Lassa fever in children in Sierra Leone, West Africa

TRANSACTIONS OF THE ROYALSOCIETYOF TROPICALMEDICINEAND HYGIENE(1986) 80, 577.582

Lassa fever

in children

P. A. WEBB,‘* J. B. MCCORMICK:

in Sierra

577

Leone, West Africa

I. J. KING,~ I. BOSMAN: K. M. JOHNSON,’ L. H. ELLIOTT,’ G. KOMBA KONO~ AND R. O’SULLIVAN’

‘Division of Vector-Borne Viral Diseases, Center for Infectious Diseases, Centers for Disease Control, Public Health Service, US Department of Health and Human Services, Fort Collins, Colorado 80522, USA; 2Division of Viral Diseases, Center for Infectious Diseases, Centers for Disease Control, Public Health Service, US Department of Health and Human Services, Atlanta, Georgia 30333, USA; 3Methodist Church Overseas Division, 25 Marylebone Rd., London, NW1 SJR; 4Nkoranza Hospital, P.O. Box 30, Nkoranza, Ghana; ‘Dept. of Epidemiology, Johns Hopkins School of Hygiene and Public Health, 615 N. Wolfe Street, Baltimore, Maryland 21205, USA; 6Endemic DiseasesControl Unit, Bo, Sierra Leone; ‘Holy Ghost Missionary College, Kimmage Manor, Dublin 12, Ireland.

Abstract A systematic study of Lassa fever in febrile children was undertaken over a four-year period, from August 1977to August 1981, in the Eastern Province of Sierra Leone, West Africa. 479 patients were studied; of these, 245 had adequatespecimensto confirm or exclude the laboratory diagnosis of Lassa fever. 51 casesof Lassa fever were identified (21% of patients from whom diagnosis was possible). Virus was isolated from 23 patients. All children had fever; cough and vomiting were present in over 60% of casesstudied. The five to nine-year agegroup had the highest prevalence rate (41% of cases). Seasonalclustering occurred in April, May, and August. A significantly higher proportion of females than males had Lassa fever, a finding which remains to be explained. It is concluded that Lassa fever is a disease of significant concern in the paediatric age group.

Introduction Little is known about Lassa fever in children, although it is known to affect persons of all agesand sexes (KNOBLOCH et al., 1982; MONATH et al., 1974; MCCORMICK 8~ JOHNSON, 1978). Most reports suggest that Lassa fever may occu; more fre&ently % adults than in children (KNOBLOCH et al.. 1982: MONATH et uZ., 1974; A&ORMICK & JOHNSON; 1978; FRASER et al., 1974). Serological surveys have shown evidence of Lassa virus antibody in children, but few studies of acute diseasein the paediatric age LOUD have been nublished (FRASER et al.. 1974; ~EE~LYSIDE et al.; 1983). . It has been suggestedthat Lassa fever may be less severe in children than in adults (MONATH, 1975). However, there are no studies of Lassa fever in children in which virus isolation was systematically utilized in diagnosis and, without this parameter, many cases in children are unrecognized. A wide spectrum of diseaseranging from inapparent to fatal infection occurs in adults with Lassa fever (FRASER et al., 1974). Early clinical diagnosis in adults is extremely difficult becauseof the lack of specific signs for Lassa fever (MONATH et al., 1974). The diseaseis no lessdifficult to diagnosein children. We undertook a systematic study over a four-year period to assessthe importance of Lassa fever as a cause of hospital admission and death in children. Additionally, we wished to find some clinical or laboratory markers to facilitate an early diagnosis. Materials

and Methods

This study took placefrom late August 1977to August

1981. We collected serum specimens from febrile children admitted to two hospitals, Panguma and Segbwema, located in the endemic Lassa fever zone in the Eastern Province of

Sierra Leone, West Africa (Fig. 1). Case records documented by the hospital physicians were used for clinical information. Each patient was assignedan accessionnumber that was kept for future admissions. General information obtained for each patient included name+ parent’s name (usually the father’s), age, sex, province, &strict, chiefdom, and village of residence, onset, admission and discharge dates, hospital of admission, tribal language, outcome, and final diaenosis. A second form was used for each St&men obtainerfrom a patient, and data included days afier onset of illness, type of specimen and serological results obtained

in the Las& fever-laboratoryat Kenema.

