American trypanosomiasis

Synonyms: Chagas' disease, South American sleeping sickness

Aetiology

The disease is caused by infection with the parasite Trypanosoma cruzi. It is one of a section of trypanosomes called stercoraria because the disease is transmitted by the faeces of its invertebrate vector. This makes it unique amongst human disease (other trypanosomes are transmitted by saliva (Salivaria section) - including the African trypanosomes such as Trypanosoma brucei). T. cruzi can affect a number of mammals, as well as humans but no other vertebrates. There are 4 phases of its life cycle:

• The trypomastigote is the infective flagellate form of the parasite found in the blood of the mammalian host (blood trypomastigote) and in the terminal part of the digestive and urinary tracts of vectors.

• The epimastigote is the reproductive form of the parasite in the insect vector and in the acellular culture medium.

• The amastigote is the intracellular reproductive form of the parasite in the vertebrate host.

• The spheromastigote is found in the stomach of the vector. It is unable to replicate and has a small free flagellum.

Transmission

Transmission is by contamination with infected faeces of reduviid bugs (known as kissing, assassin, or cone-nosed bugs) when they drop faeces and urine on to the host during or shortly after feeding. These then enter the body when rubbed into abrasions, mucosa, or conjunctiva. It can also be acquired via blood transfusion and congenitally.¹

Pathophysiology

The pathological process is characterised by an inflammatory response, cellular lesions and then fibrosis. It affects the heart, oesophagus and colon most severely. The cardiomyopathy that it produces shows high levels of fibrosis. An important aspect of the inflammatory process is autonomic denervation. In the heart the conducting system is also destroyed.

Epidemiology

• It is found in South America and the South and Southwestern USA.

• It is estimated that 8 million people in Latin America are infected with T. cruzi.²

• Mexico currently has an epidemic of Chagas' disease which has consequences for the future and the safety of blood products in that country.³⁴

• There is considerable variation in terms of prevalence and travellers should take advice about their locality.

Risk factors

• 80% of transmission is via the insect vector.

• 5-20% are transmitted by blood transfusion or transplantation.

• Ingestion of contaminated food or of the vector is probably more important in other mammals.

• Maternofetal transmission in both acute and chronic forms may occur in 2-10% of pregnant infected women.

• Transmission via breast milk is extremely rare.

Presentation

There are 3 clinical phases, called acute, latent and chronic:

Acute phase

The incubation period is 7-10 days but can be 20-40 days if transmission was by blood transfusion. 90% of patients will be asymptomatic - but, if picked up, can usually be diagnosed by the presence of trypomastigotes in fresh smears.²

Features of acute phase

• Fever, headache and myalgia.

• Generalised lymphadenopathy occurs in 60%.

• Facial or generalised oedema.

• Rash.

• Hepatosplenomegaly, particularly in children.

• Diarrhoea, vomiting and anorexia.

• Other classical features include:
  

  • Unilateral conjunctivitis and swelling around the eye, called Romaña's sign, occurs if infection was via the eye. This is a characteristic sign of infection and occurs in 20-50% of acute cases.

  • Where the skin is the portal of infection, an indurated, oedematous skin lesion called a chagoma is seen. There may be multiple chagomas.

  • ECG abnormalities include sinus tachycardia in 30-80% of cases, prolonged PR interval, T-wave changes and a low QRS voltage.

  • In congenital acute infections there is fever, oedema, metastatic chagomas, convulsions, tremors, weak reflexes, apnoea and hepatosplenomegaly. ECG is usually normal.

  • Meningoencephalitis is more common in infants and immunocompromised patients.

Latent phase

• The latent phase follows the acute phase and may last for 10-30 years.

• Patients are asymptomatic but serology is positive.

Chronic phase

Only around 30% progress from the latent to the chronic phase but, those who do, have serious pathology that may well prove fatal:

Cardiac abnormalities can produce

• Arrhythmias

• Heart failure

• Thromboemboli

This will result in symptoms which include:

• Chest pain

• Palpitations

• Dizziness

• Syncope

• Dyspnoea

Patients may also present with complications

• Possible massive cardiac enlargement with:
  

  • Chronic congestive heart failure

  • Thrombus in the right atrial appendage

  • Apical aneurysm

• Megaoesophagus - where the oesophagus becomes dilated with abnormal peristalsis leading to dysphagia, regurgitation and risk of aspiration pneumonia.

• Megacolon - dilatation of the colon with abnormal peristalsis which can lead to faecal impaction and subsequent bowel obstruction or volvulus.

Investigations

Patients who have positive smears, should undergo full history, physical examination and 12 lead ECG (with 30-second rhythm strip).⁵ If this does not reveal anything obvious then no further investigations are necessary. They should be repeated annually. If any cardiac abnormalities are detected then 24-hour ambulatory ECG monitoring, echocardiography,⁶ and exercise testing should be organised. Similarly, for gastroenterological or neurological abnormalities - if any are detected then further investigations should be organised.

