You notice a figure sitting on a porch in the North-Western region of Ecuador. As you approach it appears to be an elderly man but as you approach him you notice that he has features that you have never seen before. His skin looks as if it has been draped onto his skeletal frame causing him to lose all age indicators. Your eyes reach his and he does not make eye contact, a clear indication that he is blind. You approach the lizard man and ask his age, he replies “Cuarenta y tres.
” You wonder to yourself how could a man who is 43 years old have lost his vision and aged so prematurely?
The simple answer is Onchocerciasis or more commonly known as River Blindness. Desowitz (1981) discusses the history, causes, and possible treatments of River Blindness in his book “New Guinea Tapeworms and Jewish Grandmothers. Tales of Parasites and People. ” Desowitz mainly focuses on river blindness throughout Africa but discusses how this life-altering parasite was brought to Latin America and where it is prevalent.
Desowitz (1981, p. 92) states that river blindness was first introduced to America in two waves.
The first wave was in 1590 when slaves from West Africa were brought to Columbia and Venezuela for gold mining. The second occurred when Napoleon III sent Sudanese troops to Oaxaca (a state in Southern Mexico) in 1862 to help French forces fighting in the region. Over four centuries later, according to the Carter Center’s website for the Onchocerciasis Elimination Program of the Americas (2008), “in the Americas, 500,000 people are at risk for river blindness, and 180,000 are infected in endemic nations. ”
River Blindness is prevalent in six Latin American countries: Venezuela, Brazil, Columbia, Ecuador, Guatemala, and Mexico, and affects rural peasants who do not travel frequently. Foci, the center for main disease activity, exist in Mexico and Guatemalan highlands that are at an elevation between 1,600 and 5,000ft and areas on the banks of organically rich water sources. These areas are usually located on or near coffee plantations causing 30-75% of the workers to become infected with the disease and carry it back to their communities (Desowitz 1981, p. 93).
The disease affects Ecuadorians and Columbians living by rivers’ shores. In Brazil and Venezuela the nomadic Yanomami population (a group who hunts and travels throughout the Amazon Rainforest), is one of the most severely affected populations due to the fact that they are at continuous risk for exposure to the vector of the river blindness parasite (The Carter Center, 2008). The Pesky Filarial Worm Known as Onchocerca Volvulus Onchocerca Volvulus is the first cousin to the parasite that causes Elephantiasis a disease that causes the thickening of the skin and underlying tissues of a human.
The parasite (Onchocerca volvulus) is the cause of river blindness and is classified as a filarial nematode, shown in Figure 1. This type of parasite is an invertebrate animal more commonly known as a roundworm. The roundworms digestive tract makes it different than other invertebrates such as cnidarians or flatworms. Figure One: Onchocerca volvulus (adult worms) Opperdoes (2002) The adult worms are threadlike creatures that live within fibrous nodules beneath the human hosts skin on boney areas such as hip bones and knee caps.
Female adult worms can produce over 2,000 microfilariae (eggs) everyday for its lifespan of 15-20 years. The eggs produced by the adult female worm hatch within its uterus and disperse throughout the hosts skin once released. This dispersal causes the devastating side affects of river blindness. But before the worm can begin to take its toll on the human body, it must mature within its vector the Simulium damnosum, the black fly (Desowitz 1981, p. 93). Simulium damnosum: The Vector Desowitz (1981, p. 97) states that the black fly is highly selective in choosing where it will breed and lay its eggs.
This selectivity is fundamental to where river blindness is distributed within a specific area. The more appealing a breeding ground is the higher the population of black flies and as a result the prevalence of river blindness is higher in said area. According to Desowitz (1981, p. 98) black flies only lay their “eggs in fast flowing, well oxygenated water with enough [plant and animal material] to sustain and nourish the larvae. ” The larvae attach to stones, aquatic vegetation, or tree limbs until they mature into adult flies.
These mature flies serve as the larval host for the nematode and is the vector for river blindness. The Cycle: Ingestion, Growth, Baby Worms, Ingestion. Rinse and Repeat. Desowitz (1981, p. 94) describes the metamorphous of the nematode within the black fly (shown in Figure 2). While the fly is feeding on an infected human it ingests the eggs that are found in the uppermost layer of the human’s skin (sub-epidermal). In two weeks the eggs transform into filariform larva (the infective stage) inside the fly’s body, as illustrated in Figure 3.
