa loa, in order to implement the appropriate strategies to scale-up interventions for the elimination of lymphatic filariasis (LF). Due to the risk of severe adverse events (SAEs) to ivermectin in individuals with high L. loa microfilaraemia, the current strategy recommended by the World Health Organization (WHO) is twice yearly mass drug administration (MDA) with albendazole, supplemented by vector control targeting the Anopheles vectors. Defining W. bancrofti prevalence in areas co-endemic with L. loa is complicated by the cross-reactivity of rapid diagnostic immunochromatographic card tests (ICT), widely used for LF mapping, in individuals with high L. loa microfilaraemia. This has probably resulted in the overestimation of LF prevalence, triggering the implementation of MDA strategies, which may be unnecessary and wasteful of the limited resources for elimination programme implementation. Here we review the literature and present historical evidence, which uniformly highlight low or no prevalence of W. bancrofti infection and/or clinical LF cases across five Central African countries, in more than 30 different geographical areas covering 280 individual sites and > 22,000 individuals tested within high risk L. loa areas. This highlights the very limited information available on LF prevalence in L. loa areas, and potentially has major policy implications, which could shift the focus towards revised mapping criteria to verify low or no W. bancrofti prevalence in high risk L. loa areas. In this situation, revising the current WHO strategy from MDA, to focus more on ensuring high and effective vector control, through insecticide treated/long-lasting impregnated bednets (ITNs/LLINs), integration of point-of-care test-and-treat options into health systems, and consolidating closer links with the malaria control programme may be a more effective and appropriate use of the limited resources and drug donations available for LF elimination.

Evaluation of in vitro culture systems for the maintenance of microfilariae and infective larvae of Loa loa.

BACKGROUND: Suitable and scalable in vitro culture conditions for parasite maintenance are needed to foster drug research for loiasis, one of the neglected tropical diseases which has attracted only limited attention over recent years, despite having important public health impacts. The present work aims to develop adequate in vitro culture systems for drug screening against both microfilariae (mf) and infective third-stage larvae (L3) of Loa loa. METHODS: In vitro culture conditions were evaluated by varying three basic culture media: Roswell Park Memorial Institute (RPMI-1640), Dulbecco's modified Eagle's medium (DMEM) and Iscove's modified Dulbecco's medium (IMDM); four sera/proteins: newborn calf serum (NCS), foetal bovine serum (FBS), bovine serum albumin (BSA) and the lipid-enriched BSA (AlbuMax® II, ALB); and co-culture with the Monkey Kidney Epithelial Cell line (LLC-MK2) as a feeder layer. The various culture systems were tested on both mf and L3, using survival (% motile), motility (T90 = mean duration (days) at which at least 90% of parasites were fully active) and moulting rates of L3 as the major criteria. The general linear model regression analysis was performed to assess the contribution of each variable on the viability of Loa loa L3 and microfilarie. All statistical tests were performed at 95% confidence interval. RESULTS: Of the three different media tested, DMEM and IMDM were the most suitable sustaining the maintenance of both L. loa L3 and mf. IMDM alone could sustain L3 for more than 5 days (T90 = 6.5 ± 1.1 day). Serum supplements and LLC-MK2 co-cultures significantly improved the survival of parasites in DMEM and IMDM. In co-cultures with LLC-MK2 cells, L. loa mf were maintained in each of the three basic media (T90 of 16.4-19.5 days) without any serum supplement. The most effective culture systems promoting significant moulting rate of L3 into L4 (at least 25%) with substantial maintenance time were: DMEM + BSA, DMEM + NCS, DMEM-AlbuMax®II, DMEM + FBS all in co-culture with LLC-MK2, and IMDM + BSA (1.5%), DMEM + FBS (10%) and DMEM + NCS (5%) without feeder cells. DMEM + 1% BSA in co-culture scored the highest moulting rate of 57 of 81 (70.37%). The factors that promoted L. loa mf viability included feeder cells (ß = 0.490), both IMDM (ß = 0.256) and DMEM (ß = 0.198) media and the protein supplements NCS (ß = 0.052) and FBS (ß = 0.022); while for L. loa L3, in addition to feeder cells (ß = 0.259) and both IMDM (ß = 0.401) and DMEM (ß = 0.385) media, the protein supplements BSA (ß = 0.029) were found important in maintaining the worm motility. CONCLUSIONS: The findings from this work display a range of culture requirements for the maintenance of Loa loa stages, which are suitable for developing an effective platform for drug screening.

