India, being a tropical country, has always remained a fertile ground for malaria. Not just India but many parts of the world have at some time or the other faced the ire of a malarial outbreak. Historical accounts too state that malaria was the reason behind the decline of the Roman empire. So much so that, fever linked to malaria is normally referred to as ‘Roman fever’. Decades passed but malaria continued to dictate terms.
In recent years one more mosquito born diseases has joined the league of malaria i.e dengue. This disease has shown every promise of dethroning malaria as far as it’s nuisance value is concerned. However, unlike malaria, dengue does not have a well defined medicine for treatment and this perhaps makes it deadlier than malaria. Besides the knowledge of both being mosquito born diseases, there is still not enough understanding over the differences between the symptoms of both these diseases and care that is to be taken.
Symptoms
 “There are some reports of virus undergoing mutation. However, it has not resulted in the change of symptomatology or severity but it serves as a limitation in the development of vaccines against dengue.”Dr Vivek Nangia, Director & Head, Fortis Lung Centre |
Dr Vivek Nangia, Director and Head, Fortis Lung Centre, describes the symptoms associated with malaria and dengue, saying, “Malaria is an illness caused by Plasmodium species which is transmitted by a mosquito bite. Initial symptoms are non specific like fatigue, headache, cough, nausea, vomiting loss of appetite lasting a day or two followed by the classical moderate to high grade intermittent fever associated with chills and rigours. Conventionally, it is divided into three stages- a cold stage, when the patient shivers, a hot stage, when the patient experiences rise in body temperature and a wet stage, when the fever comes down and is accompanied by profuse sweating.”
He adds, “Symptomatic dengue virus infections can be divided into three categories- undifferentiated fever, dengue fever (DF) and dengue haemorrhagic fever (DHF). DHF was further classified into four severity grades – grades I to IV. DHF grades III – IV are labeled as dengue shock syndrome (DSS).
Dengue illness has different clinical presentations and often with unpredictable clinical evolution and outcome. The usual signs and symptoms are, high fever (3-7 days), intense headache, painful joints and muscles, pain behind eyes and often a rash which may appear as fever reduces. Dangerous complications that can occur are haemorrhagic or shock syndrome.”
Problem of many
Recent findings have shown the presence of more than one malarial strain in a patient’s body. According to scientists, finding a combination of different malarial strains has added to patients’ and scientists’ woes. The dengue virus has different strains. Will the combinations of different dengue strains prove even more fatal than malarial strains?
 “Mutations are random events that occur in all organisms in response to a change in the environmental conditions; so sooner or later mutant strains of the dengue virus may crop up like the mutant strains of the Polio virus have emerged.”Dr Manju Phadke Microbiologist & Lecturer, South Indian Education Society |
Dr Manju Phadke, Microbiologist and Lecturer, South Indian Education Society (SIES), explains, “The dengue fever virus is an RNA virus belonging to family Flaviviridiae genus Flavivirus. It is transmitted by arthropods. There are four strains of the virus which are called serotypes, namely DENV -1, DENV-2, DENV-3, DENV-4. Each serotype is capable of causing a full blown disease. Infection with one serotype can produce lifelong immunity to that particular serotype alone, but it will offer little immune protection against the other three serotypes. If a patient primarily suffering from say DENV -1 is exposed to a secondary infection by DENV-3 or DENV-2, then too there is a risk of severe disease as there is not much of an antigenic relation between the serotypes. This had posed a challenge to the researchers for producing a vaccine against dengue.”
Menacing mutations
Mutation can result in several types of genomic changes in DNA or RNA of the bacteria or the virus. For example, continuous mutation in of Human Immuno Deficiency Virus (HIV) is a major obstacle in the way of developing a final remedy to treat HIV infection. Over the years malarial strains have developed resistance to many drugs. What if dengue virus undergoes mutation when we already don’t have enough potent medicines to treat it?
According Nangia, there are some reports of the dengue virus undergoing mutation. However, it has not resulted in the change of symptomatology or severity but it serves as a limitation in the development of vaccines against dengue.
Phadke provides technical details associated with mutations. She says, “The genome of the dengue virus contains about 11,000 nucleotides which code for three core proteins that form the virus particle and seven types of proteins which are produced in the host cell and cause the infection. As of now, to the best of my knowledge, no mutant strains are reported . However mutations are random events that occur in all organisms in response to a change in the environmental conditions; so sooner or later mutant strains of the dengue virus may crop up like the mutant strains of the Polio virus have emerged.”
Gene pool
People in different parts of the world show susceptibility to different kinds of diseases. Very often, diseases dominant in the Western world were proved less menacing in other parts of the world. Differences in the responses to particular disease has largely been attributed to the varying genetic constitution of world population. The distribution of malaria and dengue incidence is also not even across the different continents. Besides environmental factors varying gene pool does determine the severity of these infections.
“The dengue virus is endemic to certain parts of the world, largely the tropical countries and the equatorial regions. Earlier each strain was endemic to a particular area, but due to global travel, growing population etc, there are no territorial boundaries known for the different strains of the virus. People living in areas that are endemic to dengue or those who are traveling to and from the endemic areas are at a higher risk of acquiring the infection. Severe disease is more common in babies and young children. Individuals who are immuno-compromised are at a higher risk of acquiring the infection,” opines Phadke.
According to Nangia, individual risk factors determine the severity of disease and include secondary infection, age, ethnicity and possibly chronic diseases (bronchial asthma, sickle cell anaemia and diabetes mellitus). Young children are more prone to having a more severe form of the infection. He adds, “Host genetics may influence the clinical outcome of infection though most studies have failed to establish this. Yet, studies in the American region show the rates of severe dengue to be lower in Africo-Americans as compared to other ethnic groups.”
Unfortunately, there is no specific anti-viral drug available to treat dengue. Hence, the treatment is only supportive. Nangia informs, “Patients are advised to maintain good oral intake and adequate hydration. Fever and body aches should be managed with paracetamol or acetaminophen. Aspirin or non steroidal anti-inflammatory agents are to be avoided completely. Platelet transfusions have not been shown to be effective at preventing or controlling bleeding. But may be warranted in patients with very low platelet counts (<10,000/mm3).”
Contrary to dengue, for malaria specific anti malarial drugs are available. As far as India is concerned, dengue is coming close to acquiring the same fear factor as malaria. The similarities between the two often add to the confusion. Both are mosquito born diseases, by different species of mosquitos. Strategies to prevent malaria and dengue outbreaks involve some attempts by civic authorities to control the responsible vector populations. For instance, guppy fish eat mosquito larvae responsible for malaria (genus Anopheles) and according to recent studies done in Vietnam and Quba, mesocyclops, a type of crustacean, preys on dengue mosquito larvae (genus Aedes).
Its up to researchers to develop more effective medicines to treat them. However, for the people, awareness about such diseases will always remain a first line of defense.
