LOIASIS AND WUCHERERIA BANCROFTI

OWOEYE AKINOLAOLUWA

These are diseases of public and community-health importance because it affect every stage of human life,the infants less than 5 yrs,childhood,maternal and paternal ,and risky for pregnant women most importantly.We cannot treat this problem except by the full participation of the community

Intro:A wide range of parasitic infections can involve the skin and subcutaneous tissues.

Depending on the species of parasite, this involvement may be transient, the parasite passing through the skin on its migration to the blood stream and so to a specific target organ, or the infection may be localised to the skin.

In the latter infections, the skin may be the primary site of infection or there may be a secondary invasion of the skin. All parasitic groups (protozoa, trematodes, cestodes, nematodes and arthropods) have species which can involve the skin or subcutaneous tissues:

Loiasis picture

Loasis as a public health problem.

The prevalence of microfilaraemia varied considerably between the study sites. Cross River State in Nigeria had the lowest prevalence (range = 0-18%, median = 2%) . In Cameroon's East Province it was much higher (range = 8- 48%, median = 30%). The Buea study sites showed the widest range of endemicity: most villages had a prevalence of less than 10% but there were seven villages with very high prevalences.

The prevalence of high intensity of L. loa infection (>8000 microfilariae/ml) increased with the prevalence of L. loa microfilaraemia at the community level. The 20% threshold prevalence of L. loa in thick smears at the community level corresponded to a 5% prevalence of high intensity of infection. There was a very clear relationship between the two indices and the pattern was similar at all study sites (Fig. 1).

 

Loiasis is limited to the areas of African equatorial rain forest. The incidence in endemic areas varies greatly (8 to 75 percent). The larger, female organisms are 60 mm by 500 micrometers; males are 35mm by 300 micrometers in size.The circulating microfilaria are 300 micrometers by 7 micrometers; the infective larvae in the fly are 200 micrometers by 30 micrometers. The life cycle of Loa loa is identical to that of onchocerca except that the vector for this worm is the deer fly. The infection results in subcutaneous (Calabar) swelling, measuring 5 to 10 cm in diameter, marked by erythema and angioedema, usually in the extremities. The organism migrates

under the skin at a rate of up to an inch every two minutes. Consequently, the swelling appears spontaneously, persists for 4 to 7 days and disappears, and is known as fugitive or Calabar swelling. The worm usually causes no serious problems, except when passing through the orbital conjunctiva or the nose bridge. The diagnosis is based on symptoms, history of deer fly bite and presence of eosinophilia. Recovery of worms from the conjunctiva is confirmatory. Treatment and control are achieved with diethylcarbamazine..

The vector for Loa loa filariasis are flies from two species of the genus Chrysops, C. silacea and C. dimidiata.  During a blood meal, an infected fly (genus Chrysops, day-biting flies) introduces third-stage filarial larvae onto the skin of the human host, where they penetrate into the bite wound .  The larvae develop into adults that commonly reside in subcutaneous tissue .  The female worms measure 40 to 70 mm in length and 0.5 mm in diameter, while the males measure 30 to 34 mm in length and 0.35 to 0.43 mm in diameter.  Adults produce microfilariae measuring 250 to 300 μm by 6 to 8 μm, which are sheathed and have diurnal periodicity.  Microfilariae have been recovered from spinal fluids, urine, and sputum.

During the day they are found in peripheral blood, but during the noncirculation phase, they are found in the lungs .  The fly ingests microfilariae during a blood meal .  After ingestion, the microfilariae lose their sheaths and migrate from the fly's midgut through the hemocoel to the thoracic muscles of the arthropod .  There the microfilariae develop into first-stage larvae  and subsequently into third-stage infective larvae .  The third-stage infective larvae migrate to the fly's proboscis and can infect another human when the fly takes a blood meal

Loiasis, caused by infection with Loa loa infects 3 to 13 million people in Western and

Central Africa. It is also the most common filaroid parasite seen in travellers and other expatriates.

It is transmitted by the bite of female flies of the genus Chrysops and has a typical filaroid life cycle. The adult worms actively migrate through subcutaneous tissue

and sheathed microfilariae appear in the blood during the day.

Many of the infected individuals are asymptomatic despite having circulating microfilariae. Expatriates seldom develop microfilaraemia but they can suffer from a range of allergic symptoms such as pruritis, urticaria, and transient angiodema or “Calabar swellings.

Calabar swellings can occur anywhere on the body but are most common on the face, arms and hands

Loiasis is often accompanied by marked eosinophilia and high serum IgE. Eosinophilia and a history of travel to a Loa loa-endemic area is often the first indication that someone may have the disease. Sometimes a migrating worm may be observed crossing the conjunctiva giving rise to the common name “eyeworm”. Patients may be alarmed, but apart from

mild transient local inflammation the worm causes no long-term damage to the eye .

Renal involvement, as revealed by haematuria and/or proteinuria may occur in up to 30% of loiasis cases and may be exacerbated by treatment .

The most serious complication is encephalitis. It is most commonly precipitated by treatment of individuals with microfilarial counts >5000 per ml of blood and is caused by a rapid increase in antigen shed from the dying microfilariae.