The nematode goes through a transformation beginning in the fly’s abdominal region after the fly ingests the eggs (microfilaria) produced in the human tissue. The ingested eggs then travel into the muscles of the fly’s thorax, this is where the nematode’s eggs metamorphose into the infective stage (filariform larvae). From the thorax the infective worms migrate to the fly’s head and mouth regions. Finally the worm is transferred from vector to host once the fly feeds on a human and implants the worm into the bottom layer (subcutaneous tissue) of its victims skin.
Once the worm is inside the host’s skin it matures and mates. Nine months after the female worm mates it begins producing the eggs that will be digested by the vector and continue the cycle. Figure Two: Simulium Black Fly Figure Three: Parasite Maturation in Fly adapted from bumblebee. org (1997) adapted from Desowitz 1981, p. 94 Once inside the human the worms begin to create nodules within the human’s skin. These nodules are obstructions causing bumps and lacerations beneath the skins surface.
As the eggs are released they begin to travel throughout the subcutaneous layer of the host’s skin (Figure 4) causing their immune system to react (Gonzales et al. 2009), this reaction causes the bodily mutilation that is associated with river blindness. The disease may range mild (dermatitis) to severe (visual impairment and blindness). Figure 4: Layers of Human Skin Bupa’s Health Information Team (September 2010) Once the immune system reacts to the parasitic egg the victim’s skin becomes inflamed causing extreme itching. This severe itching has been known to cause some to commit suicide.
This migration causes the once normal human skin to become thick and depigmented resembling and feeling like that of an elephants (pachyderm) skin. Figure 5 is a picture from the Neglected Tropical Disease website (2010) which shows “a Ugandan man suffering from [river blindness]. [The picture] shows the inflammation and de-pigmentation the condition is causing on his back. ” The immature worms travel throughout the host’s body and may reach the eye. If the disease is severe it will cause the host to become severely visually impaired or lose their vision completely.
The undeveloped worms invade the cornea, anterior chamber, retina, and optic nerve of the eyeball. As the worms invade the host’s eye their immune system begins to react causing ocular lesions and inflammation (Desowitz 1981, pg. 95). It is estimated that 770,000 people around the World are blind or visually impaired as a result of river blindness (Vierra et al. , 2007). Figure 5: Image of an African man who has river blindness and its affects on the skins structure “USAID’s Neglected Tropical Disease Program: Newsroom, Photo Galleries, Snapshots from Uganda. ” (2010)
Affects on the Community Okulicz et al. (2009) published that River Blindness does not only leave its victims maimed but it also has had detrimental effects on socioeconomic development in heavily afflicted areas. Areas in which the people of the community are employed i. e. Coffee plantations, are located near rivers and streams which are prime breeding areas for the vectors causing the transmission of RB to increase. Workers are bitten repeatedly and contract the disease causing them to become handicapped and unable to work and support themselves or their family.
As a result, their community does not grow economically and leads to extreme poverty. Eventually when the majority of the population is physically impaired by the disease they will move to an area farther away from the vectors breeding grounds, which may be an drier area or a new area along the river. This migration has left a lot of farmable land abandoned (WHOa 2010). Desowitz (1981, p. 98-99) maps out the never-ending cycle of trying to escape the disease and the choice members of these communities must make between food or sight.
Once the eye lesions begin people abandon their towns and jobs to live in a place away from the vector’s breeding grounds. The soil is not nutrient rich in these areas and the new inhabitants end up ruining the soil trying to plant crops, forcing them to either relocate again repeating the cycle of ruining the land or go back to areas closer to a water source and become blind. Another decision many communities make to relocate on the banks of rivers and streams. During the beginning of their relocation things will seem promising but as the population around the water increases so does the organic material found in the water.
Organically rich water is the ideal breeding ground for black flies, which causes the cycle of river blindness to begin in that new area. If river blindness is eliminated it will allow people to properly farm on fertile land and live without having to make the choice between “food or sight”. Not only does RB have a negative affect on the land and people physically it also keeps others from getting proper treatment for other diseases such as HIV and tuberculosis. According to Vieira et al. (2007) the elimination of this disease will also allow funds that have been used to treat it to be redirected towards other disease treatments and research.
