Filaria and filariasis. Clinical syndromes; species and diagnostic tests - Microscopic exam; IgG antibodies with antigen of Acanthocheilonema vitae; Molecular Diagnosis (PCR); Species identification (PCR and sequencing)
Filariasis are a group of diseases affecting people and animals caused by filarial worms. There are more than 100 species, but only 8 species (Wuchereria bancrofti, Brugia Malawi, timori Brugia, Onchocerca volvulus, Loa loa, Mansonella streptocerca, Mansonella ozzardi and Mansonella perstans) cause human infections. Of these, lymphatic filariasis causes the skin and filariasis, by its clinical manifestations are the most significant. Other filarial species cause incomplete filariasis, because adults do not reach maturity in the human host and can not lead to the first larva known as microfilaria, as with Dirofilaria immitis (heartworm of the dog), Dirofilaria (Nochtiella) repens and Dirofilaria tenuis (heart worm -mapache- raccoon). Lymphatic filariasis are the second leading cause of disability worldwide after leprosy, affecting some 90 million people. They have a specific geographical distribution: Wuchereria bancrofti is in sub - Saharan Africa, Southeast Asia, Pacific Islands and India, while Brugia malayi is in the same locations except sub - Saharan Africa and Brugia timori on the island of Timor in Indonesia. Onchocerca volvulus is in Africa and Central and South America and in Africa Loa loa.
These infections can be asymptomatic in 70% of those infected. Infections are usually acquired in childhood, but do not appear until adolescence or adults, when the parasite burden is greater, by repeated reinfection. Infections are usually classified according to the usual habitat of adult worms in the host vertebrate, and manifest with signs and symptoms:
• Lymphatic filariasis, caused by Wuchereria bancrofti, Brugia malayi and Brugia timori. The usual clinical manifetaciones include fever, inguinal or axillary lymphadenopathy, testicular pain and / groin, skin exfoliation, swelling of limbs or genital. Repeated episodes of inflammation and lymphedema cause lymphatic damage, chronic swelling, and elephantiasis of legs, arms, scrotum, vulva and breast. Adult (80 to 100 mm females and males 40 mm long), are located in the lymph nodes and in the efferent lymphatic, most commonly in the femoral lymph nodes epitrocleares. Sometimes they cause abscessed lymph or along the lymphatics. This abscessification is more common with Brugia timori, with Wuchereria bancrofti or Brugia malayi. Cell invasion with plasma cells, macrophages and eosinophils, together with lymphatic endothelial hyperplasia occurs in inflammatory episodes repeat. This gives rise to lymphatic damage and exudation of lymph tissue, thickening and verrucous skin change, which can superinfected with bacteria or fungi, making the skin having hyperkeratosis, acanthosis, loss of elastin fibers (presbidermia), and fibrosis, leading the box elephantiasis. Brugia malayi usually affects upper and lower extremities, and rarely produces genital and chyluria involvement.
• skin filariasis produced by Onchocerca volvulus (river blindness), Loa loa (loasis) and Mansonella streptocerca. Onchocerciasis (Onchocerca volvulus) (leopard skin, or river blindness), is characterized by the clinical triad of dermatitis, lumps (lumps) -nódulos- skin and eye damage that may eventually lead to blindness. Dermatitis include edema, pruritus, erythema, papules, rashes, pigmentary alterations and lichenification. The -oncocercomas- skin nodules are nodules that are more frequent over bony prominences. Eye injuries are related to the duration and intensity of infection and are due to the immune response to microfilariae. Loiasis (Loa loa), characterized by the Calabar swellings (name derived from the southwestern region of Nigeria), corresponding to subcutaneous localized edema in the extremities, not erythematous, frequently around joints. Subcutaneous edema usually accompanied by localized pain, pruritus and urticaria. Arthritis, meningoencephalopathy, peripheral neuropathies, pleural effusion, retinopathy, or myocardial fibrosis: Sometimes, rare events as they occur. Mansonella streptocerca infections are usually asymptomatic, and when symptoms can manifest itching, skin bumps, and lymphadenitis.
