Onchocerciasis in endemic and nonendemic populations: differences in clinical presentation and immunologic findings

Chorioretinitis among Immigrant and Travellers. Comment on Mansour et al. Presumed Onchocerciasis Chorioretinitis Spilling over into North America, Europe and Middle East. Diagnostics 2023, 13, 3626

We read, with interest, the paper by Mansour et al [...].

The design and development of a study protocol to investigate Onchocerca volvulus, Loa loa and Mansonella perstans-mediated modulation of the metabolic and immunological profile in lean and obese individuals in Cameroon

BACKGROUND

Life-style metabolic diseases are steadily rising, not only in developed countries, but also in low- and middle-income countries, presenting a global health problem. Metabolic disorders like type 2 diabetes and cardiovascular diseases are among the ten leading causes of death defined by the WHO in 2019. Results from animal and observational human studies suggest a connection between the decline in human helminth infections and rise of life-style-associated metabolic diseases in developing regions. This trial was designed to investigate filarial infections and their impact on metabolic diseases in Cameroon. We hypothesize that the induction of regulatory immune responses during filarial infection reduces obesity-induced low-grade inflammatory immune responses and thereby improves metabolic parameters, whereas anthelmintic treatment abolishes this protective effect.

METHODS/DESIGN

Participants infected with Mansonella perstans, Onchocerca volvulus and/or Loa loa being lean (BMI <25), overweight (BMI >25 and <30) or clinically obese (BMI ≥30) from Littoral regions of Cameroon will be evaluated for their parasitological, immunological, metabolic and biochemical profile before and after treatment of their parasitic infections. Anthropomorphic measurements and a detailed questionnaire will complement our analysis. The investigation will assess blood immune cell populations, serum adipokines and cytokines that could be influenced by the parasite infection and/or metabolic diseases. Further, parameters like blood glucose, homeostatic model assessment of insulin resistance (HOMA-IR), circulating lipids and circulating makers of liver function will be monitored. Parameters will be assessed before treatment, 12 and 18 months after treatment.

CONCLUSION

The focus of this study is to obtain a comprehensive metabolic profile of the participants in rural areas of Cameroon and to investigate the relationship between filarial immunomodulation and metabolic diseases. This study will elucidate the effect of anti-filarial treatment on the metabolic and immunological parameters that partake in the development of insulin resistance, narrowing in on a potential protective effect of filarial infections on metabolic diseases.

TRIAL REGISTRATION

doi.org/10.1186/ISRCTN43845142, ISRCTN43845142 February 2020 Trial title Effects of filarial parasite infection on type 2 diabetes Issue date: 27.10.22, V.1.

Differences in the Clinical and Laboratory Features of Imported Onchocerciasis in Endemic Individuals and Temporary Residents

Many parasitic infections have different presenting features in endemic individuals (ENDs) and immunologically naive temporary residents (TRs). Temporary residents with loiasis often display acute symptoms and hypereosinophilia, in contrast to a parasite-induced subclinical state in chronically infected ENDs. Few studies have examined differences in ENDs and TRs infected with the related filarial parasite Onchocerca volvulus. We identified 40 TRs and 36 ENDs with imported onchocerciasis at the National Institutes of Health between 1976 and 2016. All study subjects received an extensive pretreatment medical history, physical examination, and laboratory investigations. We performed additional parasite-specific serologic testing on stored patient sera. Asymptomatic infection occurred in 12.5% of TRs and no ENDs (P = 0.06). Papular dermatitis was more common in TRs (47.5% versus 2.7%, P < 0.001), whereas more pigmentation changes occurred in ENDs (41.7% versus 15%, P = 0.01). Only endemic patients reported visual disturbance (13% versus 0%, P = 0.03). One TR (3.3%) had onchocercal eye disease, compared with 22.6% of ENDs (P = 0.053). Absolute eosinophil counts (AECs) were similar in ENDs and TRs (P = 0.5), and one-third of subjects had a normal AEC. Endemic individuals had higher filarial-specific IgG4 and were more likely to be positive for IgG4 antibodies to Ov-16. Temporary residents and ENDs with imported O. volvulus infection presented with different dermatologic manifestations; ocular involvement occurred almost exclusively in ENDs. Unlike Loa loa, clinical differences appear not to be eosinophil-mediated and may reflect chronicity, intensity of infection, or the presence of Wolbachia in O. volvulus.

Imported onchocerciasis in migrants and travelers

PURPOSE OF REVIEW

With increasing international travel and mass global population migration, clinicians in nonendemic countries must be familiar with imported neglected tropical diseases including onchocerciasis, which is commonly known as 'river blindness'.

RECENT FINDINGS

Imported onchocerciasis manifests differently in travelers compared with migrants from endemic areas and is likely underdiagnosed in both groups. Recent clinical studies confirm that eosinophilia is not a sensitive marker for Onchocerca volvulus, with one-third of patients having a normal eosinophil count. Novel diagnostics measuring antibodies to multiple recombinant O. volvulus antigens maintain a high sensitivity while improving specificity compared with conventional pan-filarial serologic testing. A 6-week course of doxycycline has macrofilaricidal activity through Wolbachia depletion and may be useful in nonendemic areas in addition to standard serial ivermectin.