A definitive diagnosis is obtained if an adult worm is removed from the eye by surgery or if characteristic microfilariae are obtained from blood collected during the day

Microfilarial density can be low and it is advisable to use concentration tests as per diagnosis of lymphatic filariasis. PCR-based tests have been developed but are only available at a few specialised centres.Testing for antifilarial antibody is of little value

in endemic populations but is of value in expatriate cases were the absence of such antibody makes loiasis unlikely

Victim of loaloa

WUCHERERIA BANCROFTI

Different species of the following genera of mosquitoes are vectors of W. bancrofti filariasis depending on geographical distribution.  Among them are: Culex (C. annulirostris, C. bitaeniorhynchus, C. quinquefasciatus, and C. pipiens); Anopheles (A. arabinensis, A. bancroftii, A. farauti, A. funestus, A. gambiae, A. koliensis, A. melas, A. merus, A. punctulatus and A. wellcomei); Aedes (A. aegypti, A. aquasalis, A. bellator, A. cooki, A. darlingi, A. kochi, A. polynesiensis, A. pseudoscutellaris, A. rotumae, A. scapularis, and A. vigilax); Mansonia (M. pseudotitillans, M. uniformis); Coquillettidia (C. juxtamansonia). 

During a blood meal, an infected mosquito introduces third-stage filarial larvae onto the skin of the human host, where they penetrate into the bite wound .  They develop in adults that commonly reside in the lymphatics .  The female worms measure 80 to 100 mm in length and 0.24 to 0.30 mm in diameter, while the males measure about

40 mm by .1 mm.  Adults produce microfilariae measuring 244 to 296 μm by 7.5 to 10 μm, which are sheathed and have nocturnal periodicity, except the South Pacific microfilariae which have the absence of marked periodicity.  The microfilariae migrate into lymph and blood channels moving actively through lymph and blood .  A mosquito ingests the microfilariae during a blood meal . 

After ingestion, the microfilariae lose their sheaths and some of them work their way through the wall of the proventriculus and cardiac portion of the mosquito's midgut and reach the thoracic muscles .  There the microfilariae develop into first-stage larvae and subsequently into third-stage infective larvae .  The third-stage infective larvae migrate through the hemocoel to the mosquito's prosbocis and can infect another human when the mosquito takes a blood meal

Wuchereria bancrofti and W. (Brugia) malayi (elephantiasis)

EpidemiologyW. bancrofti is strictly a human pathogen and is distributed in tropical areas worldwide, whereas B. malayi infects a number of wild and domestic animals and is restricted to South-East Asia. Mosquitoes are vectors for both parasites.

MorphologyThese two organisms are very similar in morphology and in the diseases they cause . Adult female W. bancrofti found in lymph nodes and lymphatic channels are 10 cm x 250 micrometers whereas males are only half that size. Microfilaria found in blood are only 260 micrometers x 10 micrometers. Adult B. malayi are only half the size of W. bancrofti but their microfilaria are only slightly smaller than W. bancrofti.

Life cycleFilariform larvae enter the human body during a mosquito bite and migrate to various tissues. There, they may take up to a year to mature and produce microfilaria which migrate to lymphatics and, at night, enter the blood circulation. Mosquitos are infected during a blood meal. The microfilaria grow 4 to 5 fold in the mosquito in 10 to 14 days and become infective for man.

SymptomsSymptoms include lymphadenitis and recurrent high fever every 8 to 10 weeks, which lasts 3 to 7 days. There is progressive lymphadenitis due to an inflammatory response to the parasite lodged in the lymphatic channels and tissues. As the worm dies, the reaction continues and produces a fibro-proliferative granuloma which obstructs lymph channels and causes lymphedema and elephantiasis. The stretched skin is susceptible to traumatic injury and infections. Microfilaria cause eosinophilia and some splenomegaly. Not all infections lead to elephantiasis. Prognosis, in the absence of elephantiasis, is good.

DiagnosisDiagnosis is based on history of mosquito bites in endemic areas, clinical findings and presence of microfilaria in blood samples collected at night.

Treatment and controlDiethylcarbamazine quickly kills the adults worms or sterilizes the female. It is given 2 mg/kg orally for 14 days. Steroids help alleviate inflammatory symptoms. Cooler climate reduces the inflammatory reaction.

Picture of victims in our community.

Summary.

Organism

Adultworm location

Microfiliarae location

Major vector/sheath

Clinical sign /periodicity.

Distribution

Wuchereria bancrofti

Lymphatics Blood Culex species/+

Fever/Nocturnal

Tropics

Loa loa Subcutaneous

Blood Chrysops species/+

Calabar' swellings,Urticaria/diurnal

West andCentral Africa

Summary.

Organism

Transmission

Symptoms

Diagnosis Treatment

Wuchereria bancrofti; W. brugia malayi

Mosquito bite Recurrent fever, lymph-adenitis, splenomegaly, lymphedema, elephantiasis

Medical history, physical examination, microfilaria in blood (night sample)

Mebendazole; Diethyl-carbamazine

Loa loa Deer fly Nodular and erythematous dermal lesions, eosinophilia, urticaria, blindness

Medical history, physical examination, microfilaria in nodular aspirate

Diethyl-carbamazine

Community-based intervention is the current approach to elimination of lymphatic filariasis as a public health problem. The underlying tenet of this approach is that mass annual distribution of antimicrofilarial

chemotherapy—albendazole with either DEC (for all areas

except those where onchocerciasis is coendemic) or ivermectin—will profoundly suppress microfilaremia. If the suppression is sustained,then transmission can be interrupted. As an added benefit, these combination have secondary effects on gastrointestinal helminths. An alternative approach to the control of lymphatic filariasis is the use of

salt fortified with DEC. Community use of DEC-fortified salt dramatically

reduces microfilarial density with no apparent adverse reactions.

Community education and clinical care for persons already suffering from the chronic sequelae of lymphatic filariasis are important components of filariasis control and elimination programs.(creating community awareness)

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