Wuchereria Bancrofti: Biohelminth, Life Cycle, Diagnostics

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Wuchereria Bancrofti: Biohelminth, Life Cycle, Diagnostics
Wuchereria Bancrofti: Biohelminth, Life Cycle, Diagnostics

Video: Wuchereria Bancrofti: Biohelminth, Life Cycle, Diagnostics

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Video: Wuchereria bancrofti Lifecycle (English) | Wuchereria bancrofti| Lymphatic Filariasis| Elephantiasis 2023, February
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  • Pathogenesis (what happens?) During Wuchereriosis (elephantiasis)
  • Wuchereriosis (elephantiasis) symptoms
  • Development cycle
  • Epidemiology of wuchereriasis
  • Complications
  • Diagnostics
  • Treatment of wuchereriasis
  • Forecast and prevention
  • You can defeat parasites!

The causative agent of wuchereriosis is Wuchereria bancrofti, common in the tropics and subtropics. In the former USSR, elephantiasis was found in isolated cases in Central Asia. Adult filaments are most often found in the lymph glands and blood vessels. As a result of clogging of the lymphatic vessels, an inflammatory thickening of their walls occurs, as well as lymph congestion. The affected areas greatly increase in size.

Females produce a huge number of larvae, each about 0.3 mm long. They are called "nocturnal microfilariae", as they appear at night in the peripheral blood, on the day they go deep into the body and stay in the pulmonary vessels, heart and kidneys. This frequency is associated with the characteristics of the transmission of parasites, which occurs through intermediate hosts, namely, various blood-sucking mosquitoes. When mosquitoes suck the blood of filarial carriers in the evening or at night, the larvae enter the mosquito's stomach and then penetrate into its body cavity.

What to do in such a situation? To get started, we recommend reading this article. This article details the methods of dealing with parasites. We also recommend contacting a specialist. Read the article >>>

There they grow somewhat and eventually accumulate at the base of the piercing proboscis of the insect. When sucking the blood of a healthy person, such a mosquito sticks the pricking bristles of its proboscis into the skin; at this time, the larvae of filariae emerge from the proboscis and are actively drilled into the skin, then entering the blood.

Wuchereria bancrofti is the most common filariae parasitizing humans. The parasite is found in the tropics and subtropics - Asia, Oceania, Africa, in some places in South America and the Caribbean.

Wuchereria bancrofti
Wuchereria bancrofti
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Man is the only final master of Wuchereria bancrofti. Adult worms live in the human body up to 17 years, larvae in the bloodstream - up to 70 days. An estimated 120 million people are infected with wuchereriasis.

According to the terminology adopted by the WHO Expert Committee on Filariasis, periodic and sub-periodic strains of microfilariae are distinguished. Microfilariae Wuchereria bancrofti of the periodic strain (Microfilaria nocturna) are in the vessels of the lungs during the day, and at night they move into the peripheral vessels. Microfilariae Wuchereria bancrofti of a sub-periodic strain identified in the Pacific Ocean and therefore called W. pacifica are in the peripheral blood around the clock, but their number increases markedly during the day.

Pathogenesis (what happens?) During Wuchereriosis (elephantiasis)

The source of wuchereriasis is a sick person or a parasite carrier, the source of brugiosis is a person and some monkeys. Mosquitoes are the direct vectors of infection.

The causative agent of wuchereriasis Wuchereria bancrofti is transmitted by many species of mosquitoes, most often Culex fatigans, C. pipiens, Aedes polynesiensis. The development of microfilariae in mosquitoes lasts 8-35 days, depending on the ambient temperature. When a mosquito bites, the invasive forms of microfilariae enter the skin, are actively introduced into the bloodstream and are brought into the tissues by the blood stream. The transformation of microfilariae into sexually mature forms occurs 3-18 months after they enter the human body.

The pathogenesis of wuchereriosis is based on toxic-allergic reactions, the mechanical effect of helminths on the lymphatic system and secondary bacterial infection. Like many other helminthiases, wuchereriosis in some cases may not give a pronounced clinical picture. Sometimes there are no clinical signs of invasion at all. Asymptomatic wuchereriosis occurs when the parasites do not clog the lymphatic vessels and do not cause inflammatory changes in the surrounding tissues. Patients with such forms of infection are detected by chance when they find microfilariae in the peripheral blood.