• In the acute phase it may be possible to see parasites directly:
  

  • Microscopy of wet blood preparations requires inspection of at least 100 fields. Motile trypomastigotes may be seen but this is very unreliable.²

  • Concentration methods can improve the detection rate. They include centrifuging separated serum, examination of buffy coat layer or Giemsa-stained thick films or of sediment after lysis of red blood cells.

  • Indirect methods of multiplying the parasite in vector or haemoculture give results only after 1-6 months and are used only in specialist centres and for research.

• Chest X-ray may reveal cardiomegaly.

• In the latent and chronic phases, serology is required.

• Polymerase chain reaction (PCR), enzyme-linked immunosorbent assay (ELISA), haemagglutination inhibition, complement fixation, immunofluoresence and other tests for immunoglobulin G (IgG) are available.⁷

• It is important to use at least 2 tests, as many false positives occur.

• These advanced tests may not be readily available in areas of high disease prevalence.

In the chronic phase it is also important to seek complications of the disease, for example:

ECG (with 30-second lead II rhythm strip) changes which include

• Right bundle-branch block

• Sinoatrial block

• Abnormal Q-waves

• Left anterior hemiblock with possible AV block

• Ventricular tachycardia

• Sinus bradycardia

• Primary T-wave changes

Echocardiogram

• Required to detect thrombi, aneurysm, hypokinesia and dysfunction.

Chest X-ray

• Chest X-ray may reveal cardiomegaly and evidence of left ventricular failure.

Contrast studies

• Of oesophagus and colon looking for enlargement.

Management

Treatment for all

• Bed rest is advised in the severe acute phase.

• In the acute phase, benznidazole for 60 days is the drug of choice.²⁵⁸ It is not listed in the British National Formulary and expert advice should be obtained.

• Side-effects include rashes, fever, nausea, peripheral polyneuritis and leukopenia and may require treatment to be stopped.⁵

• Concurrent alcohol can cause a disulfiram-type reaction.

• It is 100% effective in children aged under 2 years, 60-70% effective in older and acutely infected cases.

• The other nitroheterocycle drug nifurtimox has also been used, but this is not licensed in UK.

Other treatment depends on presentation and may include

• Treatment for heart failure as of any cause.

• Thrombosis affects both sides of the heart with equal frequency. Prophylaxis should be considered.⁹

• Meningoencephalitis requires anticonvulsants, sedatives and IV mannitol.

• Arrhythmias - antiarrhythmics and/or a pacemaker may be required. Allopurinol and itraconazole are effective in reversing ECG alterations in the chronic phase, itraconazole being more effective in prevention of new abnormalities.¹⁰

• Specialist surgery is required for megaoesophagus and megacolon.¹¹

• Heart transplant may be an option but for only a few.¹²

Treatment options for chronic cases

• It was formerly considered untreatable but treatment of chronic cases with nitroheterocycles has recently been advised for children and those infected for less than 10 years. A cure rate of 50-60% is achieved. Eradication of the parasite should help to prevent the long-term problems.¹³

• Other agents continue to be investigated for chronic disease. Other treatments will depend upon the nature of the presentation and are similar to those discussed above.

Prognosis

Prognosis, even if treated, is uncertain due to damage caused by the acute phase of infection. Between 25 and 30% of those who are infected will have severe and possibly fatal pathology. Myocardial function is an important indicator of prognosis.¹⁴ The causes of mortality include:

• Cardiomyopathy.

• Ventricular fibrillation leading to sudden cardiac death 60%.

• Heart failure 25-30%.

• Cerebral or pulmonary embolism 10-15%.

• Sudden death is due to arrhythmias often following exercise.

• Volvulus of megacolon.

• Myocarditis or meningoencephalitis especially in the newborn, children, and particularly those co-infected with HIV.

In chronic Chagas' disease, impaired left ventricular function, New York Heart Association class III/IV heart failure, cardiomegaly and nonsustained ventricular tachycardia are all associated with a worse outcome.¹⁵

Prevention

There is no effective vaccine but the following may help aid prevention:

• Improved housing.

• Tourists avoiding mud/thatched huts.

• Mosquito nets should have a cloth roof to prevent the 'rain' of vector faeces.

• Insecticide spraying.

• Screening of blood donors and organ donors.¹⁶

Chagas' disease exists only on the American continent. Poor people in rural areas are affected mostly. Their low-quality houses provide a haven for the triatomine bugs that transmit the disease. This is made worse by civil war forcing rural migrants, who are at risk of Chagas' disease, to move to urbanised areas.¹⁷ In the early 1980s, it was recognised that the only feasible way of controlling Chagas' disease would be through attacking the triatomine vector. Canisters, which release pyrethroid insecticidal fumes when lit, were developed for use by householders. Insecticidal paints for use by spray teams were also developed. In 1991, fumigant canisters were used in the 'Initiative for the Elimination of Chagas Disease' by Southern Cone Countries (Argentina, Bolivia, Brazil, Chile, Paraguay and Uruguay). By 2001, disease transmission had been halted in Uruguay, Chile and Brazil. Unfortunately, political unrest and civil war means funding is directed away from the much needed vector-control programmes in many areas, eg Colombia.¹⁷