◆ A wide range of tropical infectious diseases can cause critical illness. Knowledge of the local epidemiology where the disease is likely acquired is essential.
◆ In addition, local resistance patterns of common bacterial pathogens can be very different in tropical countries, so that antibiotic regimens might need adaptation.
◆ The ‘surviving sepsis’ guidelines are not always appropriate for the treatment of tropical sepsis, including in dengue shock syndrome and severe malaria. Both diseases require a more restricted fluid management.
◆ Leptospirosis is another important (mainly) tropical disease that can cause sepsis with liver and renal failure or acute respiratory distress syndrome (ARDS) with pulmonary haemorrhages.
◆ Recent epidemics of respiratory viruses causing life-threatening pneumonia have had their origins in tropical countries, including Severe Acute Respiratory Syndrome (SARS), Influenza A subtype H5N1 (‘avian influenza’), and recently Middle East respiratory syndrome coronavirus (MERS-CoV).
In addition to severe malaria and viral haemorrhagic fevers (discussed in the previous chapters), there is a wide range of tropical diseases that might be encountered in the ICU setting. Knowledge about the local epidemiology of the area where the disease was most likely acquired is a prerequisite for the proper diagnostic work-up. For instance, a patient admitted with septicaemia acquired in north-eastern Thailand will have a high chance (20%) that this is caused by the soil-dwelling bacterium Burkholderia pseudomallei, whereas in Nepal Salmonella typhi or paratyphi will be the most common causes. These differences in a priori chances will have important consequences for the choice of initial empirical antibiotic therapy, e.g. B. pseudomallei should be covered by a carbamapenem or ceftazidim. HIV/AIDS is a very common disease in several tropical countries, especially in Sub-Saharan Africa, which will also affect the differential diagnosis in patients presenting with severe febrile illnesses.
It should also be realized that although a diagnosis of severe malaria often to be excluded first, the main causes for severe febrile illness acquired in tropical countries also include common bacterial pathogens like Str. pneumoniae, Staph. aureus, and Enterobacteriaceae. Resistance patterns of these bacteria acquired in tropical countries can, however, be very different, although good surveillance data from low-income countries are often lacking . Methicillin resistant Staph. aureus infections in these tropical countries are often not only hospital associated, but now also widespread in community acquired infections (up to 20%) and reported from rural areas of both Asian and African countries . Extended Spectrum β-lactamase (ESBL) producing Enterobacteriaceae (e.g. E. coli) have spread into the community in many low-income tropical countries, probably accelerated by increased consumption of 3rd generation cephalosporins. Fluoroquinolone resistance in typhoid in Asia has severely curtailed the usefulness of these drugs. More recently, and more worrying, carbapenemases producing Enterobacteriaceae (including NDM-1 producing Klebsiella pneumonia) have been identified in India and are increasingly reported in hospitals elsewhere .
Some other common tropical diseases that can present as severe sepsis include severe dengue (dengue haemorrhagic fever/dengue shock syndrome) and severe leptospirosis.
Dengue virus (serotypes DENV 1,2,4, and 4) is transmitted through the bite of infected female Aedes aegypti mosquitoes and less common Aedes albopticus. The disease is widespread throughout the tropics and more than 1 billion people are at risk in over 100 countries. Although usually infections result after an incubation time of 4–7 days only in an uncomplicated undifferentiated fever, or a febrile illness with severe headache and generalized pains in muscles and bones (‘breakbone fever’), a minority of patients develops severe disease typically starting at the time of defervescence. The hallmark of dengue haemorrhagic fever is an acute vascular permeability syndrome accompanied by abnormal haemostasis. Capillary leakage results in hypoproteinaemia, elevated haematocrit, pleural effusions, ascites, and a haemorrhagic diathesis aggravated by concomitant thrombocytopenia. In cases with more severe capillary leakage, haemodynamic shock can result called dengue shock syndrome (DSS). The relatively slow development of hypovolaemia and the prominent thrombocytopenia distinguishes DSS from other (bacterial) causes of septic shock. Treatment of DSS is supportive, with a particular focus on careful fluid management . Because of the generalized capillary leakage, fluid volumes should be restricted, but sufficient to maintain cardiovascular stability and adequate renal function. Resuscitation with colloids rather than crystalloid solutions can be recommended for patients with hypotension . The altered vascular permeability is short-lived and usually reversible after 48–72 hours . As soon as re-absorption begins intravenous fluids should be stopped. Preventive transfusion of platelet concentrates in the absence of bleeding, even for profound thrombocytopenia, and the use of corticosteroids have not shown to improve outcome .
Leptospirosis is primarily a zoonosis affecting humans in both rural and urban settings in temperate and tropical climates. Human infection most often follows exposure to soil and water contaminated with excreta of animals infected with pathogenic species of Leptospira. Leptospirosis is an important cause of febrile illness in tourists returning from the tropics, and usually manifests as a mild febrile illness typically 7–12 days after exposure. However, a minority develops a severe systemic illness characterized by a systemic vasculitis resulting in a wide spectrum of clinical features. The major affected organs include the kidneys and liver (‘Weil’s disease’) and the lungs, resulting in focal or massive intra-alveolar haemorrhage . Haemodynamic shock is also common in severe leptospirosis and myocarditis, meningoencephalitis, and uveitis can also develop. Antibiotic treatment of severe disease is with penicillin G, cefotaxim, or ceftazidime . Supportive treatment in the ICU will often have to include renal replacement therapy.
