THE NATIONAL MEDICAL JOURNAL OF INDIA VOL. 3, NO. I 7

Occult filarial infectionsP. CHATURVEDI, A. GA WDI, S. DEY

INTRODUCTIONBancroftian filariasis is an ancient disease known to man-kind since Be 600. In 1863, the filarial parasite was firstdiscovered by Demarquay in the hydrocoele fluid ofpatients in Cuba. In 1866, Wucherer demonstrated micro-filariae (mf) in the chylous urine of Brazilians. In India,Lewis in 1872 identified mf in the blood of patients withfilariasis. Bancroft discovered the adult female worm in1876 and Browne the adult male in 1888.1

Lymphatic filariasis has been reported from almost alltropical and subtropical countries in the world. It isendemic in South, Central and North America, the WestIndies, Africa, Asia and Australia. Of the 2677 millionpeople living in countries where the disease is endemic,905 million are estimated to be at risk of infection and90 million are carriers of mf. ~ Filariasis is a diseasecharacterized by a wide spectrum of clinical manifesta-tions (Fig. I). The so-called 'occult' manifestations suchas tropical pulmonary eosinophilia (TPE),.1 glornerulo-pathies." nerve palsies.! endomyocardial fibrosis (EMF),~arthritis." and filarial infections of the breast? are oftenseen in populations living in endemic areas.

The term occult filariasis is commonly used to designatefilarial infections in which mf are not found in theperipheral blood although they may be seen in tissues. K.Y

However, it has now been shown that in some cases with

ASYMPTOMATIC, NO DETECTABLE

MICROFILARAEMIA

- ASYMPTOMATIC, MICROFILARAEMIC

BANCROFTIAN _ FILARIAL FEVERSFILARIASIS

- LYMPHA TIC OBSTRUCTION

T_ OCCULT OR CRYPTIC

FIG 1. Clinical manifestations:'

Mahatma Gandhi Institute of Medical Sciences, Sevagram,Wardha 442102, Maharashtra, India

P. CHATURVEDI, A. GAWDI, S. DEY Department of Paediatrics

Correspondence to P. CHATURVEDI, Vivekanand Block,KHS Campus, PO Sevagram, Wardha 442102, Maharashtra, India

© The National Medical Journal of India 1990

occult filariasis, mf may actually be found after more care-ful blood examination despite their low density. III Theclinical features of occult filariasis are different from thoseof the classical disease and resemble many non-filarialdiseases from which they are sometimes difficult to distin-guish. Occult filarial manifestations may help explain theaetiology of many clinical syndromes which were earliernot completely understood. For example, splenic granulo-matous inflammatory reactions to mf of W. bancrofti havebeen discovered only on autopsy. II Following are some ofthe clinical manifestations of occult filarial infestation.

TROPICAL PULMONARY EOSINOPHILIAThis is perhaps the best example of occult filariasis. It wasfirst formally described by Frirnodt-Moller and Barton in194012 although in 1939 Meyer and Kouwcnaar11 haddemonstrated mf in the inguinal lymph nodes of individualswith eosinophilia and asthma. Five years later Van der Sarand Hartz!" demonstrated mf in the lymph nodes andspleens of their patients. Ottensen et al.' and Jayawardeneand Wijayaratnam 15 showed that TPE was a diseasecaused by human filarial parasites and not by animalfilarial parasites as was then believed. TPE also hasextrapulmonary manifestations. There are ethnic differ-ences in its prevalence. It is more commonly seen on theIndian subcontinent although Bancroftian filariasis isendemic in many parts of the world. It can occur at anyage and has been reported even in infants. 16 The disease canhave an acute or an insidious onset. Its clinical manifesta-tions are usually cough, fever, chest pain, breathlessness,malaise and occasional abdominal pain. Examinationof the chest reveals rhonchi and crepitations. Sometimeslymphadenitis, splenomegaly and hepatomegaly may alsobe observed. The natural course is marked by recurrencesand relapses. Long-standing untreated cases progress topulmonary fibrosis and respiratory insufficiency. 17

These patients have blood eosinophilia, raised erythro-cyte sedimentation rates and there may be evidence ofdiffuse miliary lesions or increased bronchovascularmarkings in the chest X-rays especially of children. 1M

Microfilariae are not demonstrable in the blood smearsbut can be found in the lungs. liver and lymph nodes on athorough examination.'? There is impairment of lungfunction with occurrence of both obstructive and restrictivedefects.P It responds to treatment with diethylcarbamazine(DEC) which is yet another indication of its filarial origin.

Various immunological methods using homologousand heterologous antigens have been employed for thediagnosis of the disease. Using an indirect fluorescent

8

antibody test, Ismail and Wijayaratnam found filarialantibodies in only 57% of their patients and concludedthat the cause for TPE in antibody negative patients couldbe non-filarial (unpublished data). However, a compari-son of the W. bancrofti mf excretory-secretory antigen(mfES Ag) with W. bancroft; larval (L3) excretory-secretoryantigen (L3 ES Ag) showed an antibody positivity rate ofonly 54% with mf ES Ag and a 96% positivity rate withL3 ES Ag, suggesting that L3 ES Ag was more specificin the diagnosis of TPE. 21

In TPE and other occult filarial manifestations, specificantifilarial IgE antibody titres to mf antigens from W.bancrofti, B. malayi and D. immitis are increased. But infilarial TPE, IgE antibodies are more highly sensitizedand respond more to mf antigens than the IgE antibodiesof other filarial manifestations.! Microfilariae, which aredestroyed in the lungs through an IgG mediated response,provoke hypersensitivity and lead to an increase in IgElevels. 22.23This points to the existence of a type I reaction.The occurrence of an additional type III reaction is indi-cated by an increase in IgG, IgM and IgA 24and the presenceof immunoglobulins in the lungs." Although TPE mayoccasionally present atypically, the diagnosis is seldomdifficult. However, other occult filarial syndromes such asfilarial arthritis are often not as easy to detect.

