Malaria:
Plasmodium is a parasitic protozoa that is the causal agent of the infectious disease, malaria. These single celled protozoan parasites invade and multiply in the liver and then red blood cells causing illness; malaria. The plasmodium infected red blood cells eventually burst in the bloodstream sending the parasites throughout the body and causing symptoms.
There are 5 species on plasmodium that affect humans and cause malaria. They are;
o Plasmodium vivax
o Plasmodium falciparum (the most dangerous)
o Plasmodium malariae
o Plasmodium ovulae
o Plasmodium knowlesi
The plasmodium’s life cycle involves alterations between mosquito and hosts. When the mosquito obtains the parasite, the organism undergoes various stages of sexual reproduction within the gut of the mosquito. Migrating to the insect’s salivary glands, the plasmodium is then passed onto a host when the mosquito feeds. Within the host the parasite will again go through many stages of reproduction in the form of asexual multiplication. These stages will begin in the liver before then transferring to the host’s red blood cells.
Guinea worm:
The Guinea worm or Dracunculus medinensis is a parasite that infects and affects human tissue. Obtained through larvae contaminated water, Guinea worm can live inside a host dormant for about a year before symptoms occur. Although rarely fatal, Guinea worm can cause an infected individual extreme pain that is very debilitating. Because of this pain, the host often looses some mobility and is unable to perform work. Depending on the site where the worm exits the body, long-term pain or even permanent damage may also occur.
2. Transmission- identify and describe the steps in which the pathogen is transmitted to the host. (Use diagrams or infographics to assist your description)
Malaria:
Infected female Anopheles mosquitos transmit the plasmodium parasite (malaria) through their bite. In the liver and bloodstream of the host, the parasites multiply, spreading the disease. If another mosquito bites the infected individual, they can take up the parasite and then infect another individual, spreading it from person to person.
Malaria can on occasion be transmitted by blood transfusion. It can also be passed from a mother to her fetus.
Malaria is not contagious.
Guinea Worm:
A person infected with guinea worm obtains this infectious disease by drinking water from ponds and other stagnant water, which contain “water fleas”. These water fleas are the living place for guinea worm larvae as the fleas eat the larvae as part of their diet.
Once consumed, the larvae move on to the next stage of their life. As the human stomach digests the water fleas, the guinea worm larvae are released, penetrating the wall of the intestines and migrating through the body.
After a year, a fertilized female worm will reach it exit point forming a blister and causing swelling. Along with these symptoms, people infected with guinea worm will experience an intense burning sensation. In order to soothe this pain, many people will enter the water, immersing the infection. In the presence of the water the female worm will release thousands of larvae into the water to be eaten by the water fleas, beginning the cycle again.
This disease is not communicable, meaning that it cannot be spread from person to person. Drinking water contaminated with the larvae is the only way for this disease to spread.
3. Host response- explain how the body reacts to the invasion of the pathogen and how tries to defend itself.
Malaria:
Within a mosquito vector, the Plasmodium parasite remains fairly benign as the mosquito suffers little effects from the infection of the parasites. However in a human host, the presence of the Plasmodium will cause sever illness, which can produce life threatening complications and many symptoms. These symptoms are a result of the complex interactions between the plasmodium parasite and the host’s immune system.
Part of the life cycle of the plasmodium parasite causes red blood cells to rupture and the parasites to be released into the blood stream. The release of the Plasmodium into the blood stream (along with many pigments and toxins) triggers dramatic responses from the immune system, which include the secretion of various types of cytokine molecules into the blood to kill the parasite and also dampen its effects. Despite the effectiveness and importance of the cytokines release into the bloodstream, this process can bring about many dangerous consequences such as the periodically high and intense fevers often associated with malaria. It is also believed that this over production may also play a role in life threatening complications such as cerebral malaria, which affects a small handful of patients.