SUMMARY

Recent studies characterizing distinct clinical presentations in travelers and migrants may enable clinicians to better recognize imported onchocerciasis. Although novel diagnostics have improved specificity, most remain restricted to tropical disease reference laboratories and to date there is no marker of cure. Prolonged doxycycline treatment may reduce the need for serial ivermectin, though more potent short-course macrofilaricidal drugs are being developed.

Dermatological manifestations in onchocerciasis: A retrospective study of 400 imported cases

INTRODUCTION

Onchocerciasis is caused by Onchocerca volvulus and mainly leads to pruritus and skin and visual disorders, including blindness. Seventeen million people are infected in 38 countries; 31 of these are in sub-Saharan Africa, six in Latin America and one on the Arabian Peninsula. More than 99% of cases occur in sub-Saharan Africa where 120 million people are at risk of infection. Eye disorders have been well-documented; however, skin disorders have not been described accurately. The objective of our study was to describe the epidemiology, main skin manifestations and treatment of imported onchocerciasis.

MATERIAL AND METHODS

A retrospective study was thus conducted by analysing the main demographic, clinical and treatment data regarding a cohort of 400 patients attending a reference clinical unit over a 17-year period.

RESULTS

Most patients were female (55%) with mean age 37.5±16.7 years. All the migrants came from sub-Saharan countries. The most frequently occurring dermatological symptom was pruritus. Ivermectin had been used as first-line therapy and adverse reactions had been described in 11 patients (3.2%).

CONCLUSIONS

The results indicate the fact that there should be a clinical suspicion of onchocerciasis regarding immigrants from endemic areas having skin lesions compatible with the disease's profile or asymptomatic patients having eosinophilia or unexplained high IgE. Moreover, skin snips from the buttocks region were very fruitful and treatment with ivermectin was seen to be safe. This is the largest case series regarding imported onchocerciasis described up to the present time.

Is imported onchocerciasis a truly rare entity? Case report and review of the literature

BACKGROUND

Onchocerciasis is endemic in a number of tropical countries in Africa and South America, and it is occasionally diagnosed as an imported disease in non-endemic areas.

METHODS

We describe the case of an African migrant with long-lasting pruritus and a cutaneous nodule who was diagnosed with onchocerciasis after nodulectomy, and review the medical literature regarding imported cases of onchocerciasis in the period 1994-2014.

RESULTS

Twenty-nine cases of onchocerciasis diagnosed in migrants from endemic countries, and in expatriates and travellers from non-endemic areas were retrieved. They were predominantly males (73.3%), had a median age of 37 years (two were aged <15 years), and acquired the diseases in sub-Saharan Africa, most frequently in Cameroon (43.3%). Diagnosis of onchocercosis was proven in 73.3% of patients. The most frequent clinical manifestations in these and our own patient were pruritus (23/30, 76.7%), unilateral leg or forearm swelling (13/30, 43.3%) and rash (12/30, 40.0%), whereas only two (6.9%) complained of eye symptoms. Eosinophilia was observed in almost all of the patients (92.0%), with median counts of 2915/μL among migrants and 1960/μL among travellers/expatriates. Eighteen patients underwent a skin snip biopsy, which was positive in 10 cases (55.5%); in the other 13 patients the parasite was directly demonstrated by means of a skin or nodule biopsy (n = 5), nodulectomy (n = 5) or slit lamp examination (n = 3). Eighteen received ivermectin, alone, and seven ivermectin combined with diethylcarbamazine or doxycycline. Outcome details were available for only 14 patients, all of whom were asymptomatic after a median follow-up of 10 months (range 1-48).

CONCLUSIONS

Onchocerciasis is a neglected tropical disease whose subtle and non-specific features may lead to under-diagnosis or underreporting in non-endemic areas. Physicians should consider this tropical disease when caring for migrants and travellers/expatriates with pruritus, skin lesions and eosinophilia.

Eosinophilia in Infectious Diseases

In determining the etiology of eosinophilia, it is necessary to consider the type of patient, including previous travel and exposure history, comorbidities, and symptoms. In this review, we discuss the approach to the patient with eosinophilia from an infectious diseases perspective based on symptom complexes.

Impact of Six Years Community Directed Treatment with Ivermectin in the Control of Onchocerciasis, Western Ethiopia

Background

The African Program for Onchocerciais Control (APOC) with a main strategy of community directed treatment with ivermectin (CDTI) was established with the aim of eliminating Onchocerciasis as a disease of public health and socio-economic importance. The study area was a hyper endemic area just before the implementation of CDTI. It has been implemented for six years in this district but yet not been evaluated. So, the objective of this study was to evaluate the impact of six years CDTI on parasitological and clinical indices of Onchocerciasis

Methods

This study employed a pre-post impact evaluation design. The minimum sample size for this study was 1318; the respondents were selected by multi-stage sampling technique. Data on socio-demographic characteristics using a semi-structured questionnaire, clinical examination for skin signs and symptoms of Onchocerciasis and two bloodless skin snips from each side of the gluteal fold were taken from the entire study participants. SPSS version 16.0 and Medcalc version 12.2.1.0 were used for analysis.