Due to river blindness’s detrimental impact on communities across the globe it became obvious that RB needed to be eliminated. Desowitz (1981) mentions the only drug that has been shown to be successful in treating river blindness but also has serious side affects if taken. The War Against RB Begins In 1981 when “New Guinea Tapeworms and Jewish Grandmothers. Tales of Parasites and People” was published there was no drug on the market that could safely and successfully treat river blindness. Desowitz suggested that in order to successfully get rid of RB you would have to either eliminate he black fly or the parasite itself. In his book Desowitz mentions the only known drug at the time DEC and it’s dangerous and sometimes deadly side affects. According to Stanford. edu diethylcarbamazine (DEC) was administered to treat areas in which RB was a major problem. It was developed during World War II and was given to Australian and American soldiers fighting in the Pacific Islands who were infected with a lymphatic parasite (a thread-like parasitic worms that damage the human lymphatic system).
After the war, DEC was found to be very effective at killing the eggs (microfilariae) produced by the adult parasites (O. volvulus). According to the onchocerciasis website at stanford. edu, Markell and Voges wrote in the Medical Parasitology (1999) that the sudden death of such an enormous amount of microfilariae under the skin can cause horrific affects such as irreversible eye damage, rash, peeling of the skin, diarrhea, and kidney damage. Due to DEC’s debilitating side affects the victims of river blindness were in desperate need of an alternate solution.
Thankfully, in 1983, due to the tremendous loss of livestock farmers began demanding a drug that would keep their livelihood safe from parasitic worms and as a result a new drug was discovered that would change the treatment of RB forever. The Discovery of Ivermectin W. C. Campbell et al. (1983) published a paper introducing a new drug that could help prevent and kill two types of animal parasites: nematodes (roundworms) and insects, ticks, and mites. Campbell and his colleagues’ were trying to find a drug to fight parasites that were killing livestock across the country.
They noticed that the “[usefulness] of the drug against the skin dwelling micfilariae [immature worms] of a roundworm (Onchocerca) species in horses and cattle suggested that the drug might have useful activity against the RB parasite (O. volvulus). ” While ivermectin is useful in the treatment of river blindness it is not a cure for the disease and parasitic resistance to the drug is a serious concern. Ivermectin helps in preventing the transmission of the infection but it does not kill the adult worm.
It reduces the amount of eggs a roundworm can produce and shortens the lifespan of adult worms and causes nematode paralysis by impairing its brains ability to communicate with its muscles (Gonzales et al. 2009). Studies performed in the 1980s showed that the drug Mectizan® (ivermectin), made by Merck & Co. Inc. , could effectively and safely treat and prevent river blindness. Merck decided in the late 1980’s to donate the drug to all who needed it for as long as needed (The Carter Center, 2008). The Beginning of Elimination In September of 1987 Taylor et al. onducted a study of ivermectin’s affect on a community plagued by river blindness over a three-year period (until November 1989). It was the first study to test the affects in a large community that was approximately 14,000 people.
The study was conducted at the Liberian Agriculture Company (LAC) in West Africa. It found that those who consistently stayed in the community and received their annual treatments of ivermectin that it would be “reasonable to expect not only a reduction in both the parasite densities found within the community but also the number of cases diagnosed. This study showed that Latin America was the perfect test area for a mass ivermectin trial because there was hardly any travel in and out of communities heavily burdened by RB. There was even a possibility that river blindness could be completely eliminated in these communities. In 1993 the Carter Center launched its campaign to eliminate river blindness completely in Latin America. It joined forces with the ministries of health of the six affected countries, the Pan American Health Organization (PAHO), the U. S.
Centers for Disease Control and Prevention, academic institutions, and independent organizations to form the Onchocerciasis Elimination Program of the Americas (OEPA) (The Carter Center, 2008). Study of Ivermectin Treatments in Ecuador During the year 2007 Vieira et al. published a research article which showed the affects of mass ivermectin treatments throughout communities in Ecuador that are heavily afflicted by river blindness. From 1990-2003 ivermectin was distributed twice annually in afflicted communities and tested its impact on ocular morbidity, and the parasitic (O. volvulus) infection and transmission in seven sentinel communities.
The District of Eloy Alfaro (Figure 6A) is the region in which river blindness is the most prominent. Within this district lies the Santiago basin area which is formed by three rivers, the Rio Santiago, Rio Cayapas, and Rio Onzole which forms a separate sub-focus (Figure 6B). Satellite endemic foci are areas outside of the main region caused by the migration of people who are infected with the parasite. There are five satellite endemic foci located on the Rio Canande, Rio Verde, Rio Viche, Rio Sucio, and Rio Tuluvi rivers and another focus is found on the neighboring province near Santo Domingo de los Colorados (Figure 6A).