Sequestration is another process in which the plasmodium parasite attacks the host. In this process, red blood cells seem to develop protein rich ‘knobs’ on their outer surfaces. This caused the cells to be ‘sticky’ and many adhere to one another as well as to capillary walls. Rather then flowing feely throughout the bloodstream, this forces parasite cells to remain ‘sequestered’ in particular organs assisting the plasmodium to invade the host’s immune system. The only Plasmodium parasite found to undergo the process of sequestration is P. falciparum, which leads scientists to believe that sequestration plays a role in cerebral malaria. However there is much debate about this. It has be studied and found that patients with cerebral malaria have normal levels of blood flow to the brain meaning that there are no blockages or a lack of oxygen to the brain. Scientists therefore believe that sequestered cells cause an excessive immune reaction in the brain that releases an excessive amount of Nitrous Oxide. This toxic high concentration of Nitrous Oxide is consequently hypothesized to trigger cerebral malaria. Sequestration in pregnant women can cause blockages to the blood flow to the placenta making it extremely dangerous for the fetus. Because of this, many babies whose mothers have P. falciparum are born with a low birth weight and often prematurely due to a disrupted supply of oxygen and nutrients within the womb.
Guinea Worm:
An individual’s body will first recognize the parasite when the host comes into contact with water, releasing millions of larvae into the water. This however does not happen till around a year after the host first contracted the parasite. This release of larvae triggers an allergic reaction within the host as well as extreme discomfort. At this point the body will develop a painful blister that eventually turns into an ulcer, forcing the anterior of the guinea worm to be exposed. As the worm is exposed to water and the larvae are released, so too are toxic chemicals from the immune system in an attempt to kill the invading Guinea Worm. After this point, antibodies will attach onto this invading parasite however, the parasite can disguise itself form the immune system of the host by displaying proteins on its surface that identifies their body as a part of the host. The invasion of the parasite only dissipates once the worm has been full extracted and the painful ulcer healed.
4. Major symptoms – describe symptoms of these diseases
Malaria:
Individuals infected with malaria will usually be symptomatic 1 – 3 weeks after obtaining the parasite. Patients won’t generally have all the possible symptoms. Symptoms associated with malaria may include:
o Fever
o Chills
o Profuse sweating
o Malaise (feeling of unwellness)
o Muscle and joint pain
o Headache
o Confusion/delirium
o Convulsions
o Nausea
o Loss of appetite
o Diarrhea
o Abdominal pain
o Cough
o Anemia
o Enlarged spleen
Plasmodium ovale and vivax can lie inactive in the liver for up to a year before causing symptoms.
Guinea Worm:
There are no symptoms associated with the beginning stage of guinea worm. For the first year of infection a person remains asymptomatic meaning that they experience no symptoms. However after about a year an individual may start to feel ill. Various symptoms include:
o Slight fever
o Itchy rash
o Nausea
o Vomiting
o Diarrhea
o Dizziness
After the appearance of these symptoms, a blister will begin to occur. In 80 – 90% of cases this blister will appear on the lower half of an individual’s body, however it can occur anywhere on the skin.
People that are infected by guinea worm disease can often suffer various complications later on in the infection from the wound such as:
o Redness and swelling of the skin (cellulitis)
o Boils (abscesses)
o Generalised infection (sepsis)
o Joint infection (septic arthritis) – may cause joints to lock and deform (contractures)
o Lock jaw (tetanus)
5. Treatment-describe the current and possible future treatments these diseases
Malaria:
A blood smear test is used to diagnose whether an individual has contracted malaria. As the plasmodium parasite is difficult to detect, the test may need to be repeated many times. If a plasmodium parasite is detected and an individual has contracted malaria, there are a variety of different treatment options available. According to the World Health Organization (WHO) the main objectives to be achieved by antimalarial treatments are to:
o To reduce morbidity and mortality by ensuring rapid, complete cure of Plasmodium infection, thus preventing the progression of uncomplicated malaria to severe and potentially fatal disease, as well as preventing chronic infection that leads to malaria- related anaemia;
o To reduce the frequency and duration of malaria infection during pregnancy and its negative impact on the fetus; and
o To curtail the transmission of malaria by reducing the human parasite reservoir.
