Lesson 42 : Prevention Of Arthropod Borne Infections
Malaria is a protozoal disease caused by infection with parasites of the genus Plasmodium and transmitted to man by certain species of infected female Anophline mosquito. A typical attack comprises three distinct stages: cold stage, hot stage and sweating stage. The clinical features of malaria vary from mild to severe, and complicated, according to the species of parasite present, the patient's state of immunity, the intensity of the infection and also the presence of concomitant conditions such as malnutrition or other diseases.
Agent: Plasmodium vivax has the widest geographic distribution throughout the world. In India, about 70 per cent of the infections are reported to be due to P vivax. The malaria parasite undergoes 2 cycles of development – one in human body and another in the body of mosquito, the female Anopheline (Fig).
Fig.1. Stages in the life cycle of Plasmodium
Reservoir of Infection: A human reservoir is one who harbours the sexual forms (gametocytes) of the parasite. A patient can be a carrier of several plasmodial species at the same time. Children are more likely to be gametocyte carriers than adults. The child is thus, epidemiologically a better reservoir than the adult.
Period of Communicability: Malaria is communicable as long as mature, viable gametocytes exist in the circulating blood in sufficient density to infect vector mosquitoes.
Host Factors: Elements of human being influencing malarial epidemiology are
Age: malaria affects all ages. New borns are more resistant to infection.
Sex: males are more prone to the infection than females.
Pregnancy: pregnancy increases the risk of infection. Malaria during pregnancy may cause intrauterine death of the fetus, premature labour and abortion.
Socio-Economic Development: socio-economical developments of developed countries have been a reason for disappearance of malaria.
Housing: The ill-ventilated and ill-lighted houses provide ideal indoor resting places for mosquitoes, the biting of what leads to malaria. The site, type of construction, nature of the walls, etc. influence the selection of control measures
Population MObility: People migrate from one country or part of a country to another for example labourers, nomads and wandering tribes. Some of them may import malaria parasites in their blood and reintroduce malaria 'into areas where malaria has been controlled or eliminated.
Occupation: Malaria is predominantly a rural disease and is closely related to agriculture practices.
Human Habits: Habits such as sleeping outdoors, nomadism, refusal to accept spraying of houses, replastering of walls after spraying and not using measures of personal protection (eg bed nets) influence man-vector contact, and obviously the choice of control measures.
Immunity: The epidemic of malaria is influenced by the immune status of the population. Infants born of immune mothers are generally protected during the first 3-5 months by maternal IgG antibody.
Season: Malaria is a seasonal disease, occurring between July to November .
Temperature and Huminity: affects the life cycle of the parasite, optimum temperature being 20 – 30 degree Centigrade. The relative humidity of 60 per cent is necessary for normal life span of mosquitoes.
Rainfall: Provides opportunity for breeding of mosquitoes and thus, infection rates.
Man made Factors: Burrow pits, garden pools, irrigation channels, engineering projects etc.
Vector Transmission: Malaria is transmitted by the bite of certain species of infected, female, anopheline mosquitoes. The mosquito is not infective unless the sporozoites are present in its salivary glands.
Direct Transmission: Malaria may be induced accidentally by hypodermic intramuscular and intravenous injections of blood or plasma.
Congenital malaria: infection of the new born from an infected mother.
Incubation Period: not less than 10 days.
Clinical Features: severity and complications depend on species of parasite present, patient's state of immunity, intensity of the infection, nutritional status and presence of other diseases. The typical attack comprises three distinct stages, i.e., the cold stage, the hot stage and the sweating stage. These are followed by a febrile period in which the patient feels greatly relieved. Cold Stage: starts with lassitude, headache, nausea, and chilly sensation followed by rigors. Pulse rate is rapid, and weak. The stage lasts for 15 min to 1 hour. Hot StageE: the patient feels burning hot and casts off his clothes. The skin is hot and dry with intense headache. The stage lasts for 2 to 6 hours. Sweating Stage: fever comes down, with profuse sweating. Temperature drops and skin is cool and moist. Patient feels relievd. This stage lasts for 2-4 hours.
Control:vector control is the best approach for malarial control. Strategies to control malaria: Two approaches;
Management of malaria cases in the community :
Diagnosis of all cases of fever.
Utilizing anti-malarial drug
Active intervention to control or interrupt transmission with community participation
The programme was launched in India in 1953. The programme is based on indoor residual spraying of DDT twice a year in endemic areas. The programme was modified in 1977 with the objectives to prevent death, reduce morbidity due to malaria, and to undertake antimalarial programmes with agricultural and industrial activities.