Onchocerca volvulus infection (river blindness, to affect people living in the vicinity of rapid streams, where the arthropod vector, Simulium spp. Mosca Negra- lives), affects many people living in 34 countries Africa, Middle East, South America and Central America. The countries most affected are those in sub - Saharan Africa as Ghana, Nigeria, Liberia, and part of Mali. However, it is endemic in other countries in the latitude of Africa, the Middle East and Southwest Asia, with outbreaks in Yemen and Oman on the Arabian peninsula. There are small pockets in Ecuador, Venezuela, Colombia, Brazil, Southern Mexico and Guatemala.
The main manifestations are severe skin itching, skin lesions (cutaneous nodules, inflammatory lesions and scratching areas), and after several years of infection, progressive loss of vision up to blindness. Skin reactions range from mild itching to widespread and intense localized. The intense itching causes scratching that causes skin lesions and secondary bacterial infections. These skin lesions, if left untreated, can progress to chronic redness, skin thickening and hyperpigmentation. In the final stages the skin becomes very thin (appearance of cigarette paper) and depigmented areas (leopard skin) appear. Skin nodules are caused by winding of adults in the subcutaneous tissue, where they are protected from the immune system, they are fertilized and reproduce, releasing microfilariae larvae. The nodules are preferably on bony areas with the pelvis, hips, ribs, scapula and skull. Ocular lesions are the consequence of the inflammatory reaction triggered by the larvae which die in the eye. Initially they appear opaque reversible corneal injury, which subsequently opacified cornea and cause blindness. In addition to the other eye cornea areas are affected, including the back and optic nerve.
• Filariasis cavitarias produced by Mansonella perstans and Mansonella ozzardi. These are usually asymptomatic filariasis. When symptoms can manifest as fever, itching, lump (lumps) skin, lymphadenitis, and abdominal pain.
• hidden Filariasis. This diagnosis corresponds to a filarial infection, where no microfilariae are observed. One of these corresponds to syndromic diagnoses tropical pulmonary eosinophilia (TPE: Pulmonary Eosinophilia Tropical), characterized by dry cough, paroxysmal dyspnea, anorexia, malaise, weight loss and peripheral eosinophilia. In this syndrome there hyperresponsiveness to antigens or Wuchereria bancrofti Brugia malayi, and the symptoms are the result of inflammatory and allergic reaction generated by microfilariae and parasite antigens lungs try to eliminate the bloodstream. Another syndrome is acute adenolymphangitis, corresponding to the sudden onset fever, lymphadenopathy painful due to retrograde lymphangitis, fever associated with inflammation of the inguinal lymph, testes and vas deferens, and lymphedema. Symptoms disappear within a week, but may recur.
• Infections immitis and Dirofilaria repens Diriofilaria. Infections of these species of filarial own animals, leading to a state of larva migrans, as their microfilariae do not reach adult development when they infect people. Heartworm can cause lung damage caused by immature heartworms in the lungs, which present with chest discomfort, cough, fever and hemoptysis. If the larvae are housed in the branches of the pulmonary arteries can cause pulmonary infarcts. Dirofilaria repens infections usually occur with some packages ( "lumps") subcutaneous, submucosal, or eyelids.
General biological cycle
The life cycle involves the presence in the vertebrate host, where the adults (male and female), producing the first instar (microfilaria). These microfilariae are captured by arthropod vectors, and in them a second larval stage migrate to the chest muscles, to give third instars appears. This development in the arthropod vector lasts 1 to 2 weeks. After this period can cause infection when they are inoculated to a vertebrate host, and in about a year mature into adult worms, males and females. Different species of filariasis are distinguished by body location of adults for the location of the microfilariae and arthropod vectors. In lymphatic filariasis by Wuchereria bancrofti, Brugia malayi, Brugia timori or, arthropod vectors are mosquitoes of the genera Aedes, Anopheles, Culex and Mansonia spp. Filariasis skin in Onchocerca volvulus the arthropod vector are Simulium species. Cutaneous filariasis in Loa loa, arthropod vectors are species of Chrysops.