Although many tropical infectious diseases in the ICU can present fulfilling the criteria for severe sepsis or septic shock, not all recommendations of the ‘Surviving Sepsis Campaign’ guidelines are always applicable. Fluid therapy in dengue shock syndrome should be much more careful then in septic shock from other causes, because of the generalized capillary damage and leakage. Fluids should also be restricted in patients with severe malaria, where hypotension is fortunately a rare event (10%) . Permissive hypercapnia as a ventilation strategy in patients with cerebral malaria should be avoided because of the risk of herniation of the engorged brain. Corticosteroids are not recommended in patients with severe dengue or severe malaria.
In addition to septic syndromes, severe neurological diseases might be encountered in the ICU in patients who resided in or visited the tropics. Again, in most cases, cerebral malaria will have to be excluded first. Meningitis caused by Neisseria meningitis is endemic in the so-called meningitis belt across central Africa, and it is important that travellers are asked whether they have received proper vaccinations before their trip to these areas.
Causes of meningitis and encephelitis
A large number of viruses with a prominent presence in tropical countries can cause meningitis, encephalitis, or meningo-encephelitis in humans . Common examples include enteroviruses (including EV71 and polio, now close to eradication), Nippah virus, Herpes simplex virus, Rift Valley fever (caused by a phlebovirus (Bunyaviridae), and transmitted by mosquitoes), Japanese encephalitis (transmitted from cattle by culex mosquitoes and vaccine preventable), and West Nile virus infection (transmitted from birds by culex mosquitoes), some of the tick-borne encephalitides, and Venezuelan Equine Encephalitis (also mosquito borne). Except for the herpes viruses, no specific anti-viral treatment is available for these infections.
Rabies causes between 40,000 and 70,000 deaths per year, mostly in Southeast Asia, Africa, and South America . Although the majority (99%) is caused by dog bites, other terrestrial animals transmit the disease. Vampire bats can transmit the rabies related lyssaviruses. The incubation time is usually between 3 and 12 weeks, but can be as long as 19 years . Disease can be prevented by post-exposure (bite) prophylaxis with vaccination and administration of human rabies immunoglobulin (HRIG). Once symptomatic disease develops, rabies is fatal. A rabies case related to bat transmitted lyssavirus has been reported who survived after treatment according to an experimental protocol (‘Milwaukee protocol’) including sedation with ketamine and midazolam and the antiviral drugs ribavirin and amantadine. This success has not been reproduced by other groups .
African trypanosomiasis (sleeping sickness) is endemic in most Sub-Saharan African countries (but not in South Africa, Namibia, and Botswana) and can occasionally affect travellers. The disease is a zoonosis transmitted to humans by the bite of the tsetse fly (Glossina sp.). The local skin lesion at the site of inoculation (chancre) is followed by the haemolymphatic stage of the disease (stage I) which may be followed by invasion of the central nervous system and cerebrospinal fluid, leading to a meningoencephalitis (stage II). Trypanosoma b. gambiense (Middle and West-Africa) causes a protracted illness over months, but T.b. rhodesiense (East-Africa) causes a severe acute febrile disease with rapid progression to meningoencephalitis. Treatment of stage II requires treatment of drugs that cross the blood-brain barrier, which include the toxic arsenic drug melarsoprol. Nifurtimox and eflornithine are less toxic, but only effective against T. b. gambiense .
Origins of epidemics
Many epidemics have their origins in tropical countries, and it is important for the treating physician to have up to date information, for instance through the Program for Monitoring Emerging Diseases—an Internet-based reporting system under the International Society of Infectious Diseases dedicated to rapid global dissemination of information on outbreaks of infectious diseases. Also many emerging or re-emerging infectious diseases have their origin in the tropics (see Fig. 294.1), and global spread is importantly facilitated by the nowadays intense global human movement through air traffic. Recent examples include Severe Acute Respiratory Syndrome (SARS), which originated in Hong Kong in 2002–2003, and quickly spread through the region and globally to a total of 37 countries. Acute respiratory distress syndrome (ARDS) caused by this SARS coronavirus, had a high case fatality rate and caused around 800 deaths globally . Avian Influenza caused by Influenza A subtype H5N1 is an enzootic disease of many bird species including poultry, and can cause a rapidly progressive pneumonia in humans. It has caused over 100 outbreaks since 2003 with over 300 fatalities recorded . Severe influenza with pneumonia caused by Influenza A subtype H1N1 caused a pandemic in 2009 which originated in Mexico . Epidemics with other Influenza A subtypes have been reported since then. In 2012 a novel virus causing severe pneumonia with high mortality was reported from several countries in the Middle East. This epidemic caused by Middle East respiratory syndrome coronavirus (MERS-CoV) which was worrying because its virulence and ability of person-to-person transmission .
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