Vuchereria in the lymphatic vessels, including the thoracic duct, intertwine with each other into tangles, which cause a slowdown in lymph flow and lymphostasis. The parasites cause inflammation of the lymph vessel walls, which ultimately leads to vascular occlusion as a result of stenosis or thrombosis. Thrombosed lymphatic vessels often rupture.

The altered endothelium of the lymphatic vessels, foci of necrosis in the lymph nodes and surrounding tissues are favorable places for the development of coccal infection with the formation of abscesses. As a result of the vital activity of parasites and, especially during their decay, substances are formed that lead to sensitization of the body with local and general allergic reactions - eosinophilia, skin rashes, etc.

Wuchereria bancrofti
Wuchereria bancrofti
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Wuchereriosis (elephantiasis) symptoms

The asymptomatic incubation period lasts 3-18 months.

Allergic manifestations can develop about 3 months after infection. Microfilariae are detected in the blood no earlier than 9 months later. The disease begins with various allergic manifestations. On the skin, especially on the hands, painful elements such as exudative erythema appear, lymph nodes in the groin areas, on the neck and in the armpits are enlarged, painful lymphangitis, funiculitis, orchioepididymitis often occur, synovitis with an outcome in fibrous ankylosis, in women - mastitis. With prolonged recurrent course of funiculitis and orchiepididymitis, hydrocele occurs.

Fever is characteristic, bronchial asthma and bronchopneumonia often develop. 2-7 years after infection, the disease enters the second stage, which is characterized mainly by lesions of the skin and deep lymphatic vessels with the development of varicose veins, impaired lymph flow, rupture of these vessels. Painful lymphangitis with regional lymphadenitis appears. At this time, for several days, the patient has pronounced phenomena of general intoxication against the background of high body temperature and severe headaches. Vomiting is often observed, sometimes a delirious state develops. The attack usually ends with profuse sweating. As a result of rupture of lymphatic vessels, lymph flow and a decrease in the intensity of lymphadenitis are observed.

The phases of relative well-being are periodically replaced by the next exacerbations of the disease. At the site of lymphangitis, dense cords remain, the affected lymph nodes also undergo fibrous compaction. An increase in the inguinal and femoral lymph nodes is characteristic. The initial swelling of the lymph nodes does not cause pain, but with the subsequent development of lymphangitis, severe pain in the nodes appears. The lesion can be one- or two-sided, the size of the nodes is from small to 5-7 cm in diameter. Often the so-called lymphoscrotum (chylous impregnation of tunica vaginalis) and hiluria develop in parallel.

In the countries of North Africa, India and China, hyluria or lymphuria is common in patients with wuchereriasis. The patient notices that the urine has acquired a milky white hue. In some cases, the urine turns pink or even red, sometimes it is white in the morning and red in the evening, or vice versa. The presence of blood in the urine, along with lymph, is apparently explained by ruptures of small blood vessels, dilated lymphatic vessels. Microfilariae are detected in urine only at night. Sometimes this is preceded by slight pains above the pubis or in the groin areas. Typical is urinary retention due to lymph coagulation and flocculation in the urinary tract. With lymphuria, there is an admixture of lymph in the urine, a significant amount of protein, an admixture of blood is possible, but no traces of fat. Lymphocytes are found in the urine sediment.

Get tested for worms

Symptoms Answer Itching in the anal area Yes Not Dysbacteriosis Yes Not General weakness Yes Not Dry cough Yes Not The appearance of allergic reactions Yes Not Weight loss Yes Not Headaches Yes Not Dizziness Yes Not Increased irritability Yes Not Swelling of the face and eyelids Yes Not

The bodies of dead filariae usually dissolve or calcify without a trace. However, in some cases, dead parasites are the cause of the development of abscesses, which lead to severe complications such as empyema, peritonitis, purulent inflammation of the genitals.

Wuchereria bancrofti
Wuchereria bancrofti
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Due to damage to the walls of the lymphatic vessels during wuchereriosis, microbes can enter the surrounding tissues and into the blood, which can lead to the development of sepsis. In the blood of such patients, hemolytic streptococcus is often found.

The third (obstructive) stage of the disease is characterized by elephantiasis. In 95% of cases, elephantiasis of the lower extremities develops, somewhat less often - of the upper extremities, genitals, individual parts of the body and very rarely of the face. Clinically, elephantiasis is manifested by rapidly progressing lymphangitis with the addition of dermatitis, cellulite in combination with fever, which in some cases can serve as the main symptom of the disease and is a consequence of the addition of a bacterial infection.

