Onchocerciasis in Ecuador: ocular findings in Onchocerca volvulus infected individuals

Presumed Onchocerciasis Chorioretinitis Spilling over into North America, Europe and Middle East

BACKGROUND

Newer generation ophthalmologists practicing in the developed world are not very familiar with some tropical ocular diseases due to the absence of reports in the ophthalmic literature over the past thirty years. Because of world globalization or due to influx of immigrants from sub-Saharan Africa, exotic retinal diseases are being encountered more often in ophthalmology clinics.

METHODS

A multicenter case series of chorioretinitis or optic neuritis with obscure etiology that used serial multimodal imaging.

RESULTS

Four cases qualified with the diagnosis of presumed ocular onchocerciasis based on their residence near fast rivers in endemic areas, multimodal imaging, long term follow-up showing progressive disease and negative workup for other diseases. Characteristic findings include peripapillary choroiditis with optic neuritis or atrophy, subretinal tracts of the microfilaria, progressive RPE atrophy around heavily pigmented multifocal chorioretinal lesions of varying shapes, subretinal white or crystalline dots, and response to ivermectin. Typical skin findings are often absent in such patients with chorioretinitis rendering the diagnosis more challenging.

CONCLUSIONS

Familiarity with the myriad ocular findings of onchocerciasis, and a high-degree of suspicion in subjects residing in endemic areas can help in the correct diagnosis and implementation of appropriate therapy. Onchocercal chorioretinitis is a slow, insidious, progressive, and prolonged polymorphous disease.

Elimination of onchocerciasis in Ecuador: findings of post-treatment surveillance

BACKGROUND

The Esmeraldas focus of onchocerciasis in Ecuador expanded geographically during the 1980s and was associated with severe ocular and skin disease. Mass drug administration (MDA) with ivermectin started in 1991, initially once but later twice a year, in the principle endemic focus followed by all satellite foci. Treatment was stopped in 2009 when entomological assessments determined that transmission of Onchocerca volvulus had been interrupted.

METHODS

Three years after the cessation of ivermectin treatment in 2012, as defined by the WHO guidelines for onchocerciasis elimination, blackfly collections were done in four sentinel sites in former hyperendemic areas. The presence of infective larvae in local vectors, Simulium exiguum and Simulum quadrivittatum, was assessed by detection of O. volvulus DNA by PCR. Additional flies captured in four extra-sentinel sites located in former hyper- and mesoendemic dispersed isolated areas were also assessed.

RESULTS

The results from 68,310 captured blackflies, 40,114 from four sentinel villages in the previously hyperendemic areas (Corriente Grande, El Tigre, San Miguel on Río Cayapas and Naranjal on Río Canandé) and 28,197 from extra-sentinel locations, were all negative for the presence of O. volvulus. These extra-sentinel sites (Hualpí on Río Hoja Blanca, Capulí on Río Onzole, La Ceiba on Río Tululví and Medianía on Río Verde) were included to provide additional evidence of the impact of MDA on the transmission of O. volvulus in isolated endemic areas.

CONCLUSIONS

Our data indicate that transmission of O. volvulus has been stopped in all endemic areas in Ecuador, including all satellite foci outside the main focus. These findings indicate that a strategy of ivermectin distribution twice a year to over 85% of the treatment-eligible population was effective in eliminating the infection from Ecuador in a focus with a highly competent primary vector, S. exiguum, and where the infection rates were equal to or greater than observed in many onchocerciasis foci in Africa.

A Focus on the Epidemiology of Uveitis

PURPOSE

Uveitis is a common, sight-threatening inflammatory ocular disease and includes multiple heterogeneous clinical entities. The prevalence of various types of uveitis depends upon multiple factors, such as age, sex, race, geographic distribution, environmental influence, genetics, and social habits. Epidemiologic research of uveitis is necessary to understand the etiology and immunopathogenesis of this group of diseases. The present study attempts to concentrate on the most recent information on the epidemiology of uveitis and compare it with previous knowledge.

METHODS

An extensive literature search was performed in the Medline database (PubMed) and included surveys completed until 2015. Articles that reported prevalence and incidence were studied. References cited in the articles were also studied.