All together there are 119 communities in which river blindness is prevalent. Figure 6A: Geographic location of RB in Ecuador Figure 6B: Location of 7 sentinel communities Vieira et al. (2007) Study Area Over a period of three years, from 1990 to 1993, ivermectin distribution began in most endemic communities (treatment was delayed until 1997 in some communities). In order for someone to be eligible for treatment they had to weigh over 15kg (?30. 1 lbs), women could not be pregnant or nursing, children had to be over three months of age, and each participant had to be free of any serious illness.
The drug was administered by trained health professionals and taken orally by the patient at a dose of 150g/mg. It was discovered in 1998 that twice-annual treatments could oppress the transmission in the Santiago basin where infection rates are high. Table 1 shows the number of communities, year of first ivermectin treatment, and the number of treatments given in highly (hypo), moderately (meso), and slightly (hypo) affected communities. Vieira et al. (2007)
The impact of ivermectin treatments were studied closer in seven communities within the Santiago basin: three highly infected communities along the Rio Santiago (Playa del Oro, Angostura, and Guayabal), moderately infected communities along the Rio Cayapas river (Coriente Grande, El Tigre, and San Miguel), and slightly infected communities located in the satellite focus along the Rio Canande river (Naranjal de los Chachis). The highly infected community and satellite focus were chosen to monitor the reduction in the transmission of the parasite as a result of invermectin treatments.
Data Taken from Each Community Skin snips were taken from both iliac crests (hip bones) and were placed in a micro-well plate with phosphate buffered saline. After twenty-four hours the solution caused the immature worms to emerge, once exposed they were then counted and the microfilarial densities (mf/mg) we determined. This determined the prevalence of infection and microfilarial load in each community. Eye Problems caused by river blindness were determined with eye examinations performed by experienced ophthalmologists.
The doctor’s assessed the visual acuity of each individual, examined the structures at the front of the eye by using a low-power microscope combined with a high-intensity light source that can be focused to shine in a thin beam (slit lamp examination), and examined the structures in the back of the eyeball indirectly and directly by shining a beam of light it. In 1995 Simulium blackfly samples were collected during prime biting season in the sentinel communities of Tigre and San Miguel and in the other five between 2000 and 2004.
The flies were tested for the parasites DNA in pools of 50. The prevalence of infection was calculated by using a statistical program (Pool Screen 2. 0 adapted from The University of Alabama) that estimates the prevalence of infection in the black fly population based upon the proportions of DNA found in each test pool. Results Between 1990 and 2000 ivermectin treatments were provided to all of the endemic communities except seven communities in the Rio Cayapas where treatment was delayed from 1995 to 1996 because of money issues.
Out of the seven communities five received a total of 21 treatments whereas El Tigre and San Miguel only received 13 treatments of ivermectin. The average treatment coverage was greater than or equal to 85% in all of the communities but Guayabal (84. 7%) in the Rio Santiago sub-focus and Naranjal (83. 9%) found in the Rio Canande sub-focus. By 2004, there were obvious reductions in the prevalence of river blindness found within each sentinel community (Table 3). The members of each community were tested for the presence of microfilariae, three of the sentinel communities had members who tested positive.
All positive members were in the highly infected Rio Cayapas sub-focus (Coriente Grande, 1 person; El Tigre, 2; and San Miguel, 2) and had only received a median of 11 treatments of ivermectin. It was also found that no children under the age of 5 had positive skin snips. This shows a remarkable decline in river blindness infection throughout each community. Vieira et al. (2007) Data was collected for the early frontal segment changes in the eye that are commonly found among individuals diagnosed with river blindness.
Doctor’s were looking for people who have punctate keratitis which is inflammation of the cornea, the iris (colored part of the eye), and the pupil, they were also looking for the presence of microfilariae in the front part of the eyeball. In Table 4 the prevalence of these eye afflictions are shown before and after 2004. By the end of the trial there was no evidence of inflammation or microfilariae in the frontal parts of the eyeball in any of the sentinel communities. Vieira et al. (2007) By 2004 only two communities (El Tigre and San Miguel) had flies infected with the parasite.
Table 5 illustrates the decline of infection rates among the black fly vectors in each community. Vieira et al. (2007) Is Ecuador RB Free? This study proves that twice-annual distribution of ivermectin to over 85% of the population can complete suppress transmission of the river blindness parasite. There is some evidence that the infection has been eliminated in the Rio Santiago and Rio Canande communities. If suppression of transmission can be maintained in an isolated community for the reproductive life span of adult females (13-14 years) the adult parasite will die from the inability to reproduce and the infection will die out.