Over time, the skin becomes covered with warty and papillomatous growths, there are areas of eczema-like skin changes, non-healing ulcers. Legs can reach enormous sizes, they take the form of shapeless blocks with thick transverse folds of the affected skin. The weight of the scrotum is usually 4-9 kg, and in some cases up to 20 kg, a case is described when the weight of the scrotum in a patient has reached 102 kg. In the case of elephantiasis, the upper eyelid is more often affected.

Development cycle

Infection with wuchereriosis occurs when a person is bitten by mosquitoes of the genera Culex, Anopheles, Aedes or Mansonia. Wuchereria is a biohelminth; in the cycle of its development, there are final and intermediate hosts. The final (definitive) host is a human, the intermediate ones are mosquitoes of the genera Culex, Anopheles, Aedes or Mansonia.

At the time of a mosquito bite a person, the invasive larvae (microfilariae), which are in his oral organs, tear the shell of the proboscis, get on the skin and actively penetrate it. With the blood flow, they migrate to the lymphatic system, where they grow, molt, and after 3-18 months they become sexually mature males and females. The male and female are located together, forming a common ball.

Wuchereria are viviparous. Sexually mature helminths are localized in the peripheral lymphatic vessels and nodes, where females give birth to live larvae of the second stage (microfilariae), covered with a cap. The larvae migrate from the lymphatic system to the blood vessels. During the day, they are found in large blood vessels (carotid artery, aorta) and vessels of internal organs. At night, the larvae migrate to peripheral blood vessels and are therefore called Microfilaria nocturna (nocturnal microfilariae). The daily migration of larvae is associated with the nocturnal activity of mosquitoes (carriers of the causative agent of wuchereriasis).

When a sick person is bitten by female mosquitoes, microfilariae enter the insect's digestive tract, discard the cap, and penetrate through the stomach wall into the body cavity and pectoral muscles. In the muscles, the larvae molt twice, become invasive larvae of the fourth stage, and penetrate the mouth of the mosquito. The duration of the development cycle of larvae in a mosquito depends on the temperature and humidity of the environment and ranges from 8 to 35 days. The optimal conditions for the development of invasive larvae are temperatures of 29-30 ° C and humidity of 70-100%. In the body of a mosquito, the larvae remain viable throughout their life.

Development cycle of wuchereriasis
Development cycle of wuchereriasis
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Epidemiology of wuchereriasis

Endemic foci of wuchereriasis are found in countries with tropical and subtropical climates. Wuchereriasis is common in West and Central Africa, Southeast Asia (India, Malaysia, China, Japan, etc.), South and Central America (Guatemala, Panama, Venezuela, Brazil, etc.), on the islands of the Pacific and Indian oceans. In the Western Hemisphere, the area of ​​wuchereriosis is limited to 30 ° N. sh. and 30 ° S. sh., and in the Eastern Hemisphere - 41 ° N. sh. and 28 ° S. sh.

Wuchereriasis is mainly a disease of the urban population. The growth of large cities, overcrowded population, lack of sanitary control, contaminated water reservoirs, abandoned water supply and sewerage systems favor mosquito breeding.

In the developing countries of Asia and Africa, where cities and towns are being built, infection with wuchereriasis is increasing.

The source of the spread of the disease is infected people. Mosquitoes of the genus Culex are most often the carrier of the pathogen in urban conditions. In rural areas in Africa, South America and some Asian countries, wuchereriosis is carried mainly by mosquitoes of the genus Anopheles, and in the islands of the Pacific Ocean by the genus Aedes. Human infection occurs due to the penetration of invasive larvae when bitten by a mosquito.

Complications

The most common complication is the addition of infection at the site of rupture of the lymphatic vessel with the formation of lymphangitis, thrombophlebitis, gangrene, and sepsis. In addition, lymph is a protein-rich liquid. With constant loss due to vascular damage, progressive protein deficiency develops, patients lose weight, cachexia occurs.