RESULTS

The incidence and prevalence of uveitis differs based on age, anatomic location of the inflammatory process (anterior, intermediate, posterior uveitis, panuveitis), gender, histopathology (granulomatous, non-granulomatous), type of inflammatory process (acute, chronic, recurrent), and etiology (infectious, non-infectious). Prevalence differs by geographic location. Idiopathic anterior uveitis is the most common form of uveitis in the community. Infectious causes are common (30-60%) in the developing countries. Herpes and toxoplasmosis are the leading infectious causes of uveitis. Non-infectious uveitic conditions are generally more common in the developed world. An increase in the prevalence of infectious etiologies, including tuberculosis and syphilis, has been seen in developed countries. Introduction of new treatment options has also changed patterns of disease.

CONCLUSIONS

Introduction of new uveitis entities, changes in the incidence of already known disease and increased availability of diagnostic testing have all altered the epidemiology of uveitis in recent years. Knowledge of regional patterns of disease is essential. A more detailed classification of uveitis with the establishment of uniform diagnostic criteria and prospective population based studies would certainly benefit epidemiologic research and clinical practice.

Interruption of infection transmission in the onchocerciasis focus of Ecuador leading to the cessation of ivermectin distribution

Introduction: A clinically significant endemic focus of onchocerciasis existing in Esmeraldas Province, coastal Ecuador has been under an ivermectin mass drug administration program since 1991. The main transmitting vector in this area is the voracious blackfly, Simulium exiguum. This paper describes the assessments made that support the decision to cease mass treatment.

Methodology and Principle Findings: Thirty-five rounds of ivermectin treatment occurred between 1991–2009 with 29 of these carrying >85% coverage. Following the guidelines set by WHO for ceasing ivermectin distribution the impact on parasite transmission was measured in the two vector species by an O-150 PCR technique standard for assessing for the presence of Onchocerca volvulus. Up to seven collection sites in three major river systems were tested on four occasions between 1995 and 2008. The infectivity rates of 65.0 (CI 39–101) and 72.7 (CI 42–116) in 1995 dropped to zero at all seven collection sites by 2008. Assessment for the presence of antibodies against O. volvulus was made in 2001, 2006, 2007 and 2008 using standard ELISA assays for detecting anti-Ov16 antibodies. None of total of 1810 children aged 1–15 years (between 82 and 98% of children present in the surveyed villages) tested in the above years were found to be carrying antibodies to this antigen. These findings were the basis for the cessation of mass drug treatment with ivermectin in 2009.

Significance: This fulfillment of the criteria for cessation of mass distribution of ivermectin in the only known endemic zone of onchocerciasis in Ecuador moves the country into the surveillance phase of official verification for national elimination of transmission of infection. These findings indicate that ivermectin given twice a year with greater than 85% of the community can move a program to the final stages of verification of transmission interruption.

Onchocerciasis has been known to be endemic in the northwestern coastal riverine jungle areas of the country since the early 1980's. A mass drug administration program with ivermectin was implemented in 1991, and in recent years has included consistent twice a year treatment. The impact of this program, and progress towards eliminating the transmission of Onchocerca volvulus from the endemic zone, was assessed by studying entomological parameters at sentinel sites in 1995, 2000, 2004 and 2008 using PCR detection of infective larvae in the vectors (Simulium exiguum and Simulium quadrivittatum); the survey of 2008 showed that all of the collection sites had reached a level consistent with the interruption of transmission. Serological assessment of children and adolescents in 2001–2008 also showed that transmission had been interrupted. These findings support the contention that the Ecuadorian Program has reached the post-treatment surveillance phase of the elimination program; mass drug administration _{of ivermectin was consequently stopped.} The factors contributing to this successful achievement include ivermectin coverage of consistently around 85% or greater since 1998, careful consideration and control of possible expansions of the endemic area through migration, and the maintenance of a strong community health programme.