Result

The microfilaridermia reduced from the pre-intervention value of 74.8% to 40.7%, indicating a 45.6% reduction, mean intensity from 32.1(SD = 61.5) mf/mg skin snip to 18.7(SD = 28.7)indicating 41.75% reduction, CMFL from 19.6 mf/mg skin snip to 4.7 indicating 76% reduction. The result also showed that microfilaridermia and mean intensity decreased as the number of treatment taken increased. Pruritis, leopard skin, onchocercomata and hanging groin reduced by 54.4%, 61.3%, 77.7% and 88.5% respectively.

Conclusions

The implementation of CDTI significantly reduced the parasitological and clinical indices of Onchocerciasis, so, efforts should be made to improve the annual treatment coverage and sustainability of CDTI to drastically reduce the micro filarial load to the level the disease would no longer be a public health problem.

[Filariasis in clinical practice]

Filariases are infections caused by distinct species of nematodes. These infections are transmitted through insect bites and primarily affect lymph nodes and skin. Filariases are classified as neglected diseases and affect millions, producing severe disability and social stigma. This type of infection is rarely diagnosed in travellers, as prolonged stays in endemic areas are usually required acquire infection. Infections may be asymptomatic, and clinical manifestations depend on the host immune response to the infection and the parasite burden. Diagnosis is based on the demonstration of microfilariae in blood or skin, but there are other methods that support the diagnosis. Individual treatment is effective, but community interventions, mostly mass drug administration, have helped to diminish the incidence of filariases.

Regulation of global gene expression in human Loa loa infection is a function of chronicity

Background

Human filarial infection is characterized by downregulated parasite-antigen specific T cell responses but distinct differences exist between patients with longstanding infection (endemics) and those who acquired infection through temporary residency or visits to filarial-endemic regions (expatriates).

Methods and Findings

To characterize mechanisms underlying differences in T cells, analysis of global gene expression using human spotted microarrays was conducted on CD4⁺ and CD8⁺ T cells from microfilaremic Loa loa-infected endemic and expatriate patients. Assessment of unstimulated cells showed overexpression of genes linked to inflammation and caspase-associated cell death, particularly in endemics, and enrichment of the Th1/Th2 canonical pathway in endemic CD4⁺ cells. However, pathways within CD8⁺ unstimulated cells were most significantly enriched in both patient groups. Antigen (Ag)-driven gene expression was assessed to microfilarial Ag (MfAg) and to the nonparasite Ag streptolysin O (SLO). For MfAg-driven cells, the number of genes differing significantly from unstimulated cells was greater in endemics compared to expatriates (p<0.0001). Functional analysis showed a differential increase in genes associated with NFkB (both groups) and caspase activation (endemics). While the expatriate response to MfAg was primarily a CD4⁺ pro-inflammatory one, the endemic response included CD4⁺ and CD8⁺ cells and was linked to insulin signaling, histone complexes, and ubiquitination. Unlike the enrichment of canonical pathways in CD8⁺ unstimulated cells, both groups showed pathway enrichment in CD4⁺ cells to MfAg. Contrasting with the divergent responses to MfAg seen between endemics and expatriates, the CD4⁺ response to SLO was similar; however, CD8⁺ cells differed strongly in the nature and numbers (156 [endemics] vs 36 [expatriates]) of genes with differential expression.

Conclusions

These data suggest several important pathways are responsible for the different outcomes seen among filarial-infected patients with varying levels of chronicity and imply an important role for CD8⁺ cells in some of the global changes seen with lifelong exposure.

Infection with the filarial parasite Loa loa causes a parasite-specific downregulation of T cell responses. However, differences exist (clinical and immunologic) between patients born and living in filarial endemic regions (endemics) and those who become infected during travel or short-term residency (expatriates). T cell responses are more depressed in endemics while expatriates have more clinical “allergic-type” symptoms. In this study, we showed that these differences reflect transcriptional differences within the T cell compartment. Using microarrays, we examined global gene expression in both CD4⁺ and CD8⁺ T cells of microfilaremic endemic and expatriate patients and found differences not only ex vivo, but also to parasite and, for CD8⁺ cells, to nonparasite antigens. Functional analysis showed that endemic patients expressed genes linked to inflammatory disease and caspase associated cell death at homeostasis while expatriates tended to have a more activation-induced gene profile at homeostasis and a CD4⁺ inflammatory response to parasite antigen. Patient groups were similar in their CD4⁺ response to nonparasite antigen but strongly differed in their CD8⁺ responses, demonstrating the potential global ramifications of chronic, longstanding infection. Our study describes potential transcriptional mechanisms for the variability seen in patients with different levels of exposure to and chronicity of filarial infection.