FILARIAL ARTHRITISThis is a form of arthritis which usually affects the kneejoints and is fairly common in endemic areas. Thoughit had been recognized as a possible manifestation ofBancroftian filariasis twenty years ago,2l>-2Hno detailedinvestigations were done until 1973, when Ismail andNagaratnam" using mf of W. bancrofti in a tluorescentantibody test found that 90% of their patients with filarialarthritis tested positive for filarial antibodies. Chaturvediet al.1Y found that 80% of children with arthritis, whereno other diagnosis could be made, had filarial antibodies.The need to differentiate filarial arthritis from otherdiseases, especially rheumatoid arthritis, is important asthe treatment of both conditions is entirely different.Filarial arthritis may be caused by species other thanW. bancrofti.~32

It is usually monoarticular but two-joint involvementalso occurs. Only large joints are affected and the occur-rence of the symptoms in small joints rules out the diagnosisof filarial arthritis. The condition runs a short, benigncourse and the majority of patients do not have fever buta painless swelling of one or more joints (usually theknee). Sometimes the affected joint may be painful. warmand tender with restriction of movement. 2 The symptomsmay recur, often in the same joint but occasionally insome other joint and may be mistaken for rheumatoidarthritis.s-"

These patients show normal or moderately elevatedeosinophil counts and erythrocyte sedimentation rates;X-rays of the involved joints show soft tissue swelling butno bony abnormalities. Microfilariae in night blood smearsmay be seen in some instances. The antistreptolysin 0titre is generally normal. 6

The pathogenesis of the disease is still obscure. Das

THE NATIONAL MEDICAL JOURNAL OF INDIA VOL. 3, NO. I

and Sen29 in a study of chylous arthritis (which theybelieved to be of filarial origin) found lymphangiectasia,stasis and varicosities in the popliteal lymphatics withshort blind channels leading to the joint suggestinglymphatic fistulization into the synovial sac. The condi-tion responds well to DEC but poorly to salicylates."

GLOMERULOPA THIESGlomerulonephritis associated with lymphatic filariasiswas reported by Chugh et al. in 1978.4 Chaturvedi et al.29also found that 2 of 5 children they had seen with filariasisand acute glomerulonephritis had filarial antibodies.Renal biopsies in these patients showed diffuse mesangialproliferative glomerulonephritis with C3 deposition onthe basement membrane. The condition responds well toDEC therapy. 33 The production of typical lesions ofglomerulonephritis in cats infected with Brugia pahangi'"is in keeping with this hypothesis. The demonstration offilarial antigens and specific filarial antibodies in theimmune complexes deposited in the glomeruli wouldprovide definitive evidence for a filarial aetiology.

ENDOMYOCARDIAL FIBROSISEndomyocardial fibrosis is a rare disease seen in theequatorial belts. The incrimination of filarial infection inits causation is based largely on circumstantial evi-dence.v-" The geographic distribution of the disease inareas endemic for filariasis, the detection of antibodies toLoa loa in patients with EMF, 37 certain clinical featuresresembling filarial infection and the occurrence ofeosinophilia and EMF with Loeffler's syndrome." haveled to the hypothesis of EMF being filarial in origin.Further, Harinath in 198739 found filarial antibodies in8 of the 10 patients with EMF. further supporting thetheory that EMF may be of filarial origin.

FILARIAL GRANULOMAS IN THE BREASTThis manifestation is particularly prevalent in India andSri Lanka where W. bancrofti is the predominant species.It has not been reported from areas endemic for Brugianfilariasis. Filarial granulomas present as hard breastlumps attached to the overlying skin and are at timesdifficult to distinguish from malignant tumours.t" A his-tological examination can confirm the diagnosis by thefinding of an eosinophilic granulomatous reaction aroundthe filarial parasites which are in varying stages of degenera-tion. Both adult worms and mf have been found in thegranulomas.v':" Filarial antibodies have been demonstratedin these patients and the condition responds to DECtherapy which, in many instances, can lead to completedisappearance of the lump,

Finally a variety of manifestations such as thrombo-phlebitis, tenosynovitis and nerve palsies found in endemicareas, sometimes coexisting with filariasis, have beensuggested to be of filarial origin without much convincingevidence.?

SUMMARYClassical filariasis presenting with lymphangitis, lymph-oedema, chyluria or elephantiasis with microfilaraemia is

CHATURVEDI, GAWDI, DEY: OCCULT FILARIASIS

well documented. In occult filariasis, microfilariae are notfound in the blood but may be seen in the tissues. Earlier,occult filariasis was synonymous with tropical pulmonaryeosinophilia but other manifestations such as glomerulo-pathies, endomyocardial fibrosis, arthritis and filarialinfections of the breast are now well recognized. Theoccult manifestations are generally microfilaraemic andthe clinical manifestations are sometimes impossible todistinguish from well known clinical entities. The diagnosisof these occult manifestations can be confirmed by theELISA test using specific antigens. Therefore, in endemicareas, a high index of suspicion is necessary to establish adiagnosis because specific therapy against microfilariae iseffective and easily available.

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