Blood samules were drawn with svringe and needle or bv finger-stick i&o a small plastic tube: or& to a filter-papei

disc. The specimenswere storedat 4°C for a maximumof

three days before being transported to a laboratory 30 miles away in Kenema, where the immunofluorescent (IF) antibody testing was done, and the remaining specimen was stored at -70°C for virus isolation. Shipments to the Centers for Disease Control (CDC), Atlanta, Georgia, USA, were made regularly, depending on availability of dry ice. Virus isolation from serum or cerebrospinal fluid was performed in the Maximum Containment Laboratory at CDC. The mycoplasma-free E6 cell line derived from a line of Vero 76 cells was used for virus isolation, and isolation attempts were made at a different place and time than other laboratory work involving Lassa virus. The methods used have been described by JOHNSONet al. Cells were tested for Lassa virus by the reverse passive haemagglutination test (RPHA) (GOLDWASSER et al., 1980). Those specimens that showed a cytopathic effect but a negative RPHA were

examined for other haemorrhatic fever viruses. Serum

antibody titres to Lassa virus wergdetermined by an indirect fluorescent antibody test for IgG and IgM as described previously (WULFF & JOHNSON,1979). A casewas deiined as a febrile child hospital in-patient; (i) from whom Lassa virus was isolated, (ii) who showed either a seroconversion (~4 to 216) or four-fold rise (S, with *For correspondence and reprints.

578

LASSA

FEVER

IN CHILDREN

IN SIERRA

LEONE

NORTHERN PROVINCE

SOUTHERN

SCALE

L 0

1 IO

I: 2,000,OOO ’ 20

’ 30

’ 40

1 50

, 60 miles

Fig. 1. Republic of Sierra Leone.

antibody, S2four-fold increaseover S,) in IgG antibody to Lassavirus by immunofluorescentantibody assay(IFA), or (iii) a child with an anti-Lassavirus IgG antibody titre al:256 with IgM spectic for Lassavirus of 3 1:8 in a single

I). We studied the progression of viraemia and antibody production in 23 patients from whom virus was isolated. We have shown some patterns of

specimen.

Table I-Lassa Results

During the four-year study period, we studied 479 patients. Of these, we collected specimens that we considered adequate to either conlirm or exclude the laboratory diagnosis of Lassa fever in 245 children. We identified 51 cases of Lassa fever among these children (21% of the hospital in-patient febrile children studied). We isolated virus from 23 of our patients (nearly 10% of the febrile children studied). We were able to re-isolate virus from original material in 7 of 12 attempts. 15 of the children with Lassafever would not have been clinically diagnosed by use of laboratory facilities available in Sierra Leone (Table

fever cases by criterion of diagnosis

Criterion

Virus isolation only Virus isolation and seroconversion’

Seroconversion’ only Four-fold rise’ only IgG~256/IgMX3 in a single serum specimen

No. of cases

Total

15 8 15 9 4

TOTAL “All serological tests were indirect immunofluorescent

23

24 4 51 assay.

P. A.

WEBB

579

et al.

Table II-Quantitative viraemia and antibody patterns in virus-positive patients IgG IFA DD”

8

12

l&I 1; 4

IgG IFA titre

DD

VkUS

+

210.24 3 1024 2256 16

1: 2:

neg. + 2.6

<4 64 3256 NT

m2t. neg.

NT’ ~1024

2:

3.1

<4 <4

neg. 1.6

25:

3 11

neg. +

<4 <4

6 10 3

neg. + +

<4 <4 (4

4

2.1

<4

? 6 10

+ 1.0 neg.