Actually, the transmission by mosquitoes is not very efficient and require an extended stay in an endemic area for acquiring infection. Adult infection, does not increase in an individual, unless new inoculations of microfilariae is exposed by new bites of arthropod vectors.
• blood Microscopic examination: observation in blood smears of microfilariae of the species that cause lymphatic filariasis (Wuchereria bancrofti, Brugia malayi and Brugia timori) of the species causing loiasis (Loa loa), and causing hidden infections or cavitarias as Mansonella ozzardi and Mansonella perstans. Because they may have periodicity in the peripheral circulation, tests are performed at various intervals over 24 hours. Wuchereria bancrofti and Brugia malayi often have nocturnal periodicity, so we recommend taking the samples between 10 pm and 2 am. It can induce nocturnal periodicity with a dose per day of 1.2 mg / kg diethylcarbamazine (DEC). Microfilariae are usually absent in patients with loasis, in patients with acute adenolymphangitis syndrome and chronic lymphatic late forms. For microscopic examination, blood lancing venous blood to prepare blood smears with Knott method can be used. Venous blood can also be filtered by a filter type nucleopore for easy finding. Microscopic for the presence or absence of sheath, and the location of the nuclei at the distal end (tail) features differentiate species microfilariae. Wucheria bancrofti lacking nuclei in the tail, while Brugia malayi has subterminals terminals and cores. The Onchocercomectomía can also be performed - lumpectomy (lumpectomy onchocerciasis), for observation and demonstrate the presence of adult skin nodules.
• Microscopic examination of urine: the urine quilúricas must concentrate and observe the sediment for the presence of microfilariae in the lymphangitic filariasis.
• Microscopic examination skin: this observation is required in Onchocerca volvulus infections and Mansonella streptocerca. To do this, samples of cuts / pinches skin biopsies performed in various places on both sides of the body are used. Recommended to take samples in African onchocerciasis places are the gluteus and calves, while for the American onchocerciasis are the skin over the scapula and the deltoid muscle. To observe the microfilariae is necessary to allow its exit from the skin sample. Samples should be about 3 mm in diameter, taken with an instrument needle biopsies, or cutting a surface part of skin with a scalpel, in a fold caught by pinching with fingers area inflamed skin, preferably the skin covers the iliac crests, the scapula or lower extremities. For more sensitivity should be 6 samples from different areas, but it has the problem that it can be negative in the prepatent period (when they have not yet matured adults and females still do not release microfilariae, a period that can last 1 to 1.5 years after infection), as well as in cases of low-grade infections.
• Test Mazzotti: in cutaneous filariasis, when no microfilariae are observed, Mazzotti test can be performed. This test causes intense itching, a few hours after a dose of diethylcarbamazine (50 to 100 mg). Steroids may be necessary to control the inflammatory reaction. This test must be done carefully in individuals who have a substantial infection because it can trigger a severe systemic reaction. In these patients skin patch test which triggers a localized skin reaction can be performed.
• slit lamp examination (slip-lamp) microfilariae of Onchocerca volvulus can be observed in the cornea or anterior eye chamber using the slit lamp.
• filarial antigen detection. The presence of circulating antigen in peripheral blood filaria, with or without microfilariae detected, can be performed with ELISA methods (quantitative), or immunochromatography (qualitative). Quantitative ELISA test, were used to monitor therapeutic efficacy. These tests may remain positive after three years of treatment. Usually only it has done in places where there is endemic.