According to OEPA, in order to be declared river blindness free a country must complete four phases: Phase 1) Treatment coverage of greater than 85% of the population with twice annual ivermectin treatment for a period of 2-4 years, Phase 2) Biannual high coverage treatment with no blackflies infected with the parasite and no new cases for 12-14 years (life span of adult worm), Phase 3) Treatment will be suspended for 3 years and monitored for any new infections, and Phase 4) Become certified as RB free. According to the WHO Report (2010b) Ecuador is the second country to suspend all treatment.
WHO Update. The World Health Organization published a press release from the 2009 InterAmerican Conference (2010) on the progress towards eliminating river blindness in the Americas. It appears that the number of communities requiring ivermectin treatments fell from 13 in 2006 to 7 in 2009. Those areas were: Escuintla-Guatemala, Huehuetenago and Santa Rosa located in Guatemala; Northnern Chiapas and Oaxaca found in Mexico; and Lopez de Micay in Colombia. These communities will be monitored and must be completely free of any sign of river blindness for the next three years in order to be declared free of the parasite (O. olvulus). The WHO predicts that the Yanomami area located in Brazil will be the last focus to interrupt the transmission the parasite and suspend ivermectin treatments. The reason that the Yanomami communities are so hard to reach is because they are found deep within the Amazon rainforest and are constantly exposed to the black fly vector. Banic et al. (2009) conducted a study to asses the effects of twice annual ivermectin treatments on the prevalence of river blindness in areas that are highly infected.
After six rounds of treatment over a period of six months the prevalence of infection had declined from 87% to 42%. These findings suggest that treatments should be conducted at a higher rate in this community in order to speed up the process of eliminating the river blindness parasite and halting the spread of the disease to other people in surrounding areas (WHOb 2010). Optimistically this highly infected area will be able to halt the transmission of RB by the year 2012 which means by the year 2016 all six Latin American countries will have eliminated the parasite. What Could Go Wrong? Vieira et al. 2007) noted three things that could interrupt the elimination of river blindness: 1) Different types of vectors have a different carrying capacity.
In Ecuador, the Rio Cayapas focus’ prominent vector is the S. exiguum which has a higher carrying capacity than the S. Quadivitatum the prominent vector in the Rio Santiago focus. The fact that one vector has the capacity to carry more of the parasite at any given time is a problem because with each meal the fly takes it deposits more of the parasite into the host, this means that different areas depending on what type of vector and its carrying capacity would have to alter its treatment. ) The infected individuals might refuse treatment repeatedly or be ineligible over a long period of time (i. e. repeated pregnancies). People who refuse treatment or cannot receive treatment remain and active source for transmission of the parasite and are also carriers to other areas outside of that community. 3) A small population of adult worms seemed to respond poorly to the fertility suppression caused by ivermectin.
The way in which to fix this issue is to increase the number of treatments given in combination with doxycycline (an antibiotic used to prevent the spread of bacteria) that can sterilize adult female worms. The main concern for all health officials is the possibility that the parasite will develop resistance to ivermectin, currently there are no safe alternatives available for mass distribution in a human population, this means that if resistance is developed then river blindness could come back and hit communities harder then it did before.
Conclusion As of right now it appears to be very likely that river blindness will be completely eliminated from the America’s. As a result of health education and ivermectin (Mectazin) distribution, there have been no new cases of blindness as a result of the debilitating disease (The Carter Center 2008). The research done in the America’s will allow for a better understanding of how complete elimination of such a horrific disease will benefit the nations afflicted by it both socially and economically.
Only time will tell how big of an impact this will have on each community that has been plagued by river blindness for centuries. It will allow farmers to properly cultivate fertile land without the fear of losing their sight and sustain a happy and healthy lifestyle. The research conducted shows that ivermectin treatments can eliminate the O. volvulus parasite from large areas within a country giving hope that one day it will also be eliminated in even larger areas found in Africa.
The elimination of river blindness throughout an entire country is remarkable. When I first read New Guinea Tapeworms and Jewish Grandmothers (Desowitz, 1981) I thought that the future for areas afflicted with river blindness was bleak but with the discovery of one drug that was developed for livestock has changed the lives of millions all over the world. Thanks to the Carter Center and Merck & Co. Inc. generosity river blindness will soon be completely eliminated in Latin America and no one will ever have to choose between food or sight ever again.
Cite this Onchocerciasis in Latin America
Onchocerciasis in Latin America. (2017, Apr 11). Retrieved from https://graduateway.com/onchocerciasis-in-latin-america/