Clinical & biochemical profile of trichinellosis outbreak in north India

Trichinella infection is uncommon in humans in India with the diagnosis being difficult because of the non specific symptoms of the disease. Human trichinellosis occurs following the ingestion of raw or undercooked meat containing encysted Trichinella larvae1. A presumptive diagnosis of trichinellosis should be considered in patients with fever, myalgia, periorbital oedema, eosinophilia and recent consumption of poorly cooked meat, especially pork. Diagnosis is confirmed with serology (documenting a rise in the titre of antibody) or muscle biopsy showing Trichinella larvae2.

An outbreak of this disease has not been reported from India making it a rarely thought cause of febrile myalgia in this part of the world. We came across three patients, belonging to the same community, who presented with fever and generalized myalgia after consumption of pork in a community feast. A diagnosis of trichinellosis was suspected and confirmed by the muscle biopsy. Further enquiry revealed similar symptoms in many other people belonging to the same community who had participated in that feast. An outbreak was suspected and hence this survey was undertaken with the aim of evaluating the clinical and biochemical profile of trichinellosis outbreak in the community.

Material & Methods

This observational study was undertaken from April 6-8, 2011, in a remote village, Tola, in Tehri Garhwal district of Uttarakhand State in north India, following three index cases of the same community who presented in first week of March 2011 to the medicine ward of Vardhman Mahavir Medical College and Safdarjung Hospital, a tertiary healthcare hospital in New Delhi, India. The three cases had similar complaints of acute onset fever and generalized myalgia with eosinophilia, and a background history of pork ingestion in a community gathering (Table I). After being evaluated for eosinophilia myalgia syndrome, the diagnosis of trichinellosis was confirmed on the basis of demonstration of Trichinella larvae in the muscle biopsy specimens from vastus lateralis muscle in two patients (Figure). Though no parasite was seen in the muscle biopsy of the third patient, the evidence of myositis on background symptomatology, along with laboratory features confirmed the diagnosis.

Table I Clinical and biochemical profile of three index cases

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Fig

Histopathological slide of one index case of muscle biopsy specimen showing larvae (arrow) of T. spiralis with lymphocytic infiltrate surrounding the parasite (H & E ×500).

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Following the confirmation of diagnosis of Trichinella infection in these three index cases, the concerned local authority was contacted and a team of doctors along with paramedics provided by the local authority visited the affected community five weeks after the index cases were confirmed. Detailed proforma based clinical information was collected from all the people who had eaten the same pork preparation and relevant blood investigations were done after taking an informed consent. All the symptomatic patients were treated using albendazole therapy and a short course of oral steroids.

The data collected included demographic data (age, sex), presence of clinical symptoms and signs (like fever, myalgia, breathing difficulty, dysphagia, and periorbital oedema), and type of pork consumed (cooked or uncooked). Blood samples were taken on site for evaluation of various parameters like haemoglobin, erythrocyte sedimentation rate (ESR), absolute eosinophil count, creatinine phosphokinase (CPK) levels and liver function tests. Examination and laboratory findings were recorded and analyzed.

A clinical case of Trichinella was defined as a clinically compatible case (common signs and symptoms included eosinophilia, fever, myalgia and periorbital oedema) that is confirmed by laboratory criteria of either a positive serologic test for Trichinella or demonstration of Trichinella larvae in tissue obtained by muscle biopsy3. The outbreak was confirmed as defined by the Centres for Disease Control (CDC) and California Department of Public Health34. The study was approved by the Ethics Committee.

Results

Excluding three index cases, a total of 54 people took part in the community feast in the village and were eligible for the study. One death with similar clinical profile was reported. The clinical data were collected from all of them including the relatives of the patient who died due to similar illness. Seven people refused to give consent for blood sampling.

The study population included 18 males and 36 females. The age range of patients was from 5 to 87 yr with the mean age of 40 yr and four subjects under the age of 12 yr. The type of pork consumed included uncooked in 24 per cent (n=13), open fire roasted in 39 per cent (n=21) and fried in 37 per cent (n=20) (Table II).

Table II Clinical profile of study population

Clinical symptoms were first noticed 2-3 wk after consumption of pork in 34 patients and subsided in 4-5 wk except for ten patients who had persistent myalgia at the time of the visit. The predominant symptoms observed were fever with chills and myalgia, documented in all 34 patients (100%) who consumed pork in uncooked or open fire roasted form. Periorbital oedema was found in 24 patients. Three patients also had difficulty in breathing, one person had difficulty in swallowing and one had itching all over the body. None of those 20 who consumed pork in fried form, suffered from, any form of clinical illness (Table II).

Of the 46 people who consented for blood investigations, 12 had consumed pork in uncooked form, 17 in open fire roasted form and 17 had consumed fried pork. Forty one people (89%) had high absolute eosinophil counts with normal count in two (11.7%) who consumed open fire roasted pork and in three (17.6%) who had it in fried form. A raised CPK level was seen in 39 (85%) patients suggestive of muscle involvement. Forty five (98%) patients had evidence of inflammation in form of raised ESR. Mild derangements of liver aminotransferases were noticed in three people with no icterus (Table III).

Table III Biochemical profile of study population

Discussion

T. spiralis, often found in domestic pigs, is the most common cause of human trichinellosis5. After human consumption of trichinous meat; encysted larvae are liberated by digestive acid and pepsin and invade the small-bowel mucosa to mature into adult worms4. This enteral phase, lasting for 1-8 wk, is usually asymptomatic, but diarrhoea, abdominal pain, nausea, and vomiting may occur. After about one week, female worms release newborn larvae that migrate via the circulation to striated muscle and lodge as cysts. Clinical symptoms of trichinellosis arise from the successive phases of parasite enteric invasion, larval migration, and muscle encystment2.