Parasitological and clinico-epidemiological features of onchocerciasis in West Wellega, Ethiopia

Onchocerciasis is a disease of public health and socio-economic importance in Ethiopia. The aim of this study was to assess parasitological and clinico-epidemiological features of onchocerciasis in the Anfilo District, West Wellega, prior to implementation of Community Directed Treatment with Ivermectin (CDTI) to generate epidemiological and parasitological data for use in control program of the disease and subsequent evaluation of CDTI. A cross-sectional study was conducted in Anfilo District of West Wellega zone during a period of 1 month: from mid-August to mid-September 2006. Data on socio-demographic characteristics were collected using a standardized questionnaire prepared for this purpose. All persons were examined clinically for skin signs and symptoms of onchocerciasis. Two skin snips, one from each side of the gluteal fold were taken using blood lancet and sterilized razor blade and examined for microfilaria. All data were categorized, coded, entered in a data base and analyzed using SPSS version 15.0. for windows. A total of 1114 individuals ≥15 years were examined for microfilariae (mf) of Onchocerca volvulus and onchocercal skin disease (OSD). The prevalence of onchocercal (mf) carrier was 74.8% (833/1114). In both genders, the prevalence of onchocerciasis showed direct correlations with the age of individuals (R (2) = 0.79, P < 0.05). The infection rate varied with the occupation of the study subjects, with preponderance among farmers. Among the subjects with onchocerciasis, the mf density ranged from 1.0 to 711.0 per mg of skin snip with a mean density (SD) and median values of 32.1 (61.5) and 10.4 respectively. The overall community microfilariae load (CMFL), the most sensitive parasitological indicator of onchocerciasis was 19.6. The pervasiveness of OSD among the study subjects was 26.4%. OSD was more frequent in males (32.4%) than their female counterparts (20.8%, P < 0.05). The overall prevalence of onchocercal nodule carrier, the symptom opted for determining the community-wide prevalence of onchocerciasis was 12.1%. Leopard skin, the proxy of longstanding infection of onchocerciasis in the community, was also relatively high (19.1%). The abundance of mf in skin would definitely lead to high transmission potential in the Anfilo District. The situation in the Anfilo District should call for continued CDTI, owing to success of similar recommendations for such programmes in other parts of the country and elsewhere.

Filarial infections in travelers and immigrants

Filarial infections including loiasis, onchocerciasis, and lymphatic filariasis are important causes of morbidity in endemic populations worldwide, and they present a risk to travelers to endemic areas. Definitive diagnosis is complicated by overlap in the geographic distribution and clinical manifestations of the different filarial parasites, as well as similarities in their antigenic and nucleic acid composition. This has important implications for treatment, because the efficacies and toxicities of available antifilarial agents differ dramatically among filarial species. Recent advances, including the visualization of adult filarial worms in vivo by high-frequency ultrasound and the identification of the bacterial endosymbiont, Wolbachia, have greatly improved our understanding of the pathogenesis of filarial infection and have led to novel approaches to the diagnosis and treatment of travelers and immigrants from filarial-endemic regions.

Filariasis in travelers presenting to the GeoSentinel Surveillance Network

BACKGROUND

As international travel increases, there is rising exposure to many pathogens not traditionally encountered in the resource-rich countries of the world. Filarial infections, a great problem throughout the tropics and subtropics, are relatively rare among travelers even to filaria-endemic regions of the world. The GeoSentinel Surveillance Network, a global network of medicine/travel clinics, was established in 1995 to detect morbidity trends among travelers.

PRINCIPAL FINDINGS

We examined data from the GeoSentinel database to determine demographic and travel characteristics associated with filaria acquisition and to understand the differences in clinical presentation between nonendemic visitors and those born in filaria-endemic regions of the world. Filarial infections comprised 0.62% (n = 271) of all medical conditions reported to the GeoSentinel Network from travelers; 37% of patients were diagnosed with Onchocerca volvulus, 25% were infected with Loa loa, and another 25% were diagnosed with Wuchereria bancrofti. Most infections were reported from immigrants and from those immigrants returning to their county of origin (those visiting friends and relatives); the majority of filarial infections were acquired in sub-Saharan Africa. Among the patients who were natives of filaria-nonendemic regions, 70.6% acquired their filarial infection with exposure greater than 1 month. Moreover, nonendemic visitors to filaria-endemic regions were more likely to present to GeoSentinel sites with clinically symptomatic conditions compared with those who had lifelong exposure.

SIGNIFICANCE

Codifying the filarial infections presenting to the GeoSentinel Surveillance Network has provided insights into the clinical differences seen among filaria-infected expatriates and those from endemic regions and demonstrated that O. volvulus infection can be acquired with short-term travel.