Heterogeneity in the in vitro susceptibility of Loa loa microfilariae to drugs commonly used in parasitological infections.

BACKGROUND: Co-infection with loiasis remains a potential problem in control programs targeting filarial infections. The effects of many anti-parasitic drugs often administered to Loa loa infected people are not well documented. This study compared the in vitro activity of several of these drugs on the viability of L. loa microfilariae (mf). METHODS: Human strain L. loa mf were isolated from baboon blood using iso-osmotic Percoll gradient, and cultured in RPMI 1640/10% FBS with antimalarial drugs (mefloquine, amodiaquine, artesunate, chloroquine and quinine), anthelmintics (ivermectin, praziquantel, flubendazole and its reduced and hydrolyzed metabolites), two potential trypanocidal agents (fexinidazole and Scynexis-7158) and the anticancer drug imatinib. The drug concentrations used varied between 0.156 µg/ml and 10 µg/ml. Mf motility (CR50 = 50% immotility) and a metabolic viability assay (MTT) were used to assess the effects of these drugs on the parasites. RESULTS: Mf in control cultures showed only a slight reduction in motility after 5 days of culture. Active inhibition of Loa loa motility was seen with mefloquine and amodiaquine (CR50 values of 3.87 and 4.05 µg/ml, respectively), immobilizing > 90% mf within the first 24 hours: mefloquine killed the mf after 24 hours of culture at concentrations ≥ 5 µg/ml. SCYX-7158 also induced a concentration-dependent reduction in mf motility, with > 50% reduction in mf motility seen after 5 days at 10 µg/ml. The anticancer drug imatinib reduced mf motility at 10 µg/ml from the first day of incubation to 55% by day 5, and the reduction in motility was concentration-dependent. Praziquantel and fexinidazole were inactive, and FLBZ and its metabolites, as well as ivermectin at concentrations > 5 µg/ml, had very minimal effects on mf motility over the first 4 days of culture. CONCLUSIONS: The considerable action of the anti-malarial drugs mefloquine and amodiaquine on Loa mf in vitro highlights the possibility of repurposing the existing anti-infectious agents for the development of drugs against loiasis. The heterogeneity in the activity of anti-parasitic agents on Loa loa mf supports the need for further investigation using animal models of loiasis.

The Population Biology and Transmission Dynamics of Loa loa.

Endemic to Central Africa, loiasis - or African eye worm (caused by the filarial nematode Loa loa) - affects more than 10 million people. Despite causing ocular and systemic symptoms, it has typically been considered a benign condition, only of public health relevance because it impedes mass drug administration-based interventions against onchocerciasis and lymphatic filariasis in co-endemic areas. Recent research has challenged this conception, demonstrating excess mortality associated with high levels of infection, implying that loiasis warrants attention as an intrinsic public health problem. This review summarises available information on the key parasitological, entomological, and epidemiological characteristics of the infection and argues for the mobilisation of resources to control the disease, and the development of a mathematical transmission model to guide deployment of interventions.

Loa loa vectors Chrysops spp.: perspectives on research, distribution, bionomics, and implications for elimination of lymphatic filariasis and onchocerciasis.