NT

i

cont. 4.6

ViNSb

1.6

titre

2:6 neg. neg. +

57; 5 1024 128 NT

4.1 + cont. cont. + cont.


1:

Cl

<4 64

5

+

21024

5

+

32

Deaths

? 6.5 liver 5.1 spleen NT 6 2.6 64 7 + “DD = day of disease after onset of illness. bLog,,, PFU/ml; + = virus-positive, not titrated, neg. = negative; cont. = contaminated. ‘Not tested.

responsein Table II. The earliest virus isolations were made on day 3, and the latest isolation was made on day 25. Virus titres were low, except in organs at death. Virus was isolated in the presenceof high IgG IFA titres as seen in the first five cases;four patients had no detectable antibody at the time of admission but seroconverted as early as nine days after onset of illness. Three patients, from whom virus was isolated, showed no serological responseeven though a second serum sample was taken at an appropriate time. Data on virus-positive cases with single specimens are included. The children with Lassa fever came from scattered villages in the Eastern Province, although more than half were from villages located in a large highly - populated diamond mining area. We recorded the occurrence of naediatric casesbv month (Fig. 2). The cumulative total of casesin the children was compared to the adult cases of Lassa fever seen during the same period. Adult cases are ten-fold the number seen in children. The signs and symptoms in 26 children for whom we had a completed standard record form (Table III) were tallied. Sore throat and pharyngitis were much less frequent in children than in adult patients (MONATH et al., 1974), while coughing and vomiting were common in both. Case records were available

ii:

256 31024 FE

from four of the fatal cases.Frequency of symptoms were similar to those noted in Table III; however, three of the four fatal caseshad a cerebrospinal tap performed becauseof seixures or nuchal rigidity. Less than 10 cells were found in the c.s.f., and no abnormality of protein or sugar was noted. Facial oedema, bleeding, and chest signs were present in three of four cases. Haemoglobin values ranged from 3 to 10 g, total WBC counts from 4,500 to 13,000. Six cases(23%) had malaria parasites, and three cases (12%) were sickle cell-positive. The age and sex distribution of the children with Lassa fever is shown in Table IV. There were six death+three in male children, two in females, and one in a child for whom the sex was not recorded. Although the case fatality rate in males (3113) was higher than in females (2/32), the difference was not significant @I= 13, Fisher’s exact test, 1 tail). Virus was isolated from five of the six patients who died. There was a 2 to 1 ratio of female to male cases,which could not be explained on the basis of differences in the proportion of male to female admissions. Of the 479 total patients we saw, diagnosis was possible for 116 males and 129 females. A significantly higher percentage of females tested (26%) had Lassa infection than males (14%) (x2 = 5.93, p<-05).

LASSA

FEVER

IN CHILDREN

IN SIERRA

LEONE

ICIL

Paediatric _

9I -

Adult (x10) Scale i.e. 10 = 100

8, 7 6 5 4 3 2 I 0I

JFMAMJJASOND

Fig. 2. Case distribution of confirmed lassa fever cases in paediatric patients.

Table

III-Clinical

findings

Symptoms Fever Cough vomiting Abd. Pam Diarrhoea Anorexia Sore throat

in 26 confirmed

Lassa fever cases in children

No. of cases 26

Frequency (percent)

:;I 10 9

ii:

;

:t

100

:t

Signs Pharyngitis Purulent 5 Ulcers 7 Lethargy Chest signs Abd. tenderness Adenopathy Facial oedema yF;;:g Dehydration Rash Splenomegalyb Hepatomegalyb

No. of cases 7

Frequency (percent) 27

: 5

:6”

:

is) 15

d

i: 15

i 9 7

38 26

‘Epistaxis, haemoptysis, bloody stool, oral haemorrhage. bWithout background information, the significance of these signs in Lassa fever cannot be accurately assessed. Table

IV-Age

and sex distribution

of Lassa fever cases Sex

unknown Cl

1-4

O/2” 213”

5-9

117”

10-14 unknown TOTAL “Number died/total cases.

o/4

3116”

o/14 l/8” O/l 2134”

Prevalence 3

O/l l/10’

l/l l/l”

:: 12

2:.: 41.1 23.5

6/k

1:.;

I’.

