Impact of Climate Change on Insect-borne Diseases

The existence of global warming has been extensively discussed and hotly debated for decades across oceans and continents. Most of the discussions have been focusing on climate change, increased incident of natural disasters, negative impact on farming and fishery, wildlife survival and the resultant human suffering because of all these negativities.

With the sudden outbreak of mosquitoes-borne Zika virus in Central and South America countries, it appears global warming likely to bring forth another serious threat to the public- the spread of pandemic diseases in areas that are previously spared from. According to an American biologist, Daniel Brooks – “whenever the planet has faced a major climate change event, man-made or not, species have moved around and their pathogens have come into contact with species with no resistance.” The alarming rate of birth defects attributed to Zika virus is a good example of dire consequences of the chance encounter between usually benign pathogens with non-immune species. Zika virus named after the Zika Forest of Uganda was identified in 1947. Prior to 2015, Zika fever is under the radar of most world health authorities as it causes minor discomfort at most. It is now reached pandemic levels in several Central and South America countries with suspected link to unusually high numbers of babies born with microcephaly (congenital condition of severely undeveloped brain) and a neurologic conditions in adults, Guillain–Barré syndrome.

With escalating temperature, changed rainfall systems, increased human mobility and globalization, the World Health Organization has found it is necessary to remap the landscape of water-borne and vector diseases. According to WHO, a worldwide temperature rise of 2-3 C likely translate to additional 3-5% (several million) of people risking contracting malaria, another disease that is spread by mosquitoes. Female Aedes aegypti, the daytime-active mosquito that carries Yellow Fever, Zika, and other diseases, thrive in warmer conditions with plenty of stagnant water. Many other insects, including fleas and certain species of ticks, also spread faster during warmer climate. A prolong spell of temperature could see cat-scratch disease and tick-borne diseases spiking around your neighborhood.

According to Dr Diarmid Campbell-Lendrum, a WHO climate change expert scientist – “Infectious agents in water will proliferate with more flooding. It’s clear that we need to strengthen our surveillance and response to a range of diseases. Globalization, the movement of people, is an important factor too. In a world where we are disrupting the climate system, we’ll have to pay the price for that.”

Cat-scratch Disease’s Ophthalmic

Cat-scratch disease is an infection of organism Bartonella Henselae bacteria. In the United States, about 22,000 new infections of cat-scratch disease are reported annually, usually caused by scratch or bite by cats. Clinically, official identification of the disease demands confirmation of three out of four of the following criteria:

  • Swollen or enlarged lymph nodes (Lymphadenopathy)
  • Confirmed cat interaction, preferably with blister or papule at contact point
  • Affirmative Bartonella H. skin or titer test
  • Presence of bacilli, and necrosis (premature death of cells) in lymph node biopsy

Bartonella is transmitted via the common flea, Ctenocephalides felis, to the cat, subsequently to the human host.

Slightly above 10% of cat-scratch disease patients may develop ophthalmic manifestations. They includes:

  • Neuroretinitis (inflammation of the neural retina and optic nerve)
  • Parinaud’s oculoglandular (pink eye) syndrome
  • Focal chorioretinitis (inflammation of retina and choroid)


Treatment is debated. It is widely attested that patients usually will improve in a timely manner. However, many reports support treatment may reduce recovery duration. Treatments usually include doxycycline, rifampin, erythromycin, ciprofloxacin, azithromycin, with steroid drop at the later stage.

After full recovery from the disease, a patient may still experience residual vision field shortcoming, decreased contrast sensitiveness and vision acuteness, and discoloration of the sectoral disc on examination. Typically, lipid exudates in the form of a star is seen on the macular with a swollen optic disc. Eventually, the macular star will be resolved too.

Risk of Pregnant Woman Catching Toxoplasmosis From Pet Cat

Like the cat-scratch disease, toxoplasmosis is a common disease in cats and can be transmitted to humans. The study has shown that six out of every ten cats are affected by toxoplasmosis at some stage of their life. Toxoplasmosis is a parasitic illness that target warm-blooded creatures, including human. Its effects on both cat and human are mostly limited to flu-like symptoms. However, there are exceptions:

  • In pregnant women, the illness may cause irreversible damage to the unborn baby.
  • In an individual with a compromised immune system, the disease can sometimes be deadly.


Causes of Toxoplasmosis:
Toxoplasmosis is caused by a single-celled organism called Toxoplasma gondii, it is prevalent in birds and mammals. Toxoplasma lives and proliferates inside infected cat’s intestines. The offspring discharges out of the cat’s body through cat defecation in egg-like forms. Several spores are released after a few days from these forms. The spores can survive for months until they are picked up by a rodent or bird. Inside these mammal bodies, the spores hatched and the parasites enter the bloodstream after tunnel through the gut wall and travel all over the body. Cats are infected or reinfected when they kill and eat the infected mammals.

How Do I Know If My Cat Is Infected:
Stray and free-ranging cats are more likely to be infected by toxoplasmosis as they hunt and consume small mammals that could be a host of toxoplasmosis. The infection is usually harmless and the infected cat may not exhibit any sign of illness at all. However, kittens, elderly cats and cats with a weaker immune system may show signs of illness. If kittens are infected while in their mother’s womb, the implication could be serious.

Symptoms And Treatments of Toxoplasmosis In Cats:
Most healthy cats do not show any sign of illness when infected by toxoplasmosis. If they do, the cats may initially seem depressed, tired, disinterest in food, and fever. At later stage, pneumonia may induce breathlessness, liver damage may induce jaundice, and damages to eyes and brain may lead to blindness and changed behavior
There is no vaccine developed to prevent your cat from the infection. If negatively affected cat was treated sufficiently early with a drug that stop the parasites from multiplying, recovery is swift.

The effects of Toxoplasmosis on Human:
Toxoplasma will infect fifty percent of the population during our lifetime, but normally it causes nothing more than a short flu-like infection in humans. However, it can lead to serious issues if a pregnant woman comes into contact with it for the first time during pregnancy. The parasites may cause loss of the baby or the baby born with eyes or brain impairment. About fifty percent of infected pregnant women will infect the baby through the placenta. Out of this fifty percent, ten percent will result in grave damage. Immunodeficiency individuals such as HIV patients, cancer patients should be very cautious with toxoplasmosis as well.

Steps to avoid toxoplasmosis infection:
Consuming rare or undercooked meat, unpasteurized dairy products, or unwashed vegetables is the common mean of infection in America. Contaminated cat feces can be a source of infection as well.
Cook all source of meat completely. Food heated to 160°F (71°C) for not less than 15 minutes destroys the parasites effectively.

  • Wash thoroughly all cooking surfaces and utensils after handling raw meat.
  • Commercially prepared foods are safer for your cat.
  • If possible, keep them indoor to prevent them from hunting small mammals and birds.
  • Wash vegetables thoroughly and trim root end to remove any traces of soil.
  • Wear gloves when gardening and wash your hands thoroughly afterwards.
  • Cover sandpit after play to prevent cats using it as a toilet.
  • Clear cat’s litter tray every day.
  • Wash litter trays routinely with hot water and detergent.

What if I am, or wish to become, pregnant?
Any woman who is currently pregnant or wishes to become pregnant in the near future should avoid raw foods as listed above and should avoid clearing out the litter box. Touching or petting a cat will not lead to toxoplasmosis, even a cat scratches or bites will not infect you with the parasites, unlike cat-scratch disease.