Onchocerciasis--river blindness

Onchocerciasis results from infestation by the nematode Onchocerca volvulus and is characterized by troublesome itching, skin lesions, and eye manifestations. Although partially controlled by international mass prevention programs, onchocerciasis remains a major health hazard and is endemic in Africa, Arabia, and the Americas. Onchocerciasis is spread by bites from infested black flies, which transmit larvae that subsequently develop into adult filariae. Skin symptoms are commonly nonspecific and include severe pruritus, acute and chronic dermatitis, vitiligo-like hypopigmentation, and atrophy. Onchocercal ocular disease covers a large spectrum of manifestations, which in severe cases, may lead to blindness. Diagnosis is usually made by direct visualization of the larvae emerging from superficial skin biopsies, "skin snips." In some cases, the microfilariae can also be directly observed at the slit lamp when migrating into the anterior chamber of the eye. Ivermectin is, at present, the drug of choice for skin and ocular manifestations. Recent research using a chemotherapeutic approach that targets filarial Wolbachia symbionts in the treatment and control of onchocerciasis, however, suggests that 100 mg/d of doxycycline for 6 weeks might be effective in reducing the filarial load and preventing ocular symptoms.

Special infectious disease risks of expatriates and long-term travelers in tropical countries. Part II: infections other than malaria

A wide range of viral, bacterial, and protozoal diseases pose risk to long-term tropical travelers. Risk varies geographically and with lifestyle. For some infections, risk increases with duration of stay, coming to resemble that of the local population. Risk management strategies include vaccination, chemoprophylaxis, avoidance measures, and screening, where appropriate. Vaccination against hepatitis A and B, typhoid, and rabies is recommended for all long-term travelers to (sub-)tropical areas. Lowering of the vaccination threshold for Japanese encephalitis is suggested. Meningococcal disease is rare in travelers, but vaccination is safe and acceptable. The efficacy of Bacillus Calmette-Guérin (BCG) is uncertain; immunological testing avoids BCG's confounding of tuberculin testing. Diarrhea is common, and self-treatment may be recommended. Sexually transmitted infections including human immunodeficiency virus (HIV) are serious risks; education, screening, and HIV postexposure prophylaxis following involuntary exposure are recommended. Many infections are chronic or asymptomatic, and appropriate screening is recommended on return or after prolonged exposure.

Onchocerciasis-associated limb swelling in a traveler returning from Cameroon

Travelers to West Central Africa are at risk for infection with Onchocerca volvulus. We describe the case of an adventurous traveler who became infected with O volvulus after a 10-day stay in rural Cameroon. Two years after his return, he was diagnosed with a 3-month history of limb swelling with pruritus and fixed edema of the right arm. He was successfully treated by a single dose of ivermectin, with an additional treatment with doxycycline. The patient was followed-up during 1 year after therapy without relapse. Such travelers experiencing unusual dermatitis syndromes should prompt evaluation for onchocerciasis.

Immunomodulation by filarial nematodes

In order to chronically infect their hosts, filarial nematodes have generated a range of strategies to evade and down-modulate the host's immune system. The recent concept of suppression of immune responses by regulatory T cells has in part benefited from examinations in human and murine filariasis. Its further development in basic immunology animal models has in turn helped to better understand down-regulatory immune mechanisms in filariasis. Thus, filarial nematodes orchestrate down-regulation by inducing regulatory T cells and alternatively activated macrophages, which are able to suppress both Th1 and Th2 responses. Regulatory T cells can also induce the secretion of IgG4 from B cells as another arm of modulation. Dendritic cells are down-regulated upon first encounter with infective L3 larvae. Failure to respond to down-regulatory induction is based on genetic traits in hosts and leads to reduced parasite loads, albeit at the expense of pathology and disease. Since down-regulation in chronically and heavily infected hosts extends to third-party antigens, it is essential to analyse the impact of filarial infection for vaccination, allergy and important coinfections such as malaria, in order to foresee and avert potentially disastrous consequences of filariasis control programmes.

Cutaneous onchocerciasis in an American traveler

A case report of cutaneous onchocercias acquired during travels to Africa is presented. The salient epidemiologic, clinical, diagnostic, and therapeutic aspects are reviewed. Clinical and laboratory differences between onchocerciasis patients who are inhabitants of endemic areas and those who are occasional visitors to such areas are discussed. Parasitic infections, including onchocerciasis, should be considered in the differential diagnosis of pruritic eruptions in patients with a history of foreign travel to Africa, Central and South America.

Parasite antigen-driven basophils are a major source of IL-4 in human filarial infections

Basophil contribution to the IL-4 pool in filarial infections was assessed using PBMC from 20 patients with active filarial infections and from 9 uninfected subjects. Patient basophils released histamine in response to Brugia malayi Ag (BmAg). They also released IL-4 within 2 h after exposure to BmAg, as assessed by intracellular cytokine flow cytometry. This IL-4 induction was Ag specific, as IL-4 was not detected in BmAg-exposed basophils obtained from uninfected subjects. Although there were, on average, 64 times more CD4(+) T cells than basophils in the peripheral circulation of filaria-infected patients, the absolute numbers of basophils and CD4(+) T cells producing IL-4 per 100000 PBMC were equivalent (geometric mean: 16 IL-4-producing basophils/100000 PBMC vs 22 IL-4-producing CD4(+) T cells/100000 PBMC). Basophils also released IL-4 in response to both low and high concentrations of BmAg, whereas CD4(+) T cells released IL-4 only after incubation with a high concentration of BmAg, raising the possibility that basophils, due to their lower threshold for activation, may actually release IL-4 more frequently than CD4(+) T cells in vivo. Furthermore, IL-4 production in vitro by Ag-stimulated purified basophils or CD4(+) T cells provided evidence that basophils release greater quantities of IL-4 per cell than CD4(+) T cells in response to BmAg. These results suggest that, when Ag-specific IgE is present in a filaria-infected individual, basophils function to amplify the ongoing Th2 response by releasing IL-4 in greater amounts and possibly more frequently than CD4(+) T cells in response to filarial Ag.