BACKGROUND: Loiasis is a filarial disease caused Loa loa. The main vectors are Chrysops silacea and C. dimidiata which are confined to the tropical rainforests of Central and West Africa. Loiasis is a mild disease, but individuals with high microfilaria loads may suffer from severe adverse events if treated with ivermectin during mass drug administration campaigns for the elimination of lymphatic filariasis and onchocerciasis. This poses significant challenges for elimination programmes and alternative interventions are required in L. loa co-endemic areas. The control of Chrysops has not been considered as a viable cost-effective intervention; we reviewed the current knowledge of Chrysops vectors to assess the potential for control as well as identified areas for future research. RESULTS: We identified 89 primary published documents on the two main L. loa vectors C. silacea and C dimidiata. These were collated into a database summarising the publication, field and laboratory procedures, species distributions, ecology, habitats and methods of vector control. The majority of articles were from the 1950-1960s. Field studies conducted in Cameroon, Democratic Republic of Congo, Equatorial Guinea, Nigeria and Sudan highlighted that C. silacea is the most important and widespread vector. This species breeds in muddy streams or swampy areas of forests or plantations, descends from forest canopies to feed on humans during the day, is more readily adapted to human dwellings and attracted to wood fires. Main vector targeted measures proposed to impact on L. loa transmission included personal repellents, household screening, indoor residual spraying, community-based environmental management, adulticiding and larviciding. CONCLUSIONS: This is the first comprehensive review of the major L. loa vectors for several decades. It highlights key vector transmission characteristics that may be targeted for vector control providing insights into the potential for integrated vector management, with multiple diseases being targeted simultaneously, with shared human and financial resources and multiple impact. Integrated vector management programmes for filarial infections, especially in low transmission areas of onchocerciasis, require innovative approaches and alternative strategies if the elimination targets established by the World Health Organization are to be achieved.

Loiasis in US Traveler Returning from Bioko Island, Equatorial Guinea, 2016.

The filarial parasite Loa loa overlaps geographically with Onchocera volvulus and Wuchereria bancrofti filariae in central Africa. Accurate information regarding this overlap is critical to elimination programs targeting O. volvulus and W. bancrofti. We describe a case of loiasis in a traveler returning from Bioko Island, Equatorial Guinea, a location heretofore unknown for L. loa transmission.

Using Community-Level Prevalence of Loa loa Infection to Predict the Proportion of Highly-Infected Individuals: Statistical Modelling to Support Lymphatic Filariasis and Onchocerciasis Elimination Programs.

Lymphatic Filariasis and Onchocerciasis (river blindness) constitute pressing public health issues in tropical regions. Global elimination programs, involving mass drug administration (MDA), have been launched by the World Health Organisation. Although the drugs used are generally well tolerated, individuals who are highly co-infected with Loa loa are at risk of experiencing serious adverse events. Highly infected individuals are more likely to be found in communities with high prevalence. An understanding of the relationship between individual infection and population-level prevalence can therefore inform decisions on whether MDA can be safely administered in an endemic community. Based on Loa loa infection intensity data from individuals in Cameroon, the Republic of the Congo and the Democratic Republic of the Congo we develop a statistical model for the distribution of infection levels in communities. We then use this model to make predictive inferences regarding the proportion of individuals whose parasite count exceeds policy-relevant levels. In particular we show how to exploit the positive correlation between community-level prevalence and intensity of infection in order to predict the proportion of highly infected individuals in a community given only prevalence data from the community in question. The resulting prediction intervals are not substantially wider, and in some cases narrower, than the corresponding binomial confidence intervals obtained from data that include measurements of individual infection levels. Therefore the model developed here facilitates the estimation of the proportion of individuals highly infected with Loa loa using only estimated community level prevalence. It can be used to assess the risk of rolling out MDA in a specific community, or to guide policy decisions.

A Step Toward Eradication of Human Filariases in Areas Where Loa Is Endemic.

Mass drug administration (MDA) programs have achieved remarkable success in limiting the pathology and transmission of the human parasitic infections onchocerciasis and lymphatic filariasis. The full implementation of MDA campaigns for filariasis elimination has been stymied by the unacceptable incidence of severe adverse events observed following drug treatment of a subset of individuals who harbor high loads of Loa loa microfilaria. Extending MDA strategies to regions where loiasis is coendemic could be done confidently if a simple, inexpensive, and rapid diagnostic method was available that could accurately identify individuals who have L. loa microfilarial loads above the risk threshold and could thus be excluded from treatment. A recent paper in mBio reports the discovery of an antigen unique to L. loa microfilaria that can be detected in blood and urine and may form the basis for such an assay. Further work will reveal whether this discovery will smooth the path to achieve filariasis eradication.

