Vector borne disease

Non-Venomous insects include mosquitoes, sand flies, ticks, chiggers and fleas. They tend to bite to feed on blood and often transmit disease

Mosquitoes

It is vital to research your area. The Anopheles mosquito which spreads malaria has massive global health implications. Each year 350–500 million cases of malaria occur worldwide, and over one million people die, most of them young children in sub-Saharan Africa. Mosquitoes also spread dengue fever, west nile virus, Japanese encephalitis, yellow fever and other diseases. The key as previously is to research the hazards in your area, both the FCO and CDC have helpful websites.

Malaria

Malaria occurs extensively in tropical and subtropical regions and is caused by the malaria parasite, Plasmodium, which is a small, single-cell organism (protozoan) that lives as a parasite in man and a specific species of mosquito (Anopheles). There are four different types of malaria parasite: Plasmodium falciparum is the cause of fatal malaria, while P. vivax, P. ovale and P. malariae cause more benign types of malaria. Malaria is passed on by the female Anopheles mosquito biting a person who has malaria parasites in their blood. The parasites develop in the intestine and salivary glands of the mosquito and can be passed on to other people the next time the mosquito bites. In man, the parasite travels to the liver via the blood and then out into the bloodstream again, where it invades the red blood cells (the cells which carry oxygen in the blood). Malaria can also be passed on by blood transfusions and the use of infected needles. If you are pregnant, you are more at risk of catching malaria than normal. This is because your immune system can be weaker during pregnancy, which means your body is less able to fight off bacteria and infection. If you are pregnant and have malaria, you may pass the infection on to your baby

Symptoms generally begin approximately 10 to 15 days after being infected, but but it may be longer if the patient has taken a preventive medicine. The actual attacks of malaria develop when the red blood cells burst, releasing a mass of parasites into the blood. The attacks do not begin until a sufficient number of blood cells have been infected with parasites.

Classic symptoms would be:

• fever and shivering. The attack begins with fever, with the temperature rising as high as 40ºC and falling again over a period of several hours
• feeling generally unwell with flu-like headaches
• diarrhoea, nausea and vomiting

When the temperature drops, the patient often sweats profusely and feels much better. Then the same day, or one to two days later, further attacks occur with feeling generally unwell, high temperature and so on. If proper treatment is given, the fever and parasites can disappear within a few days. Malaria can feel like mild flu and tiredness can be the only initial symptom or just simple diarrhoea.

In severe malaria, the classic symptoms above would be expected with increased drowsiness, leading to coma and associated failure of all the major organ systems. No-one is ever completely immune to malaria, but the concept of semi or partial immunity exists, in which attacks are less severe and less likely to kill. But the price for this is multiple exposures (which kill many children).

In severe malaria the illness may evolve with a number of complications:

• low blood pressure (hypotension)
• kidney failure
• haemorrhage (bleeding)
• effects on the liver (eg infectious jaundice)
• shock and coma may also develop, and the condition may prove fatal.
• severe falciparum malaria can affect the brain and the rest of the central nervous system. It's characterised by changes in the level of consciousness, convulsions and paralysis.

Prevention of malaria is important. If you travel to a region where malaria is prevalent, you should take preventive medication against the parasite and take whatever steps you can to avoid being bitten. The gold standard actual diagnosis is made by detecting the parasite in the blood using a microscope slide. But many laboratories now use rapid antibody based screening tests. These can also be carried on expeditions.

The treatment of malaria normally calls for admission because it may be falciparum malaria that can have a fatal outcome in only a few days or hours. Outpatient or self-treatment of malaria is something only to be undertaken when no qualified medical help is available, i.e. if you develop malaria in a remote area. There are a number of different antimalarial medications, and use varies widely depending on local protocols and local resistance patterns.

West Nile Virus

This has been around since 1937 in Africa, Middle East, Eastern Europe and Asia and spread to North America in summer 1999 – it is now in many States and most provinces in Canada. There are 3000 cases annually in US. So far in Ireland and UK the only cases seen have been caught elsewhere. It is spread by the Culex mosquito and mainly affects birds - carried by crows, ravens, jays and magpies. It can be passed to humans by infected mosquito bite and in most cases, there are no symptoms. Mild symptoms are similar to a mild flu-like illness with fever, headache and muscle aches. About one in 150 people develops more severe illness, such as encephalitis or meningitis.

Management strategies include prevention (through covering up, using mosquito nets and DEET), mitigation (through mosquito reduction programmes and reporting of dead birds) and treatment, which is mainly supportive.

Sandflies

Sandflies are found all over the world and can transmit a number of diseases. Leishmaniasis is the most serious of these. Every year Leishmaniasis causes 57,000 deaths. The WHO has estimated that 14 million people are currently infected and estimates that another 1.5 million people become infected with the Leishmania species that cause Cutaneous, Mucucutaneous and Diffuse cutaneous leishmaniasis each year. Furthermore, it is thought that an additional 500,000 people become infected with Visceral Leishmaniasis on an annual basis.

Leishmaniasis

There are two forms of the disease – dependant on type of leishmania parasite – very few take both forms. Cutaneous Leishmaniasis is when infection is restricted to the skin at the site of the bite where it manifests as skin nodules on the face, arms and legs which may form ulcers. The disease is normally self limiting but can leave the victim with disfiguring scars.

Visceral Leishmaniasis is when parasites invade the liver, spleen and bone marrow, leading to massive spleen enlargement, anaemia and weight loss. If untreated it has a  95% mortality and this is made worse with HIV co-infection. The gold standard for diagnosis is visualisation of the amastigotes in splenic or bone marrow aspirate. Serological testing is now much more frequently used in areas where leishmaniasis is endemic and this is a new development over the last 10 years

Most cases of VL respond well to treatment with an antimony drug if diagnosed early enough, but treatment is long and very unpleasant. Trials are underway to look at alternatives. Nutrition is a vital component of VL management.

Ticks 

Tick-borne infections include diseases caused by bacteria, viruses, rickettsiae, and protozoa. Different ticks transmit different disease-causing agents, and some ticks can transmit multiple organisms. There are 2 families of ticks: Argasidae (soft ticks) and Ixodidae (hard ticks). Major tick-borne diseases include:

• Bacteria           
• Lyme disease
• Rocky Mountain Spotted Fever
• Relapsing fever
• Tularemia
• Virus                
• Tick-borne meningoencephalitis
• Colorado tick fever
• Crimean-Congo hemorrhagic fever
• Protozoa          
• Babesiosis
• Cytauxzoonosis
• Toxin   
• Tick paralysis (Toxin)

Lyme disease

Lyme disease is caused by the bacterium Borrelia burgdorferi and is transmitted to humans by the bite of infected blacklegged ticks. There are approximately 100,000 cases annually and the main carrier animals are deer, sheep and white-footed mice. The bacteria is inside the tick and humans can get infected when the tick bites them

The disease is usually a mild flu-like illness with aches, fever and fatigue. Occasionally it can be more serious affecting the brain, heart and other organs. Some patients have no symptoms and the illness can develop a long time after the tick bite. Lyme disease does often present with a classic rash, which is a spreading red rash around the bite or on another part of the body, which can reach 30cm in diameter. Treatment is with antibiotics, either penicillin or tetracycline.

Protection is through covering up and using repellent, avoiding ticks and removing them if found. Advice and diagrams on tick removal using fine tipped tweezers can be found at http://www.bada-uk.org/defence/removal/removaltweezers.php