• Detection of antibodies. Detection of IgG or IgE antibodies with antigen other species as Acanthocheilonema viteae, is not species specific. They are trialing recombinant antigens to detect IgG4 onchocerciasis. These tests can give cross reaction with Strongyloides. Positivity of antibodies have little value for patients living in endemic areas because most residents in areas where filariasis is endemic have been sensitized to filarial antigens over the years by exposure to mosquitoes. Additionally, antigens filarial may cross - react with other antigens of parasitic nematodes such areas. Therefore, a serological result is necessary, but it is not definitive for the diagnosis of filariasis by Wuchereria bancrofti or Brugia malayi. The situation is different in patients who are not natives of endemic areas. In these (for example, a European or an American) a negative result in a patient whose symptoms (clinical) suggests a lymphatic filariasis after a trip to an area where filariasis is endemic powerfully suggests that there is no infection. Antibody tests can not distinguish between past or current infection, nor is there any correlation between the serological response and the parasite load. These comments are valid for Onchocerciasis (parasitism by Onchocerca volvulus).
• Molecular detection by PCR. These tests are being applied to diagnosis, and are very useful for diagnosis of blood samples or skin.
• Molecular identification. Molecular identification amplification can be performed by PCR, followed by sequencing.
Filariasis are treated with various drugs, but should not be made self - medication by patients themselves , because some drugs are toxic and require medical supervision during administration. It should be noted that some drugs affect the larvae (microfilaricidal) and do not remove the infection to continue present in the adult organism. Other drugs act against adult worms (macrofilaricides), and some against both microfilariae and adults. The most useful drugs are as follows
• diethylcarbamazine (DEC) has action against microfilariae, inducing immobilization through a hyperpolarizing effect, and altering their surface membrane, which facilitates its disintegration. It is used for onchocerciasis and loiasis, but by itself does not eliminate the infection.
• Ivermectin: it has action against microfilariae and adult helminths (microfilaricide and macrofilaricide) is the drug of choice for Wuchereria bancrofti. It can be used alone or in combination with diethylcarbamazine. It exerts its effect by acting as antagonists of the receptors for gamma - aminobutyric (GABA). To not cross the blood - brain barrier, acts neither exerts effect on people.
• Suramin: it has action against adults. It is the only useful drug for onchocerciasis, but it is quite toxic, with potential to cause complications so its use is restricted, and should be limited to manage in geographic areas without transmission vectors, patients leaving an endemic area and in patients with hipereactiva onchodermatitis, if your symptoms are not well controlled with ivermectin.
• Doxycycline: this antimicrobial has been used in treatments 6 to 8 weeks for lymphatic filariasis, and is better tolerated than treatment with ivermectin. It has also been used in 3 - week regimen, followed by a dose of diethylcarbamazine. Mansonella for filariasis perstans, which is resistant to anthelmintics, contributes to the endosymbiont Wolbachia eradicate and thereby eliminate the infection.
• Other drugs: mebendazole and albendazole Flubendazole.
Tests in IVAMI:
• Microscopic examination of blood samples, urine quilúrica, biopsies of skin cuts or pinches (see above indication of each sample by type of filariasis), time of sampling, and clinical manifestations.
• Detection of antibodies by ELISA using as antigen Acanthocheilonema viteae. This test has a sensitivity of 80%, and allows diagnosis in the prepatent period (when they have not yet matured adults and there are no microfilaria).
• PCR test on blood samples, urine or skin quilúrica parts (or cuts of skin biopsies pinches).
• Microscopic examination: no coagulated blood tube, quilúrica urine, or biopsy / pinch skin cut introduced in microtubes with a few drops of sterile physiological saline, as appropriate (see above).
• PCR tests: no coagulated blood tube, quilúrica urine, or biopsy / pinch skin cut, as appropriate (see above).
• Antibodies: serum (0.5 to 1 mL) in sterile polypropylene tube.
Preservation and shipment of sample:
Refrigerated (preferred) for less than two days for microscopic examination, PCR and antibodies.
Frozen (PCR tests or antibody detection. More than 2 days not freeze to microscopic examination.