Filarial infection modulates the immune response to Mycobacterium tuberculosis through expansion of CD4+ IL-4 memory T cells.

Exaggerated CD4(+) T helper 2-specific cytokine producing memory T cell responses developing concomitantly with a T helper 1 response might have a detrimental role in immunity to infection caused by Mycobacterium tuberculosis. To assess the dynamics of Ag-specific memory T cell compartments in the context of filarial infection, we used multiparameter flow cytometry on PBMCs from 25 microfilaremic filarial-infected (Inf) and 14 filarial-uninfected (Uninf) subjects following stimulation with filarial Ag (BmA) or with the M. tuberculosis-specific Ag culture filtrate protein-10 (CFP-10). Our data demonstrated that the Inf group had a marked increase in BmA-specific CD4(+)IL-4(+) cells (median net frequency compared with baseline [Fo] = 0.09% versus 0.01%; p = 0.038) but also to CFP-10 (Fo = 0.16% versus 0.007%; p = 0.04) and staphylococcal enterotoxin B (Fo = 0.49% versus 0.26%; p = 0.04). The Inf subjects showed a BmA-specific expansion of CD4(+)CD45RO(+)IL-4(+) producing central memory (TCM, CD45RO(+)CCR7(+)CD27(+); Fo = 1.1% versus 0.5%; p = 0.04) as well as effector memory (TEM, CD45RO(+)CCR7(-)CD27(-); Fo = 1.5% versus 0.2%; p = 0.03) with a similar but nonsignificant response to CFP-10. In addition, there was expansion of CD4(+)IL-4(+)CD45RA(+)CCR7(+)CD27(+) (naive-like) in Inf individuals compared with Uninf subjects. Among Inf subjects with definitive latent tuberculosis, there were no differences in frequencies of IL-4-producing cells within any of the memory compartments compared with the Uninf group. Our data suggest that filarial infection induces Ag-specific, exaggerated IL-4 responses in distinct T cell memory compartments to M. tuberculosis-specific Ags, which are attenuated in subjects who are able to mount a delayed type hypersensitivity reaction to M. tuberculosis.

CD4+CD25hiFOXP3+ cells in cord blood of neonates born from filaria infected mother are negatively associated with CD4+Tbet+ and CD4+RORγt+ T cells.

BACKGROUND: Children who have been exposed in utero to maternal filarial infection are immunologically less responsive to filarial antigens, have less pathology, and are more susceptible to acquire infection than offspring of uninfected mothers. Moreover children from filaria infected mothers have been shown to be less responsive to vaccination as a consequence of an impairment of their immune response. However, it is not well known how in utero exposure to parasite antigens affects cellular immune responses. METHODOLOGY: Here, 30 pregnant women were examined for the presence of microfilaria of Loa loa and Mansonella perstans in peripheral blood. At delivery, cord blood mononuclear cells (CBMC) were obtained and the CD4+T cells were phenotyped by expression of the transcription factors Tbet, RORγt, and FOXP3. RESULTS: No significant difference was observed between newborns from infected versus uninfected mothers in the frequencies of total CD4+T cells and CD4+T cells subsets including CD4+Tbet+, CD4+RORγt+ T and CD4+CD25hiFOXP3+ T cells. However, there was a negative association between CD4+CD25hiFOXP3+T cells and CD4+Tbet+ as well as CD4+RORγt+ T cells in the infected group only (B = -0.242, P = 0.002; B = -0.178, P = 0.013 respectively). CONCLUSION: Our results suggest that filarial infection during pregnancy leads to an expansion of functionally active regulatory T cells that keep TH1 and TH17 in check.

The human parasite Loa loa in cytokine and cytokine receptor gene knock out BALB/c mice: survival, development and localization.