The migrating Trichinella larvae provoke a marked local and systemic hypersensitivity reaction, with fever and hypereosinophilia. Periorbital and facial oedema is common. A maculopapular rash, headache, cough, dyspnoea, or dysphagia may be seen. After onset of larval encystment in muscle 2-3 wk after infection, symptoms of myositis with myalgias, muscle oedema, and weakness develop, usually overlapping with the inflammatory reactions to migrating larvae. The most commonly involved muscle groups include the extra ocular muscles; the biceps, the muscles of the jaw, neck, lower back, and diaphragm. Peaking around three weeks after infection, symptoms subside only gradually during a prolonged convalescence over the next few weeks2.

Although most infections are mild and asymptomatic, heavy infections can cause severe cardiovascular or neurological complications, enteritis, periorbital oedema, myositis, and rarely death. Diagnosis of this disease is confirmed by documenting a rise in the titre of antibodies on serology or demonstration of larvae in the muscle biopsy specimen taken usually from biceps or vastus lateralis.

The duration of the incubation period is related to the number of larvae ingested, which, usually determines the severity of disease. The incubation period varies from a few days to two months and is generally shorter when the disease follows a more severe course following a high infective larval load. In our study, the duration of incubation period ranged from 2-3 wk. The average incubation period noted in a recent case series from Vietnam was 3-9 days with previous studies suggesting an average period of 7-14 days (mean 8.6 days)1.

In the present study, incidence of fever and myalgia was found to be almost 100 per cent in all patients who had consumed pork in raw form. This conforms to the findings in previous studies on Trichinella outbreaks in Vietnam and other studies where these two are the predominant findings seen in 90-100 per cent of the cases16789. Periorbital oedema, though thought to be an important symptom seen in up to 80-95 per cent cases19 in the previous studies, was seen in less number of cases (67%) in our study, possibly due to milder infection in most of the patients.

The outcome and duration of symptoms vary greatly along with the severity of the disease depending upon host immunity, age, sex, and general health of the infected individual as well as the infective larval load and the infecting species of Trichinella. In mild infection resulting from the ingestion of low numbers of larvae in muscle, symptoms related to the migratory and parenteral phases are usually the first to be clinically detected since these patients experience no symptoms during the enteral phase. In our study, none of the affected patients developed abdominal symptoms. This may be possibly due to low larval load thereby developing systemic symptoms directly.

In our study, three patients were diagnosed to be the index cases with marked symptoms suggesting the diagnosis. In majority of the patient population in village, symptoms subsided before the visit of our team. Only a few people with prolonged myalgia were noted, which has been shown to persist in upto 98 per cent of patients at two years and in 25 per cent of patients at ten years in a retrospective study10.

In the laboratory parameters, eosinophilia is the earliest and most characteristic finding of trichinellosis. It has been reported to occur as early as the first week and is almost universal in all patients, the incidence reported close to 88 per cent in an outbreak from Turkey11. In our study eosinophilia was found to be present in 90 per cent of the patient population including both symptomatic and asymptomatic patients. This eosinophilia was present despite the subsidence of symptoms in most of the affected people.

Another positive laboratory finding is an elevation in circulating levels of muscle enzymes [e.g. CPK, 1, 6-diphosphofructoaldolase, lactate dehydrogenase (LDH), aldolases, and aminotransferases]. These may be elevated in 35 to 100 per cent of infected individuals and are present in the serum due to the destruction of muscle tissue by migrating newborn larvae12. In a few studies the presence of elevated CPK and LDH levels has been shown to be as high as 70-90 per cent911. However, their levels do not correlate with the severity of the disease. In our study, 85 per cent patients had raised CPK.

The confirmatory diagnosis of Trichinella is done by either serology or demonstration of parasite by muscle biopsy. Antibody detection tests are useful adjuncts to diagnosis starting after 12^th day of infection. The sensitivity of the IgG-ELISA reaches 100 per cent on day 50. The test remains positive for more than 2 years in 88 per cent of infected people13. However, in regions where other helminthic infections are common, cross-reactions could give rise to false positive results14. An earlier report has demonstrated cross-reactivity between Trichinella and Schistosoma mansoni using anti-gp50 monoclonal antibodies15.

Many asymptomatic patients in our study demonstrated eosinophilia and raised CPK levels. A few case reports in the past have shown similar result where a clinically implicated meat was consumed and no clinical symptoms were observed though they fulfilled the laboratory criteria for diagnosis16. In a study comparing acute trichinellosis in children with adults, the incubation period was found to be similar, but myalgia (66 versus 96%), facial and/or eyelid oedema (57 versus 86%), eosinophilia (52 versus 96%) and increased serum CPK (38 versus 79%) were less common in children than in adults17. In our study, the number of children affected were only four and all were asymptomatic.

Trichinellosis is cosmopolitan, ranging from the Arctic to the tropics18. Human trichinellosis has been documented in 55 countries around the world19.

In conclusion, Trichinella infection is not uncommon in India but usually remains undiagnosed due to lack of awareness about the disease. In cases of Acute febrile myalgia especially in areas where habit of consumption of raw meat is prevalent, Trichinella infection should be suspected. Public awareness and food hygiene are important components of prevention.