DENGUE AND YELLOW FEVER

What you should know about these infections:

Dengue is an acute febrile illness seen in the tropics, in Africa and South America, though in the latter years it has also been seen in Europe and in North America. It has a geographic distribution similar to Malaria, though Dengue is seen chiefly in urban areas of tropical countries, including India, Indonesia, Philippines, Taiwan and north Australia. It is caused by 4 viruses (DEN-1, DEN-2, DEN 3, and DEN-4), closely related to the serotypes of the family of Flaviviridae.

It is transmitted to humans by the mosquito Aedes aegypti which is the principal vector, though it can be transmitted also by Aeges albopictus.  They are most active in the early and mid-morning, and in the late afternoon. Transmission from person to person is not possible, though recently transmission from mother to baby ‘in uteri’ before birth has been described.  Once infected by one of the 4 serotypes, immunity is acquired to that type, but not to any of the other three, for which a ‘relapse’ is really a new infection. It is thought that a reinfection produces more severe illness.



In red: Epidemic dengue.    In Blue: range of Aedes Aegypti
http://en.wikipedia.org/wiki/Dengue_fever

This genus of mosquito has an approximate range of 100 metres, for which an infection denotes a reservoir for the larvae in the immediate area of contagion. The virus is absorbed by the mosquito during the days that the patient is running a fever, so that he or she must be protected from offering a ‘virus meal’ for the mosquito. There is no carrier state in humans.

The illness consists of abrupt onset of fever –which lasts from 3 to 7 days-, headache, pains in the muscles and bones/joints (hence the name of “bone breaking fever” in many countries), a reddish rash in the skin of the chest and lower limbs, spreading from there to the rest of the body. In mild cases when the rash is absent, it can be mistaken for influenza or other viral illnesses. Other symptoms can appear such as abdominal pain, nausea and vomiting, constipation, and bleeding of the gums and the nose.

Though fortunately much fewer, severe cases are known as haemorrhagic dengue. In these cases, the production of platelets, which are important in forming clots to avoid bleeding, is affected, and bleeding from different organs do occur, a fact which is ominous if accompanied by shock: rapid pulse, very low blood pressure and profuse sweating. In these cases deaths have been reported. During epidemic outbreaks, the diagnosis is strongly suspected with the clinical picture, and can be confirmed by the demonstration of high antibody levels and by Polymerase Chain Reaction determination.

There is no specific treatment for this infection. Adequate care consists of bed rest, and adequate hydration, be it by mouth or intravenously in the more severe cases. Aspirin and commonly used anti-inflammatory drugs such as ibuprofen should be avoided as they can precipitate or enhance bleeding due to their effect on platelet aggregation. Changes of skin temperature to bring the temperature down should also be avoided. Paracetamol can be used carefully for the temperature and the pains.  In some cases, platelet infusions, and whole blood transfusions are necessary.

Prevention is the hallmark of infection control in this illness, the elimination of recipients with stagnant clean waters close to habitations being crucial.  Also, chemical skin repellents, protective clothing, and crib and bed protection with mosquito netting are very important to prevent mosquitoes accessing to their ‘viral meal’. Other sanitary measures such as fumigation, insecticides for stagnant waters and adequate educational measures for the population at large are essential.  In the right context such as larger bodies of water, guppy fish (Poecilia reticualata) have been added as they feed on the mosquito larvae.

Yellow fever is also an acute febrile illness which is seen in Africa, Central and South America, and in the Caribbean. It is caused by a virus of the Flaviridae family, known as Flavivirus amaril, which is transmitted mainly by the mosquito Aedes Aegypti and others of the same family. In the wet and hot tropical forests of  Central and South America –and some Caribbean islands- the virus is carried by “screaming monkeys” and transmitted from monkey to monkey and from thence to humans by the Hæmagogus mosquito. These mosquitoes usually are not found over 1.300 metres above sea level, and in the close-to-urban setting lay their larvae in stagnant clean waters, and as mentioned for Dengue, are active mostly in the morning and evening, never at night.   

Endemic range of yellow fever (2005)                                                 

                                                                                         SOUTH AMERICA  

                                           AFRICA      

                                                               

After being bitten by an infected mosquito, the incubation time to onset of symptoms is 3 to 7 days. A mild form of the illness begins with a high fever, shaking chills and headaches, and occasionally is accompanied by nausea, vomiting and muscle pains, all lasting barely one to three days. It can only be suspected in endemic areas and during epidemic outbreaks.

The classic or severe form begins in the same fashion, and after a brief period of normal temperature the fever reappears, all patients become jaundiced, and bleeding in different areas appear. Typical of this illness are the black vomits, which means bleeding from the stomach.  As it progresses, kidney or liver failure can follow, with marked dehydration.  In endemic areas, diagnosis is established with the clinical picture. Other methods include demonstration of a four-fold increase in specific antibodies, or the findings of the virus and its antigens in tissues, blood or other body fluids.

There is no specific treatment for this disease, and symptomatic support is indicated: fluid replacement, control of complications and dialysis if renal failure is present. A mortality rate of 5% in indigenous populations in endemic areas is reported, though in epidemic outbreaks this number can rise to a 50%. In 2001, the World Health Organization reported that mortality for the 15% of patients, who had developed severe or “toxic” disease, was 50% in 10 to 14 days.  The WHO also estimated that there would be 200.000 non-vaccinated patients per year worldwide, with 30.000 deaths.

An effective vaccine was developed at the Rockefeller Foundation by Max Heiler in 1937, and is a must for residents and for anybody travelling to endemic areas. After vaccination, within 10 days protective antibodies appear in blood.

 

Author:  Dr. John Emery
              Buenos Aires British Hospital

 

References