Vaccines:
At this current time, there is no vaccination for malaria available, nor for any parasitic disease that affects humans. However science and health organizations such as the National Institute of Allergy and Infectious Disease (NIAID), pharmaceutical companies and the World Health Organization (WHO) are perusing research into malaria vaccinations with some headway already being made. One ‘novel’ vaccine strategy currently being explored is a transmission-blocking vaccine that works by blocking the transmission of the plasmodium parasite to a mosquito vector.
It is difficult to create a vaccine for malaria, as it is an extremely complex disease. Little is known on some of the critical processes of the plasmodium parasite, which is hindering many vaccine efforts. Despite this, there is still much hope that at some point in the future people will be able to be vaccinated for malaria.
Antimalarial drugs:
Antimalarial drugs are a major factor contributing to the prevention, reduction and treatment of malaria worldwide.
Quinine is known as one of the most effective antimalarial drugs available. First used in the late 1600’s to treat malaria, quinine was extracted from the bark of the Peruvian cinchona tree. It was the very first successful chemical compound that treated an infectious disease. Quinine remained the main antimalarial drug until the 1920’s when more effective synthetic anti-malarials were discovered.
One of these synthetic drugs, Chloroquine, was extensively used, particularly in the 1940’s, however slow resistance stated to appear to this drug in the 1950’s in parts of Asia and South America. By the 1980’s resistance was widespread and so Quinine once again became the main anti-malarial drug.
Today the most common antimalarial drugs available are:
o Chloroquine
o Atovaquone-proguanil (Malarone®)
o Artemether-lumefantrine (Coartem®)
o Mefloquine (Lariam®)
o Quinine
o Quinidine
o Doxycycline (used in combination with quinine)
o Clindamycin (used in combination with quinine)
o Artesunate (not licensed for use in the United States, but available through the CDC malaria hotline)
The biggest risk associated with the use of antimalarial drugs is the emergence of drug resistant parasites.
The search for new and effective antimalarial drugs has become a huge and critical priority on the global malaria research agenda. Organization such as the National Institute of Allergy and Infectious Disease are currently researching the molecular structure of the Plasmodium parasite and how each stage of its lifecycle interacts with the human host. With this new information, scientists hope to develop drugs that block these important molecular processes required for the survival of the parasite. Research is also going into the mechanisms for drug resistance.
How to treat a patient with malaria depends on a variety of factors:
o The type of Plasmodium parasite contracted
o The area in which the infection was acquired (taking into account drug resistance)
o The patients clinical status
o An additional/accompanying ailment or condition
o Pregnancy
o Drug or medication allergy
o Other medications taken by the patient
Malaria can be fatal if not treated correctly however it is important to note that it is both preventable and curable.
Guinea Worm:
At this point, there is no vaccination or medication available to prevent or treat guinea worm. However, preventative techniques have been extremely successful as it is on the verge of being eradicated. (Preventative strategies will be addressed in the next question).
Currently, the only treatment of guinea worm is worm extraction. However, this can only take place once the worm starts to be released through the blistered skin, about a year after infection.
Info graphic explaining the process taken to extract a Guinea Worm: (PTO)
6. Prevention-explain the strategies recommended by medical authorities to prevent the occurrence of these diseases in individuals
Malaria:
Many practices and procedures are utilized to assist in the prevention of malaria. The aim of these preventative strategies is to reduce the chances of an individual being bitten by a disease-carrying mosquito and therefore reducing chances of contracting malaria.
The two most broadly used preventative techniques are long lasting insecticidal nets and indoor residual spraying.
The long lasting insecticidal nets reduce human-mosquito contact, as mosquitos cannot reach the person inside the net. The insecticide net additionally kills the mosquitos that come into contact with it, helping to protect the wider community. Indoor residual spraying reduces the lifespan of female mosquitos so that they are unable to transmit the parasite before death. It requires the application of insecticides to the inside walls of dwellings as that is where mosquitos often rest after having a blood meal. Both of these preventative strategies are extremely effective however scientists have recently found some insecticidal resistance by mosquitos.