BACKGROUND: Immunological mechanisms involved in the survival and development of human filarial species in the vertebrate host are poorly known due to the lack of suitable experimental models. In order to understand the role of cytokines in the survival and development of filarial larvae in the vertebrate host, we infected different strains of BALB/c mice deficient in a number of cytokine or cytokine receptor genes with Loa loa. The survival and development of larvae were monitored. METHODS: BALB/c mice genetically deficient in IL-4R, IFN-γ, IFN-γ/IL-5, IL-5, and IL-4R/IL-5 cytokine or cytokine receptor genes were infected with a human strain of L. loa and necropsies were performed at different time intervals up to 70 days post infection to monitor the survival and development of L. loa larvae. The larvae were teased out of the skin, muscles, peritoneal and pleural cavities, heart and lung tissues. The length and width of the recovered larvae were measured to assess their growth. RESULTS: In mice deficient for IL-4R, IFN-γ, IFN-γ/IL-5, IL-5 and IL-4R/IL-5, the larvae survived up to 5, 20, 40, 50 and 70 days respectively. Worms recovered 70 days post infection in IL-4R/IL-5 DKO mice were young adults and measured 10.12 mm in length and 0.1 mm in width. Overall, 47% of larvae were recovered from subcutaneous tissues, 40% from muscles, 6% from the peritoneal cavity and 4% from the pleural cavity, lungs and heart. CONCLUSION: L. loa exhibits a differential survival and development in different strains of cytokine or cytokine receptor gene knockout mice with IL-4R and IL-5 playing critical roles in the host resistance to L. loa infection. The knock out BALB/c mouse therefore represents a useful tool to explore the key effectors of adaptive immunity involved in the killing of the L. loa parasite in a mammal host.

Loa loa microfilarial periodicity in ivermectin-treated patients: comparison between those developing and those free of serious adverse events.

The main risk factor of post-ivermectin serious adverse events (SAEs) is the presence of a high Loa loa microfilaremia. However, the majority of patients with such high loads do not develop SAEs, suggesting that co-factors may be involved. An infection with simian Loa parasites, whose microfilariae show a nocturnal periodicity, might be such a co-factor. The periodicity of Loa microfilariae was compared, using cosinor methodology, in 4 patients who had developed a post-ivermectin neurologic SAE, 4 patients who had experienced a non-neurologic SAE, and 14 control individuals. The periodicity was similar in all three groups, with a peak of microfilaremia occurring between 12:30 and 2:00 PM. The results of this study, which for the first time characterizes the periodicity of Loa microfilariae mathematically, suggest that post-ivermectin SAEs are not related to an infection with a Loa simian strain.

The migration and localization of Loa loa infective and fourth-stage larvae in normal and immunosuppressed rodents.

The migration and localization of the human filarial parasite Loa loa in laboratory mice (BALB/c and Swiss) and jirds (Meriones unguiculatus) was investigated. The rodents, either left immunocompetent or immunosuppressed with hydrocortisone, were each inoculated subcutaneously or intraperitoneally with 50 or 200 infective, third-stage larvae (L(3)) of L. loa. Groups of the rodents were killed at various times post-infection, up to day 40, to enable histological studies and permit developing larvae to be recovered. Larvae survived and developed for only 1 week in the immunocompetent rodents but for a mean of 3 weeks in the immunosuppressed. Most of the larvae were found in the subcutaneous tissues (81.9%), peritoneal cavity (14.9%), pleural cavity (1.8%) or the lungs and heart (1.3%) and none was detected in the spleen, kidney, intestine, liver or pancreas. Localization of the larvae appeared unaffected by the site of inoculation, the rodent species or strain, or the dose of L(3) used. The recovery of larvae (as a percentage of the number inoculated) was better among the rodents inoculated with 50 L(3) each than among those given four times as many L(3). The results of the histological studies not only confirmed the presence of larvae in the subcutaneous tissue (72.5%), muscles (11.7%) and peritoneal and pleural cavities (7.8%) of the infected rodents but also revealed worms in the lymphatic vessels of the mesentery and spinal cord (7.3%). These results indicate that most L. loa L(3) inoculated into a mammalian host localize in the cutaneous sites and that only a small proportion of them might migrate, using the lymphatic system, into the internal organs. The observation of migrating L. loa larvae in the lymphatic vessel of the meningeal envelope of the spinal cord, albeit in an experimental host, may explain why, in areas where human loiasis is endemic, neurological manifestations occasionally occur in those with L. loa infections.