Due to obturation of the urinary tract with blood and lymph clots, acute urinary retention is often noted. Zones of aseptic inflammation appear around the bodies of dead nematodes in the internal organs of a person. Infection of such structures leads to the development of abscesses. With self-opening of the formed abscesses in the serous cavities, pleural empyema, peritonitis, purulent arthritis are formed. A breakthrough of lymph into the lumen of internal organs leads to hyluria, chylous ascites, diarrhea.

Complications
Complications
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Diagnostics

If you suspect wuchereriasis, consultation with an infectious disease specialist, a parasitologist, followed by hospitalization of the patient in an infectious diseases hospital is mandatory. In the case of the formation of elephantism, a surgeon's examination is necessary. Physical examination findings depend on the stage of the disease. In the acute phase, the symptoms of a toxic-allergic reaction come first, and in the chronic phase, the consequences of lymphostasis.

Objectively, palpation is usually determined by unilateral enlargement of the inguinal lymph nodes. The nodes are painful. On the lower extremities, the presence of varicose lymphatic vessels is noted. At the site of their rupture, there are wounds with lymph leakage. At the stage of formation of elephantism, the lower limbs, mainly the legs and feet, are of enormous size, there are many warts and trophic ulcers on the skin. The scrotum, penis, labia majora are significantly enlarged, edematous. The mammary glands can sink below the waist.

The following clinical and laboratory methods are used in diagnostics:

  • Clinical and biochemical research. In the general analysis of blood during an exacerbation, the presence of eosinophilia is characteristic, signs of inflammation are possible; with the progression of protein deficiency, a decrease in the level of total protein and fractions is noted. In the analysis of urine, hiluria is determined.
  • Detection of the pathogen. For direct detection of the parasite, smears or preparations of a thick drop of blood are examined. Microscopy identifies microfilariae. Blood for such studies must be taken at night or during the day when conducting a provocative test with diethylcarbamazine.
  • Determination of infectious markers. To detect specific antigens, rapid ELISA tests are used, a method of rapid immunochromatography. The antibody titer is determined using ELISA, NRIF. Nematode DNA is identified by PCR.
  • Ultrasound procedure. An ultrasound scan of the lymph nodes, scrotum organs, lymphatic vessels of the extremities is performed. An important sonographic sign of wuchereriosis is the detection of moving microfilariae and adult parasites in the lymphatic structures.

Differential diagnosis should be carried out with bacterial lymphangitis, as well as with causes of nodular lymphangitis, such as sporotrichosis and leishmaniasis. It should be borne in mind that serological diagnostic methods can cross-react with Strongyloides stercoralis antigens. Pulmonary eosinophilia must be distinguished from tuberculosis. It is important to differentiate the chronic forms of wuchereriosis from diseases that can cause lymphostasis (hereditary pathologies of the lymphatic vessels, chronic heart failure, varicose veins of the lower extremities).

Treatment of wuchereriasis

All infected must be hospitalized and isolated. Treatment is aimed at the destruction of both larvae and adults. The main drug is diethylcarbamazine. It is taken orally at 6-7 mg / kg / day. 14 days or according to a scheme with a gradual dose increase. The decay products of nematodes can cause allergic reactions, so the drug is prescribed in conjunction with antihistamines and glucocorticosteroids. According to the indications, symptomatic treatment is carried out (taking antipyretic drugs, opening and draining abscesses).

When using diethylcarbamazine, side reactions are often observed in the form of pruritus, lymphadenopathy, hepato- and splenomegaly. In addition, with concomitant onchocerciasis, irreversible eye damage may develop. In order to reduce undesirable effects, alternative schemes have been developed with the addition or isolated use of albendazole and ivermectin. The manifestations of the chronic stage of wuchereriosis are not cured by these medicines. Drugs are prescribed to prevent further progression of the process. Surgical correction of lymphostasis, as well as wearing bandages, helps to improve the quality of life.

Albendazole
Albendazole
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Forecast and prevention

With timely recognition of the disease and timely initiation of therapy, the prognosis is favorable. Fatal cases are most often associated with the development of infectious complications. Non-specific protection measures are aimed at destroying mosquito breeding sites, isolating and treating patients. In countries endemic for wuchereriosis, it is necessary to use mosquito nets, repellents.

Chemoprophylaxis with diethylcarbamazine or albendazole with ivermectin is widespread among the local population. As part of the WHO program for mass coverage of the population in order to prevent the development of the disease, diethylcarbamazine is used as an additive to salt throughout the year. Biological agents for specific prophylaxis have not been developed.

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