A.

WEBB

Discussion The 51 children identified as having Lassa fever indicate that this disease is of significant concern in the paediatric age group in the Eastern Province of Sierra Leone. We were sur rised at the large proportion of febrile children wKo had clear evidence of Lassa virus infection as the causeof their illness. The actual number of cases is much higher since our patients represent only those from whom adequate sampleswere obtained. Indeed, there were hundreds more children admitted to the hospitals with fever who were never evaluated by our programme. Of the 479 with whom we had some contact, adequately timed specimens were obtained only on 245. Some of the limitations of our study were: (i) inconsistency in sampling was due to shortage of personnel and variation in the degree of interest and training on the part of the hospital staff over the four-year period of the study; (ii) essentially no home follow-up was conducted; (iii) blood samples were limited in quantity and usually had to be diluted to have sufficient volume for antibody testing and virus isolation; (iv) there was a high degree of bacterial contamination found when virus isolation was attempted; and (v) finally, specimens were stored for long periods before isolation was attempted, resulting in some diminution of virus titre. Despite these limitations, virus was isolated from 23 children. 15 of whom would not have been diagnosed by serological testing. Thus, only 70% of cases on whom we were able to obtain specimens would have been diagnosed without the base laboratory in Atlanta. Quantitative determinations of viraemia were made in only a few instances. Most titrations were done at the time of re-isolation, which meant that the specimen had been thawed and refrozen at least twice. In general, titres obtained were higher in caseswith a fatal outcome, a finding similar to the observations made in adults (JOHNSON et al., 198 ).

Seasonal clustering occurred in April, May, and August; however, we believe August to be falsely represented because of a major effort to find Lassa casesin paediatric patients in 1978, when eight cases were noted. The additional case in August was in 1977. but no cases were found in that month subsequently. Information on the clinical course of the disease is scanty. It is not surprisina that the admitting diagnosis -seldom included Las&t fever in the differential diaenosis. The non-soecificitv of the signs and symptoms offers little cl&al diagnostic assistance. Although an enlarged liver and spleen were observed with high frequency, this cannot be assumed to be a vital part of the Lassa fever picture since we do not have background data on the paediatric age group regarding this condition. A careful case-control study-of the-signs and symptoms on admission of all febrile children miaht be of some help in arriving at findings with higher diagnostic value. It would also be of considerable interest to know if the admission SGOT and viraemia are predictive of a higher risk of death in children as they appear to be in adults (JOHNSON et al., 1986). The higher proportion of Lassa fever in female children than male children follows a trend seen in adults, although the figures for adults are not statistically significant. We do not think that this is a

et

581

Cd.

sampling artefact since, among the 480 children with febrile illness. 241 were males and 238 females (one had no sex recorded). Further, among the ‘245 children with adequate samples to allow a diagnosis, 116 were males and 129 were females. One hypothesis is that female children may spend more time in and around the houses thereby increasing their chancesof exposure to Mastomys natalensis, the mouse that is the implicated reservoir of Lassa virus (KEENLYSIDE et al., 1983; ROBBINS et al., 1983). If this were the case, one would expect to see an increased proportion of female cases, primarily in the older age groups. However, the higher proportion of femaleswith Lassa fever extended throughout the entire age range of children. A second hypothesis might be that females have more severedisease, but this was not supported by the case-fatality ratio of our study (although the numbers are small). It seems probable that some other, as yet unidentified, practice may explain this observation. We recognize that this study of Lassa fever in children is incomplete. In spite of the lack of infrastructure in the developing world (BASCH, 1978) it is possible to make a significant study of children with Lassa fever infections. We believe that this disease problem must be present in similar proportions in other areasof West Africa where Lassa fever is endemic and that other studies will confirm this. In the meantime, we are initiating studies of ribavirin therapy in children suspected to have Lassa fever, since it has been shown to be effective in adults (MCCORMICK et al., 1986). We also believe that Lassa

fever has not received adequate attention from the agencies involved in funding studies of health problems in the developing world, and we trust that this study will justify increased attention to this disease. Acknowledgements