Causes of blindness and visual impairment in Latin America

We review what is known in each country of the Latin American region with regards to blindness and visual impairment and make some comparisons to Hispanic populations in the United States. Prevalence of blindness varied from 1.1% in Argentina to 4.1% in Guatemala in people 50 years of age and older, with the major cause being cataract. Diabetic retinopathy and glaucoma are starting to make serious inroads, although epidemiological data are limited, and age-related macular degeneration is now a concern in some populations. Infectious diseases such as trachoma and onchocerciasis are quickly diminishing. Although progress has been made, retinopathy of prematurity remains the major cause of childhood blindness. If VISION 2020 is to succeed, many more epidemiological studies will be needed to set priorities, although some can be of the Rapid Assessment of Avoidable Blindness design. Developing the infrastructure for screening and treatment of ophthalmic disease in Latin America continues to be a challenge.

Impact of long-term treatment of onchocerciasis with ivermectin in Ecuador: potential for elimination of infection

BACKGROUND

Onchocerciasis is a leading cause of blindness worldwide, hence elimination of the infection is an important health priority. Community-based treatment programs with ivermectin form the basis of control programs for the disease in Latin America. The long-term administration of ivermectin could eliminate Onchocerca volvulus infection from endemic areas in Latin America.

METHODS

A strategy of annual to twice-annual treatments with ivermectin has been used for onchocerciasis in endemic communities in Ecuador for up to 14 years. The impact of ivermectin treatment on ocular morbidity, and O. volvulus infection and transmission was monitored in seven sentinel communities.

RESULTS

Over the period 1990-2003, high rates of treatment coverage of the eligible population were maintained in endemic communities (mean 85.2% per treatment round). Ivermectin reduced the prevalence of anterior segment disease of the eye to 0% in sentinel communities and had a major impact on the prevalence and transmission of infection, with possible elimination of infection in some foci.

CONCLUSION

The distribution of ivermectin in endemic communities in Ecuador might have eliminated ocular morbidity and significant progress has been made towards elimination of the infection. A strategy of more frequent treatments with ivermectin may be required in communities where the infection persists to achieve the objective of elimination of the infection from Ecuador. The elimination of the infection from an endemic country in Latin America would be a major public health achievement and could stimulate the implementation of elimination strategies in other endemic countries.

The pathogenesis of chorioretinal disease in onchocerciasis

The pathogenesis of onchocercal chorioretinopathy is poorly understood. In this article, Philip Cooper, Ronald Guderian, Roberto Proaño and David Taylor discuss the important clinical, histological and epidemiological features of the resulting lesions that cause blindness, and review the numerous mechanisins that have been put forward to explain its pathogenesis. The pathogenesis of anterior segment disease, particulary sclerosing keratitis, has been reviewed in depth previously(1) and will not be discussed here.

Parasites and the eye

Systemic parasitic infections can result in intraocular inflammation. They are a major cause of blindness in many parts of the world. Infection usually results from bloodborne transmission of the organism to the eye or ocular adnexal structures. Diagnosis is often made from clinical patterns of disease in the eye, with laboratory investigations and imaging to support the diagnosis. Various local and systemic therapies are available, but may have limited success in preserving vision.

Corneal changes of uncertain etiology in mesoendemic onchocercal communities of Northern Nigeria

BACKGROUND

We report an unusual type of corneal change in some communities mesoendemic for onchocerciasis in Kaduna State of Northern Nigeria.

METHODS

Thirty-four villages with an overall average microfilarial skin snip positivity rate of 71% and a total population of about 10,000 were included in a controlled trial of ivermectin for onchocerciasis. Detailed slit lamp examination of 806 persons within this population revealed at least 27 individuals with these lesions. There were 11 women and 16 men, aged between 5 and 70 years with a mean age of 45 years and a SD of 15 years. Drawings and photographs of 22 of these individuals were available for assessment.

