Case Report: Fatal Human Leptospirosis Caused by Leptospira interrogans Genotype ST149

INTRODUCTION

Leptospirosis is a re-emerging zoonotic disease caused by Leptospira species, a group of spirochete bacteria with 29 described serogroups and more than 200 different Leptospira serovars. ¹ This disease occurs in diverse epidemiological settings but highly prevalent in tropical and subtropical areas. The worldwide incidences of leptospirosis were reported to be 0.1–1 per 100,000 inhabitants. However, the increase in incidence is likely during seasonal breaks, heavy rainfalls, and among high-risk populations. ² Leptospira species infect a wide range of hosts such as mammals, fish, birds, and reptiles as well as humans. Rodents constitute as an essential reservoir for several pathogenic Leptospira. ³ In this report, we describe a fatal case of leptospirosis in a young woman infected by pathogenic Leptospira genotype ST149.

CASE PRESENTATION

An unemployed 41-year-old woman of Indian descent with an unremarkable medical history was brought in dead to the forensic department of Selayang Hospital. The deceased had a history of fever, mild flu-like symptoms, dizziness with headache, myalgia, diarrhea, and vomiting that began 10 days before. On day 3 of her illness, she had visited a general practitioner for being sick, where antibiotics were prescribed and no further blood investigation was made. She had no recent history of traveling, jungle trekking, or swimming in a lake or pool. She is a divorcee, living with her family (eight of them), and owned two healthy dogs. Her body was shifted to the mortuary for routine inquest and autopsy.

Autopsy findings.

Autopsy revealed pale liver with no enlargement, hemorrhagic lungs, and edematous brain without sign of bleeding. Microscopic examination of tissue specimens revealed dissociation and separation of the hepatocyte plate prominent at the perivenular area (zone 3) with macro-vesicular steatosis of the liver (Figure 1B), diffuse congestion with extensive intra-alveolar hemorrhages mixed with fibrins and macrophages of the lungs (Figure 1A), mild perivascular histiocyte and lymphocyte infiltration within brain parenchyma and meninges suggestive of mild meningoencephalitis changes (Figure 1C), mild myocarditis, and pericarditis morphologies. At the same time, diffuse autolysis of the gallbladder and mild hypertensive vascular changes of the kidneys were observed. No significant pathological changes were seen in the pancreas, stomach, and small intestine. Because of histopathological findings and epidemiology of hemorrhagic fever in Malaysia, the deceased was screened for dengue fever and leptospirosis (Table 1).

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Histopathologic evaluation of tissue specimens collected postmortem from the deceased. Tissue specimens were taken from the lung (A), liver (B), and brain (C) stained with hematoxylin–eosin (A–C: original magnification ×20). Picture (D1, D2, and D3) is probed CD68 and leukocyte common antigen immunohistochemistry stain to identify histiocytes and lymphocytes, respectively.

Citation: The American Journal of Tropical Medicine and Hygiene 104, 1; 10.4269/ajtmh.20-0267

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Table 1

Laboratory and microbiological investigation performed on the deceased

Investigation	Result
Vitreous fluid analysis
Appearance	Clear
Urea, Ur (mmol/L)	17.3
Creatinine, Cr (μmol/L)	251
Sodium, Na (mmol/L)	134
Potassium, K (mmol/L)	7.7
Glucose (mmol/L)	< 0.6
CSF analysis
Appearance	Turbid
White blood cell count (cells/mm3)	25 cells, predominantly lymphocytes
Glucose (mmol/L)	< 0.6
Protein (g/dL)	2.48
Dengue screening
NS1 Ag	Nonreactive
IgM	Nonreactive
IgG	Reactive
PCR assay (targeting DENV1-4 genes)	Not detected
Leptospirosis screening
Microscopic agglutination test	Nonreactive (titer < 1:50)
Specimen for Leptospira PCR assay, Ct-value
Blood	29.70
CSF	36.50
Lung	35.28
Liver	32.78
Kidney	31.70
Heart	34.45
Conventional culture
Blood culture	Clostridium limosum
Lung tissue culture	Mixed growth
CSF culture	No growth
Leptospira culture	No growth

CSF = cerebrospinal fluid.

DISCUSSION

Leptospirosis is an important emerging zoonotic disease with global distribution. Malaysia is known to be endemic for leptospirosis partly because of the tropical weather with a humid environment that prolongs the survival period of pathogenic Leptospira in the environment. ⁵ Reservoir animals play a critical role in the continued persistence of Leptospira in the environment, causing outbreaks by direct or indirect exposure. Humans are an accidental host, and risk of infection is commonly associated with the nature of occupation. ⁶

Although, the deceased is not associated with any occupational risk groups as described by Jalii and Bahaman, ⁷ environmental exposure cannot be excluded. Nevertheless, the deceased companion dogs can transmit this infection, but to no avail for serological study or leptospiral isolation. On the other hand, ST149 is not a frequently reported genotype among dogs. ⁸ However, Leptospira genotype ST149 obtained from the deceased shared similar sequence typing (ST) with Leptospira interrogans serovar Bataviae strain LepIMR 22, ⁹ a persistently found serovar in the urban rat populations in Malaysia. Rattus rattus, Rattus norvegicus, and Rattus exulans were the common host reservoirs of this serovar in Malaysia. ^10,11 It can be assumed that the deceased was directly or indirectly in contact with rodents carrying Leptospira ST149. However, this assumption cannot be demonstrated as culture isolation of infecting serovars from the deceased or the companion dogs was not performed to illustrate the existence of epidemiological linkage.

Common targeted organs in leptospirosis are lungs, liver, kidney, and brain. Despite lack of laboratory investigation in our case report, the severity of illness can be appreciated by the histopathology findings of the involved organs. Pulmonary hemorrhage secondary to severe leptospirosis was the likely cause of death in this case report. Other typical pathological changes in this case study was observed in the liver, heart, kidney, and brain which may suggest high leptospiral load. ⁵ Leptospira DNA was detected in all the tissue samples and body fluid of the deceased, with PCR cycle threshold-value ranging from 29 to 37 (Table 1). However, Agampodi et al. ¹² have demonstrated that leptospiral load is not a predictive factor of severity of illness. On the contrary, although not studied in larger scale, it is presumed that the virulence factor of Leptospira species/serovar/strain may be associated with severity of the illness.

In conclusion, Leptospira PCR assay is valuable in postmortem diagnosis of acute illness because Leptospira culture is laborious, tedious, and less sensitive. Leptospirosis serology assay is not helpful as it requires paired sera to confirm a diagnosis with certainty, and many patients succumbed to death during the acute phase of illness. ⁵ At the same time, this case report demonstrates the need for surveillance on the deceased companion dogs and housing ecosystems by leptospiral isolation or serological study to identify the epidemiological link and mitigate the risk and exposure to the fatal disease.