Without the co-operation and encouragement of the Ministry of Health, Sierra Leone, this study would not have been done. We are particularly grateful to Dr. Belmont Williams, who generously assigned personnel from the Endemic DiseaseControl Unit, Bo, Sierra Leone, to the Lassa Fever ResearchProject (LFRP). We would also like to thank the staff of the U.S. Embassv for their SUDDORand assistance, particularly Ambassadors J. A. L&han and Theresa Healey, who both voluntarily came to the Lassa study villages and SegbwemaHospital to demonstrate to the Sierra Leone people their support of the Project. References

Basch, P. F. (1978). International health. New York: Oxford University Press. Fraser, D. W., Clinton, C., Campbell, C., Mona& T. P., Goff, P. A. & Greaa, M. B. (1974). Lassa fever in the eastern Province -Of Sierra‘ Leone, 1970-1972. I. Epidemiologic studies. American Journal of Tropical Medicine and Hygiene, 23, 1131-1139. Goldwasser, R. A., Elliott, L. H. & Johnson, K. M. (1980). Preparation and useof erythrocyte-globulin conjugates to Lassa virus and reversed passive hemagglutination and inhibition. Journal of Clinical Microbiology, 11, 593-599. Johnson, K. M., McCormick, J. B., Webb, P. A., Smith, E.., Elliott, L. H. & King, I. J. (1986). Lassa fever in Sierra Leone: Clinical virology in hospitalized patients. (Submitted for publication) Keenlyside, R. A., McCormick, J. B., Webb, P. A., Smith, E., Elliott, L. & Johnson, K. M. (1983). Case-control study of Masamys natalensis and humans in Lassa virus-infected households in Sierra Leone. Am&can 3ownal of Tropical Medicine and Hygiene, 32, 829-837,

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FEVER

IN CHILDREN

Knobloch, J., Albiez, E. J. & Schmitz, H. (1982). A serological survey on viral haemorrhagic fevers in Liberia. Annals of Virology, 133E, 125-128. McCormick, J. B. & Johnson, K. M. (1978). Lassa fever: Historical review and contemporary investigation. U.S. Public Health Service, p. 279-285. McCormick, J. B., King, I. J., Webb, P. A., Scribner, C. L., Craven, R. B., Johnson, K. M., Elliott, L. H. & Belmont-Williams, R. (1986). Lassa fever: Effective therapy with ribavirin. New EnglandJournal of Medicine, 314, 20-26. Mona& T. P. (1975). Lassa fever: review of epidemiology and epiwotiology. Bulletin of the WortY Health Organieatian, 52, 577-592. Monath, T. P., Maher, M., Casals, J., Kissling, R. E. & Cacciapuoti, A. (1974). Lassa fever in the eastern

IN SIERRA

LEONE

Province of Sierra Leone, 1970-1972. II. Clinical observations and virological studies on selected hospital cases.AmerkanJoumal of Tropical Medicine and Hygiene, 23., 61140-61149. Robbms, C. B., Krebs, J. W., Jr. &Johnson? K. M. (1983). Mastomys (Rodenna: Muridae) species distinguished by hemoglobin pattern differences. American Journal of Tropical Medicine and Hygiene, 32, 624-630.

Wulff, H. & Johnson, K. M. (1979). Immunoglobulin M and G responses measured by immunofluorescence in patients with Lassa or Marburg virus infections. Bulletin of the World Health Organization,

Accepted

57, 631-635.

for publication 29th May, 1985.

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