[Onchocerciasis]

Onchocerciasis is an infestation caused by the nematode, Onchocerca volvulus, and characterized by eye manifestations, skin lesions and troublesome itching. Although partially controlled by international mass treatment programs, onchocerciasis remains a major health hazard in endemic areas in Africa, Arabia, and the Americas. Onchocerciasis is spread by bites from infested blackflies which transmit larvae that subsequently develop into adult filariae. Skin findings are commonly non-specific, and include severe pruritus, acute and chronic dermatitis, vitiligo-like hypopigmentation and atrophy. Onchocercal ocular disease has a large spectrum of manifestations and may even lead to blindness. Diagnosis is usually made by direct visualization of the larvae emerging from superficial skin biopsies, "skin snips". In some cases, the microfilariae can also be directly observed with a slit lamp when they migrate into the anterior chamber of the eye. Ivermectin is highly microfilaricidal, and is the current drug of choice for both skin and ocular manifestations.

Elevated immunoglobulin E against recombinant Brugia malayi gamma-glutamyl transpeptidase in patients with bancroftian filariasis: association with tropical pulmonary eosinophilia or putative immunity

A major allergen of the lymphatic filarial nematode Brugia malayi, a homologue of gamma-glutamyl transpeptidase (gamma-GT), is involved in the pathology of tropical pulmonary eosinophilia (TPE) through its potent allergenicity and the induction of antibodies against the host pulmonary epithelium. To investigate the immunoglobulin G (IgG) subclass and IgE responses to recombinant B. malayi gamma-GT, we analyzed the results obtained from 51 patients with differing clinical manifestations of bancroftian filariasis. gamma-GT-specific IgG1, rather than IgG4, was the predominant IgG subclass, particularly in patients with TPE (geomean, 6,321 ng/ml; range, 78 to 354,867 ng/ml) and was 75 times higher than in patients with elephantiasis (CP) (P < 0.003) and 185 times higher than in endemic normal individuals (ENL) (P < 0.010). IgG2 responses were low and IgG3 was almost absent, with no significant differences among the groups. gamma-GT-specific IgG4 responses were significantly elevated in those with subclinical microfilaremia (MF) compared to the CP and ENL groups and correlated with the presence of circulating filarial antigen (CAg). More significantly, gamma-GT-specific IgE antibody levels were strikingly elevated in patients with TPE (geomean, 681 ng/ml; range, 61 to 23,841 ng/ml) and in the ENL group (geomean, 106 ng/ml; range, 13 to 1,405 ng/ml) whereas the gamma-GT-specific IgE level was 44 and 61 times lower in those with MF and CP, respectively (P < 0.001). Elevated gamma-GT-specific IgE/IgG4 ratios were demonstrated in patients with TPE (ratio, 45) and ENL (ratio, 107). Because expression of gamma-GT in Brugia infective third-stage larvae (L3) was demonstrated by immunoblot analysis, the elevated gamma-GT-specific IgE antibodies appear to be associated not only with pulmonary pathology but also with possible resistance to infection in lymphatic filariasis.

Resistance and susceptibility in human onchocerciasis--beyond Th1 vs. Th2

As research progress has led to programs for the elimination of onchocerciasis as a public health problem, research must now be intensified to protect elimination efforts. A profound understanding of the immunology in the human-parasite relationship is required for predicting the impacts of an altered immune response in a population post-microfilaricide treatment, and for the development of a vaccine against onchocerciasis, a highly desirable tool to guarantee sustained elimination success. This article summarizes the recent advancements in understanding the human immune mechanisms against onchocerciasis, and focuses on the new concept of T-cell suppressor responses as a major counterbalance mechanism for effector responses driven by T helper 1 and T helper 2 cells against the filarial worms.

Regulation of the immune response in lymphatic filariasis: perspectives on acute and chronic infection with Wuchereria bancrofti in South India

Delineating the immune responses in lymphatic filariasis has been complicated not only by the rapidly expanding knowledge of new immunological mediators and effortors, but also by new methodologies (in particular, circulating filarial antigen detection) for defining and categorizing filarial-infected individuals. By using assays for circulating antigen in the sera collected as part of the many immunological studies performed on individuals in a Wuchereria bancrofti-endemic region of South India, we have attempted to explore the influence of patency on the antigen-driven proliferative and cytokine responses seen in peripheral blood mononuclear cells of individuals with varying clinical manifestations of lymphatic filarial infection. Moreover, we have provided perspectives on the differences between acute and chronic infection with W. bancrofti and suggested mechanisms that may underly the modulation of the immune response as patency occurs.