Some other preventative strategies include
o Avoidance of mosquito contact
o Screening for malaria parasites
o Anti mosquito measures such as:
• Spraying bodies of water with oils
• Introducing larvae eating fish to mosquito breeding areas
• Draining mosquito habitats
• Wearing protective clothing
Guinea Worm:
There are many preventative strategies taken to inhibit the spread of the guinea worm infection. As published by the World Health Organization (WHO), possible strategies include:
o Heightening surveillance to detect every case within 24 hours of worm emergence;
o Preventing transmission from each worm by treatment, cleaning and bandaging regularly the affected skin-area until the worm is completely expelled from the body;
o Preventing drinking water contamination by advising the patient to avoid wading into water;
o Ensuring wider access to improved drinking-water supplies to prevent infection;
o Filtering water from open water bodies before drinking;
o Implementing vector control by using the larvicide temephos;
o Promoting health education and behaviour change.
Part 1B
7. Control refers to strategies that are employed to keep the incidents of diseases to a minimum in the population. Discuss the role of quarantine and public health authorities in preventing the entry and spread of mosquito born diseases into Australia. You should consider each of the border control, public health education, travel advisory e.g. smart traveller initiatives, CSIRO
To be completed.
8. Report on the global eradication program for guinea worm disease in terms of:
a. Principles behind the program (Why it was chosen as a target?)
Guinea worm was chosen as a target as it has met certain criteria.
1. Eradication of Guinea Worm is biologically and technically possible.
o After the last human case, guinea worm will become extinct meaning there is no chance for the disease to occur
o Due to its easy to recognize signs and symptoms Guinea worm disease is rarely confused with other diseases. Many affected communities also know and recognize the worm.
o The emergence of worms is very predictable as they usually emerge at certain times of the year
o It has previously been eliminated in countries such as parts of the Soviet Union and Iran
2. The benefits associated with the eradication of guinea worm outweigh the costs.
o Studies undertaken by the World Bank on the socioeconomic impact of Guinea Worm concluded that economic costs and morbidity reduction would be significantly less than continued costs if the disease continued.
o The global community would indirectly benefit from the eradication of guinea worm, as there would be more social equity in countries affected by guinea Worm. There would also be a more enhanced disease prevention culture.
o Other benefits would include:
• More employment opportunities for a group of trained health workers who could provide disease management for Guinea Worm and other basic health services.
• Improvement in water supplies such as;
• Water not contaminated with guinea worm
• Enhanced advocacy for new safe water sources.
Beyond the benefits of the eradication of guinea Worm, these programs have also helped to establish village-based health systems in thousands of communities. These communities now have access to health personnel and volunteers that are able to provide health education as well as advise on and implement interventions on other diseases.
b. Progress towards eradication (how has the number of cases changed overtime?)
The eradication of Guinea Worm Disease has made great progress over the last 30 years as it is now poised to be the next disease, after smallpox, to be eradicated. There were an estimated 3.5 million people being afflicted by this disease in 1986, however in 2016 only 25 cases were reported. Recently, no Guinea worm cases have been reported in 17 of the 21 countries originally affected by this disease. The four remaining endemic countries to eradicate guinea worm are South Sudan, Chad, Ethiopia and Mali, however due to the 99.99% global decrease in cases since 1986, scientists are extremely hopeful that Guinea Worm will soon be eradicated.
c. Strategies being implemented (what methods are being used to prevent any worm infection?)
Guinea Worm eradication programs are educating locals in order to change behaviors and stop the spread of this disease. Ideas emphasized by these programs are to filter all drinking water and to prevent anyone with an emerging guinea worm to remain away from all water sources. The Crater center is one organization currently working on this. They are also helping in maintaining political will of governments to cooperate and assist in the fight against Guinea Worm.
d. And challenges facing the success of the program (What might prevent or delay the global eradication of GWD)
One new challenge that has recently affected the success of the Guinea Worm eradication program is the emergence of Guinea Worm infections in dogs. First detected in 2012 in chad, these infections in domestic dogs are linked to the consumption of fish that contain Guinea Worm larvae. Strategies in place to prevent this disease in dogs include:
o Encouraging individuals living in Guinea Worm affected areas to bury fish discards, particularly entrails
o Encouraging people to keep their animals away from water sources and to report infected animals for a cash reward.
o Scientists are also investigating possible vaccines or drugs that could be used to prevent guinea worm (including the use of established veterinary deworming drugs)