RESULTS

The lesions were peripheral, silvery white, and of two main types: the first group's lesions were flaky, refractile, and crystalline in appearance; the second group's lesions were more cylindrical in outline and were crisscrossed, giving a lattice-like pattern. There were indeterminate forms in between these polar topographies. Of the 25 subjects who had skin snips performed, 23 were microfilaria-positive. There was no accompanying inflammation and the posterior segments showed no evidence of crystalline deposits or retinitis pigmentosa, as is found in Bietti's dystrophy. The lesions coexisted with typical sclerosing keratitis in six individuals, and changes noted in the posterior pole of ten individuals were typical of onchocercal chorioretinitis. The evidence for consanguinity was not compelling. Differences between and similarities to Bietti's and Schnyder's crystalline corneal dystrophy, which are known to be composed of cholesterol crystals, are discussed. The lesions are also compared with lattice dystrophy known to be composed of amyloid. These lesions may be related to onchocercal infection.

CONCLUSIONS

We describe some unusual peripheral corneal changes in individuals living within areas of Northern Nigeria mesoendemic for onchocerciasis. These changes take the form of flaky crystals or lattice within the anterior stroma and are common in middle-aged individuals. This may be related to onchocercal infection.

Infectious causes of uveitis in the developing world

Infectious causes of uveitis are common in the developing world and include some causes that are rarely encountered in industrialized nations, such as tuberculosis, leptospirosis, leprosy, onchocerciasis, and cystercicosis. Ocular toxoplasmosis occurs in all countries but is more common in Central and South America, the South Pacific, and western Europe. AIDS-related opportunistic infections occur wherever HIV infection is prevalent, including North and South America, western and eastern Europe, the former Soviet Union, sub-Saharan Africa, and South and Southeast Asia. Physicians who care for patients in the developing world should consider these infectious possibilities whenever their patients develop uveitis.

Successful control of onchocerciasis with community-based ivermectin distribution in the Rio Santiago focus in Ecuador

Onchocerciasis is a major blinding disease in equatorial Africa and Central and South America. Ivermectin is a safe and effective drug in the treatment of this disease and now forms the basis of disease control in most endemic areas. We report the findings of long-term control of this infection in the Río Santiago focus in Ecuador, between January 1990 and December 1996, using a strategy of giving ivermectin treatments biannually in hyperendemic communities and annually in meso- and hypoendemic communities. Ivermectin was administered by local health workers from each community. A high level of compliance to ivermectin was achieved, with 81.9% to 98.0% of those eligible receiving the drug at each treatment instance. The impact of ivermectin therapy was monitored using a cohort of 120 randomly selected infected individuals from 8 hyperendemic communities. The geometric mean microfilarial density of this group declined from 19.3 to 0 mf/mg over the 84-month observation period. Ivermectin had a significant impact on anterior segment ocular disease, acute onchodermatitis and sowda. The rate of infection of blackflies declined from 1.1% in 1989-0.08% in 1996, which is below the vectorial capacity of the Simulium vector and, as no new nodules were detected after 1994 and no children under 5 became infected over the observation period, it is likely that the transmission of this infection was interrupted in the study area.

Onchocerciasis in Ecuador: evolution of chorioretinopathy after amocarzine treatment

AIMS

To investigate the impact of the macrofilaricidal drug, amocarzine, on the evolution of chorioretinopathy in onchocerciasis.

METHODS

A prospective uncontrolled cohort study was performed using subjects infected with Onchocerca volvulus in a hyperendemic onchocerciasis focus in Esmeraldas Province in Ecuador. Study subjects were recruited into four cohorts in which ophthalmic and parasitological data were collected for 2, 3, 4, and 5 years respectively.

RESULTS

Complete ophthalmic follow up was obtained for 294 individuals in the four cohorts. The incidence of retinal pigment epithelial atrophy tended to remain constant between cohorts while that of chorioretinal scarring with a greater observation period. The incidence rate of cases with new or extending chorioretinal lesions was greater with an increasing period of follow up. An association was seen between the cumulative microfilarial loads in the skin and the development of new chorioretinal lesions (p < 0.05). No relation was noted between cumulative microfilarial loads and the progression of existing disease.

CONCLUSION

Amocarzine therapy did not prevent the natural evolution of chorioretinal disease. It was suggested that ocular microfilariae were necessary for the induction of chorioretinopathy in previously unaffected eyes and that extension of existing disease might also be related to the presence of ocular microfilariae or to other immunological mechanisms.