Human onchocerciasis and tetanus vaccination: impact on the postvaccination antitetanus antibody response

To investigate whether helminth infections may affect the efficacy of vaccines by impairing the immune response to nonparasite vaccine antigens, we compared the antibody responses to tetanus toxoid (TT) after tetanus vaccination in 193 subjects with Onchocerca volvulus infection with 85 comparable noninfected controls. After vaccination, the proportions of subjects in each group attaining protective levels of antitetanus antibodies were similar (96.9% infected versus 97.6% noninfected). Postvaccination increases in antitetanus immunoglobulin G (IgG) and the predominant IgG isotype, IgG1, were equivalent in both groups, as were increases in specific IgG4 and IgE; however, significantly greater increases in specific IgG2 (P < 0.05) and IgG3 (P < 0.001) were observed in the noninfected group. Stratification of the O. volvulus-infected group into two groups representing light and heavy infections revealed a significantly impaired antitetanus IgG response in those with heavy infections compared to those with light infections (P < 0.01) or no infection (P < 0.05). The impact of concurrent intestinal helminth infections on the antitetanus response was also examined; an increased IgG4/IgE ratio was seen in those infected with Strongyloides stercoralis (P < 0.05) and when all helminth infections were combined as a single group (P < 0.05). These findings indicate that concurrent infection with O. volvulus does not prevent the development of a protective antitetanus response, although heavier O. volvulus infections are able to alter the magnitude of this response, and concurrent helminth infections (O. volvulus and intestinal helminths) may alter TT-specific antibody isotype responses.

Pathogenesis of onchocercal keratitis (River blindness)

Onchocerciasis is a major cause of blindness. Although the World Health Organization has been successful in reducing onchocerciasis as a public health problem in parts of West Africa, there remain an estimated 17 million people infected with Onchocerca volvulus, the parasite that causes this disease. Ocular pathology can be manifested in any part of the eye, although disease manifestations are frequently characterized as either posterior or anterior eye disease. This review focuses on onchocerca-mediated keratitis that results from an inflammatory response in the anterior portion of the eye and summarizes what is currently known about human disease. This review also describes studies with experimental models that have been established to determine the immunological mechanisms underlying interstitial keratitis. The pathogenesis of keratitis is thought to be due to the host inflammatory response to degenerating parasites in the eye; therefore, the primary clinical symptoms of onchocercal keratitis (corneal opacification and neovascularization) are induced after injection of soluble O. volvulus antigens into the corneal stroma. Experimental approaches have demonstrated an essential role for sensitized T helper cells and shown that cytokines can regulate the severity of keratitis by controlling recruitment of inflammatory cells into the cornea. Chemokines are also important in inflammatory cell recruitment to the cornea, and their role in onchocerciasis is being examined. Further understanding of the molecular basis of the development of onchocercal keratitis may lead to novel approaches to immunologically based intervention.

Induction of specific cell-mediated immunity in mice by oral immunization with Salmonella expressing Onchocerca volvulus glutathione S-transferase

Cellular and humoral immune responses of mice to Onchocerca volvulus glutathione S-transferase (OvGST) presented via in vivo expression in attenuated Salmonella typhimurium were examined and compared with the same antigen administered by subcutaneous injection with Freund's adjuvant. After infection with recombinant S. typhimurium, maximal numbers of bacteria were recovered from the mesenteric lymph nodes and spleens during the second week postinfection. By weeks 3-4, bacteria were absent from these tissues. Splenocytes from mice infected with S. typhimurium expressing OvGST showed significant and specific proliferative responses to OvGST, whereas the non-recombinant S. typhimurium controls and those which received the antigen by subcutaneous injection with Freund's adjuvant did not. Mice infected with recombinant S. typhimurium had elevated IFN-gamma levels over non-recombinant S. typhimurium and placebo controls. but IL-4 and IL-5 levels were low and did not differ significantly between these groups. Antibody responses to OvGST antigen expressed by a recombinant Salmonella vaccine or delivered in a purified form with Freund's adjuvant were moderate to high. These data suggest that Salmonella can be used as a vaccine delivery vector that induces specific cellular and humoral immune responses to Onchocerca volvulus antigens. This is the first report to describe the successful application of a filarial antigen in a live-vector delivery system as well as the first recombinant based filarial vaccine to elicit a cellular immune response similar to that described for putative immune endemics.

Eosinophilia in the returning traveler

Eosinophilia is one of the most common laboratory abnormalities seen in the returning traveler. Although elevations in peripheral eosinophil levels can occur in a wide variety of disease processes, worldwide, helminth parasites are the major group of infectious agents responsible for eosinophilia. While often directed at helminth infections in their early stages of clinical evolution, the approach to the evaluation of the returning traveler with eosinophilia must consider the many causes of eosinophilia including those not casually related to travel. This article reviews the major parasitic causes of eosinophilia and provides a systematic approach to the evaluation of eosinophilia following travel.

Skin problems in the traveler

Skin lesions are common in travelers and include a mix of mundane dermatologic problems and rare diseases acquired only in remote or tropical regions. The morphology, distribution, and progression of the lesions are useful in assessing possible causes. Early in the evaluation it is important to determine whether the patient might have a process that is rapidly progressive, treatable, or transmissible. In addition to routine laboratory studies, biopsy and serologic tests are often necessary to confirm a specific diagnosis.

Onchocerciasis in an expatriate living in Cameroon

Travelers to West, central and eastern Africa as well as to selected areas of Latin America are at risk for infection with Onchocerca volvulus. Infection with this tissue nematode may cause chorioretinitis and keratitis, and it is responsible in endemic areas for blindness in millions.1 In addition to ocular manifestations, it can produce a distressing pruriginous dermatitis or subcutaneous nodules. Clinical manifestations vary according to the parasitic load, previous immunity, and duration of infection.1 Infection is initiated by inoculation with larvae during the bite of the Simulium black fly. Once in the connective tissue, larvae mature to filiform adults and may remain in tissues for years, with the clinical manifestations being produced by the inflammatory reaction to dying parasites. Female adults produce large amounts of microfilaria that migrate through skin and connective tissue; once an infected host is bitten, the infectious larvae develop again in the female Simulium black fly and the life cycle is completed. Transmission is from person to person, and may occur even after a relatively short exposure.2 Although infection of travelers with O. volvulus is rare, according to the Centers for Disease Control and Prevention, 46 new cases of onchocerciasis were diagnosed in the United States in 1994 (Dr. David Addis, personal communication, June 1996). We describe the case of an expatriate who became infected with O. volvulus and we review the treatment and recommendations for prevention of this parasitic infection.

In vivo molecular analysis of cytokines in a murine model of ocular onchocerciasis. I. Up-regulation of IL-4 and IL-5 mRNAs and not IL-2 and IFN gamma mRNAs in the cornea due to experimental interstitial keratitis

Sclerosing keratitis is the major cause of blindness due to onchocerciasis which results from chronic infection with the filarial parasite Onchocerca volvulus. Using a murine model of onchocercal sclerosing keratitis, we have demonstrated previously that predominantly (> 85%) CD3 + /CD4+ T-cells as well as the IL-2 receptor bearing cells infiltrate into the cornea in vivo during development and progress of the disease. The identification of CD4+ subsets TH1 and TH2 based on the cytokine secretion patterns of murine T-lymphocytes has been useful for understanding the immune basis of resistance and pathogenesis in murine models of several parasitic diseases. The present investigation was carried out to demonstrate whether the local immune response at the corneal lesion due to onchocercal interstitial keratitis correlated with such distinct patterns of cytokine production. For that purpose, mRNA was extracted separately from corneas obtained from the diseased eyes and the normal eyes of A/J mice with onchocercal interstitial keratitis, reverse transcribed and amplified by the polymerase chain reaction with four different cytokine specific primers. In corneas obtained from the eyes affected with onchocercal interstitial keratitis, mRNAs coding for IL-4 and IL-5 were up-regulated compared to the normal eyes having no lesions from the same animals. However, the levels of mRNAs for IL-2 and IFN gamma were found to be the same in the diseased and normal eyes. Taken together, these data suggest that IL-4 and IL-5 producing TH2-lymphocytes are active at the corneal lesion due to onchocercal interstitial keratitis.

Interleukin 4 and T helper type 2 cells are required for development of experimental onchocercal keratitis (river blindness)

Inflammation of the corneal stroma (stromal keratitis) is a serious complication of infection with the nematode parasite Onchocerca volvulus. Because stromal keratitis is believed to be immunologically mediated in humans, we used a murine model to examine the role of T cells and T helper cell cytokines in the immunopathogenesis of these eye lesions. BALB/c mice immunized subcutaneously and injected intrastromally with soluble O. volvulus antigens (OvAg) developed pronounced corneal opacification and neovascularization. The corneal stroma was edematous and contained numerous eosinophils and mononuclear cells. Stromal keratitis in immunized mice was determined to be T cell dependent based on the following observations: (a) T cell-deficient nude mice immunized and injected intrastromally with OvAg fail to develop corneal pathology; and (b) adoptive transfer of spleen cells from OvAg-immunized BALB/c mice to naive nude mice before intrastromal injection of OvAg results in development of keratitis. OvAg-stimulated lymph node and spleen cell cytokine production was dependent on CD4 cells and included interleukin (IL)-4 and IL-5, but not interferon gamma, indicating a predominant T helper type 2 cell-like response. Inflamed corneas from immunized BALB/c mice and from reconstituted nude mice had greatly elevated CD4 and IL-4 gene expression compared with interferon gamma. Mice in which the IL-4 gene was disrupted failed to develop corneal disease, demonstrating that IL-4 is essential in the immunopathogenesis of O. volvulus-mediated stromal keratitis.